Bulb shape is an interesting topic that you don't hear much information on. For most R/C model yachts, the round torpedo is the most common shape of keel bulb used. This is understandable because the round torpedo bulbs are easy to design and build. Round bulbs also have another characteristic that is worth noting; round bulbs have minimum frictional drag.

Frictional drag is water flowing over the surface of an object. The larger the surface the greater the drag. What that means to the model yachter is, the more wetted area of a bulb, the greater the frictional drag. The more frictional drag there is the, greater the resistance to the boat speed. Any way to lower the wetted area will improve the performance of the boat.

If this is the cast, is there any other ways to increase the performance of the boat? Ever thought about elliptical keel bulbs? How can elliptical shape bulb improve sailing performance? Elliptical keel bulbs are round bulbs that have been flatten to some degree. Elliptical bulbs are still torpedo in shape like the round bulb, but with a difference.

The difference between the round bulb and the elliptical bulb is the elliptical bulb has a slightly more wetted surface. How can having more wetted area over a round bulb have a good effect on more boat performance? Well, it is a trade-off between more wetted area and two advantages that the elliptical shaped bulb gives.

The first advantage is the elliptical bulb has a lower center of gravity, which adds improved stability. The second advantage is more keel fin is exposed above the elliptical bulb thus giving more lift! (See figure below.) So with a slightly larger wetted surface is not much of a problem after all when a sailboat gains a little more lift to the keel.

As the figure shows, the elliptical bulb's center of gravity is lower, and this gives more keel length over the round bulb. This added keel length gives a little more lift to the keel fin. By adding more lift to the fin, the sailboat can sail a slightly straighter course.

At this point in time I have not seen any elliptical shaped torpedo keel bulbs. I do not know if any skippers have looked into elliptical bulbs, but it may be worth doing so for a little more advantage.