Merchant Shipping (Safety and Load Line Conventions) Act 1932

PART IIILoad Line for Steamers.

RULE XXXIILength (L).

The length used with the Rules and Freeboard Table is the length in feet on the summer load water-line from the foreside of the stem to the afterside of the rudder post. Where there is no rudder post, the length is measured from the foreside of the stem to the axis of the rudder stock. For ships with cruiser stems, the length is to be taken as 96 per cent. of the total length on the designed summer load water-line or as the length from the fore side of the stem to the axis of the rudder stock if that be the greater.

RULE XXXIIIBreadth (B).

The breadth is the maximum breadth in feet amidships to the moulded line of the frame in iron or steel ships, and to the outside of the planking In wood or composite ships.

RULE XXXIVMoulded Depth.

The moulded depth is the vertical distance in feet, measured amidships, from the top of the keel to the top of the freeboard deck beam at side. In wood and composite ships 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 depth is measured from the point where the line of the flat of the bottom continued inwards cuts the side of the keel.

RULE XXXVDepth for Freeboard (D).

The depth used with the Freeboard Table is the moulded depth plus the thickness of stringer plate, or plus if that be greater, where—

• T is the mean thickness of the exposed deck clear of deck openings, and

• S is the total length of superstructures as defined in Rule XL.

Where the topsides are of unusual form, D is the depth of a midship section having vertical topsides, standard round of beam and area of topside section equal to that in the actual midship section. Where there is a step or break in the topsides (e.g., as in the Turret Deck ship) 70 per cent. of the area above the step or break is included in the area used to determine the equivalent section.

In a ship without an enclosed superstructure covering at least .6 L amidships, without a complete trunk or without a combination of intact partial superstructures and trunk extending all fore and aft, where D is less than , the depth used with the Table is not to be taken as less than .

RULE XXXVICoefficient of Fineness (c).

The coefficient of fineness used with the Freeboard Table is given by—

RULE XXXVIIStrength.

The Assigning Authority is to be satisfied with the structural strength of ships to which freeboards are assigned.

Ships which comply with the highest standard of the rules of a Classification Society recognised by the Administration, shall be regarded as having sufficient strength for the minimum freeboards allowed under the Rules.

Ships which do not comply with the highest standard of the rules of a Classification Society recognised by the Administration, shall be assigned such increased freeboards as shall be determined by the Assigning Authority, and for guidance the following strength moduli are formulated :—

• Material.—The strength moduli are based on the assumption that the structure is built of mild steel, manufactured by the open hearth process (acid or basic), and having a tensile strength of 26 to 32 tons per square inch, and an elongation of at least 16 per cent. on a length of 8 inches.

• Strength Deck.—The strength deck is the uppermost deck which is incorporated into and forms an integral part of the longitudinal girder within the half-length amidships.

• Depth to Strength Deck (Ds).—The depth to strength deck is the vertical distance in feet amidships from the top of the keel to the top of the strength deck beam at side.

• Draught (d).—The draught is the vertical distance in feet amidships from the top of the keel to the centre of the disc.

• Longitudinal Modulus.—The longitudinal modulus is the moment of inertia I of the midship section about the neutral axis divided by the distance y measured from the neutral axis to the top of the strength deck beam at side, calculated in way of openings but without deductions for rivet holes. Areas are measured in square inches and distances in feet.

Below the strength deck, all continuous longitudinal members other than such parts of under deck girders as are required entirely for supporting purposes, are included. Above the strength deck, the gunwale angle bar and the extension of the sheerstrake are the only members included.

The required longitudinal modulus for effective material is expressed by f.d.B., where f is the factor obtained from the following table :—

For intermediate lengths, the value of f is determined by interpolation.

This formula applies where L does not exceed 600 feet; B is between and , both inclusive, and is between 10 and 13.5, both inclusive.

• Frame.—For the purpose of the frame modulus, the frame is regarded as composed of a frame angle and a reverse angle each of the same size and thickness.

• Frame Modulus.— The modulus of the midship frame below the lowest tier of beams is the moment of inertia I of the frame section about the neutral axis divided by the distance y measured from the neutral axis to the extremity of the frame section, calculated without deduction for rivet and bolt holes. The modulus is measured in inch units.

The required frame modulus is expressed by , where—

• s is the frame spacing in inches.

• t is the vertical distance in feet measured at amidships from the top of the keel to a point midway between the top of the inner bottom at side and the top of the heel bracket (see Figure 2); where there is no double bottom, t is measured to a point midway between the top of the floor at centre and the top of the floor at side.

• f₁ is a coefficient depending on H, which, in ships fitted with double bottoms, is the vertical distance in feet from the middle of the beam bracket of the lowest tier of beams at side to a point midway between the top of the inner bottom at side and the top of the heel bracket (see Figure 2). Where there is no double bottom, H is measured to a point midway between the top of the floor at centre and the top of the floor at side. Where the frame obtains additional strength from the form of the ship, due allowance is made in the value of f₁

• f₂ is a coefficient depending on K, which is the vertical distance in feet from the top of the lowest tier of beams at side to a point 7 feet 6 inches above the freeboard deck at side, or, if there is a superstructure, to a point 12 feet 6 inches above the freeboard deck at side (see Figure 2). The values of f₁ and f₂ are obtained from the following tables :—

  H in feet	0	7	9	11	13	15	17	19	21	23	25
  f1	9	11	12.5	15	19	24	29.5	36	43	51	59

  Intermediate values are obtained by interpolation.
  K in feet	0	5	10	15	20	25	30	35	40
  f2	0	0.5	10	2.0	30	4.5	6.5	90	12.0

This formula applies where D is between 15 feet and 60 feet, both inclusive, B is between and both inclusive, is between 10 and 13.5, both inclusive; and the horizontal distance from the outside of the frame to the centre of the first row of pillars does not exceed 20 feet.

In single deck ships of ordinary form, where H does not exceed 18 feet, the frame modulus determined by the preceding method is multiplied by the factor f₃where

.

Where the horizontal distance from the outside of the frame to the centre of the first row of pillars exceeds 20 feet, the Assigning Authority is to be satisfied that sufficient additional strength is provided.

Superstructures.

RULE XXXVIIIHeight of Superstructure.

The height of a superstructure is the least vertical height measured from the top of the superstructure deck to the top of the freeboard deck beams minus the difference between D and the moulded depth (see, Rules XXXIV and XXXV).

RULE XXXIXStandard Height of Superstructure.

The standard height of a raised quarter deck is 3 feet for ships up to and including 100 feet in length, 4 feet for ships 250 feet in length and 6 feet for ships 400 feet in length and above. The standard height of any other superstructure is 6 feet for ships up to and including 250 feet in length and 7 feet 6 inches for ships 400 feet in length and above. The standard height at intermediate lengths is obtained by interpolation.

RULE XLLength of Superstructure (S).

The length of a superstructure is the mean covered length of the parts of the superstructure which extend to the sides of the ship and lie within lines drawn perpendicular to the extremities of the Summer load water-line, as defined in Rule XXXII.

RULE XLIEnclosed Superstructure.

A detached superstructure is regarded as enclosed only where—

(a)the enclosing bulkheads are of efficient construction (see Rule XLII);

(b)the access openings in these bulkheads are fitted with Class 1 or Class 2 closing appliances (see Rules XLIII and XLIV);

(c)all other openings in sides or ends of the superstructure are fitted with efficient weathertight means of closing; and

(d)independent means of access to crew, machinery, bunker and other working spaces within bridges and poops are at all times available when the bulkhead openings are closed.

RULE XLIISuperstructure Bulkheads.

Bulkheads at exposed ends of poops, bridges and forecastles are deemed to be of efficient construction where the Assigning Authority is satisfied that, in the circumstances, they are equivalent to the following standard for ships with minimum freeboards under which standard the stiffness and plating are of the scantlings given in Table 3, the stiffeners are spaced 30 inches apart, the stiffeners on poop and bridge front bulkheads have efficient end connections, and those on after bulkheads of bridges and forecastles extend for the whole distance between the margin angles of the bulkheads.

Appliances for Closing Access Openings in Bulkheads at ends of Detached Superstructures.

RULE XLIIIClass 1 Closing Appliances.

These appliances are of iron and steel, are in all cases permanently and strongly attached to the bulkhead, are framed, stiffened and fitted so that the whole structure is of equivalent strength to the unpierced bulkhead, and are weathertight when closed. The means for securing these appliances are permanently attached to the bulkhead or to the appliances and the latter are so arranged that they can be closed and secured from both sides of the bulkhead or from the deck above. The sills of the access openings are at least 15 inches above the deck.

RULE XLIVClass 2 Closing Appliances.

These appliances are (a) strongly framed hard wood hinged doors, which are not more than 30 inches wide nor less than 2 inches thick; or (6) shifting boards fitted for the full height of the opening in channels riveted to the bulkhead, the shifting boards being at least 2 inches thick where the width of opening is 30 inches or less, and increased in thickness at the rate of 1 inch for each additional 15 inches of width, or (c) portable plates of equal efficiency.

Temporary Appliances for Closing Openings in Superstructure Decks.

RULE XLV

Temporary closing appliances for middle line openings in the deck of an enclosed superstructure consist of—

(a)a steel coaming not less than 9 inches in height efficiently riveted to the deck;

(b)hatchway covers as required by Rule X, secured by hemp lashings; and

(c)hatchway supports as required by Rules XI and XII and Table 1 or 2.

Effective Length of Detached Superstructures.

RULE XLVIGeneral.

Where exposed bulkheads at the ends of poops, bridges, and forecastles are not of efficient construction (see Rule XLII) they are considered as non-existent.

Where in the side plating of a superstructure there is an opening not provided with permanent means of closing, the part of the superstructure in way of the opening is regarded as having no effective length.

Where the height of a superstructure is less than the standard its length is reduced in the ratio of the actual to the standard height. Where the height exceeds the standard, no increase is made in the length of the superstructure.

RULE XLVIIPoop.

Where there is an efficient bulkhead and the access openings are fitted with Class 1 closing appliances, the length to the bulkhead is effective. Where the access openings in an efficient bulkhead are fitted with Class 2 closing appliances and the length to the bulkhead is .5 L or less, l00 per cent. of that length is effective; where the length is .7 L or more, 90 per cent. of that length is effective; where the length is between .5 L and .7 L, an intermediate percentage of that length is effective; where an allowance is given for an efficient adjacent trunk (see Rule LI), 90 per cent. of the length to the bulkhead is to be taken as effective. 50 per cent. of the length of an open poop or of an open extension beyond an efficient bulkhead is effective.

RULE XLVIIIRaised Quarter Deck.

Where there is an efficient intact bulkhead, the length to the bulkhead is effective. Where the bulkhead is not intact, the superstructure is considered as a poop of less than standard height.

RULE XLIXBridge.

Where there is an efficient bulkhead at each end, and the access openings in the bulkheads are fitted with Class 1 closing appliances, the length between the bulkheads is effective.

Where the access openings in the forward bulkhead are fitted with Class 1 closing appliances and the access openings in the after bulkhead with Class 2 closing appliances, the length between the bulkheads is effective; where an allowance is given for an efficient trunk, adjacent to the after bulkhead (see Rule LI), 90 per cent. of the length is effective. Where the access openings in both bulkheads are fitted with Class 2 closing appliances, 90 per cent. of the length between the bulkheads is effective. Where the access openings in the forward bulkhead are fitted with Class 1 or Class 2 closing appliances and the access openings in the after bulkhead have no closing appliances, 75 per cent. of the length between the bulkheads is effective. Where the access openings in both bulkheads have no closing appliances, 50 per cent. of the length is effective. 75 per cent. of the length of an open extension beyond the after bulkhead, and 50 per cent. of that beyond the forward bulkhead, are effective.

RULE LForecastle.

Where there is an efficient bulkhead and the access openings are fitted with Class 1 or Class 2 closing appliances, the length to the bulkhead is effective. Where no closing appliances are fitted and the sheer forward of amidships is not less than the standard sheer, 100 per cent. of the length of the forecastle forward of -1 L from the forward perpendicular is effective; where the sheer forward is half the standard sheer or less, 50 per cent. of that length is effective; and where the sheer forward is intermediate between the standard and half the standard sheer, an intermediate percentage of that length is effective. 50 per cent. of the length of an open extension beyond the bulkhead or beyond .1 L from the forward perpendicular is effective.

RULE LITrunk.

A trunk or similar structure which does not extend to the sides of the ship is regarded as efficient provided that—

(a)the trunk is at least as strong as a superstructure;

(b)the hatchways are in the trunk deck, and comply with the requirements of Rules VIII to XVI, and the width of the trunk deck stringer provides a satisfactory gangway and sufficient lateral stiffness;

(c)a permanent working platform fore and aft fitted with guard rails is provided by the trunk deck, or by detached trunks connected to other superstructures by efficient permanent gangways;

(d)ventilators are protected by the trunk, by watertight covers or by equivalent means;

(e)open rails are fitted on the weather portions of the free board deck in way of the trunk for at least half their length;

(f)the machinery casings are protected by the trunk, by a superstructure of standard height, or by a deck house of the same height and of equivalent strength.

Where access openings in poop and bridge bulkheads are fitted with Class 1 closing appliances, 100 per cent. of the length of an efficient trunk reduced in the ratio of its mean breadth to B is added to the effective length of the superstructures. Where the access openings in these bulkheads are not fitted with Class 1 closing appliances 90 per cent. is added.

The standard height of a trunk is the standard height of a bridge.

Where the height of the trunk is less than the standard height of a bridge, the addition is reduced in the ratio of the actual to the standard height; where the height of hatchway coamings on the trunk deck is less than the standard height of coamings (see Rule IX), a reduction from the actual height of trunk is to be made which corresponds to the difference between the actual and the standard height of coamings.

Effective Length of Enclosed Superstructures with Middle Line Openings.

RULE LIIEnclosed Superstructure with Middle Line Openings in the deck not Provided with Permanent Means of Closing.

Where there is an enclosed superstructure with one or more middle line openings in the deck not provided with permanent means of closing (see Rules VIII to XVI), the effective length of the superstructure is determined as follows :—

(1)Where efficient temporary closing appliances are not provided for the middle line deck openings (see Rule XLV), or the breadth of opening is 80 per cent. or more of the breadth B₁, of the superstructure deck at the middle of the opening, the ship is considered as having an open well in way of each opening, and freeing ports are to be provided in way of this well. The effective length of superstructure between openings is governed by Rules XLVII, XLIX, and L.

(2)Where efficient temporary closing appliances are provided for middle line deck openings and the breadth of opening is less than .8 B_1, the effective length is governed by Rules XLVII, XLIX, and L, except that where access openings in 'tween deck bulkheads are closed by Class 2 closing appliances, they are regarded as being closed by Class 1 closing appliances in determining the effective length. The total effective length is obtained by adding to the length determined by (1) the difference between this length and the length of the ship modified in the ratio of—

where is greater than .5 it is taken as .5.

Deductions for Superstructures.

RULE LIIIDeductions for Superstructures.

Where the effective length of superstructures is 1.0 L, the deduction from the freeboard is 14 inches at 80 feet length of ship, 34 inches at 280 feet length, and 42 inches at 400 feet length and above; deductions at intermediate lengths are obtained by interpolation. Where the total effective length of superstructures is less than 1.0 L the deduction is a percentage obtained from the following Table :—

Sheer.

RULE LIVGeneral.

The sheer is measured from the deck at side to a line of reference drawn parallel to the keel through the sheer line at amidships.

In ships designed to trim by the stern in service, the sheer may be measured in relation to the load line, provided an additional mark is placed at .25 L forward of amidships, to indicate the assigned load line. This mark is to be similar to the load line disc amidships.

In flush deck ships and in ships with detached superstructures the sheer is measured at the freeboard deck.

In ships with topsides of unusual form in which there is a step or break in the topsides, the sheer is considered in relation to the equivalent depth amidships (see Rule XXXV).

In ships with a superstructure of standard height which extends over the whole length of the freeboard deck, the sheer is measured at the superstructure deck; where the height exceeds the standard, the sheer may be considered in relation to the standard height.

Where a superstructure is intact or access openings in its enclosing bulkheads are fitted with Class 1 closing appliances, and the superstructure deck has at least the same sheer as the exposed freeboard deck, the sheer of the enclosed portion of the freeboard deck is not taken into account.

RULE LVStandard Sheer Profile.

The ordinates (in inches) of the standard sheer profile are given in the following Table, where L is the number of feet in the length of the ship :—

RULE LVIMeasurement of Variations from Standard Sheer Profile.

Where the sheer profile differs from the standard, the seven ordinates of each profile are multiplied by the appropriate factors given in the table of ordinates. The difference between the sums of the respective products, divided by 18, measures the deficiency or excess of sheer. Where the after half of the sheer profile is greater than the standard and the forward half is less than the standard, no credit is allowed for the part in excess and the deficiency only is measured.

Where the forward half of the sheer profile exceeds the standard, and the after portion of the sheer profile is not less than 75 per cent. of the standard, credit is allowed for the part in excess; where the after part is less than 50 per cent. of the standard no credit is given for the excess sheer forward. Where the after sheer is between 50 per cent. and 75 per cent. of the standard, intermediate allowances may be granted for excess sheer forward.

RULE LVIICorrection for Variations from Standard Sheer Profile

The correction for sheer is the deficiency or excess of sheer (see Rule LVI), multiplied by , where S is the total length of superstructure, as defined in Rule XL.

RULE LVIIIAddition for Deficiency in Sheer.

Where the sheer is less than the standard, the correction for deficiency in sheer (see Rule LVII) is added to the freeboard.

RULE LIXDeduction for Excess Sheer.

In flush deck ships and in ships where an enclosed superstructure covers .1 L before and .1 L abaft amidships, the correction for excess of sheer (see Rule LVII) is deducted from the freeboard; in ships with detached superstructures where no enclosed superstructure covers amidships, no deduction is made from the freeboard; where an enclosed superstructure covers less than .1 L before and .1 L abaft amidships, the deduction is obtained by interpolation. The maximum deduction for excess sheer is 1 ½ inches at 100 feet and increases at the rate of 1 ½ inches for each additional 100 feet in the length of the ship.

Hound of Beam.

RULE LXStandard Round of Beam.

The standard round of beam of the freeboard deck is one-fiftieth of the breadth of the ship.

RULE LXIRound of Beam Correction.

Where the round of beam of the freeboard deck is greater or less than the standard, the freeboard is decreased or increased respectively by one-fourth of the difference between the actual and the standard round of beam, multiplied by the proportion of the length of the freeboard deck not covered by enclosed superstructures. Twice the standard round of beam is the maximum for which allowance is given.

Minimum Freeboard.

RULE LXIISummer Freeboard.

The minimum freeboard in Summer is the freeboard derived from the Freeboard Table after corrections for departures from the standards and after deduction for superstructures.

The freeboard in salt water measured from the intersection of the upper surface of the freeboard deck with the outer surface of the shell is not to be less than 2 inches.

RULE LXIIITropical Freeboard.

The minimum freeboard in the Tropical Zone is the freeboard obtained by a deduction from the Summer freeboard of J inch per foot of Summer draught measured from the top of the keel to the centre of the

The freeboard in salt water measured from the intersection of the upper surface of the freeboard deck with the outer surface of the shell is not to be less than 2 inches.

RULE LXIVWinter Freeboard.

The minimum freeboard in Winter is the freeboard obtained by an addition to the Summer freeboard of J inch per foot of Summer draught, measured from the top of the keel to the centre of the disc.

RULE LXVWinter North Atlantic Freeboard.

The minimum freeboard for ships not exceeding 330 feet in length on voyages across the North Atlantic, North of latitude 36° N., during the winter months, is the Winter freeboard plus two inches; for ships over 330 feet in length it is the Winter freeboard.

RULE LXVIFresh Water Freeboard.

The minimum freeboard in fresh water of unit density is the freeboard obtained by deducting from the minimum freeboard in salt water inches, where

• Δ = displacement in salt water in tons at the Summer load water-line, and

• T = tons per inch immersion in salt water at the Summer load water-line.

Where the displacement at the Summer load water-line cannot be certified, the deduction is to be J inch per foot of Summer draught measured from the top of the keel to the centre of the disc.

RULE LXVIIFreeboard Table for Steamers.

Basic Minimum Summer Freeboards for Steamers which Comply with the Standards Laid Down in the Rules.

(i)The minimum freeboards for flush deck steamers are obtained by an addition to the above Table at the rate of 1½ inches for every 100 feet of length.

(ii)The freeboards at intermediate lengths are obtained by interpolation.

(iii)Where c exceeds .68, the freeboard is multiplied by the factor .

(iv)Where D exceeds the freeboard is increased by inches, where R is at lengths less than 390 feet, and 3 at 390 feet length and above.

In a ship with an enclosed superstructure covering at least .6 L amidships, with a complete trunk, or with a combination of intact partial superstructures and trunk which extends all fore and aft, where D is less than , the freeboard is reduced at the above rate. Where the height of superstructures or trunk is less than the standard height, the reduction is in the ratio of the actual to the standard height.

(v)Where the actual depth to the surface of the freeboard deck amidships is greater or less than D, the difference between the depths (in inches) is added to or deducted from the freeboard.