Advice please on best depth for cavitation plate on Carolina Skiff

[Bigdaddy]

I hope someone out there can help me with this one. I have a J14 Carolina skiff and a 15hp suzuki 4 stroke motor. Both the Boat and the motor are 20" transom long shaft designs. When I attempted to mount the motor on the back of the transom, the cavitation plate ran about 2.5 inches below the bottom of the boat. The highest that I could manage to adjust it still places the cavitation plate about 1.75" below the bottom of the hull. The only option I can think of is a jack plate to get the cavitaion plate up to about 1 inch below or maybe "even with the bottom of the hull. The jack plate i have been looking at is made by th marine and has a 4" setback. Is the setback a problem? any suggestions will be appreciated. thanks

[Corpus Skipper]

The highest that I could manage to adjust it still places the cavitation plate about 1.75" below

This is on the lowest mounting holes? Should be even with the bottom of the hull, or your shaft length is too long

The jack plate i have been looking at is made by th marine and has a 4" setback. Is the setback a problem?

No problem.

[Bigdaddy]

This is just a small boat and because of the 14ft length, would it be better to have the cavitation plate at 1" below the hull or even with the hull. I have heard that the advantage to having more prop in the water is that you can ge up on plane quicker, but then there is drag. with a static plate, what is the best scenario? thanks for advice

[Eric Sponberg]

The cavitation plate being too deep is better than being too shallow. It should never be higher than the bottom of the boat, but it is OK to be deeper. The cavitation plate is meant to be a "barn door" to prevent the propeller from sucking air from the surface. If you did not have a cavitation plate, the propeller could suck a little whirlpool of air down from the surface. It looks like a little tornado. The little tornado is trying to reach the propeller and equalize the vacuum pressure on the back (forward side) of the propeller. Without a cavitation plate, there is nothing to prevent this. A cavitation plate just above the propeller "closes the door" to the little tornado. The deeper a propeller is below the surface of the water, the harder it is for the tornado to reach it. So depth is good, and a few more inches below the bottom of the boat is not going to hurt. What will hurt more if the lower end is too deep is that the boat will be harder to balance in trim and there will be more form drag from the lower unit, and so less speed. You want as shallow a depth as possible, but a cavitation plate a few inches below the hull should be OK.

I hope that helps.

Eric