---
kind: "range"
citation: "46 C.F.R. §§ 42.13-1–42.20-75"
title: "46"
from: "42.13-1"
to: "42.20-75"
count: 50
url: "https://uscodex.org/cfr/46/42.13-1..42.20-75"
---

# §42.13-1. Assumptions.

- (a) The regulations in this part are based on the assumption that the nature and stowage of the cargo, ballast, etc., are such as will secure sufficient stability of the vessel and avoid excessive structural stress.
- (b) The regulations in this part are also based on the assumption that, where there are other international requirements relating to stability or subdivision applicable to vessels, these requirements have been met.

# §42.13-5. Strength of vessel.

- (a) The assigning and issuing authority shall satisfy itself that the general structural strength of the vessel is sufficient for the draft corresponding to the freeboard assigned, and when requested shall furnish pertinent strength information to the Commandant.
- (b) Vessels built and maintained in conformity with the requirements of a classification society recognized by the Commandant are considered to possess adequate strength for the purpose of the applicable requirements in this subchapter unless deemed otherwise by the Commandant.

# §42.13-10. Freeboards assigned vessels.

- (a) Vessels with mechanical means of propulsion, or lighters, barges, or other vessels without independent means of propulsion, shall be assigned freeboards in accordance with the provisions of [§§ 42.13-1 to 42.20-75](/cfr/46/42.13-1..42.20-75.md), inclusive.
- (b) Vessels carrying timber deck cargoes may be assigned, in addition to the freeboards required by [paragraph (a)](#a) of this section, timber freeboards in accordance with the provisions of [§§ 42.25-1 to 42.25-20](/cfr/46/42.25-1..42.25-20.md), inclusive.
- (c) Vessels designed to carry sail, whether as the sole means of propulsion or as a supplementary means, and tugs, shall be assigned freeboards in accordance with the provisions of [§§ 42.13-1 to 42.20-75](/cfr/46/42.13-1..42.20-75.md), inclusive, and such additional freeboards as determined necessary by the Commandant under the procedure of [paragraph (f)](#f) of this section.
- (d) Vessels of wood or of composite construction, or of other materials the use of which the Commandant has approved, or vessels whose constructional features are such as to render the application of the provisions of [§§ 42.13-1 to 42.25-20](/cfr/46/42.13-1..42.25-20.md) unreasonable or impracticable, shall be assigned freeboards as determined necessary by the Commandant under the procedure of [paragraph (f)](#f) of this section.
- (e) The requirements in [§§ 42.15-1 to 42.15-80](/cfr/46/42.15-1..42.15-80.md), inclusive, shall apply to every vessel to which a minimum freeboard is assigned. Relaxations from these requirements may be granted to a vessel to which a greater than minimum freeboard is assigned provided the safety conditions of the vessel are determined to be satisfactory under [paragraph (f)](#f) of this section.
- (f) In each case specified by [paragraphs (c) to (e)](#c..e) inclusive of this section, the assigning authority shall report to the Commandant the specific matters in which the vessel is deficient or requires special freeboard consideration due to design, arrangement, construction materials, propulsive method, or relaxation of requirements in this part. The report shall also furnish background data and recommendations of the assigning authority (including freeboard additions), as will enable the Commandant to reach a decision.

# §42.13-15. Definitions of terms.

- (a) **Length.** The length (L) shall be taken as 96 percent of the total length on a waterline at 85 percent of the least molded depth measured from the top of the keel, or as the length from the foreside of the stem to the axis of the rudder stock on that waterline, if that be greater. In vessels designed with a rake of keel the waterline on which this length is measured shall be parallel to the designed waterline.
- (b) **Perpendiculars.** The forward and after perpendiculars shall be taken at the forward and after ends of the length (L). The forward perpendicular shall coincide with the foreside of the stem on the waterline on which the length is measured.
- (c) **Amidships.** Amidships is at the middle of the length (L).
- (d) **Breadth.** Unless expressly provided otherwise, the breadth (B) is the maximum breadth of the vessel, measured amidships to the molded line of the frame in a vessel with a metal shell and to the outer surface of the hull in a vessel with a shell of any other material.
- (e) **Molded depth.**
  - (1) The molded depth is the vertical distance measured from the top of the keel to the top of the freeboard deck beam at side. In wood and composite vessels the distance is measured from the lower edge of the keel rabbet. Where the form at the lower part of the midship section is of a hollow character, or where thick garboards are fitted, the distance is measured from the point where the line of the flat of the bottom continued inwards cuts the side of the keel.
  - (2) In vessels having rounded gunwales, the molded depth shall be measured to the point of intersection of the molded lines of the deck and sides, the lines extending as though the gunwale were of angular design.
  - (3) Where the freeboard deck is stepped and the raised part of the deck extends over the point at which the molded depth is to be determined, the molded depth shall be measured to a line of reference extending from the lower part of the deck along a line parallel with the raised part.
- (f) **Depth for freeboard—** (D). (1) The depth for freeboard (D) is the molded depth amidships, plus the thickness of the freeboard deck stringer plate, where fitted, plus
  - (2) The depth for freeboard (D) in a vessel having a rounded gunwale with a radius greater than 4 percent of the breadth (B) or having topsides of unusual form is the depth for freeboard of a vessel having a midship section with vertical topsides and with the same round of beam and area of topside section equal to that provided by the actual midship section.
- (g) **Block coefficient.** The block coefficient (Cb) is given by
- (h) **Freeboard.** The freeboard assigned is the distance measured vertically downward amidships from the upper edge of the deck line to the upper edge of the related load line.
- (i) **Freeboard deck.**
  - (1) The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part thereof, and below which all openings in the sides of the vessel are fitted with permanent means of watertight closing. In a vessel having a discontinuance freeboard deck, the lowest line of the exposed deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck. At the option of the owner and subject to the approval of the assigning authority a lower deck may be designated as the freeboard deck, provided it is a complete and permanent deck continuous in a fore and aft direction at least between the machinery space and peak bulkheads and continuous athwartships. When this lower deck is stepped the lowest line of the deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck.
  - (2) When a lower deck is designated as the freeboard deck, that part of the hull which extends above the freeboard deck is treated as a superstructure so far as concerns the application of the conditions of assignment and the calculation of freeboard. It is from this deck that the freeboard is calculated.
- (j) **Superstructure.**
  - (1) A superstructure is a decked structure on the freeboard deck, extending from side to side of the vessel or with the side plating not being inboard of the shell plating more than 4 percent to the breadth. (B). A raised quarter deck is regarded as a superstructure.
  - (2) **An enclosed superstructure is a superstructure with—**
    - (i) Enclosing bulkheads of efficient construction;
    - (ii) Access openings, if any in these bulkheads fitted with doors complying with the requirements of [§ 42.15-10](/cfr/46/42.15-10.md); and,
    - (iii) All other openings in sides or ends of the superstructure fitted with efficient weathertight means of closing.
  - (3) The height of a superstructure is the least vertical height measured at side from the top of the superstructure deck beams to the top of the freeboard deck beams.
  - (4) The length of a superstructure (S) is the mean length of the part of the superstructure which lies within the length (L).
- (k) **Flush deck vessel.** A flush deck vessel is one which has no superstructure on the freeboard deck.
- (l) **Weathertight.** Weathertight means that in any sea conditions water will not penetrate into the vessel.

# §42.13-20. Deck line.

- (a) **The deck line is a horizontal line 12 inches in length and 1 inch in breadth.** It shall be marked amidships on each side of the vessel, and its upper edge shall normally pass through the point where the continuation outwards of the upper surface of the freeboard deck intersects the outer surface of the shell (as illustrated in Figure 42.13-20(a)), provided that the deck line may be placed with reference to another fixed point on the vessel on condition that the freeboard is correspondingly corrected. The location of the reference point and the identification of the freeboard deck shall in all cases be indicated on the International Load Line Certificate (1966), and, as applicable, on all other load line certificates issued pursuant to this part 42.

# §42.13-25. Load line mark.

- (a) The load line mark shall consist of a ring 12 inches in outside diameter and 1 inch wide which is intersected by a horizontal line 18 inches in length and 1 inch in breadth, the upper edge of which passes through the center of the ring. The center of the ring shall be placed amidships and at a distance equal to the assigned summer freeboard measured vertically below the upper edge of the deck line (as illustrated in Figure 42.13-25(a)).

# §42.13-30. Lines to be used with the load line mark.

- (a) The lines which indicate the load line assigned in accordance with the regulations in this part shall be horizontal lines 9 inches in length and 1 inch in breadth which extend forward of, unless expressly provided otherwise, and at right angles to, a vertical line 1 inch in breadth marked at a distance 21 inches forward of the center of the ring (as illustrated in Figure 42.13-25(a)).
- (b) The following load lines shall be used:
  - (1) The summer load line indicated by the upper edge of the line which passes through the center of the ring and also by a line marked S.
  - (2) The winter load line indicated by the upper edge of a line marked W.
  - (3) The winter North Atlantic load line indicated by the upper edge of a line marked WNA.
  - (4) The tropical load line indicated by the upper edge of a line marked T.
  - (5) The fresh water load line in summer indicated by the upper edge of a line marked F. The fresh water load line in summer is marked abaft the vertical line. The difference between the fresh water load line in summer and the summer load line is the allowance to be made for loading in fresh water at the other load lines.
  - (6) The tropical fresh water load line indicated by the upper edge of a line marked TF, and marked abaft the vertical line.
- (c) If timber freeboards are assigned, the timber load lines shall be marked in addition to ordinary load lines. These lines shall be horizontal lines 9 inches in length and 1 inch in breadth which extend abaft unless expressly provided otherwise, and are at right angles to, a vertical line 1 inch in breadth marked at a distance 21 inches abaft the center of the ring (as illustrated in Figure 42.13-30(c)).
- (d) The following timber load lines shall be used:
  - (1) The summer timber load line indicated by the upper edge of a line marked LS.
  - (2) The winter timber load line indicated by the upper edge of a line marked LW.
  - (3) The winter North Atlantic timber load line indicated by the upper edge of a line marked LWNA.
  - (4) The tropical timber load line indicated by the upper edge of a line marked LT.
  - (5) The fresh water timber load line in summer indicated by the upper edge of a line marked LF and marked forward of the vertical line.
  - (6) The tropical fresh water timber load line indicated by the upper edge of a line marked LTF and marked forward of the vertical line.
- (e) Where the characteristics of a vessel, or the nature of the vessel's service or navigational limits make any of the seasonal lines inapplicable, these lines may be omitted.
- (f) Where a vessel is assigned a greater than minimum freeboard so that the load line is marked at a position corresponding to, or lower than, the lowest seasonal load line assigned at minimum freeboard in accordance with the present Convention, only the fresh water load line need be marked.
- (g) On sailing vessels only the fresh water load line and the winter North Atlantic load line need be marked (as illustrated in Figure 42.13-30(g)).
- (h) Where a winter North Atlantic load line is identical with the winter load line corresponding to the same vertical line, this load line shall be marked W.
- (i) Additional load lines required by other international conventions in force may be marked at right angles to and abaft the vertical line specified in [paragraph (a)](#a) of this section.

# §42.13-35. Mark of assigning authority.

- (a) The mark of the assigning authority by whom the load lines are assigned may be indicated alongside the load line ring above the horizontal line which passes through the center of the ring, or above and below it. This mark shall consist of not more than four initials to identify the assigning authority's name, each measuring approximately 4 1/2 inches in height and 3 inches in width.

# §42.13-40. Details of marking.

- (a) The ring, lines and letters shall be painted in white or yellow on a dark ground or in black on a light ground. They shall also be permanently marked on the sides of the vessels to the satisfaction of the assigning authority. The marks shall be plainly visible and, if necessary, special arrangements shall be made for this purpose.

# §42.13-45. Verification of marks.

- (a) The International Load Line Certificate (1966) shall not be delivered to the vessel until [§ 42.07-5](/cfr/46/42.07-5.md) has been fully complied with under the authority and provisions of subparts [42.07](/cfr/46/subpart42.07.md) and [42.09](/cfr/46/subpart42.09.md) of this part.

# §42.15-1. Information to be supplied to the master.

- (a) The master of every new vessel shall be supplied with sufficient information in a form approved by the assigning and issuing authority, to enable him to arrange for the loading and ballasting of his vessel in such a way as to avoid the creation of any unacceptable stresses in the vessel's structure: Provided, That this requirement need not apply to any particular length, design or class of vessel where the Commandant considers it to be unnecessary and so notifies the assigning and issuing authority.
- (b) The master of every new vessel, which is not already provided with stability information under an international convention for the safety of life at sea in force, shall be supplied with sufficient information in a form approved by the Commandant, to give him guidance as to the stability of the vessel under varying conditions of service, and a copy shall be furnished to the Commandant.

# §42.15-5. Superstructure end bulkheads.

- (a) Bulkheads at exposed ends of enclosed superstructures shall be of efficient construction and shall be to the satisfaction of the assigning authority.

# §42.15-10. Doors.

- (a) All access openings in bulkheads at ends of enclosed superstructures shall be fitted with doors of steel or other equivalent material, permanently and strongly attached to the bulkhead, and framed, stiffened and fitted so that the whole structure is of equivalent strength to the unpierced bulkhead and weathertight when closed. The means for securing these doors weathertight shall consist of gaskets and clamping devices or other equivalent means and shall be permanently attached to the bulkhead or to the doors themselves, and the doors shall be so arranged that they can be operated from both sides of the bulkhead.
- (b) Except as otherwise provided in these regulations, the height of the sills of access openings in bulkheads at ends of enclosed superstructures shall be at least 15 inches above the deck.

# §42.15-15. Positions of hatchways, doorways and ventilators.

- (a) For the purpose of this part two positions of hatchways, doorways and ventilators are defined as follows:
  - (1) **Position 1—** Upon exposed freeboard and raised quarter decks, and upon exposed superstructure decks situated forward of a point located a quarter of the vessel's length from the forward perpendicular.
  - (2) **Position 2—** Upon exposed superstructure decks situated abaft a quarter of the vessel's length from the forward perpendicular.

# §42.15-20. Cargo and other hatchways.

- (a) The construction and the means for securing the weathertightness of cargo and other hatchways in positions 1 and 2 shall be at least equivalent to the requirements of §§ [42.15-25](/cfr/46/42.15-25.md) and [42.15-30](/cfr/46/42.15-30.md).
- (b) Coamings and hatchway covers to exposed hatchways on decks above the superstructure deck shall comply with the requirements of the assigning authority.

# §42.15-25. Hatchways closed by portable covers and secured weathertight by tarpaulins and battening devices.

- (a) **Hatchway coamings.**
  - (1) The coamings of hatchways closed by portable covers secured weathertight by tarpaulins and battening devices shall be of substantial construction, and their height above the deck shall be at least as follows:
    - (i) 23 1/2 inches if in position 1.
    - (ii) 17 1/2 inches if in position 2.
- (b) **Hatchway covers.**
  - (1) The width of each bearing surface for hatchway covers shall be at least 2 1/2 inches.
  - (2) Where covers are made of wood, the finished thickness shall be at least 2 3/8 inches in association with a span of not more than 4.9 feet.
  - (3) Where covers are made of mild steel, the strength shall be calculated with assumed loads not less than 358 pounds per square foot on hatchways in position 1, and not less than 266 pounds per square foot on hatchways in position 2, and the product of the maximum stress thus calculated and the factor 4.25 shall not exceed the minimum ultimate strength of the material. They shall be so designed as to limit the deflection to not more than 0.0028 times the span under these loads.
  - (4) The assumed loads on hatchways in position 1 may be reduced to 205 pounds per square foot for vessels of 79 feet in length and shall be not less than 358 pounds per square foot for vessels of 328 feet in length. The corresponding loads on hatchways in position 2 may be reduced to 154 pounds per square foot and 266 pounds per square foot respectively. In all cases values at intermediate lengths shall be obtained by linear interpolation.
- (c) **Portable beams.**
  - (1) Where portable beams for supporting hatchway covers are made of mild steel the strength shall be calculated with assumed loads not less than 358 pounds per square foot on hatchways in position 1 and not less than 266 pounds per square foot on hatchways in position 2 and the product of the maximum stress thus calculated and the factor 5 shall not exceed the minimum ultimate strength of the material. They shall be so designed as to limit the deflection to not more than 0.0022 times the span under these loads. For vessels of not more than 328 feet in length the requirements of [paragraph (b)(4)](#b-4) of this section are applicable.
- (d) **Pontoon covers.**
  - (1) Where pontoon covers used in place of portable beams and covers are made of mild steel the strength shall be calculated with the assumed loads given in [paragraph (b)(3)](#b-3) of this section, and the product of the maximum stress thus calculated and the factor 5 shall not exceed the minimum ultimate strength of the material. They shall be so designed as to limit the deflection to not more than 0.0022 times the span. Mild steel plating forming the tops of covers shall be not less in thickness than 1 percent of the spacing of stiffeners or 0.24 inches if that be greater. For vessels of not more than 328 feet in length the requirements of [paragraph (b)(4)](#b-4) of this section are applicable.
  - (2) The strength and stiffness of covers made of materials other than mild steel shall be equivalent to those of mild steel to the satisfaction of the assigning authority.
- (e) **Carriers or sockets.**
  - (1) Carriers or sockets for portable beams shall be of substantial construction, and shall provide means for the efficient fitting and securing of the beams. Where rolling types of beams are use, the arrangements shall ensure that the beams remain properly in position when the hatchway is closed.
- (f) **Cleats.**
  - (1) Cleats shall be set to fit the taper of the wedges. They shall be at least 2 1/2 inches wide and spaced not more than 23 1/2 inches center to center; the cleats along each side or end shall be not more than 6 inches from the hatch corners.
- (g) **Battens and wedges.**
  - (1) Battens and wedges shall be efficient and in good condition. Wedges shall be of tough wood or other equivalent material. They shall have a taper of not more than 1 in 6 and shall be not less than 1/2-inch thick at the toes.
- (h) **Tarpaulins.**
  - (1) At least two layers of tarpaulin in good condition shall be provided for each hatchway in positions 1 and 2.
  - (2) The tarpaulins shall be waterproof and of ample strength. They shall be of a material of at least a standard weight and quality as approved by the assigning and issuing authority.
    - (i) **Security of hatchway covers.**
  - (1) For all hatchways in position 1 or 2, steel bars or other equivalent means shall be provided in order efficiently and independently to secure each section of hatchway covers after the tarpaulins are battened down. Hatchway covers of more than 4.9 feet in length shall be secured by at least two such securing appliances.

# §42.15-30. Hatchways closed by weathertight covers of steel or other equivalent material fitted with gaskets and clamping devices.

- (a) **Hatchway coamings.** At positions 1 and 2 the height above the deck of hatchway coamings fitted with weathertight hatch covers of steel or other equivalent material fitted with gaskets and clamping devices shall be as specified in [§ 42.15-25(a)(1)](/cfr/46/42.15-25.md?p=a-1). The height of these coamings may be reduced, or the coamings omitted entirely, on condition that the assigning authority is satisfied that the safety of the vessel is not thereby impaired in any sea conditions. Where coamings are provided they shall be of substantial construction.
- (b) **Weathertight covers.**
  - (1) Where weathertight covers are of mild steel the strength shall be calculated with assumed loads not less than 358 pounds per square foot on hatchways in position 1, and not less than 255 pounds per square foot on hatchways in position 2, and the product of the maximum stress thus calculated and the factor of 4.25 shall not exceed the minimum ultimate strength of the material. They shall be so designed as to limit the deflection to not more than 0.0028 times the span under these loads. Mild steel plating forming the tops of covers shall be not less in thickness than one percent of the spacing of stiffeners or 0.24 inches if that be greater. The provisions of [§ 42.15-25(b)(4)](/cfr/46/42.15-25.md?p=b-4) are applicable for vessels of not more than 328 feet in length.
  - (2) The strength and stiffness of covers made of materials other than mild steel shall be equivalent to those of mild steel to the satisfaction of the assigning authority.
- (c) **Means for securing weathertightness.**
  - (1) The means for securing and maintaining weathertightness shall be to the satisfaction of the assigning authority.
  - (2) The arrangements shall ensure that the tightness can be maintained in any sea conditions. For this purpose tests for tightness shall be required at the initial surveys, and may be required at periodical surveys and at annual surveys or at more frequent intervals.

# §42.15-35. Machinery space openings.

- (a) Machinery space openings in position 1 or 2 shall be properly framed and efficiently enclosed by steel casings of ample strength, and where the casings are not protected by other structures their strength shall be specifically considered. Access openings in such casings shall be fitted with doors complying with the requirements of [§ 42.15-10(a)](/cfr/46/42.15-10.md?p=a), the sills of which shall be at least 23 1/2 inches above the deck if in position 1, and at least 15 inches above the deck if in position 2. Other openings in such casings shall be fitted with equivalent covers, permanently attached in their proper positions.
- (b) Coamings of any fiddley, funnel, or machinery space ventilators in an exposed position on the freeboard or superstructure deck shall be as high above the deck as is reasonable and practicable. Fiddley openings shall be fitted with strong covers of steel or other equivalent material permanently attached in their proper positions and capable of being secured weathertight.

# §42.15-40. Miscellaneous openings in freeboard and superstructure decks.

- (a) Manholes and flush scuttles in position 1 or 2 or within superstructures other than enclosed superstructures shall be closed by substantial covers capable of being made watertight. Unless secured by closely spaced bolts, the covers shall be permanently attached.
- (b) Openings in freeboard decks other than hatchways, machinery space openings, manholes, and flush scuttles shall be protected by an enclosed superstructure, or by a deckhouse or companionway of equivalent strength and weathertightness. Any such opening in an exposed superstructure deck or in the top of a deckhouse on the freeboard deck which gives access to a space below the freeboard deck or a space within an enclosed superstructure shall be protected by an efficient deckhouse or companionway. Doorways in such deckhouses or companionways shall be fitted with doors complying with the requirements of [§ 42.15-10(a)](/cfr/46/42.15-10.md?p=a).
- (c) In position 1 the height above the deck of sills to the doorways in companionways shall be at least 23 1/2 inches. In position 2 they shall be at least 15 inches.

# §42.15-45. Ventilators.

- (a) Ventilators in position 1 or 2 to spaces below the freeboard decks or decks of enclosed superstructures shall have coamings of steel or other equivalent material, substantially constructed and efficiently connected to the deck. Where the coaming of any ventilator exceeds 35 1/2 inches in height it shall be specially supported.
- (b) Ventilators passing through superstructures other than enclosed superstructures shall have substantially constructed coamings of steel or other equivalent material at the freeboard deck.
- (c) Ventilators in position 1 the coamings of which extend to more than 14.8 feet above the deck, and in position 2 the coamings of which extend to more than 7.5 feet above the deck, need not be fitted with closing arrangements unless specifically required by the assigning authority.
- (d) Except as provided in [paragraph (c)](#c) of this section ventilator openings shall be provided with efficient weathertight closing appliances. In vessels of not more than 328 feet in length the closing appliances shall be permanently attached; where not so provided in other vessels, they shall be conveniently stowed near the ventilators to which they are to be fitted. Ventilators in position 1 shall have coamings of a height of at least 35 1/2 inches above the deck; in position 2 the coamings shall be of a height at least 30 inches above the deck.
- (e) In exposed positions, the height of coamings may be required to be increased to the satisfaction of the assigning authority.

# §42.15-50. Air pipes.

- (a) Where air pipes to ballast and other tanks extend above the freeboard or superstructure decks, the exposed parts of the pipes shall be of substantial construction; the height from the deck to the point where water may have access below shall be at least 30 inches on the freeboard deck and 17 1/2 inches on the superstructure deck. Where these heights may interfere with the working of the vessel, a lower height may be approved, provided the assigning authority is satisfied that the closing arrangements and other circumstances justify a lower height. Satisfactory means permanently attached, shall be provided for closing the openings of the air pipes.

# §42.15-55. Cargo ports and other similar openings.

- (a) Cargo ports and other similar openings in the sides of vessels below the freeboard deck shall be fitted with doors so designed as to ensure watertightness and structural integrity commensurate with the surrounding shell plating, to the satisfaction of the assigning authority. The arrangements shall be subject to tightness tests at the initial survey and at such subsequent surveys or more frequent intervals as deemed necessary. The number of such openings shall be the minimum compatible with the design and proper working of the vessel.
- (b) Unless permitted by the Commandant the lower edge of such openings shall not be below a line drawn parallel to the freeboard deck at side, which has at its lowest point the upper edge of the uppermost load line.

# §42.15-60. Scuppers, inlets, and discharges.

- (a) Discharges led through the shell either from spaces below the freeboard deck or from within superstructures and deckhouses on the freeboard deck fitted with doors complying with the requirements of [§ 42.15-10](/cfr/46/42.15-10.md) shall be fitted with efficient and accessible means for preventing water from passing inboard. Normally, each separate discharge shall have one automatic nonreturn valve with a positive means of closing it from a position above the freeboard deck. Where, however, the vertical distance from the summer load waterline to the inboard end of the discharge pipe exceeds 0.01L, the discharge may have two automatic nonreturn valves without positive means of closing: Provided, That the inboard valve is always accessible for examination under service conditions; where that vertical distance exceeds 0.02L a single automatic nonreturn valve without positive means of closing may be accepted subject to the approval of the assigning authority. The means for operating the positive action valve shall be readily accessible and provided with an indicator showing whether the valve is open or closed.
- (b) In manned machinery spaces main and auxiliary sea inlets and discharges in connection with the operation of machinery may be controlled locally. The controls shall be readily accessible and shall be provided with indicators showing whether the valves are open or closed.
- (c) Scuppers and discharge pipes originating at any level and penetrating the shell either more than 17 1/2 inches below the freeboard deck or less than 23 1/2 inches above the summer load waterline shall be provided with a nonreturn valve at the shell. This valve, unless required by [paragraph (a)](#a) of this section, may be omitted if the piping is of thickness as specified in [part 56](/cfr/46/part56.md) in subchapter F (Marine Engineering) of this chapter.
- (d) Scuppers leading from superstructures or deckhouses not fitted with doors complying with the requirements of [§ 42.15-10](/cfr/46/42.15-10.md) shall be led overboard.
- (e) All valves and shell fittings required by this section shall be of steel, bronze, or other approved ductile material. Valves of ordinary cast iron or similar material are not acceptable. All pipes to which this section refers shall be of steel or other equivalent material to the satisfaction of the assigning authority.

# §42.15-65. Side scuttles.

- (a) Side scuttles to spaces below the freeboard deck or to spaces within enclosed superstructures shall be fitted with efficient hinged inside deadlights arranged so that they can be effectively closed and secured watertight.
- (b) No side scuttle shall be fitted in a position so that its sill is below a line drawn parallel to the freeboard deck at side and having its lowest point 2.5 percent of the breadth (B) above the load waterline, or 19 1/2 inches, which ever is the greater distance.
- (c) The side scuttles, together with their glasses, if fitted, and deadlights, shall be of substantial and approved construction.

# §42.15-70. Freeing ports.

- (a) Where bulwarks on the weather portions of freeboard or superstructure decks form wells, ample provision shall be made for rapidly freeing the deck of water and for draining them. Except as provided in paragraphs [(b)](#b) and [(c)](#c) of this section, the minimum freeing port area (A) on each side of the vessel for each well on the freeboard deck shall be that given by the following formulae in cases where the sheer in way of the well is standard or greater than standard. The minimum area for each well on superstructure decks shall be one-half of the area given by the formulae.
  - (1) Where the length of bulwark (l) in the well is 66 feet or less A = 7.6 + 0.115l (square feet)
  - (2) Where l exceeds 66 feet A = 0.23l (square feet)
  - (3) **l—** need in no case be taken as greater than 0.7L.
  - (4) If the bulwark is more than 3.9 feet in average height the required area shall be increased by 0.04 square feet per foot of length of well for each foot difference in height. If the bulwark is less than 3 feet in average height, the required area may be decreased by 0.04 square feet per foot of length for each foot difference in height.
- (b) In vessels with no sheer the area calculated according to [paragraph (a)](#a) of this section shall be increased by 50 percent. Where the sheer is less than the standard the percentage shall be obtained by linear interpolation.
- (c) Where a vessel is fitted with a trunk which does not comply with the requirements of [§ 42.20-55(a)(5)](/cfr/46/42.20-55.md?p=a-5) or where continuous or substantially continuous hatchway side coamings are fitted between detached superstructures the minimum area of the freeing port openings shall be calculated from table 42.15-70(c):
- (d) In vessels having superstructures which are open at either or both ends, adequate provision for freeing the space within such superstructures shall be provided to the satisfaction of the assigning authority.
- (e) The lower edges of the freeing ports shall be as near the deck as practicable. Two-thirds of the freeing port area required shall be provided in the half of the well nearest the lowest point of the sheer curve.
- (f) All such openings in the bulwarks shall be protected by rails or bars spaced approximately 9 inches apart. If shutters are fitted to freeing ports, ample clearance shall be provided to prevent jamming. Hinges shall have pins or bearings of noncorrodible material. If shutters are fitted with securing appliances, these appliances shall be of approved construction.

# §42.15-75. Protection of the crew.

- (a) The strength of the deckhouses used for the accommodation of the crew shall be to the satisfaction of the assigning authority.
- (b) Efficient guard rails or bulwarks must be fitted on all exposed parts of the freeboard and superstructure decks as follows:
  - (1) The height of the bulwarks or guard rails must be at least 39 1/2 inches from the deck, provided that where this height would interfere with the normal operation of the vessel, a lesser height may be approved if the Commandant and the assigning authority are satisfied that adequate protection is provided.
  - (2) On each vessel that is initially surveyed for load line assignment after January 1, 1976, and that is exclusively engaged in towing operations, the minimum bulwark or rail height on the freeboard deck may be reduced to 30 inches provided the assigning authority is satisfied that adequate grabrails are provided around the periphery of the deckhouse.
  - (3) Portable rails may be used when operating conditions warrant their use.
- (c) The opening below the lowest course of the guard rails shall not exceed 9 inches. The other courses shall be not more than 15 inches apart. In the case of vessels with rounded gunwales the guard rail supports shall be placed on the flat of the deck.
- (d) Satisfactory means (in the form of guard rails, life lines, gangways or underdeck passages, etc.) shall be provided for the protection of the crew in getting to and from their quarters, the machinery space and all other parts used in the necessary work of the vessel.
- (e) Deck cargo carried on any vessel shall be so stowed that any opening which is in way of the cargo and which gives access to and from the crew's quarters, the machinery space and all other parts used in the necessary work of the vessel, can be properly closed and secured against the admission of water. Effective protection for the crew in the form of guard rails or life lines shall be provided above the deck cargo if there is no convenient passage on or below the deck of the vessel.

# §42.15-80. Special conditions of assignment for Type “A” vessels.

- (a) **Machinery casings.** Machinery casings on Type “A” vessels as defined in [§ 42.09-5(b)](/cfr/46/42.09-5.md?p=b) must be protected by an enclosed poop or bridge of at least standard height, or by a deckhouse of equal height and equivalent strength, except that machinery casings may be exposed if there are no openings giving direct access from the freeboard deck to the machinery space. A door complying with the requirements of [§ 42.15-10](/cfr/46/42.15-10.md) is permitted in the machinery casing if it leads to a space or passageway which is as strongly constructed as the casing and is separated from the stairway to the engine room by a second weathertight door of steel or equivalent material.
- (b) **Gangway and access.**
  - (1) An efficiently constructed fore and aft permanent gangway of sufficient strength shall be fitted on Type “A” vessels at the level of the superstructure deck between the poop and the midship bridge or deckhouse where fitted, or equivalent means of access shall be provided to carry out the purpose of the gangway, such as passages below deck. Elsewhere, and on Type “A” vessels without a midship bridge, arrangements to the satisfaction of the assigning authority shall be provided to safeguard the crew in reaching all parts used in the necessary work of the ship.
  - (2) Safe and satisfactory access from the gangway level shall be available between separates crew accommodations and also between crew accommodations and the machinery space.
- (c) **Hatchways.** Exposed hatchways on the freeboard and forecastle decks or on the tops of expansion trunks on Type “A” vessels shall be provided with efficient watertight covers of steel or other equivalent material.
- (d) **Freeing arrangements.**
  - (1) Type “A” vessels with bulwarks shall have open rails fitted for at least half the length of the exposed parts of the weather deck or other effective freeing arrangements. The upper edge of the sheer strake shall be kept as low as practicable.
  - (2) Where superstructures are connected by trunks, open rails shall be fitted for the whole length of the exposed parts of the freeboard deck.

# §42.20-3. Freeboard assignment: Type “A” vessels.

- (a) A Type “A” vessel is assigned a freeboard not less than that based on table 42.20-15(a)(1) provided that the vessel meets the flooding standard in [§ 42.20-6](/cfr/46/42.20-6.md).
- (b) A vessel that meets the requirements of subpart [D](/cfr/46/subpartD.md), [F](/cfr/46/subpartF.md), or G of [part 172](/cfr/46/part172.md) of this chapter is considered by the Coast Guard as meeting the flooding standard referenced in [paragraph (a)](#a) of this section.

# §42.20-5. Freeboard assignment: Type “B” vessels.

- (a) Each Type “B” vessel is assigned a freeboard from table 42.20-15(b)(1) that is increased or decreased by the provisions of this section.
- (b) Each Type “B” vessel that has a hatchway in position 1, must have the freeboard assigned in accordance with [paragraph (a)](#a) of this section increased by the amount given in table 42.20-5(b) unless the hatch cover complies with:
  - (1) [Section 42.15-25(d)](/cfr/46/42.15-25.md?p=d); or
  - (2) [Section 42.15-30](/cfr/46/42.15-30.md).
- (c) Any Type “B” vessel that is greater than 100 meters (328 feet) in length and any hopper dredge meeting the requirements in [subpart C of part 44](/cfr/46/part44-subpartC.md) of this chapter may have a reduced freeboard from that assigned under table 42.20-15(b)(1) in accordance with [paragraph (d)](#d) or [paragraph (e)](#e) of this section if—
  - (1) The measures provided for the protection of the crew are adequate;
  - (2) The freeing arrangements are adequate; and
  - (3) The hatchway covers in positions 1 and 2 comply with the provisions of [§ 42.15-30](/cfr/46/42.15-30.md) and have adequate strength, special care being given to their sealing and securing arrangements.
- (d) The freeboards for a Type “B” vessel which comply with [paragraph (c)](#c) of this section may be reduced up to 60 percent of the total difference between the freeboards in table 42.20-15(b)(1) and table 42.20-15(a)(1) provided that the vessel meets the flooding standard in [§ 42.20-7](/cfr/46/42.20-7.md).
- (e) The freeboards for a Type “B” vessel which complies with [paragraph (c)](#c) of this section may be reduced up to the total difference between the freeboard tables referenced in [paragraph (d)](#d) of this section provided that the vessel meets the flooding standard in [§ 42.20-8](/cfr/46/42.20-8.md) and the provisions of § [42.15-80 (a)](/cfr/46/42.15-80.md?p=a), [(b)](/cfr/46/42.15-80.md?p=b) and [(d)](/cfr/46/42.15-80.md?p=d) as if it were a Type “A” vessel.

# §42.20-6. Flooding standard: Type “A” vessels.

- (a) Design calculations must be submitted that demonstrate that the vessel will remain afloat in the conditions of equilibrium specified in [§ 42.20-12](/cfr/46/42.20-12.md) assuming the damage specified in [§ 42.20-11](/cfr/46/42.20-11.md) as applied to the following flooding standards:
  - (1) If the vessel is over 150 meters (492 feet) in length it must be able to withstand the flooding of any one compartment, except the machinery space.
  - (2) If the vessel is over 225 meters (738 feet) in length, it must be able to withstand the flooding of any one compartment, treating the machinery space as a floodable compartment.
- (b) When doing the calculations required in [paragraph (a)](#a) of this section, the following permeabilities must be assumed:
  - (1) 0.95 in all locations except the machinery space.
  - (2) 0.85 in the machinery space.

# §42.20-7. Flooding standard: Type “B” vessel, 60 percent reduction.

- (a) Design calculations must be submitted that demonstrate that the vessel will remain afloat in the conditions of equilibrium specified in [§ 42.20-12](/cfr/46/42.20-12.md) assuming the damage specified in [§ 42.20-11](/cfr/46/42.20-11.md) as applied to the following flooding standards:
  - (1) If the vessel is 225 meters (738 feet) or less in length, it must be able to withstand the flooding of any one compartment, except the machinery space.
  - (2) If the vessel is over 225 meters (738 feet) in length, it must be able to withstand the flooding of any one compartment, treating the machinery space as a floodable compartment.
- (b) When doing the calculations required in [paragraph (a)](#a) of this section, the following permeabilities must be assumed:
  - (1) 0.95 in all locations except the machinery space.
  - (2) 0.85 in the machinery space.

# §42.20-8. Flooding standard: Type “B” vessel, 100 percent reduction.

- (a) Design calculations must be submitted that demonstrate that the vessel will remain afloat in the conditions of equilibrium specified in [§ 42.20-12](/cfr/46/42.20-12.md) assuming the damage specified in [§ 42.20-11](/cfr/46/42.20-11.md) as applied to the following flooding standards:
  - (1) If the vessel is 225 meters (738 feet) or less in length, it must be able to withstand the flooding of any two adjacent fore and after compartments excluding the machinery space;
  - (2) If the vessel is over 225 meters (738 feet) in length, the flooding standard of [paragraph (a)(1)](#a-1) of this section must be applied, treating the machinery space, taken alone, as a floodable compartment.
- (b) When doing the calculations required in [paragraph (a)](#a) of this section, the following permeabilities must be assumed:
  - (1) 0.95 in all locations except the machinery space.
  - (2) 0.85 in the machinery space.

# §42.20-9. Initial conditions of loading.


When doing the calculations required in §§ [42.20-6(a)](/cfr/46/42.20-6.md?p=a), [42.20-7(a)](/cfr/46/42.20-7.md?p=a) and [42.20-8(a)](/cfr/46/42.20-8.md?p=a), the initial condition of loading before flooding must be assumed to be as specified in this section:

- (a) **The vessel is assumed to be loaded to its summer load waterline with no trim.**
- (b) **When calculating the vertical center of gravity, the following assumptions apply—**
  - (1) **The cargo is assumed to be homogeneous.**
  - (2) Except as specified in [paragraph (b)(3)](#b-3) of this section, all cargo compartments are assumed to be fully loaded. This includes compartments intended to be only partially filled. In the case of liquid cargoes, fully loaded means 98 percent full.
  - (3) If the vessel is intended to operate at its summer load waterline with empty compartments, these empty compartments are assumed to be empty rather than fully loaded if the resulting height of the vertical center of gravity is not less than the height determined in accordance with [paragraph (b)(2)](#b-2) of this section.
  - (4) Fifty percent of the total capacity of all tanks and spaces fitted to contain consumable liquids or stores must be assumed to be distributed to accomplish the following:
    - (i) Each tank and space fitted to contain consumable liquids or stores must be assumed either completely empty or completely filled.
    - (ii) The consumables must be distributed so as to produce the greatest possible height above the keel for the center of gravity.
  - (5) **Weights are calculated using the following values for specific gravities—**

# §42.20-10. Free surface.


When doing the calculations required in §§ [42.20-6(a)](/cfr/46/42.20-6.md?p=a), [42.20-7(a)](/cfr/46/42.20-7.md?p=a) and [42.20-8(a)](/cfr/46/42.20-8.md?p=a), the effect of free surface of the following liquids must be included:

- (a) For each type of consumable liquid, the maximum free surface of at least one transverse pair of tanks or a single centerline tank must be included. The tank or combination of tanks must be that resulting in the greatest free surface effect.
- (b) For cargo liquids, unless the compartment is assumed to be empty as required by [§ 42.20-9(b)(3)](/cfr/46/42.20-9.md?p=b-3), the free surface of those compartments containing liquids is calculated at an angle of heel of not more than 5 degrees.

# §42.20-11. Extent of damage.


When doing the calculations required by §§ [42.20-6(a)](/cfr/46/42.20-6.md?p=a), [42.20-7(a)](/cfr/46/42.20-7.md?p=a) and [42.20-8(a)](/cfr/46/42.20-8.md?p=a), the following must be assumed:

- (a) The vertical extent of damage in all cases must be assumed to be from the baseline upward without limit.
- (b) The transverse extent of damage is assumed to be equal to B/5 or 11.5 meters (37.7 feet), whichever is less. The transverse extent is measured inboard from the side of the ship perpendicularly to the center line at the level of the summer load waterline.
- (c) If damage of a lesser extent than that specified in paragraph [(a)](#a) or [(b)](#b) of this section results in a more severe condition, the lesser extent must be assumed.
- (d) The following assumptions apply to the transverse damage specified in [paragraph (b)](#b) of this section for a stepped or recessed bulkhead:
  - (1) A transverse watertight bulkhead that has a step or recess located within the transverse extent of assumed damage may be considered intact if the step or recess is not more than 3.05 meters (10 feet) in length.
  - (2) If a transverse watertight bulkhead has a step or recess of more than 3.05 meters (10 feet) in length, within the transverse extent of assumed damage, the two compartments adjacent to this bulkhead must be considered as flooded.
  - (3) If within the transverse extent of damage, a transverse bulkhead has a step or recess more than 3.05 meters (10 feet) in length that coincides with the double bottom tank top or the inner boundary of a wing tank, respectively, all adjacent compartments within the transverse extent of assumed damage must be considered to be flooded simultaneously.
- (e) If a wing tank has openings into adjacent compartments, the wing tank and adjacent compartments must be considered as one compartment. This provision applies even where these openings are fitted with closing appliances except:
  - (1) **Valves fitted in bulkheads between tanks which are controlled from above the bulkhead deck.**
  - (2) **Secured manhole covers fitted with closely spaced bolts.**
- (f) Only transverse watertight bulkheads that are spaced apart at least 1/3(L) 2/3 or 14.5 meters (0.495(L) 2/3 or 47.6 feet), whichever is less, may be considered effective. If transverse bulkheads are closer together, then one or more of these bulkheads must be assumed to be non-existent in order to achieve the minimum spacing between bulkheads.

# §42.20-12. Conditions of equilibrium.


The following conditions of equilibrium are regarded as satisfactory:

- (a) **Downflooding.** The final waterline after flooding, taking into account sinkage, heel, and trim, is below the lower edge of any opening through which progressive flooding can take place. Such openings include air pipes, ventilators, and openings which are closed by means of weathertight doors (even if they comply with [§ 42.15-10](/cfr/46/42.15-10.md)) or covers (even if they comply with [§ 42.15-30](/cfr/46/42.15-30.md) or [§ 42.15-45(d)](/cfr/46/42.15-45.md?p=d)) but may exclude those openings closed by means of:
  - (1) Manhole covers and flush scuttles which comply with [§ 42.15-40](/cfr/46/42.15-40.md);
  - (2) Cargo hatch covers which comply with [§ 42.09-5(b)](/cfr/46/42.09-5.md?p=b);
  - (3) Hinged watertight doors in an approved position which are secured closed while at sea and so logged; and
  - (4) Remotely operated sliding watertight doors, and side scuttles of the non-opening type which comply with [§ 42.15-65](/cfr/46/42.15-65.md).
- (b) **Progressive flooding.** If pipes, ducts, or tunnels are situated within the assumed extent of damage penetration as defined in § [42.20-11 (a)](/cfr/46/42.20-11.md?p=a) and [(b)](/cfr/46/42.20-11.md?p=b), progressive flooding cannot extend to compartments other than those assumed to be floodable in the calculation for each case of damage.
- (c) **Final angle of heel.** The angle of heel due to unsymmetrical flooding does not exceed 15 degrees. If no part of the deck is immersed, an angle of heel of up to 17 degrees may be accepted.
- (d) **Metacentric height.** The metacentric height of the damaged vessel, in the upright condition, is positive.
- (e) **Residual stability.** Through an angle of 20 degrees beyond its position of equilibrium, the vessel must meet the following conditions:
  - (1) The righting arm must be positive.
  - (2) The maximum righting arm must be at least 0.1 meter (4 inches).
  - (3) The area under the righting arm curve within the 20 degree range must not be less than 0.0175 meter-radians (0.689 inch-radians).
  - (4) Each submerged opening must be weathertight (e.g. a vent fitted with a ball check valve).
- (f) **Intermediate stages of flooding.** The Commandant is satisfied that the stability is sufficient during intermediate stages of flooding.

# §42.20-13. Vessels without means of propulsion.

- (a) A lighter, barge, or other vessel without independent means of propulsion is assigned a freeboard in accordance with the provisions of this subpart as modified by paragraphs [(b)](#b), [(c)](#c), and [(d)](#d) of this section.
- (b) A barge that meets the requirements of [§ 42.09-5(b)](/cfr/46/42.09-5.md?p=b) may be assigned Type “A” freeboard if the barge does not carry deck cargo.
- (c) An unmanned barge is not required to comply with [§ 42.15-75](/cfr/46/42.15-75.md), [§ 42.15-80(b)](/cfr/46/42.15-80.md?p=b), or [§ 42.20-70](/cfr/46/42.20-70.md).
- (d) An unmanned barge that has only small access openings closed by watertight gasketed covers of steel or equivalent material on the freeboard deck, may be assigned a freeboard 25 percent less than that calculated in accordance with this subpart.

# §42.20-15. Freeboard tables.

- (a) **Type “A” vessel.**
  - (1) The tabular freeboard for Type “A” vessel shall be determined from table 42.20-15(a)(1):
- (b) **Type “B” vessels.**
  - (1) The tabular freeboard for Type “B” vessels shall be determined from table 42.20-15(b)(1):

# §42.20-20. Correction to the freeboard for vessels under 328 feet in length.

- (a) The tabular freeboard for a Type “B” vessel of between 79 feet and 328 feet in length having enclosed superstructures with an effective length of up to 35 percent of the length of the vessel shall be increased by:

# §42.20-25. Correction for block coefficient.


If the block coefficient (Cb) exceeds 0.68, the tabular freeboard specified in [§ 42.20-15](/cfr/46/42.20-15.md) as modified, if applicable, by §§ [42.20-5 (b)](/cfr/46/42.20-5.md?p=b) and [(d)](/cfr/46/42.20-5.md?p=d), and [42.20-20(a)](/cfr/46/42.20-20.md?p=a) must be multiplied by the factor (Cb + 0.68)/1.36.


# §42.20-30. Correction for depth.

- (a) Where D exceeds L 1/15 the freeboard shall be increased by [D−(L/15)] R inches, where R is L/131.2 at lengths less than 393.6 feet and 3 at 393.6 feet length and above.
- (b) Where D is less than L/15 no reduction shall be made except in a vessel with an enclosed superstructure covering at least 0.6L amidships, with a complete trunk, or combination of detached enclosed superstructures and trunks which extend all fore and aft, where the freeboard shall be reduced at the rate prescribed in [paragraph (a)](#a) of this section.
- (c) Where the height of superstructure or trunk is less than the standard height, the reduction shall be in the ratio of the actual to the standard height as defined in [§ 42.20-40](/cfr/46/42.20-40.md).

# §42.20-35. Correction for position of deck line.

- (a) Where the actual depth to the upper edge of the deck line is greater or less than D, the difference between the depths shall be added to or deducted from the freeboard.

# §42.20-40. Standard height of superstructure.

- (a) The standard height of a superstructure shall be as given in table 42.20-40(a):

# §42.20-45. Length of superstructure.

- (a) Except as provided in [paragraph (b)](#b) of this section, the length of a superstructure (S) shall be the mean length of the parts of the superstructure which lie within the length (L).
- (b) Where the end bulkhead of an enclosed superstructure extends in a fair convex curve beyond its intersection with the superstructure sides, the length of the superstructure may be increased on the basis of an equivalent plane bulkhead. This increase shall be two-thirds of the fore and aft extent of curvature. The maximum curvature which may be taken into account in determining this increase is one-half the breadth of the superstructure at the point of intersection of the curved end of the superstructure with its side.

# §42.20-50. Effective length of superstructure.

- (a) Except as provided for in [paragraph (b)](#b) of this section the effective length (E) of an enclosed superstructure of standard height shall be its length.
- (b) In all cases where an enclosed superstructure of standard height is set in from the sides of the vessel as permitted in [§ 42.13-15(j)](/cfr/46/42.13-15.md?p=j), the effective length shall be the length modified by the ratio of b/Bs,
  - (1) Where a superstructure is set in for a part of its length, this modification shall be applied only to the set in part.
- (c) Where the height of an enclosed superstructure is less than the standard height, the effective length shall be its length reduced in the ratio of the actual height to the standard height. Where the height exceeds the standard, no increase shall be made to the effective length of the superstructure.
- (d) The effective length of a raised quarter deck if fitted with an intact front bulkhead, shall be its length up to a maximum of 0.6L. Where the bulkhead is not intact, the raised quarter deck shall be treated as a poop of less than standard height.
- (e) Superstructures which are not enclosed shall have no effective length.

# §42.20-55. Trunks.

- (a) A trunk or similar structure which does not extend to the sides of the vessel shall be regarded as efficient on the following conditions:
  - (1) The trunk is at least as strong as a superstructure;
  - (2) The hatchways are in the trunk deck, and the hatchway coamings and covers comply with the requirements of [§§ 42.15-15 to 42.15-30](/cfr/46/42.15-15..42.15-30.md), inclusive, and the width of the trunk deck stringer provides a satisfactory gangway and sufficient lateral stiffness; however, small access openings with watertight covers may be permitted in the freeboard deck;
  - (3) A permanent working platform fore and aft fitted with guard rails is provided by the trunk deck, or by detached trunks connected to superstructures by efficient permanent gangways;
  - (4) Ventilators are protected by the trunk by watertight covers or by other equivalent means;
  - (5) Open rails are fitted on the weather parts of the freeboard deck in way of the trunk for at least half their length;
  - (6) The machinery casings are protected by the trunk, by a superstructure of at least standard height, or by a deckhouse of the same height and of equivalent strength;
  - (7) The breadth of the trunk is at least 60 percent of the breadth of the vessel; and,
  - (8) Where there is no superstructure, the length of the trunk is at least 0.6L.
- (b) The full length of an efficient trunk reduced in the ratio of its mean breadth to B shall be its effective length.
- (c) The standard height of a trunk is the standard height of a superstructure other than a raised quarter deck.
- (d) Where the height of a trunk is less than the standard height, its effective length shall be reduced in the ratio of the actual to the standard height. Where the height of hatchway coamings on the trunk deck is less than that required under [§ 42.15-25(a)](/cfr/46/42.15-25.md?p=a), a reduction from the actual height of trunk shall be made which corresponds to the difference between the actual and required height of coaming.

# §42.20-60. Deduction for superstructures and trunks.

- (a) Where the effective length of superstructures and trunks is 1.0L, the deduction from the freeboard shall be 14 inches at 79 feet length of vessel, 34 inches at 279 feet length, and 42 inches at 400 feet length and above; deductions at intermediate lengths shall be obtained by linear interpolation.
- (b) Where the total effective length of superstructures and trunks is less than 1.0L the deduction shall be a percentage obtained from table 42.20-60(b)(1) or table 42.20-60(b)(2):
- (c) **For vessels of Type “B”—**
  - (1) Where the effective length of a bridge is less than 0.2L, the percentages shall be obtained by linear interpolation between lines I and II;
  - (2) Where the effective length of a forecastle is more than 0.4L, the percentages shall be obtained from line II; and,
  - (3) Where the effective length of a forecastle is less than 0.07L, the percentages in table 42.20-60(b)(2) of this paragraph shall be reduced by:

# §42.20-65. Sheer.

- (a) **General.**
  - (1) The sheer shall be measured from the deck at side to a line of reference drawn parallel to the keel through the sheer line amidships.
  - (2) In vessels designed with a rake of keel, the sheer shall be measured in relation to a reference line drawn parallel to the design load waterline.
  - (3) In flush deck vessels and in vessels with detached superstructures the sheer shall be measured at the freeboard deck.
  - (4) In vessels with topsides of unusual form in which there is a step or break in the topsides, the sheer shall be considered in relation to the equivalent depth amidships.
  - (5) In vessels with a superstructure of standard height which extends over the whole length of the freeboard deck, the sheer shall be measured at the superstructure deck. Where the height exceeds the standard the least difference (Z) between the actual and standard heights shall be added to each end ordinate. Similarly, the intermediate ordinates at distances of 1/6L and 1/3L from each perpendicular shall be increased by 0.444Z and 0.111Z respectively.
  - (6) Where the deck of an enclosed superstructure has at least the same sheer as the exposed freeboard deck, the sheer of the enclosed portion of the freeboard deck shall not be taken into account.
  - (7) Where an enclosed poop or forecastle is of standard height with greater sheer than that of the freeboard deck, or is of more than standard height, an addition to the sheer of the freeboard deck shall be made as provided in [paragraph (c)(4)](#c-4) of this section.
- (b) **Standard sheer profile.**
  - (1) The ordinates of the standard sheer profile are given in table 42.20-65(b)(1):
- (c) **Measurement of variation from standard sheer profile.**
  - (1) Where the sheer profile differs from the standard, the four ordinates of each profile in the forward or after half shall be multiplied by the appropriate factors given in the table of ordinates. The difference between the sums of the respective products and those of the standard divided by 8 measures the deficiency or excess of sheer in the forward or after half. The arithmetical mean of the excess or deficiency in the forward and after halves measures the excess or deficiency of sheer.
  - (2) Where the after half of the sheer has an excess and the forward half of the sheer has a deficiency, no credit shall be allowed for the part in excess and deficiency only shall be measured.
  - (3) Where the forward half of the sheer profile exceeds the standard, and the after portion of the sheer profile is not less than 75 percent of the standard, credit shall be allowed for the part in excess; where the after part is less than 50 percent of the standard, no credit shall be given for the excess sheer forward. Where the after sheer is between 50 percent and 75 percent of the standard, intermediate allowances may be granted for excess sheer forward.
  - (4) Where sheer credit is given for a poop or forecastle, the following formula shall be used:
    - (i) The formula in this [paragraph (c)(4)](#c-4) of this section provides a curve in the form of a parabola tangent to the actual sheer curve at the freeboard deck and intersecting the end ordinate at a point below the superstructure deck a distance equal to the standard height of a superstructure. The superstructure deck shall not be less than standard height above this curve at any point. This curve shall be used in determining the sheer profile for forward and after halves of the vessel.
- (d) **Correction for variations from standard sheer profile.**
  - (1) The correction for sheer shall be the deficiency or excess of sheer (see [paragraphs (c)](#c) (1) to (4) inclusive of this section) multiplied by:
- (e) **Addition for deficiency in sheer.**
  - (1) Where the sheer is less than the standard, the correction for deficiency in sheer (see [paragraph (d)(1)](#d-1) of this section) shall be added to the freeboard.
- (f) **Deduction for excess sheer.**
  - (1) In vessels where an enclosed superstructure covers 0.1L before and 0.1L abaft amidships, the correction for excess of sheer as calculated under the provisions of [paragraph (d)(1)](#d-1) of this section shall be deducted from the freeboard; in vessels where no enclosed superstructure covers amidships, no deduction shall be made from the freeboard; where an enclosed superstructure covers less than 0.1L before and 0.1L abaft amidships, the deduction shall be obtained by linear interpolation. The maximum deduction for excess sheer shall be at the rate of 1 1/2 inches per 100 feet of length.

# §42.20-70. Minimum bow height.

- (a) The bow height defined as the vertical distance at the forward perpendicular between the waterline corresponding to the assigned summer freeboard and the designed trim and the top of the exposed deck at side shall be not less than:
  - (1) For vessels below 820 feet in length,
  - (2) For vessels of 820 feet and above in length,
- (b) Where the bow height required in [paragraph (a)](#a) of this section is obtained by sheer, the sheer shall extend for at least 15 percent of the length of the vessel measured from the forward perpendicular. Where it is obtained by fitting a superstructure, such superstructure shall extend from the stem to a point at least 0.07L abaft the forward perpendicular, and it shall comply with the following requirements:
  - (1) For vessels not over 328 feet in length it shall be enclosed as defined in [§ 42.13-15(j)](/cfr/46/42.13-15.md?p=j); and,
  - (2) For vessels over 328 feet in length it need not comply with [§ 42.13-15(j)](/cfr/46/42.13-15.md?p=j) but shall be fitted with closing appliances to the satisfaction of the assigning authority.
- (c) Vessels which, to suit exceptional operational requirements, cannot meet the requirements of paragraphs [(a)](#a) and [(b)](#b) of this section may be given special consideration by the assigning authority.

# §42.20-75. Minimum freeboards.

- (a) **Summer freeboard.**
  - (1) The minimum freeboard in summer must be the freeboard derived from the tables in [§ 42.20-15](/cfr/46/42.20-15.md) as modified by the corrections in §§ [42.20-3](/cfr/46/42.20-3.md) and [42.20-5](/cfr/46/42.20-5.md), as applicable, and §§ [42.20-20](/cfr/46/42.20-20.md), [42.20-25](/cfr/46/42.20-25.md), [42.20-30](/cfr/46/42.20-30.md), [42.20-35](/cfr/46/42.20-35.md), [42.20-60](/cfr/46/42.20-60.md), [42.20-65](/cfr/46/42.20-65.md) and, if applicable, [§ 42.20-70](/cfr/46/42.20-70.md).
  - (2) The freeboard in salt water, as calculated in accordance with [paragraph (a)(1)](#a-1) of this section, but without the correction for deck line, as provided by [§ 42.20-35](/cfr/46/42.20-35.md), shall not be less than 2 inches. For vessels having in position 1 hatchways with covers which do not comply with the requirements of §§ [42.15-25(d)(1)](/cfr/46/42.15-25.md?p=d-1), [42.15-30](/cfr/46/42.15-30.md), or [42.15-80](/cfr/46/42.15-80.md), the freeboard shall be not less than 6 inches.
- (b) **Tropical freeboard.**
  - (1) The minimum tropical freeboard shall be the freeboard obtained by a deduction from the summer freeboard of one forty-eighth of the summer draft measured from the top of the keel to the center of the ring of the load line mark.
  - (2) The freeboard in salt water, as calculated in accordance with [paragraph (b)(1)](#b-1) of this section, but without the correction for deck line, as provided by [§ 42.20-35](/cfr/46/42.20-35.md), shall not be less than 2 inches. For vessels having in position 1 hatchways with covers which do not comply with the requirements of [§ 42.15-25(d)(1)](/cfr/46/42.15-25.md?p=d-1), [§ 42.15-30](/cfr/46/42.15-30.md), or [§ 42.15-80](/cfr/46/42.15-80.md), the freeboard shall be not less than 6 inches.
- (c) **Winter freeboard.**
  - (1) The minimum winter freeboard shall be the freeboard obtained by an addition to the summer freeboard of one forty-eighth of summer draft, measured from the top of the keel to the center of the ring of the load line mark.
- (d) **Winter North Atlantic freeboard.**
  - (1) The minimum freeboard for vessels of not more than 328 feet in length which enter any part of the North Atlantic defined in [§ 42.30-35](/cfr/46/42.30-35.md) during the winter seasonal period shall be the winter freeboard plus 2 inches. For other vessels the winter North Atlantic freeboard shall be the winter freeboard.
- (e) **Fresh water freeboard.**
  - (1) The minimum freeboard in fresh water of unit density shall be obtained by deducting from the minimum freeboard in salt water:
  - (2) Where the displacement at the summer load waterline cannot be certified, the deduction shall be one forty-eighth of summer draft, measured from the top of the keel to the center of the ring of the load line mark.