Outboard height question

[wado66]

I have a Yamaha C115 outboard mounted to the transom of an 18.5' Alumaweld Xpress.
The boat porpoises at about 43mph. This does this with or without a fin mounted to the cavitation plate.
Is my motor to low/high on the transom? I have 4 mounting adjustment hole on the motor.
Just really confused and frustrated. Thanks for any info you can give.
Scott

 

[tashasdaddy]

Re: Outboard height question

proper trim will take care of porposing, also weight distribution.

 

[tysonnathan]

Re: Outboard height question

Have you tried trimming the motor down when it starts to do it? My uncle has a 19' aluminum with a 90 horse and it will porpoise really bad, but it is easily fixed by trimming the motor down...

 

[JB]

Re: Outboard height question

I doubt that a C115 has PT&T.

Readjust the engine tilt pin so that the antiventilation plate is parallel with the bottom of the boat.

 

[wado66]

Re: Outboard height question

It does have PT&T. But it seems to me I'm defeating the purpose if I have to trim my boat back down in the water.
I want it to run on the pad, like it was designed to do. Do you think my horsepower is too low to get the boat on the pad and stay there?

 

[JoLin]

Re: Outboard height question

It does have PT&T. But it seems to me I'm defeating the purpose if I have to trim my boat back down in the water.
I want it to run on the pad, like it was designed to do. Do you think my horsepower is too low to get the boat on the pad and stay there?

Your horsepower really has nothing to do with the porpoising issue. Every boat needs trimming depending on its speed, weight distribution and water conditions. That's why your motor manufacturer provided PT&T- so you can fine tune your running angle as you go.

 

[tashasdaddy]

Re: Outboard height question

ride on the pad and bounce, or trim it properly and have a good ride.

 

[wado66]

Re: Outboard height question

Ok, maybe my thinking is getting distorted.
I owned a Skeeter sx186 with a 150 on it, before this Alumiweld.
Maybe I'm expecting to jump up on the pad and scoot on down the lake.
This boat is actually heavier than the Skeeter. So, i guess i just need to trim her down a little and find my fishin' hole.
Thanks for yalls input.....

 

[LubeDude]

Re: Outboard height question

Your horsepower really has nothing to do with the porpoising issue.

Sorry, this statement is absolutly not true, in fact, it has almost everything to do with it! That and the prop!

If he gets to a point with the trim that the boat does not porpose with the HP he has, if he had more HP he could trim more. It's the HP that holds the bow from falling back down.

The fin has nothing to do with WOT performance as it "Should" be out of the water at WOT!