How to determine what prop I need?

[wijames]

I recently had a strange thing happen. My 2000 20 foot tri-toon Sylvan with a 2000 BF90 on it has been running at 5900 RPM and doing around 25 MPH. The prop was looking a little knarley so I had it rebuilt. Now I can only get 5200 RPM out of it and 20 MPH. I tried a second prop and got the same result. The prop I have now is a 3 13.5 x 15R, does anyone know what I should be using? I've looked at half a dozen prop calculators on the web and every one of them give me a different answer.

[MH Hawker]

Prop calculators are useless for a pontoon. Common pitches are 7,9.11,13 and on some of the newer tri toons a 15.
I would guess a 13

[rdeterman]

is it a fuel injected motor? have you checked your fuel filters? The motor could be running out of fuel causing the lack of RPM. Just an idea...

[wijames]

is it a fuel injected motor? have you checked your fuel filters? The motor could be running out of fuel causing the lack of RPM. Just an idea...

That would be a real coincidence having the fuel filter go at exactly the same time I had the prop done. I'm just talking about a week between when it was getting 5900RPM, having the prop redone and then getting 5200 RPM so I doubt if that is it but I'll check.

[wijames]

Prop calculators are useless for a pontoon. Common pitches are 7,9.11,13 and on some of the newer tri toons a 15.
I would guess a 13

I'll see if the prop shop has a 13 I can try before buying one.

[Bryden24shp]

I suspect the prop shop rebuilt it using the wrong set of blocks. I would send it back to them and tell them where you were performance wise, before and after the rebuild. They would probably recheck it and fix it for free.

[MH Hawker]

I was guessing the shop added some extra cup to it