204 A. Hadjidakis 
A. Hadjidakis 
I don’t agree, because although the heave is there, of course, the pitch will be more 
important, making the craft nosedive. In that case the angle of attack of the foils decreases, 
which means that lift decreases too (Fig. 5). Quite a big lift reserve on the forward foils 
is then needed to take the craft up again for the next wave, because otherwise the nose will 
touch that wave and then what we call seaworthiness in that particular case is finished and 
one cannot go at full speed. That is what I meant; I insist on the pitch being the most 
important factor on a following sea because, if you would go down horizontally, which is 
the case when heave is the main factor, you still have the same lift-coefficient, and it would 
be a very poor design if the craft wouldn’t go up then in time. 
P. Kaplan 
I want to know just how you get better performance from a small craft to a large one. 
You did not just increase the size, you also changed the speed. Now with Froude scaling 
we get the same relative values. Is there any particular way in which you did this or do 
you see any particular optimum way of carrying out this change in size and speed to obtain 
an improvement in the craft? . 
A. Hadjidakis 
The speed of 45 knots was chosen for the big craft with a capacity of about 400 passen- 
gers because of economic and efficiency reasons, and in my opinion it is not necessary to 
have higher speeds. The owner of the passenger-carrying craft will generally not gain 
more money by a somewhat higher speed and I think the passengers will not even realize 
the small time gains they will have in that case. Hence the number of 45 knots was not 
chosen for some physical reason. There is, however, another aspect to this matter. We 
have experience with all sorts of craft of different sizes and the biggest one could carry 
about 70 passengers. We found weight is not going up as the cube of the length of the 
craft, but somewhat less than that. It is logical to give a bigger craft a higher speed, 
which helps a lot in keeping the foil dimensions and weight down. In our designs the foil 
weight is about 5 to 8 percent of the total displacement weight. 
