being under strict obligation to pay for services rendered by the owners, the charterers are obviously concerned over uninterrupted employment of the vessel. On the other hand, there are many factors peculiar to shipping business make delays inevitable. To deal with consequences of such delays parties insert certain provisions into the time charter contract, which are primarily collected in an ‘off-hire’ clause.
Royal Greek Government v Minister of Transport (The Ilissos)  1 KB 525,  1 All ER 171, 82 Ll L Rep 196, CA by Cohen LJ at pp.173-4:
I agree with the learned judge that in the context in which it appears in this charterparty "deficiency" means numerical insufficiency. Counsel invited us to say that the word imported a qualitative as well as a quantitive element. He cited definitions from the Oxford Dictionary which show that the meaning he argued for is a possible meaning of the word, but I agree with counsel for the shipowners that "deficiency" is normally used in contrast to "sufficiency" and that, if it were desired to introduce the qualitative element, the natural contrast would be between efficiency and inefficiency. I think I should have come to this conclusion from the consideration of cl 11A by itself, but, in my opinion, that view is reinforced by a reference to cl 34, where the side note to the clause is "Deficiency of crew," and the operative words, so far as material, are:
“Addendum to cl. 11A. Notwithstanding the provisions of cl. 11A it is agreed that in the event of loss of time due solely to inability to get or to complete a crew (a) full hire will be paid for the first 72 hours of such loss of time ”
I think the natural meaning of the words in the body of the clause suggests that the clause is dealing only with numerical deficiency in the numbers of the crew. Reading it with the marginal note, it seems to me to throw light on the sense in which the word "deficiency" is used in this charterparty. Be it remembered that the clause is described as "Addendum to cl 11A." I cannot believe that "deficiency of crew" in the marginal note to cl 34 is used in a different sense to "deficiency of men" in cl 11A. I will add that, if there is an ambiguity, the ambiguity appears in an exceptions clause, and the charterer must show that he is clearly within the exceptions clause.