Need some advice please

[whomeno]

I have a evinrude 65 hp triumph mounted on a glasspar 16' fibsrglass v-haul.
With a prop of 13 1/4 X 17P at WOT speed I'm turning 4800 rpm's.
The rpm range is 4500 to 5500.with the gps that is 33 mph. Should I drop 1 pitch to bring the rpm's up a little more?the prop would be a 13 3/4 x 15 p. If I do drop 1 pitch will that drop my speed down from 33 mph?
Thanks

 

[whomeno]

Re: Need some advice please

ok I'll give a little more info

1) Performance issue you are trying to correct.

over all best performance

2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
omc,aluminum,

3) Current prop diameter and pitch (required).
13 1/4 x 17 pitch
4) Wide open throttle RPM and speed with an average load (very helpful)
4800
5) Engine/drive make, model, year, and HP
evinrude,outboard triumph 1972 65 hp wieght 208ibs

6) Boat make model, year, length and weight
glasspar,citation 1968 17' 1200lbs

If I drop to a 15 pitch prop too bring my rpm's up will my speed drop?

 

[hwsiii]

Re: Need some advice please

I need the gear ratio for your motor please.

H

 

[whomeno]

Re: Need some advice please

The gear ratio is 12:29

 

[Dhadley]

Re: Need some advice please

I'd work the set up first with the existing prop. Dropping pitch to simply gain rpm rarely yields more speed or efficiency.

Does your motor have power trim?

 

[whomeno]

Re: Need some advice please

No it don't have power trim. I have set it at all settings and did find the best one.

 

[Dhadley]

Re: Need some advice please

I actually just went thru this exact scenario (V4 Yamaha) with someone last Friday. He had a 17 Stiletto in perfect condition. He was down on rpm and wanted to get the prop reworked to a 15. I convinced him to work the set up and he called this afternoon saying the top rpm went to 5800 and he gained almost 5 mph (large heavy boat). The new set up indicates he can actually go higher with the motor to gain even more but he's at the upper end of the rpm range now.

Basically he went from reducing pitch (efficiency) from a 17 to a 15 to now possibly going to a 19 and gainig even more.

 

[whomeno]

Re: Need some advice please

AS it it is now. I can't change the height of it with out a lot of work. the trim is set for the highest speed,If I go in 1 hole or out 1 hole speed goes down. with the 13 1/4 x 17 prop my wot is 4800 rpm. specs for the outboard is 4500 to 5500. is there any thing I'm missing or is this the best it gets?
Thanks

 

[Dhadley]

Re: Need some advice please

We're kinda handicapped without power trim. And if we are not going to change the X dimension then we're limited on options and may well be settling for reducing the pitch to gain the rpm.

 

[whomeno]

Re: Need some advice please

will gaining the rpm produce more hp? I've been looking for a power trim for it but no luck yet