Ships – Boats – boat component – or attachment – Hull construction
Reexamination Certificate
1999-07-26
2001-05-01
Avila, Stephen (Department: 3617)
Ships
Boats, boat component, or attachment
Hull construction
C114S056100, C114S274000
Reexamination Certificate
active
06223679
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to vessels' hulls, especially of sailboats, namely to hulls' shapes and way of designing such hulls.
2. Background of the Invention
Sailboats heel as wind pressure increases on the sails. As a result, the wetted surfaces shape of the boat's hull changes, losing its symmetry and making the boat turn to the windward side. To compensate for this, and in order to keep the boat on a straight course the helmsman needs to turn the rudder which then, being at an angle, creates an unnecessary drag underwater, slowing the boat's speed as a result.
SUMMARY OF THE INVENTION
This invention reduces the effect of weather helm on sailboats, as well as improves vessels' behavior and steering, in rolling conditions of vessels in general (including vessels under power). Additionally, by using this invention, it is easier to achieve lower or even lowest possible water resistance for a given displacement, width and waterline length.
A hull designed according to the invention does not lose its wetted surface's symmetry when not on even keel, and the underwater resistance remains equal on both sides of its metacentric radius.
The only time when the conventional hull's wetted surface (excluding its keel) is symmetrical is when the hull is on even keel. Once the boat starts heeling, the wetted surface becomes asymmetrical. This, together with the boat's keel resistance, which moves to one side of the metacentric radius while the boat heels, makes the boat turn in one direction.
This invention will eliminate one of those two factors. The problem of asymmetry of wetted surface is solved by creating a hull structure of which the cross-section is a section of a circle. This is true because no matter which part of a circle is considered, it always has its symmetry. Thus, a hull of which the cross section is part of a circle will retain symmetry of its wetted surface, regardless of which side the wetted surface is going to move towards, as a result of rolling or heeling.
This symmetry of the wetted surface is defined by the plane on which the metacentric radius lies, and which always coincides with the direction of vertical force of buoyancy, and divides the wetted surface's cross section in half.
If a boat designed according to this invention did not have a keel, the water flow and the hull's underwater resistance would be always equal on both sides of its metacentric radius. To reduce the effect of a keel's resistance, two keels can be provided (instead of one) symmetrically spaced on both sides of the hull. At certain angles of heel, one keel would start partially coming out of the water reducing drag on the side where more drag has occurred due to both keels shifting to that side. This would start equalizing the drag on both sides of the metacentric radius at the point where it becomes significantly unequal. This embodiment of the invention is especially preferred for sailboats with shallow draft desire.
REFERENCES:
patent: 518702 (1894-04-01), Schermerhorn
patent: 3054372 (1962-09-01), Jone, Jr.
patent: 3427671 (1969-02-01), Livaudais
patent: 3598076 (1971-08-01), Saxton
patent: 4509447 (1985-04-01), Smith, Sr.
patent: 4638753 (1987-01-01), Marschewski
patent: 5594852 (1997-01-01), Tankelevich
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