On the existing ships of about from 250 to 385 feet in length, usually there are two cargo hatchways for each of their fore and aft holds irrespective if there is a bulkhead in the hold or not.
It is not only convenient for ships to have one cargo hatchway to each hold to handle the cargoes of the usual size, but it is quite necessary to divide each of fore and aft holds by a bulkhead from the safety point of view, though their permeability, as shown in Table 1, is less than 60%.
All of the above stated ships are able to have a bulkhead in each of their fore and aft holds without disturbing the arrangement of their cargo hatchways.
On the other hand, though an ideal arrangement of the cargo handling gear is that the time to be needed for handling cargo is made equal for all holds. In fact, as shown in Table 4, it is difficult to do so for several reasons.
Thence the reasonable position of the bulkhead which divides the hold is such that the adjacent holds will have the same permeability.
The position of the bulkhead to be fitted in the hold is not equal for all ships as shown in Fig. 1.
Therefore, at the early stage of the design, it is convenient to fix the hold length by the following formula :-
l3-L3=(l2-l1){3/2(100/μ-1)-3/2(100/M-1)}
μwhich was derived from the well known formula
l3=(l2-l1)×3/2(100/μ-1)+l1
where l1, l2 and l3=permissible lengths of the referred ship,
μμ =permeability of the referred ship,
L3 =permissible length of the new ship,
M =permeability of the new ship.
The results calculated are shown in Tables 2 and 3.