Is there a rule of thumb on the depth of the cavitation plate on an outboard in relation to the bottom of the transom? If it's too deep, can it adversely affect performance/speed? My old Gheenoe has a small, narrow transom - looks similar to a NMZ, but transom appears to be shorter. I've got a Mercury 8 hp 4 stroke with 15" shaft (and hydrofoil) but it seems really slow.
Batt34786
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7,582 Posts
The less lower unit there is in the water, the less wetted surface you have, the less friction you end up with.
Cav plate height depends on the hull shape and propeller.
Flat bottom hulls trap aerated water under the hull and this makes it difficult
for factory props to get a clean bite in the top inch and a half
of the water coming out from under the transom.
In this situation the engine is usually mounted so that the cav plate
(really the anti-ventilation plate) is 1/4 inch below the bottom of the hull.
On a vee hull the starting height is with the cav plate 1/2 inch above the bottom of the hull.
The reason being that the water coming out from under the center of the hull
has less aeration due to the vee shape.
Cav plate height depends on the hull shape and propeller.
Flat bottom hulls trap aerated water under the hull and this makes it difficult
for factory props to get a clean bite in the top inch and a half
of the water coming out from under the transom.
In this situation the engine is usually mounted so that the cav plate
(really the anti-ventilation plate) is 1/4 inch below the bottom of the hull.
On a vee hull the starting height is with the cav plate 1/2 inch above the bottom of the hull.
The reason being that the water coming out from under the center of the hull
has less aeration due to the vee shape.
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