Engine location on boat

[BayouRunner]

I got the part where the engine goes on the BACK of the boat, but I'm having troubles at to what HEIGHT the engine goes. i.e., in pic 1, the anti-cavitation plate is just a hair above the bottom of the boat. But is that right? Or should pic 2, which shows the "plate" ABOVE the anti-cavitation plate, should THAT be level or as close to level as possible, with the bottom of the boat?

 

[Bob_VT]

Re: Engine location on boat

About an 1" above and because you have it mounted on that plate you might even go higher.....but I would start 1" high above the keel

 

[BayouRunner]

Re: Engine location on boat

I probably didn't explain myself enough. In the 2 pictures, which plate should be 1" above/below the bottom of the boat? I current have the plate in picture 1 about an inch or so above the bottom of the boat. I'm wondering if that would/is putting my prop to close to the surface of the water, which would probably cause cavitation issues.

 

[ondarvr]

Re: Engine location on boat

The lower one is the AV plate (anti ventilation, not cavitation, but frequently referred to as one), the upper one is to divert water from spraying up.

There is no knowing the exact right height before testing it, pick a height, check the RPM's, speed and handling, move it up or down a measured amount and do the same testing. After testing several heights you will get it dialed in. Having it too high will allow it to ventilate, cavitation is a totally different animal.

 

[BayouRunner]

Re: Engine location on boat

So the anti-ventilation plate is the one that should be close to level with the bottom of the boat, and not the one that diverts water from spraying up?? And would a lil below the bottom of the boat be better than a lil above? I have a feeling when I'm on plane, the prop is to close to the surface and I'm not getting the correct "bite" from the prop in the water as I should.

 

[airshot]

Re: Engine location on boat

ondarvr is correct in his explanation no known formula. Another thing to consider is the tilt angle needed to plane your boat the quickest with a typical load. Changing that tilt angle can change the height of the AV plate in reference to the boat hull. Many years back I worked at a boat shop part time and what we did on small boats as a start was to lay a straight edge (yardstick) up under the hull so it stuck out to the AV plate on the motor. We then would adjust the tilt until it was parallel or slightly tilted up and away from being parallel to the bottom as a starting place. If the AV plate was to high above or to far below we would add a piece of wood under the clamp strap on the motor to raise or lower the motor. Normally we had to raise it a little to get the AV plate right on or slightly above the boat bottom when the motor was tilted correctly. Might be a place for you to start.........

 

[ondarvr]

Re: Engine location on boat

So the anti-ventilation plate is the one that should be close to level with the bottom of the boat, and not the one that diverts water from spraying up?? And would a lil below the bottom of the boat be better than a lil above? I have a feeling when I'm on plane, the prop is to close to the surface and I'm not getting the correct "bite" from the prop in the water as I should.

Depending on the prop and other things the tips of the blades can be out of the water at top speed and run well. But....every boat, hull, motor and prop combination will be different, so this is where the testing comes into play. The AV plate is rarely below or even with the bottom of the hull, normally it's above the hull. You will never find out unless you try different heights, it will let you know the correct height for your setup rather quickly.

 

[UncleWillie]

Re: Engine location on boat

So the anti-ventilation plate is the one that should be close to level with the bottom of the boat, and not the one that diverts water from spraying up?? And would a lil below the bottom of the boat be better than a lil above? I have a feeling when I'm on plane, the prop is to close to the surface and I'm not getting the correct "bite" from the prop in the water as I should.

The AV Plate is the one Directly above the Propeller.

You also need to think dynamically.
The propeller is not exactly at the edge of the transom, it may be Two feet or more behind it.
The hull of the boat creates a trough in the water and as soon as the transom passes, the water starts to refill the hole.
By the time it gets to the propeller the water may have already risen an inch or two.
So even though the AV plate is an inch above the keel, it may still be too low, and under water, Two feet back.



This is why it is trial and error situation.
If the Nose of the AV plate is right at the surface, the tail of the plate can still be well below surface level.