how to ID a prop?

[pcrussell50]

merry christmas all!

bought a used boat this past fall with small, 16 foot performance hull and an evinrude 135hp. it's been a blast, but the previous owner used it for towing skiers/wakeboarders, so he had put an aluminum "pulling" prop on it. it seems like a pulling prop too because with just me and my wife in the boat, it explodes straight to the redline, and it's really easy to go way above the 5000rpm where this engine is rated at max power.

but he also included with the boat when he sold it to me, another aluminum prop, which i can't tell anything about, and a stainless prop that he said is a "speed" prop. trouble is, i can't find any markings on any of them that tell things like pitch and diameter, unless i'm just looking in the wrong place. hmmm... these are all "exhaust-through-the hub" johnnyrude style props. i am brand new to boating as of summer '08, but i'm mechanically inclined, [build and repair automotive racing engines], and have a science/engineering background, so i understand things about pitch and load on engines and such.

anyway, how can i find the specs on these props? is it possible the specs were on a sticker that wore off, or a stamping that eroded?

-peter

 

[steelespike]

Re: how to ID a prop?

Usually you will find numbers on the barrel of the prop _ _ X _ _.
Diameter X pitch. Sometimes you may find a part number many times ending in the pitch size.Sometimes number is under the prop nut.
I can't say specifically but most would run that motor at about 5,500 with a light load.The Stainless "speed" prop probably has a higher pitch number and more sofisticated design. You may note a little cup to the blades.
A prop with more pitch will usually deliver more speed and less hole shot
lower rpm.Assuming the motor can turn up to its rpm.Less pitch generally delivers better hole shot more rpm and less speed.
Diameter of a prop is the product of its application.Usually not considered
except to be certain it fits.I would think with careful setup that boat will run over 50 mph.Be careful.at those kind of speeds waves can be deadly.
In rare conditions a boat could stuff a wave (submarine into it)Like running into a wall.Driven at speeds appropriate to conditions you'll be ok.