21 Location of Watertight Bulkheads for Subdivision

21.1 The maximum distance between adjacent main transverse watertight bulkheads on a vessel, required by regulation III/20 to comply with this regulation, shall not be more than the smaller of the following:

.1 one third of the length of the bulkhead deck; or

.2 the distance given by the following equation:

	=	where:
F	=	the floodable length factor from Table III/21.1 ;
f	=	the effective freeboard in metres calculated for each pair of adjacent bulkheads in accordance with III/21.2;
L	=	Length Over Deck in metres measured over the bulkhead deck; and
D	=	the depth in metres (feet), measured amidships at a point one-quarter of the maximum beam out from the centreline, from the inside of the bottom planking or plating to the level of the top of the bulkhead deck. (See Figure III/21-1 ).

Table III/21 Table of Floodable Length Factors

(d/L)x100		F
0-15		0.33
20		0.34
25		0.36
30		0.38
35		0.43
40		0.48
45		0.54
50		0.61
55		0.63
60		0.58
65		0.53
70		0.48
75		0.44
80		0.40
85		0.37
90-100		0.34
NOTE 1:	Where: d = distance in metres (feet) from the midpoint of the compartment to the forward-most point on the bulkhead deck excluding sheer; and L = length over deck in metres (feet) measured over the bulkhead deck.
NOTE 2:	Intermediate values of floodable length factor may be obtained by interpolation.

Figure III/21-1 Transverse Location for Measuring Depth(D)

21.2 The effective freeboard for each compartment is calculated by the following equation:

f = (a+b)/2
where:
	f	=	the effective freeboard in metres (feet).
	a	=	the freeboard in metres (feet) measured:
			.1	at the forward main transverse watertight bulkhead; and
			.2	from the deepest waterline to:
				.1	the top of the bulkhead deck on a flush deck vessel; and
				.2	where a vessel has a stepped bulkhead deck, then to the line shown in Figure III/21-2 ; or
				.3	where a vessel has an opening scuttle (porthole) below the bulkhead deck, then to the line shown in Figure III/21-3 .

	b	=	the freeboard in metres (feet) measured:
			.1	at the aft main transverse watertight bulkhead; and
			.2	from the deepest waterline to:
				.1	the top of the bulkhead deck on a flush deck vessel;
				.2	where a vessel has a stepped bulkhead deck, the line shown in Figure III/21-2 ; or
				.3	where a vessel has an opening scuttle (porthole) below the bulkhead deck, the line shown in Figure III-21-3 .

Figure III/21-2 Freeboard Measurement - Vessel with Stepped Bulkhead Deck

(a and b shown for two sample compartments)

Figure III/21-3 Freeboard Measurement - Vessel with Stepped Bulkhead Deck and a Porthole Below the Bulkhead Deck

21.3 A vessel, required by regulation III/20 to be fitted with watertight bulkheads shall be measured and subdivided in accordance with the simplified subdivision calculation given in Annex 3 .