transom height?

[freddyray21]

1957 Johnson 35hp on a 12ft wooden boat dual cockpit runabout. It is a dog out of the hole. A lot of bow rise and very slow plane. Once on plane it runs faster than I want to do and it poirposes. I am told the motor is too low. The cavitation plate is about 2 inches below the bottom on the boat.

 

[5150abf]

Re: transom height?

Start raising it a hole at a time until it finds a spot it likes, should be level or just below.
I run mine right at level.
I have played with engine height alot and it does make a huge difference, up and out.
The porposing maybe a trim issue as well, try trimming down to get rid of that.
Between the too you should find a happy place.

 

[jbjennings]

Re: transom height?

No doubt I agree, it is trimmed up too high. try dropping it down 2 slots or holes in the transom bracket. Don't drop the pin in the lake!!! Do it on the trailer. It won't porpoise and it won't stick the bow up when you give it throttle. It will also feel much safer at high speed. If you trim it down too low, it will push the bow down and lift the back up making it hard to control. Porpoising for sure is caused by the motor trimmed to high or too much weight in the back of the boat. A 35 seems like too much power for a 12 ft. boat unless it's pretty heavy though. That could be the problem. If your cavitation plate is parallel to the bottom of the boat, that should be the correct position. If it is, then too much weight in the back or too much power for the boat.
Just my experience anyway, and I've never been lucky enough to have a wooden boat.
JBJ

 

[jbjennings]

Re: transom height?

Oh, one more thing---can you guess what I want Fred???
JBJ

 

[samo_ott]

Re: transom height?

My 14' aluminum porpoises with a 10hp on it. So I tossed (gently placed?) a big rock in the front! Works great now. Trimming did not help. Neither does a 240 lb driver!

And not many 12' boats are rated for a 35hp. Is it a safe set up? And if you don't have a jack plate, a method to raise the engine is to put shims under it on top of the transom to raise it up.

 

[F_R]

Re: transom height?

Not knowing anything about the boat, I suspect it is way too much weight and horsepower. Especially weight. Those old motors were meant to run with the bottom line somewhere between the cav plate and pump bulge. Yes, raise it up as high as you can without getting cavitation but don't expect to be able to get the plate up to the bottom line. I really don't think motor height will make much difference in hole shot in this situation.

 

[Willyclay]

Re: transom height?

Good luck!

 

[tashasdaddy]

Re: transom height?

i agree move the tilt pin toward the transom. that will cut porposing, and will get the bow down.