Pontoon prop

Topkanman

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Oct 29, 2021
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I bought a 99 landau 20 foot pontoon. The prop is a 14 inch 9 pitch aluminum . It goes above the recommended rpm of 6000 if you open it up. The motor is a 50 hp Bigfoot. I was wondering if someone had a similar setup and the prop you use. Top speed at 6000 is 17 mph on gps . I was thinking about a 14 inch with 11 or 13 pitch. Thanks
 

Texasmark

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Dec 20, 2005
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14,060
Guessing the Big Foot gear ratio at 2.33 if your BF is using the standard LU that comes on the 90 hp engine.....if not correct it in the equation and move on. You didn't say how far above 6k it runs at WOT....guess on this 6500 for a number. Assume your prop slip to be 20 %...have no idea as to your prop mfgr/design, nor tune 2 pod or 3 pod, what is the normal slip for a toon with your dimensions/load and all that other stuff one needs to know to answer this question effectively.

So plugging your numbers into the Go Fast.com prop slip calculator and adding some SWAGs, I come up with: 2.33 gear ratio, 9" pitch, 6000 RPM, 22 theoretical speed with zero slip, estimating 23% slip gives you your 17 MPH.

So, only changing pitch to 11 and solving for RPM gives you: 4921 RPM at 17 MPH...assuming exactly the same prop other than pitch change and that the boat didn't change any characteristics with the change in pitch in terms of performance which would/could change the slip and the outcome.

Moving up to 13 gives you: Too much load on the engine and you don't want that one.

In the calculator, change what I have wrong and delete the answer to what you want to know. Punch that title block and it will fill in the blank with the pertinent information.

So, possibly the 11P at WOT will keep you at or below your 6k RPM. I'd put my money on an 11P for a SWAG.
 
Last edited:

ahicks

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Sep 16, 2013
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I agree with all of the above working from a practical standpoint, and would suggest that even though max rpm is 6k, they're sounding pretty busy at that speed. Unless pulling tubes or something, suggest 5500 rpm makes a better target speed. They sound/feel much better at that rpm, and speed will be the same or maybe just a hair better than when turning 6k.

Another vote for the 11p.
 

Topkanman

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Oct 29, 2021
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I agree with all of the above working from a practical standpoint, and would suggest that even though max rpm is 6k, they're sounding pretty busy at that speed. Unless pulling tubes or something, suggest 5500 rpm makes a better target speed. They sound/feel much better at that rpm, and speed will be the same or maybe just a hair better than when turning 6k.

Another vote for the 11p.
Thanks for the reply’s. I found a 14 inch 11 pitch prop and put it on the 20 foot landau with a 50 hp Bigfoot. My rpm with a 9 pitch was over 6000. Now with the 11 pitch the max rpm was 5300 and gps speed was 21 mph. It seems to be the right combo or real close. My other pontoon is a 24 ft Lowe with a dealer installed and tested 60hp Bigfoot. It has a 11 pitch and runs 22 mph max. Hope this helps some others.
 
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