Who knows why ships and yachts sometimes have a bulbous bow?

The bulbous bow is a standard feature on most round bilge yachts. It works as follows: The bow of a ship will cause a wave. Directly aft of the bow will be a wave peak, and some distance behind that, a wave trough. A bulb itself will cause the water to flow over it, and aft of it to form a wave trough. When the bulb is designed such that the wave trough aft of the bulb coincides with the bow’s wave peak, the two waves will cancel each other out.

I hope this answers your question?