Marine propulsion – Means for accomodating or moving engine fluids – Means for handling exhaust gas
Patent
1994-01-13
1995-08-15
Swinehart, Edwin L.
Marine propulsion
Means for accomodating or moving engine fluids
Means for handling exhaust gas
B63H 2132
Patent
active
054414326
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a boat propeller drive unit comprising a gear housing, in which at least one propeller shaft with a propeller is rotatably mounted, and an anti-cavitation plate which extends out over the propeller from the gear housing, has a distal end located aft of the sweep of the tips of the propeller blades and contains an exhaust duct with an outlet port for exhaust from an engine coupled to the drive unit.
BACKGROUND OF THE INVENTION
In a known common boat propeller drive unit of this type, a so-called inboard-outboard drive, in which the exhaust is conducted through a duct in the anti-cavitation plate, the distal end of the anti-cavitation plate is open aft and forms a rearwardly directed exhaust ejector. When operating planing motorboats equipped with such drive units at planing speed,, the exhaust is ejected directly out into the atmosphere, which has the advantage of low exhaust counter-pressure. In boats with vertical transoms with a relatively large surface and large superstructures, back-suction can occur however at certain speeds, with the result: that a cloud of exhaust will remain behind the transom and accompany the boat. In boats with the cockpit aft, exhaust can even be sucked into the cockpit creating discomfort to the passengers. Another common method of conducting exhaust away from a motorboat with an inboard-outboard drive unit is to allow the exhaust to exit through an exhaust duct in the propeller hub. The exhaust is thus ejected into the water even at planing speeds and the risk of exhaust being sucked into the cockpit due to back-suction is eliminated. Exhaust ejection through the propeller hub below the surface of the water creates however a higher exhaust counter-pressure than ejection through the cavitation plate directly out into the atmosphere.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide a propeller drive unit with an exhaust duct into the anti-cavitation plate which, while retaining a low exhaust counter-pressure, eliminate the risk of exhaust being sucked into the boat cockpit due to back-suction.
This is achieved according to the invention by virtue of the fact that the outlet port of the exhaust duct opens on the underside of the cavitation plate and is directed towards and is spaced from the distal end of the cavitation plate, said spacing being at least equal to the distance from said end to the sweep of the tips of the propeller blades.
It has been determined quite surprisingly that by moving the exhaust port slightly downwards and forwards as compared to the known design, together with the arrangement of a relatively short "screen" behind and above the port, it is possible to completely eliminate the risk of exhaust due to back-suction, being sucked into the cockpit and with no increase in the exhaust counter-pressure.
According to a preferred embodiment of the propeller drive unit according to the invention, the exhaust duct is defined by an arched hood which extends over the major portion of the length of the anti-cavitation plate and is sloped in the direction from the gear housing relative to the surrounding planar surface portions of the underside of the anti-cavitation plate and has, in horizontal projection, an essentially triangular shape with the tip of the triangle directed towards the gear housing. Such an embodiment results in the least possible deflection of the exhaust and eliminates the risk that the water flowing past the unit will exert an undesirable lifting force on the drive unit via the anti-cavitation plate.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described below in more detail with reference to an example shown in the accompanying drawings, where
FIG. 1 shows a longitudinal section through the lower gear housing of a propeller drive unit according to the invention,
FIG. 2 shows a cross section along the line II--II in FIG. 1 and
FIG. 3 is a view from below of the anti-cavitation plate.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, 1 designa
REFERENCES:
patent: 2111325 (1938-03-01), Linthwaite
patent: 4600394 (1986-07-01), Dritz
patent: 4840136 (1989-06-01), Brandt
patent: 4871334 (1989-10-01), Mc Cormick
patent: 4891025 (1990-01-01), Brandt
Rodskier Christian
Sellman Lennart
AB Volvo Penta
Swinehart Edwin L.
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