Issue Number Eighty One

Go To Photo Log INDEX Page

Interesting Boats:  Stability & Speed of Compromise hulls

Compromise Hulls were first developed by the Truscott Boat Manufacturing Company of St. Joseph's Michigan, prior to 1900.  It was obvious by then that the popular fantail hulls  had a number of distinct disadvantages.
First; the waterline length was short, being only 85% of the overall length of the hull.  This meant that the hull speed was unnecessarily slow and energy was wasted in an attempt to move the boat at reasonable speeds.
Second; because of the fact that much of the hull was not in the water (notably the fine fantail or stern) much buoyancy was lost and stability was precarious.
Wide stout hulls avoided these drawbacks, but again were very wasteful of propulsion power, as their larger cross sectional areas required extra energy to push them through the water.
The Compromise Hull was developed and became a compromise between these various hull shapes.  Its hull has a wide stern, which is fairly flat contributing to fore and aft, and athwartship stability.  Moreover the stern remains in the water until the very back of the boat resulting in the waterline length being 95% of the boat length and consequently, a greater hull speed.

The photos above and below show excellent views of the longer waterline length and of the flatness of the hull aft.  Note too the slow dead rise of the hull from the center to the outer bilge, another contributor to the desired transverse stability.

The graph above shows the speed attainable for both the Rose 20 (fantail hull: LOA 20', LWL 17', 85%) and the Compromise 21 (compromise hull LOA 21', LWL 20', 95%). Note that at one horsepower the Rose 20 speed is 4.7 knots, while for the same power the Compromise speed is 5.5 knots.

Go To Photo Log INDEX Page