Prop for first time pontoon owner

[SWR1]

Just picked up a 1981 90hp mercury to put on my 18' fishing pontoon. The motor has a 19 on it now since it was on a little speedboat. I'm thinking a 13.75x15 for the pontoon but I'm not sure where to start. It has the wraparound rear couch and 2 fishing seats on the front most of the time only 2 people on it as well so not a heavy setup. Boat is a riveria cruiser.

 

[Thirsty Endgrain]

What are your rpms at WOT? Start and go from there.

 

[SWR1]

What are your rpms at WOT? Start and go from there.

Haven't ran it yet. I know the 19 is to much so I need to order one for a starting point.

 

[ahicks]

That motor, on an 18' pontoon with rear seating, is WAY over the top. I'm thinking you're going to be disappointed with how low it sits in back, even when empty.

That said, a 15" prop should be close.

 

[SWR1]

That motor, on an 18' pontoon with rear seating, is WAY over the top. I'm thinking you're going to be disappointed with how low it sits in back, even when empty.

That said, a 15" prop should be close.

I've never owned a pontoon before and I'm not sure what you mean. It has a 40 on it now and it's slow as Christmas. Boat is rated for a 60hp. From my research the 90hp 45lbs heavier than a 60. If it's not gonna work right then I won't do it.

 

[airshot]

The issue becomes a problem when something happens. You are putting a much larger hp than mfgr recomends, so your stressing the chasis to begin with. If you ever get into a mishap, your insurance co will drop you like a rock probably. You open the door for a lawsuit if anyone gets injured. With that said....pontoons are slow by nature, they take far more fuel and hp to get the performance you would in a similiar sized speedboat. Going a little over the rating might not be to bad, but going 33% higher is a gamble... Newer pontoons are being built and designed for large hp engines....just the other day I saw what looked like a 30' triple toon with twin 300 hp Mercs on back !!!!

 

[ahicks]

I would plan on putting, a 90 hp motor on an 18' pontoon, especially one with rear seating. Way too heavy....