46 CFR 45.53 - Summer freeboard.

(a) Except as required in paragraph (c) of this section, the minimum freeboard in summer for a type A vessel is F in the following formula modified by the corrections in this subpart:

F (inches) = 10.2 × P1 × D

where P1 is defined in § 45.55 and D is the depth for freeboard in feet.

(b) Except as required in paragraph (c) of this section, the minimum freeboard in summer for a type B vessel is F in the formula modified by the corrections in this subpart:

F (inches) = 12 × P1 × D

where P1 is defined by § 45.55 and D is the depth for freeboard in feet.

(c) Seasonal freeboards assigned under §§ 45.71 through 45.75 must be calculated on the basis of the summer freeboard calculated under paragraph (a) or (b) of this section.

(d) If a minimum freeboard is required for a vessel under this part which is greater than that required by paragraph (a) or (b) of this section because of scantling or subdivision requirements, the summer freeboard and the seasonal freeboards assigned under this subpart must be no less than that minimum freeboard, except the midsummer seasonal freeboard may be calculated on the basis of the summer freeboard assigned under this paragraph.

(e) If a greater than the calculated minimum freeboard is requested by the applicant for the load line certificate, that greater freeboard may be assigned as the summer freeboard and—

(1) The intermediate and winter seasonal freeboards assigned must be calculated under paragraph (a) or (b) of this section; and

(2) The midsummer seasonal freeboard must be calculated on the basis of the summer freeboard assigned under this paragraph.

§ 45.55 - Freeboard coefficient.

(a) For ships less than 350 feet in length (L), the freeboard coefficient is P1 in the formula:

P1=P + A[(L/D)-(L/Ds)]

where P is a factor, which is a function of the length from table 1 and “A” is a coefficient, which is a function of length (L), from table 2; L/D is the ratio of the length (L) to the depth for freeboard (D); L/Ds is the ratio of the length (L) to a standard depth (Ds) from table 3.

D is not to be used as less than that which will give a ration of L to D that is:

(a) More than 15 when L = 400 feet or less, or

(b) More than 21 when L = 700 feet or more, with the ratio for intermediate lengths being calculated proportionately.

(b) For ships 350 feet or more in length (L), the coefficient “A” is zero and the formula is:

P1=P

where P is a factor, which is a function of length from table (1).

§ 45.57 - Correction: Position of deckline.

(a) Where the depth to the upper edge of the deckline is greater or less than D, the difference between the depths must be added to or deducted from the freeboard.

(b) When the Commandant or the approved assigning authority approves a location for the deckline that is above or below the freeboard deck, the minimum summer freeboard must be corrected by—

(1) Adding the difference between the depth and D if the depth is greater than D; and

(2) Subtracting the difference between the depth and D, if the depth is less than D.

§ 45.58 - Correction: Short superstructure.

The minimum freeboard in summer for a type B vessel that is 79 ft. or more but less than 500 ft. in length and has enclosed superstructures with an effective length of 25 percent or less of the length of the vessel must be increased by—

0.03 (500—L) (0.25—E/L) inches

where:

(L) = length of vessel in feet;

(E) = effective length of superstructure in feet as defined in § 45.59.

§ 45.59 - Definitions for superstructure corrections.

For the purpose of §§ 45.58 through 45.61—

(a) The standard height of a superstructure (Hs) other than a raised quarter deck and the standard height of a trunk (Hs) is determined by the formula:

Hs=[6.0 + (L/300)] ft

(b) The length of superstructure (S) is the length of those parts of the superstructure which extends to the sides of the vessel and that lie within the length (L).

(d) The effective length (E) of an enclosed superstructure of standard height or greater is its length “S”.

(e) Where the height of an enclosed superstructure or trunk is less than the standard height (Hs),the effective length (E) is its length reduced in the ratio of its height to Hs.

(f) The effective length (E) of a raised quarter deck of 2/3 Hs or greater that has no openings in the front bulkhead is its length up to a maximum of 0.6L.

(g) The effective length (E) of a raised quarter deck of less than 2/3 Hs or that does not have an intact front bulkhead is its length reduced by the ratio of its height to Hs.

Table 12(1)

tables of p values

Length of Ship (feet)	Value of P
80	0.1100
90	0.1136
100	0.1172
110	0.1208
120	0.1244
130	0.1281
140	0.1318
150	0.1355
160	0.1393
170	0.1430
180	0.1468
190	0.1506
200	0.1545
210	0.1583
220	0.1622
230	0.1661
240	0.1700
250	0.1740
260	0.1780
270	0.1820
280	0.1860
290	0.1900
300	0.1941
310	0.1982
320	0.2023
330	0.2065
340	0.2106
350	0.2148
360	0.2190
370	0.2233
380	0.2275
390	0.2318
400	0.2361
410	0.2400
420	0.2437
430	0.2472
440	0.2506
450	0.2537
460	0.2567
470	0.2595
480	0.2621
490	0.2645
500	0.2667
510	0.2688
520	0.2706
530	0.2723
540	0.2738
550	0.2751
560	0.2762
570	0.2772
580	0.2779
590	0.2785
600	0.2788
610	0.2790
620	0.2790
630	0.2789
640	0.2785
650	0.2779
660	0.2772
670	0.2768
680	0.2760
690	0.2751
700	0.2740
710	0.2728
720	0.2715
730	0.2700
740	0.2684
750	0.2667
760	0.2648
770	0.2628
780	0.2607
790	0.2584
800	0.2560
810	0.2532
820	0.2504
830	0.2476
840	0.2448
850	0.2420
860	0.2392
870	0.2364
880	0.2336
890	0.2308
900	0.2280
910	0.2252
920	0.2224
930	0.2196
940	0.2168
950	0.2140
960	0.2112
970	0.2084
980	0.2056
990	0.2028
1000	0.2000

Table 12(2)

values of “a” for use in the expression

Length of Ship (feet)	Value of “A”
80	0.00864
90	0.00806
100	0.00750
110	0.00696
120	0.00644
130	0.00594
140	0.00546
150	0.00500
160	0.00456
170	0.00414
180	0.00374
190	0.00336
200	0.00300
210	0.00266
220	0.00234
230	0.00204
240	0.00176
250	0.00150
260	0.00126
270	0.00104
280	0.00084
290	0.00066
300	0.00050
310	0.00036
320	0.00024
330	0.00014
340	0.00006
350	0.00000

Table 12(3)

values of l/ds

Length of Ship (feet)	Value of L/D5
80	6.50000
90	6.76563
100	7.03125
110	7.29688
120	7.56250
130	7.82813
140	8.09375
150	8.35938
160	8.62500
170	8.89063
180	9.19625
190	9.42188
200	9.68750
210	9.95313
220	10.21875
230	10.48438
240	10.75000
250	11.01563
260	11.28125
270	11.54688
280	11.81250
290	12.07813
300	12.34375
310	12.60938
320	12.87500
330	13.14063
340	13.40625
350	13.67188
360	13.93750
370	14.20313
380	14.46875
390	14.73438
400	15.00000

(h) Superstructures which are not enclosed have no effective length.

(i) 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.

(j) A bridge or poop is enclosed only when access is provided whereby the crew may reach accommodations, machinery, or other working spaces inside the superstructure by alternative means that are available at all times when bulkhead openings are closed.

§ 45.61 - Correction for superstructures and trunks.

(a) Where the effective length E of superstructures and trunks that meet the requirements of subpart D of this part is 1.0L, the minimum summer freeboard may be corrected by subtracting 1/2Hs.

(b) Where the effective length of superstructures and trunks is less than 1.0L the minimum summer freeboard may be corrected by subtracting a percentage of one-half of the standard superstructure height (Hs) determined by the formula:

Percentage = (E/2L) (1 + E/L) × 100

(1) Be at least as strong and as stiff as a superstructure;

(2) Have no opening in the freeboard deck in way of the trunk, except small access openings;

(3) Have hatchway coamings and covers that meet §§ 45.143 through 45.147;

(4) Provide a permanent working platform fore and aft with guardrails;

(5) Provide fore and aft access between detached trunks and superstructures by permanent gangways;

(6) Be at least 60 percent of the breadth of the ship in way of the trunk; and

(7) Be at least 0.6 L in length, if no superstructure, is provided.

§ 45.63 - Correction for sheer.

(a) The minimum summer freeboard must be increased by the deficiency, or may be decreased by the excess as limited by § 45.65, of sheer calculated from table 4, multiplied by:

0.75—(S/2L)

where S is the total length of enclosed superstructures. Trunks are not included.

§ 45.65 - Excess sheer limitations.

The decrease in freeboard allowed in § 45.63 is limited as follows:

Sheer Calculation—Table 4

Station	S. M.	Product
After Half:
AP	1
L/6-AP	3
L/3-AP	3
Midship	1	______________
Sum of Aft Products
After Standard Sheer .2665L + 26.65 ¹		______________
Difference: Sum-STD		______________ + Excess/−Deficiency
AFT Sheer: Diff ÷ 8		______________ Excess/Deficiency
Fwd. Half:
FP	1
L/6-FP	3
L/3-FP	3
Midships	1	______________
Sum of Fwd Products
Fwd Standard Sheer .5330L + 53.30 ¹		______________
Difference: Sum-STD		______________ + Excess/−Deficiency
FWD Sheer: Diff ÷ 8		______________ Excess/Deficiency

¹ L in Standard Sheer = L or 500 whichever is less.

Sheer Summation

Aft Sheer±	______________
Fwd Sheer±	______________
Net Sheer±	______________
Mean: Net−2	______________ Excess/Deficiency

(a) In vessels having no enclosed superstructure from 0.1 L abaft amidships to 0.1 L forward of amidships, no decrease is allowed.

(b) In vessels having enclosed superstructures amidships less than 0.1 L before and abaft amidships, the decrease must be reduced by linear interpolation.

(c) If excess sheer exists in the forward half, and the after half is at least 75 percent of standard sheer, the full decrease is allowed. If the after sheer is between 50 percent and 75 percent of standard sheer an intermediate decrease, determined by linear interpolation, is allowed for the excess sheer forward. If the after sheer is 50 percent of standard or less, no decrease is allowed for the excess sheer forward.

(d) Where an enclosed poop or forecastle is of standard height with greater sheer than that of the freeboard deck, or is greater than standard height, an addition to the sheer of the freeboard deck may be made using the following formula:

S=vL′/3L

Where

s = sheer credit, to be deducted from the deficiency or added to the excess of sheer.

v = difference between actual and standard height of superstructure at the end ordinate.

L′ = mean enclosed length of poop or forecastle up to a maximum length of 0.5 L.

The superstructure deck must not be less than standard height above this curve at any point. This curve must be used in determining the sheer profile for forward and after halves of the vessel.

(e) The maximum decreased for excess sheer must be no more than 1 1/2 inches per 100 feet of length.

(f) 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 cannot be taken into account.

§ 45.67 - Sheer measurement.

(a) The sheer is measured from the freeboard deck at side to a line of reference drawn parallel to the keel through the sheer line at amidships;

(b) In ships designed with a rake of keel or designed to trim by the stern, the sheer must be measured in reference to a line drawn through the sheer line at amidships parallel to the design load waterline.

(d) In ships with a step or break in the topsides, the sheer must be measured from the equivalent depth amidships.

(e) In vessels with a superstructure of standard height that extends over the whole length of the freeboard deck, the sheer must be measured on the superstructure deck. Where the height of superstructure exceeds the standard, the least difference (Z) between the actual and standard heights must be added to each end ordinate. Similarly, the intermediate ordinates at distance of 1/6 L and 1/3 L from each perpendicular must be increased by 0.444 Z and 0.111 Z respectively.

§ 45.69 - Correction for bow height.

(a) The minimum summer freeboard of all manned vessels must be increased by the same amount in inches as any deficiency which may be shown by the following formulas:

(1) For vessels having a length of not less than 79 feet and not greater than 550 feet,

0.593 L (1.0-L/1640) inches—actual bow height

(2) For vessels having a length greater than 550 feet,

(341.6—0.227 L) inches—actual bow height

(b) Where the bow height is obtained by sheer, the sheer must extend for at least 15 percent of the length of the vessel measured from the forward perpendicular.

(c) Where the bow height is obtained by a superstructure, the superstructure must be enclosed and extend from the stem to a point at least 0.06 L abaft the forward perpendicular.

(d) Vessels which, to suit exceptional operational requirements, cannot meet the requirements of paragraph (c) of this section may be given special consideration by the Commandant.

(e) The bow height is defined as the vertical distance at the forward perpendicular between the waterline corresponding to the assigned summer freeboard at the designed trim and the top of the exposed deck at side.

§ 45.71 - Midsummer freeboard.

The minimum midsummer freeboard (fms) in inches is obtained by the formula:

fms = f(s) − 0.3Ts

where:

f(s) = summer freeboard in inches

Ts = distance in feet between top of keel and the summer load line.

§ 45.73 - Winter freeboard.

The minimum winter freeboard (fw) in inches is obtained by the formula:

fw=f(s) + T s (200)/L

where:

L = length L in feet but not less than 400 feet.

§ 45.75 - Intermediate freeboard.

The minimum intermediate freeboard (fI) in inches is obtained by the formula:

fI=f(s) + T s(100)/L

where:

L = length L in feet but not less than 400 feet.

§ 45.77 - Salt water freeboard.

(a) The salt water addition in inches to freeboard applicable to each fresh water mark is obtained by the formula:

Addition=Δ/41T

where:

Δ = displacement in fresh water, in tons of 2,240 pounds, at the summer load waterline.

T = tons per inch immersion, of 2,240 pounds, in fresh water at the summer load waterline.

(b) When the displacement at the summer load waterline cannot be certified, the addition in inches to the minimum freeboard in fresh water may be obtained by multiplying 0.25 by the summer draught in feet measured from the top of the keel to the center of the load line diamond.

authority: 46 U.S.C. 5104,5108; Department of Homeland Security Delegation No. 0170.1

source: CGD 73-49R, 38 FR 12290, May 10, 1973, unless otherwise noted.

cite as: 46 CFR 45.53