Need Prop pitch help.

[seapro_stevo]

I have a 2004 18' cc sea pro(equivalent to new18'seaboss) with a yamaha
115 four stroke. When i got the boat it had a 13 1/4 x 17 aluminum k series prop that turned 6200 rpm with full tank and 1 person trimmed all the way up. The prop was slightly bent so i went to a stainless steel stiletto 13 1/4 x 17. Now it will only turn 5800 with full tank and one person. Not bad except that is trimmed as far up as i can without ventalting. How are you supposed to test the max rpm of your prop? If i have it trimmed just right so it doesnt porpoise running at 4500 rpm and give it full throttle it will only hit 5300 rpm. If i trim it up real high it will rise to 5800 rpm. Am i over proped?





No buying or selling on the forums.

 

[sweebs]

Re: Need Prop pitch help.

why not give a SS 13 1/4 by 15 pitch a try,,, likely will get your rpms (and max speed) up to proper range

 

[Crownie2]

Re: Need Prop pitch help.

As you are trimming up, watch your speed. If it starts to drop then you are trimmed too high - trim back down a little.

Also - can you raise the engine a little? That will help get some of the rev's back if it doesn't hurt anything else. Are you satisfied with the performance you are achieving now?

What is the recommended rpm range for your engine?

Bob

 

[seapro_stevo]

Re: Need Prop pitch help.

The rpm range is 5000 to 6000 rpm. I cant raise the motor another hole. It was up one more but i had to move it down one. it was cavatating under hard cornering. I was too high. Now the height is perfect. It performs pretty good. My main concern is if im lugging it.
I hate to buy a 15 pitch to try because i know i will loose more top speed. Right know i gps it at 46mph max. Not to mention, the first prop i bought for it was a stilleto 19 pitch which was fast, but to much prop. now i have to sell it.


So trim up the motor until the speed stops increasing, then trim down just a hair and that should be where my max rpm should be tested?

 

[Silvertip]

Re: Need Prop pitch help.

4500 RPM means nothing. Your runs need to be made at WOT with full trim (where speed does not increase or it decreases with additiional trim) and all of this with an average load. If you are at 5800 and the recommended WOT rpm is 6000 you have the right prop. Dropping to a 15P (same style prop) will put you back over 6000. You just learned that a SS prop is generally more efficient than the aluminum (less slippage). I think you need to do more testing with trim. It may also help to install Smart Tabs to get a little more stern lift and help with porpoising.

 

[seapro_stevo]

Re: Need Prop pitch help.

I just finished installing some lenco trim tabs. should help with porpoising.

This may be a stupid question, but what level is full trim? How do you know when your at full trim? Does that mean trimmed as far down as it will go?

 

[U Rest U Rust]

Re: Need Prop pitch help.

Stevo

I believe full trim is when you have the boat at peak operating condition. I have found my full trim is when the spray comes off around the steering wheel.

but I am kinda new at this as well. This is the place for the answers though..