prop question?

[rrbullred]

I posted the following information yesterday. bstephens gave me some information on another boat...but I am not ready to act yet.

I have a 2000 1880 Bay Stealth Classic with a 1999 Yamaha 115 2-stroke 4v. The prop is a Powertech 13" diameter with 15" pitch with cup(#ym90pfs4r15). Engine is mounted on second hole from the top. I don't know the distance.

I bought this boat in March 2005 used with only 50 hours. I had a technican go through the carbs, new spark plugs, test the compression (145 # per cylinder), drain the gas tank, new fuel filter and fuel pump, and a few other things not important to this problem.

Here is the problem: WOT RPMS 4900-5000. Top end speed is 31-32 empty (me only). When I have the motor trimmed all of the way up, I run the fastest...but it does porpoise (the boat comes up and down). Hole shot sucks. With it trimmed all of the way down, it is like the rear of the boat squats...which in not good on the bay. The prop is stainless and in good shape. I don't blow out of the water when I turn at high speeds.

Reading this forum (searching for hours) and comparing it to other 115's, the prop seems to be the correct size, pitch, etc....but I may be wrong.

Does anyone have any ideas? Do I have the right prop size? Should I get the motor checked? Should I raise the motor? Is something wrong with the motor?

 

[Ron G]

Re: prop question?

How high is your motor now?sounds like you should be able to raise it up some,is there a jackplate?

 

[rrbullred]

Re: prop question?

There is no jack plate.

Pardon my ignorance but when you ask about height, where are you measuring? (is it from the top of the prop to the bottom of the boat?)

Right now my boat is being stored about an hour away. I can run by there this weekend and take the measurements. I might take a few pics to show everything...if you think it would help.

 

[ivar]

Re: prop question?

How high is the cavitation plate (the plate above the propeller) in relation to the bottom of the boat? Trim so the plate is level with the bottom. Should not be below, and can be raised , amount depending on prop used, hull shape etc.

 

[rrbullred]

Re: prop question?

Thanks ivar.

I will definitely check that. If my memory serves me right, think it is a little too low. I know that when the trailer is hooked onto the truck, I can't trim all of the way down without the skeg hitting the ground. Now the trailer is pretty low...making me unsure...but I will definitely check the cavitation plate.

I'm sitting here thinking that the most cost effective thing to do is raise the motor a little, try it and see if things improve, maybe raise it a little more...and if no improvement, get the motor checked out, if all good there, try going with a 3 blade prop.

What do you guys think?

 

[Dhadley]

Re: prop question?

Start with getting the motor check out. Doesn't matter if you do it os a tech does it. We have to have a good platform to build on.

Then work with the set up. Changing props to gain rpm is always a last resort.