Boat bottom hull design

Details Boat bottom hull design Boat bottom hull design

1997-10-03

2001-01-23

Sotelo, Jesus D. (Department: 3617)

Ships

Hull or hull adjunct employing fluid dynamic forces to...

C114S291000

Reexamination Certificate

active

06176196

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a planing boat hull design, and more particularly to a boat hull bottom design that provides improved performance, from the standpoints of both (1) higher speed for a given installed power, and (2) reduced impact acceleration in waves for a given speed.
BACKGROUND ART
Planing refers to the hydrodynamic process whereas, on increasing speed, the boat is lifted up relative to the water surface by dynamic pressure acting over the surface of the boat hull bottom. This dynamic pressure is an increasing function of boat speed. At rest, the boat is supported (floats) by pressure provided by hydrostatics at zero speed, resulting in the boat being positioned deeper in the water, displacing a larger water volume than in planning.
Conflicting conditions of operation therefore exist with the typical planning craft:
1. displacement (low speed) mode, requiring relatively large displaced volume and larger wetted surface area, and
2. planing (high speed) mode, requiring relatively small displacement and smaller wetted surface area.
The conflict is that, in order to have the area needed for displacement operation, excessive area and its accompanying excessive drag tend to occur in high speed planing operation.
Modern planing craft resolve this conflict to some degree by the use of stepped sterns, lifting strakes, internal chines, and/or combinations thereof. [Note
FIG. 1
(“Prior Art”).] All three of the hull form modifications shown function to separate the flow in steady planing (as well as in seaway slamming) to produce a smaller area for reduced planing resistance (and impact acceleration).
In the current state-of-the-art of internal chines and lifting strakes, relatively small “flow trips” are used that are often not effective. The main shortcoming is that the flow separated at the chine, or strake, can reattach, and thus the prior art has not consistently achieved the relatively low wetted surface area needed for optimum planing performance. [Note
FIG. 2
(“Prior Art”).]
The present invention over-comes the prior art deficiencies.
GENERAL SUMMARY DISCUSSION OF INVENTION
The present invention over-comes the prior art's deficiencies by, in part, using a boat bottom hull with a much deeper, transverse step, as shown in
FIG. 3
in comparison to, for example,
FIG. 2
, to more effectively exploit the potential advantages of internal chines and lifting strakes. Thus, in the present invention, the hull bottom has a much deeper transverse step which effectively achieves a bi-modal hull form—displacement and planing.
The hull form of the present invention consistently achieves and maintains the flow separation needed to assure the relatively low surface area needed for minimum planing resistance and minimum sea wave impact acceleration. Comparative, specific analyzes, comparing the present invention's approaches to those of the prior art, are presented below, toward the end of the description portion of this specification.
In addition and in combination with the deeper transverse step, the concave curvature of the narrow planing region of the hull shifts the center of dynamic pressure forward and provides a more balanced acceleration, with less extreme boat attitudes, in the transition from displacement to planing mode, as well as when operating at steady speeds over the entire speed range.
It is thus an object of the invention to provide a planing boat hull that effectively achieves a bi-modal hull form—displacement and planing—by using a much deeper transverse step than that of the prior art.
It is a further object of the invention to provide a planing boat hull that consistently achieves and maintains the flow separation needed to assure the relatively low surface area needed for minimum planing resistance and minimum sea wave impact acceleration.
It is a further object of the invention to provide a planing boat hull that utilizes the concave curvature of the narrow planing region of the hull to shift the center of dynamic pressure forward, providing a more balanced acceleration, with less extreme boat attitudes, in the transition from displacement to planing mode, as well as when operating at steady speeds over the entire speed range.
It is a secondary object of the invention to provide a planing boat hull with a center of buoyancy and center of gravity in the same longitudinal position or as close thereto as practical.
It is also a secondary object of the invention to provide a boat hull that is able to ride on less wetted surface, thereby reducing power requirements, fuel costs, and increasing potential speed.


REFERENCES:
patent: 3698342 (1972-10-01), Jackson
patent: 4128072 (1978-12-01), Wood, Jr.
patent: 4409922 (1983-10-01), Mambretti

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