Out of curiosity, I have done some testing of the hull characteristics of a Footy hull. This is part of an effort to defeat a V-12 that has been constantly beating me on the race course every Thursday, causing unbearable humiliation. My current boat is the Pepsi Torpedo, made of two 2-liter Pepsi bottles glued together lengthwise. As an improvement, I am now making a fatter and lighter hull, using a single 3-liter soda bottle. The testing was done with an empty 3-liter bottle, with moveable weights to adjust the pitch trim (nose-up vs nose-down). A skeg was added to provide some directional stability. This provides a cheap test vehicle that can be lost at sea with no regrets.
The characteristics of concern were pitch stability (submarining) and drag.
The pitch stability was measured in the bathtub by moving weights inside the bottle, on a velcro track. A 16 oz hull, using the 3-liter bottle, had a pitch stability of 32 oz-in/in, which means a 1 oz weight, 32 inches forward of center, will cause the prow to dip 1 inch. This test did not include a keel or bulb, which will add a small amount of pitch stability. This result is significantly better than the existing Pepsi Torpedo, and should allow it to carry more sail without nose-diving. It is probably not quite as good as the V-12, but it is getting close. The soda bottle hull actually sails quite well with its entire nose under water, as long as part of the rudder stays wet.
Drag was measured in two configurations. First with an approximately level 16 oz hull, which was actually about 1/4" nose-up. Secondly with a deliberately nose-down hull, also of 16 oz. The nose was 3/4" down. The data is:
Speed Drag Comments
0.57 0.24 nose-up 1/4"
0.86 0.72 nose-up 1/4"
0.96 0.72 nose-down 3/4"
1.44 1.20 noe-down 3/4"
The probable accuracy of the data is:
Speed data = 10%
Drag data = 1/8 oz
This data was taken with very primitive methods, but the results do not appear unreasonable. The data did not go significantly past the theoretical hull speed, where I am sure the drag will rise much faster. The gain in speed at the 0.72 ounce drag point, when going from nose-up to nose-down, may not be real, as it falls within the measurement accuracy.
If you plot the data, you will see that it has an approximate square-law shape, but strangely does not rise more sharply at the higher speeds. This may be due to inaccuracy in the data, or it may be real (the high prismatic coefficient of the hull may be advantageous as the hul speed is approached). The testing method was VERY primitive.
This data is being presented because I have never found anything at all on hulls this small at such low speeds. Others are probably also looking for this kind of information, so this may be a useful starting point.
Bear in mind that the hull shape is probably nowhere close to optimal for drag, because it is essentially a long cylinder with a little rounding at the ends. But it is a better than average shape for pitch stability. Hopefully that will enable it to carry enough sail to make up for the difference.
I would be interested in any other data of this kind on other Footy hull types.