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I just went UP 1 hole the bring the cavitation pleate UP to .75 ich below bottom. Have not tried it yet. I wounder if I should go up 1 more hole (the last hole actually to bring it about even with the bottom. What do you guys think.
Thanks
Jim
PS this boat is new to me. It had a 17 pitch prop and I went to a 15 pitch prop to get the revs up to (so far) 5300. The 17 went to about 4500.

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For each hole you raise the engine, the WOT rpm's will increase by 150-200 as a result of less drag.

Raise the engine and retest, noting WOT rpm and speed with the un-named make/model and diameter prop.

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Plate should be roughly 2" ABOVE the keel. Need a pic. 3/4" below is MAJOR drag on the lower unit. You need to raise it up considerably. What plate are we looking at?(pic?)

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Sorry guys. Been running around like a crazy person. Just got back from yearly cruise and I am late for everything. 1 day and wife and kid are screaming for the whaler to be back in the water. It's a filthy mess and I have not had time to sort anything out at all.
Anyway here is a couple of picks.
The old prop was a brand X 13.25 x 17. The new prop is a yamaha 13.5 x 15. The cavitation plate was pretty deep when I got it. 1 Hole up leaves it about .75" below. If I go to the top hole it should be close to even or slightly above. Would prefer not to have any cavitation.
Thanks.

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The holes.
I don't know why the pics appear squished.

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Raise it all the way up and put the 17" on it and report back with performance numbers. Make sure to trim it until it slips and then blip it down till it grabs for WOT runs.

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I raised it all the way up and I will try the 15 pitch prop first. Whenever it gets back in the water and whenever there is some flat water. But I will report back.

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Cool...I think the 15" all the way up might be too small but what the hell do I know? Double check your throttle linkage and make sure you are getting a full WOT.

I am running both my Whalers with 4 strokes all the way up. My 13' with a 40hp Suzuki 4s is running a 16" Rapture SS prop and bumps the rev limiter. <y 18 Outrage is all the way the up with a F115 and a stamped Yamaha 17" SS prop running right at 6k at 40+. Props and height are essential in dialing in a boat. Problem is some people have different conditions to deal with, My setup would NOT work in San Fran Bay for instance.

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When I got this boat I plopped in the water next day without doing anything. I never looked at motor height. I noticed I had to have it trimmed all the way down to keep from porpoising like crazy and there was water spraying all over. Speed was about 32 mph at about 4600 RPM indicated. It was jumpy and would not plane at slower speeds. Would slowly fall off. I installed doel fins and it smoothed things out and would plane slower. Of coarse top end suffered. Installed the new semi chopper looking yamaha prop at 15 pitch and it went much better and revs came up to about 5200, but it would ventilate at lower speeds. Don't know why. So I hauled it, removed doel fin and moved motor cav plate up to about .5 inch above the bottom. Did not remove the new yamaha 15" prop. Maybe I can get it in tomorrow to check it out.
BTW the reason I am trying the 15" first is that's whats on there and I am out of cotter pins.

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OK so I got it in the water a little while ago. It was breezy with some chop. I opened it up anyway and she took off like a scared rabbit. Between the boat sailing out of the water and my wife screaming and clutching the dog, I managed about 5500 RPM at about 30 knots. I think in flatter water with some trimming it will do better, but I am calling it a success and done for now. She was planing nice at 3500 RPM and 18 to 20 knots. That's mostly where I will be.
Thanks all for the nudge to get that cavitation plate up. That made all the difference.
Understand I'm not after max performance. It's an old boat and an old motor and I am an old man. I just want it to do what it should do and it wasn't doing it.
Jim

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Isn't 5500 redline? If so play with the 17" prop as well.

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Actually I tried it again by myself and got 36.1 mph at about 5500 rpm with a quarter tank of gas. Don't know what redline is but 36 mph felt like ludicrous speed in that tiny boat. Most likely never run that fast again.

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Redline is 5500 so you are good, especially with added bodies & fuel. I read a performance report on a 850lb flats boat and with a SS Yamaha 18" prop it did 39.1 @ 5500. You are only 3mph shy of that with a 15" means that must be an aggressive 15" prop.

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My GPS records max speed (thankfully) and it said 31.1 knots. So just a hair under 36mph. It's hard to read any numbers while all hell is breaking loose.