Looking for '82 70hp Evinrude Specs

[kiddynomite]

Hi all!

I'm looking into getting a new propeller for my 70hp '82 Evinrude and wanted to get the most bang for my buck. It's on a 15' 1976 tri-hull Renken and will mostly be used for pulling skiers and peddling around to different marinas.

I have found several topics on here that come close to answering that, but I'm more interested in knowing what the diameter, the pitch, etc. - do and how it effects performance. Any info would be greatly appreciated.

JJ

 

[Silvertip]

Re: Looking for '82 70hp Evinrude Specs

Various engines within a given family use a given diameter prop because that diameter fits the gearcase without hitting anything and because the hub diameter must match the gearcase. So don't fret over prop diameter -- besides, pitch has far more effect on performance than diameter. Your engine typically runs a 13-1/4 diameter prop and for your boat I would have to guess, but a prop with 17 or 19 inches of pitch would at least get you in the ballpark. Selecting props is not an exact science. What you need to do is first determine what you have on the engine now. Then make several wide open throttle runs with an average load. Note the maximum speed you achieved and the maximum rpm the engine turned at that speed. Any values less than wide open throttle are useless so don't even bother posting those. Your engine has a maximum recommended wide open throttle rpm in the 5000-5500 rpm range. During your tests, if the engine ran faster than recommended it is considered underpropped, overreving, and therefore requires a prop with more pitch. You cut down rpm by about 200 - 250 rpm for each inch of pitch increase. On the other hand, if your engine fails to reach that rpm band it is being "lugged" which is death for a two-stroke engine and therefore requires a prop with less pitch. You gain 200 - 250 rpm for each inch of pitch decrease. Armed with this information, you can make some better choices. However, you MUST make sure the engine is properly tuned. It is a waste of money to attempt getting better performance from a poorly running engine (or one that is worn out) by changing props. The link below is to the iBoats (host of this forum). They sell props and you can plainly see you want a prop somewhat close to what you have now, but the final choice needs to be made after the tests. You obviously need a tach and speedometer or a handheld GPS. Props also come in aluminum or stainless steel. I would highly recommend you stay with aluminum for cost purposes. If you are up for all-out performance, break out your wallet and go for stainless but don't let the "shiny" appearance cloud your judgement.


http://www.boat-props.com/propeller...power=70&year=1982&rotation=Standard&x=26&y=6