Ships – Displacement-type hull – Multiple hulls
Reexamination Certificate
1999-11-16
2001-06-26
Sotelo, Jesus D. (Department: 3617)
Ships
Displacement-type hull
Multiple hulls
C114S271000
Reexamination Certificate
active
06250240
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improvement in water craft of single-hull type or multi-hull type and equipped with one or more ventilated propellers of so called “surface piercing propeller” type, especially water craft intended to be driven at high speeds over water, for instance speeds of at least 20-30 knots, preferably up to 50 knots or more.
BACKGROUND OF THE INVENTION
Normally propellers of surface piercing propeller type are arranged and mounted so that the propeller, upon driving the boat in a water surface planing position, operates with at least 50% of the driving surface above the sea water surface or otherwise in a corresponding gas or air flow. Propellers of this type exhibit many advantages over conventional propeller arrangements, where the propeller as a complete operates under water. Among other things, the fact that the propeller in part operates in the air involves the advantage that there will be very little, if any, cavitation, and that the propeller, in spite exhibiting very strong propulsion force, is subjected to very small, if any, cavitation damages.
In some respects, however, a surface piercing propeller also can give rise to some problems. Since the propeller blades to a great part of their revolution operates in air there will appear a lifting force when the propeller, after having rotated in the air, hits the water surface. The propeller blades thereby hit the water surface with a substantially horizontal force. Said lifting force can amount even up to 30% of the propulsion force of the propeller, and this will reduce the effective propulsion ability of the propeller.
Since only half the propeller operates under water the impact force of the propeller against the water surface also will make the propeller shaft be subjected to a certain unevenly distributed load which may cause problems with wear of bearings, vibrations, and in the worst case, rupture of the propeller shaft.
There has been a desire to make it possible to make use of the favourable properties of surface piercing propellers by using such surface piercing propellers also for propulsing ships in the cases where the propeller, even at full speed of the ship, operates entirely under water. This, however, has not met with success depending on a problem which has been difficult to solve:
Since the propeller operates entirely under the water surface there will be a strong sub pressure against the surface of the propeller facing forwardly and this leads to cavitation and cavitation damages depending therefrom. Cavitation damages can generally be compared with corrosion damages. For eliminating such problem it is necessary that the surface piercing propellers are ventilated, so that the sub pressure against front surfaces of the propeller blades can be unloaded at each individual revolution of the propeller, and whereby air bubbles, which tend to appear at the (front) suction side of the propeller in case of cavitation, are removed. The ventilation also should be such that the propeller blades, during the greatest part of their revolution, for instance up to 90% of their revolution, are allowed to operate in the water, whereas said propeller blades, during a very little part is its revolution, operate in the air. In this last mentioned case the sub pressure on the suction side of the propeller blade is unloaded, and this strongly reduces the risk of appearance of cavitation.
The ventilation of a surface piercing propeller, which operates entirely under water has, in turn, caused special problems.
SUMMARY OF THE INVENTION
According to the invention the drive, or the hub of the water craft, with the surface piercing propeller is mounted adjacent the bottom of a fin like hull body, or a part of a complete hull body comprising a fin like hull part extending down towards the propeller hub, and whereby said hull part has a rear side extending transversally to the longitudinal direction of the water craft and has an average width in said direction which is substantially less than the propeller diameter. In the vertical direction the transversely cut conical fin body should extend at an angle upwards-forwards from the propeller centre of not more than 45° to an angle upwards-rearwards from the propeller of not more than 45°. While propulsing the water craft forwards at a medium to high speed the fin like hull part creates a cone shaped air column down to the propeller hub, and behind the propeller a successively reduced cone shaped air chamber. Said air column down to the propeller centre should be as narrow as possible, and preferably it should not cover more than 10% of the propulsion surface of the propeller, at a maximum. It is very important that said air column at the propeller hub is so narrow as possible. When the propeller rotates each propeller blade passes once per revolution through said air column, whereby the sub pressure against the propeller blade is practically completely unloaded.
Tests in water have proved that a water craft of the described type having a surface piercing propeller and having the above described V-shaped hull fin does not give such cavitation sling of air which is normally seen after conventional water craft having sub-water driven propellers giving a high propulsion force.
Both sides of the fin like sub water body or hull body portion preferably are concave and can have such arc shape that the tangent of the sides of the fin body adjacent the propeller hub is 0°, that is that said sides extend in the vertical direction. An angle between the propeller centre and the contact point of the hull body with the sea water surface, when the water craft is running at medium to high speed, can for instance be ±45°, at a maximum.
In a special embodiment of the invention the drive or hub is formed like a type of torpedo having a circular cross section, which torpedo has, at its rear end, a propeller, and the length of which is about 10-20 times the greatest diameter thereof, most preferably about 12-16 times the torpedo diameter. The front end of the fin with the torpedo portion can preferably meet the ordinary hull body portion in the form of a clipper stem like part, that is in a kind of C-formation.
In a still further preferred embodiment of the invention the torpedo like body mounted under the ordinary hull of the water craft is formed as a housing for the drive engine, for instance the gas turbine, and possibly also for the fuel tank, whereby the centre of gravity of the water craft will be placed lower than is possible in ordinary water craft, in which the drive engine is normally mounted inside the hull above, or at least close, to the sea water level. Therefore the torpedo with the engine acts as a type of heavy keel for the water craft.
A further advantage with the such an apparatus also is that the propeller can be mounted with the propeller shaft extending horizontally, meaning parallelly the sea water level when the water craft is running at cruising speed. This gives an optimum good propulsion ability, in particular since the propeller can be mounted with the thrust surfaces thereof at an optimum angle in relation to the sea and the running, water craft.
In a still further embodiment of the invention the front end of the torpedo like submarine body, which is opposite to the propeller end, is formed with a streamline cone which can be extended some distance thereby forming an annular space between the torpedo body and the front cone, in which annular space air band/or exhaust gases from the drive engine can be pressed out, which air forms an air jacket round the torpedo body, which air jacket extends as far as to, and past the propeller thereby ventilating same. By expelling the front cone more or less in relation to the torpedo body there is obtained a more narrow or more widened air/gas jacket. Thereby the ventilation of the propeller can be adjusted to an optimum, adapted to different speeds and/of different loading ot the water craft.
Thus, the invention relates to an improvement in water craft of single-hull or multi-hull t
Thiger Hans
Thiger Pierre
Larson & Taylor PLC
Sotelo Jesus D.
Thiger Pierre
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