what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most speed

[stanfordky]

right now the boat has a ss 13 3/8 x 17 prop. with me and equipment on it at 5400 rpms it runs about 42mph. i have another boat that has a ss prop that i tryed but it was a 15 x 19 i planed faster but had a slower top speed. what do you guys suggest if anything or am i wanting to much out of it.

 

[guy74]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

I'd say you are doing pretty good if you are acually getting 42mph @ 5400rpm, gonna be hard to improve much on that. I run a 13 3/4 X 15 prop, a vented Hustler, on my 16ft trihull with a 60hp Johnson. I get 33mph at 5900rpm with that setup. I'm not sure how you can get a 15" diameter prop on you 70hp, I can't even swing a 14" on mine. Unless there is a big difference in the lower units in different years. Mine is a 1988.

 

[stanfordky]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

it fits, mine is a 84 but it was very close probably within a inch. it brings it up on plane really fast with very little trimming. but it brought my top speed down to about 35 mph

 

[guy74]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

Your 1984 has the same lower unit as my 1988. Are you sure it isn't a 15 inch pitch on the prop, as that would make since, as you say it helped you holeshot, but hurt your top speed?

 

[stanfordky]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

well on the prop it said 15 x 19 and the that was on it said 13 3/8 x 17. all i know is that it fit and ive tried it and it worked.lol.

 

[stanfordky]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

well i just went out to my boat and took the prop off and after cleaning some of the black off from the exhaust the prop says 13 x 19 lol.
should i be getting more speed or should i put the 13 3/8 x17 back on or should i buy a total diffrent prop with different pitch, and size?

 

[guy74]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

Seems strange that the 13X19 slowed you down, but different props and setups react differently. I personally think you are probably maxing out your potential with the 13 3/8 X 17. If you are looking for more speed, you might try raising the motor one hole and see what you get.

 

[Texasmark]

Re: what size prop should i run on a 15 ft fiberglass boat 70 hp evinrude for most sp

I would be thrilled with 42 on your rig at 5400 rpm's. I agree with guy that you have surely hit your limit on performance. Having run several rigs of that general size, you are doing great.

Agree with guy on prop design could be a problem with the 19 or something else with it. What you failed to do is tell us what your rpm's were with the 19P. If they fell off, which they would do if you overloaded the engine with that much pitch, then you have your answer.....you are maxed out with the current setup.

"Don't fix it if it ain't broke". Grin

Mark