The bulb that you are refering to works for different reasons.



The bulb that is underwater creates a counterwave system that is the inverse of the wavesystem that would be caused by the shipshull is the bulb wasn't there. And these two wavesystems that are the inverse (reciprokal) of eachother cancel one another out. Therefor the wave system that is left is much reduces in magnitude and accounts for much less drag.



Also anything that is less tahn say 5 mtr. below the surface doesn't behave as if it were really submerged like a submeraine. The surface is just to near and water and the surface will be disturbed.



And the bulb you see on navy ships near the bow is the sonar housing.



Can these bulbs be used on sailboats ? Yes, but it will only be effective at a certain speed. This is ofcourse no problem for motor ships with a cruise speed but sailboats typcially sail at different speeds depending on the windconditions. Therefor is unlikely that such a bulb is of real interest to sailboat designers. A better solution (compromise) is to have a fine wedge as a bow and less displacement.hence the trend towards sharp bowed monohulls and catamarans.



Wouter