What propellor diameter and pitch should i get?

Question

i have a 1978 evinrude 140hp and need a propellor to fit good. i wanna be able to pull a wakeboarder up easy and skiiers. Im not too concerned with being the fastest out there. What should i get? Also what is the difference between a 17 pitch and a 21 pitch?

Answer 1

you will need a four blade prop for ski and tow/ size and pitch can vary with your boat type. most dealers that sell props have loaner props so that you can test to see the best prop for the job. an evinrude dealer can help you decide.

Answer 2

Depends what size boat and that vintage 17P so you don't put so much load on it>

Answer 3

you really don't want to be over-revving a 1976 motor. The recommended wide open throttle revs for yours is 4500-5500. 1 way to work out what prop you need is to take the boat out with a light load and see what the maximum revs are then try pulling a skier. Take note of your revs then look at the markings on your prop ( on the hub under the washer behind the prop nut if it's omc original , on the outside of the prop otherwise.)If it's not over-revving with the light load but struggling to pull a skier up you need a smaller pitch prop. To determine how much smaller i use the online prop calculator http://www.rbbi.com/folders/prop/propcal...

your gear ratio is 2:1 and your slip should be around 10%. I've never used or needed a 4 blade on my 115 to tow 2 skiers. a good cupped 3 blade should be fine and give you better top end speed.

Answer 4

Your best bet is to go to a prop shop and give them the length and weight of your boat along with the engine horsepower. They can give you a prop for what you want to do.

Pitch is the angle of the prop blade and is the theoretical distance the prop moves through the water in one revolution, without any cavitation or slippage. So a 17" pitch prop would move 17 inches in one complete revolution and a 21 would theoretically move 21 inches. More pitch means more speed but slower acceleration, less pitch gives more power but slower top speed. If you have maximum pitch that your engine can handle and you increase the load or weight of the boat (more passengers etc) then the engine may not be able to reach max revs. So the pitch is set as a compromise between the two.