Looking for new prop but not sure on dia. and pitch ??

Hi everyone this is my first post to this site, ran across the url looking up info on my boat motor
the question is what size prop would be best for my motor, I just bought the boat a few days ago and the prop looks in very bad shape, what i have is a

1999 Johnson 70 hp model number is J70PLEEE
this is a 3 cylinder motor 2 cycle

this motor is on a Tracker sportsman 20 boat
it is a 20' jon boat and i am looking for a prop that can get me up and out of the water pretty fast and with good speed..

i am not sure what all the dia. and pitch is for

I think the boat is around 400 pounds

Thanks

Re: Looking for new prop but not sure on dia. and pitch ??

Still looking for a prop size, but i did change the weight of the boat a little, I added a 8 foot deck on the front and added a lot of other little extras i added around 300 more pounds to the boat....

Any one have a good idea on a good prop size

Re: Looking for new prop but not sure on dia. and pitch ??

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Hi. I'm a new boat owner as well and a few weeks ago, I too asked the same question (to replace my boat's chipped up prop) as well.

In summary, many experienced folks stated:
- Load up the boat for a normal "on the water" ride.
- Take boat on calm water and run WOT (Wide Open Throttle) test - for short time period.
- At steady WOT pace, what is its engine's RPM?
- How does that "under load" engine RPM needle number compare to engine's recommended engine's MAX RPM number?
- If engine has too much RPM, then a larger Pitch Prop can be installed. re: Its enginge has remaining power and can handle a larger Pitch prop.
- If engine has too little RPM (and/or seems to struggle at upper WOT range), then its current Prop (or pitch) is too large. re: Its engine is struggling too much with the existing large prop size.

Note: Before this WOT "on the lake" test, one needs to obtain the recommended engine RPM - for your exact 70 HP engine.

After the WOT test (for short period of time), pull the existing PROP off and confirm its numbers. Many props have the pitch code within its stamped numbers. For example, my 120 HP's boat's prop is xxxxxx21P. I was told this 21P is the Pitch.

SS (Stainelss Steel) props have very little drag. Aluminum props have more drag. Therefore, go lower pitch number when picking aluminum props. For example, my boat currently has a 21P aluminum prop. For my "average usage" needs, I will replace with 19P aluminum prop. But if going with SS replacement, I might stay with the 21P prop. And if I always loaded my boat heavy and didn't do upper speeds very much, I'd go with a 17P aluminum prop. Thus, creating more bottom end power (and less top end speed).

For your 70 HP motor, do obtain engine's max RPM number first. Perhaps its within an engine's manual? Then, perform a WOT test with "average" loaded boat. Then, decided if more or less pitch prop is needed. re: Compare against "under load" with engine's WOT RPM needle number. Perhaps your existing Prop is good match already?

Hope this helps...

Re: Looking for new prop but not sure on dia. and pitch ??

Does your boat look anything like this tracker 20 ft boat? If so, I recommend you look for a 17" pitch prop. My choice would be the Solas Rubex 13.3 X 17 for $108(from iboats).

Your 1999 Johnson's rpm range is 5000-6000 rpm at WOT. The gear ratio is 2.42:1. It has a 13 spline shaft. The motor weighs about 250 pounds.

That brings the package dry weight to about 950 lbs. Now add fuel, folks and stuff to get your total weight. It's going to be heavier than you thought. Hence the 17" pitch prop.

Re: Looking for new prop but not sure on dia. and pitch ??

jestor68 said:

View attachment 169235 Does your boat look anything like this tracker 20 ft boat? If so, I recommend you look for a 17" pitch prop. My choice would be the Solas Rubex 13.3 X 17 for $108(from iboats).

Your 1999 Johnson's rpm range is 5000-6000 rpm at WOT. The gear ratio is 2.42:1. It has a 13 spline shaft. The motor weighs about 250 pounds.

That brings the package dry weight to about 950 lbs. Now add fuel, folks and stuff to get your total weight. It's going to be heavier than you thought. Hence the 17" pitch prop.

Click to expand...

Thank you very much and yes that picture looks a lot like mine other then the steering on my is around half way of the boat instead of more to the back and i have a 8 foot deck on mine now, I ordered the prop and hope to get it soon and once again thank you very much for your help