Looking for a new prop (?)

[vabassfisher]

I have a slight issue. My 1984, 70hp Johnson runs about 6000rpm at WOT, which I'm 99% sure is too much. I'm thinking a new prop with different pitch will help correct, but I'm not sure which way to go. Current prop is 13 3/8 x 17, which I was told by the guy at the prop shop was correct for my boat. But looking at all the sizes from diff mfgs, I'm not sure which way to go. My boat is a 15' fiberglass bass boat.<br /><br />Any help on this one would be great!

 

[JB]

Re: Looking for a new prop (?)

Howdy, Bassfisher. <br /><br />Try a 19" prop. That should bring your WOT down to around 5600rpm.<br /><br />Red sky at night. . .<br />JB

 

[vabassfisher]

Re: Looking for a new prop (?)

Thanks JB. The one I was looking at is a 21°. Do you think that will be too much? I've also heard that if you use a alum. with cupped ends, knock off 2°, which would bring me right to 19° as you suggested. Is this making sense, or am I just babbling? Just a little excited to get the season going...I can't WAIT till March 23rd!!!

 

[Digdug]

Re: Looking for a new prop (?)

I would try the 19 pitch. I recently purchased a prop from a prop shop and they let me try out the prop before I purchased it. (had to leave deposit). Good luck!

 

[Hawkeye1]

Re: Looking for a new prop (?)

1st off What is the max rpm range rating for that engine?

 

[Ross J]

Re: Looking for a new prop (?)

Hi,Ho Vabassfisher,<br />I had the same problem recently and have had success with a 13" x 19" prop. I have found my 85hp runs this well and I'm even achieving better km per $. The only time I have to switch back to the 13 1/4 x 17 is when I'm towing or hauling a big weight on board. I suggest you borrow one from your local shop and try it. <br />Ross

 

[steve forsythe]

Re: Looking for a new prop (?)

Is there a tool that is cheap to measure the pitch on the prop? I want to check mine, then try out some with different pitches from the dealer. One more time.....the lower the pitch means....higher rpm's more top end???or lower rpm's more low end power???

 

[vabassfisher]

Re: Looking for a new prop (?)

Purse Snatcher,<br />The dia. and pitch should be written/stamped on the prop. Mine is located on the hub/inside. And in regards to your question about where the power is, I hope you are exactly right. That is what I'm hoping for because currently, my boat is just a wake-maker for about 30 yards or so before it tries to get on plane (very frustrating!)

 

[Hawkeye1]

Re: Looking for a new prop (?)

vabassfisher, going up in pitch is going to make it worse getting on plane and you will have a 50 yrd wake maker. What is the wot rpm range for that engine????Oh I live in Manassas, not too far from you.

 

[steve forsythe]

Re: Looking for a new prop (?)

So going up in pitch means less low end power, harder to get on plane and more top end power? If i am at 5600-5800 at WOT i dont mind losing some top end to get on plane faster. So i want to go lower in pitch....right?????

 

[Hawkeye1]

Re: Looking for a new prop (?)

Nope, if you are already in the upper range of your wot max then you need more HP. I guess you could underprop it a little but have to be carefull on over reving it. See the mfg rate the max rpm range as a loading effect against the engine. If you under or overprop a engine then it will screw up the air/fuel mixture. A overproped engine will tend to run a hair on the rich side and a under proped wil be a hair on the lean side. But all with in a good range if proped correctly that is within the max rated rpm range stated for the engine.

 

[vabassfisher]

Re: Looking for a new prop (?)

Hawkeye,<br />Based on the SELOC Johnson/Evinrude Repair Manual, the WOT range for my boat is 4500-5500 rpm. I've also talked with people who say that getting a larger diameter prop will help some. Have you heard anything regarding this?

 

[DJ]

Re: Looking for a new prop (?)

vabassfisher,<br /><br />You're kind of in a quandry here. 6K is a little too fast for the 70. But not too far out. Going to a 19" will slow the engine down to about 5600 like JB said.<br /><br />I'm assuming your prop is aluminum. A 13 1/4 X 17 stainless cupped prop will do about the same thing as a 19 aluminum.<br /><br />As far as wake making goes, the 70 is not a real strong engine out of the hole. You may want to try a fin to improve the holeshot.

 

[Hawkeye1]

Re: Looking for a new prop (?)

Vabassfisher, you really need to come down to the 5500 range. If you 17p prop is cuped now then you need to go up to a 19p cuped. Stiletto make a good cheap ss prop that wakes up many boats. Larger dia does not mean it will do better out the hole. Really with only a 70 you dont want too much on the dia side. As Djohns19 said a dolefin type fin might be the answer for planning or even trim tabs.

 

[vabassfisher]

Re: Looking for a new prop (?)

Thank you everyone. I have a lot of options to try now. Unfortunately, it's still February, so there's no telling when I'll get to try them out. But if we get another 70° day like 2 weeks ago, LOOK OUT!<br /><br />Thanks again!