Pontoon boat for 25hp Merc, 2 Stroke

[film495]

I have in my yard on a project boat that I guess I don't want to mess with it, it can just become a rowboat at some point. I have a 2005 25hp Mercury 20" Shaft, Two Stroke on it. I've been wondering what I could do with this motor and the possibility of throwing it on a smaller pontune boat came to mind. Brings up a couple questions.

I fully assume with a loaded crew that motor will not plane out a pontoon boat of any size, but - basically I'm wondering how fast it might go with two people. I have in mind, that this might be a way to just run the lake, 7 miles long, end to end, and maybe be able to do that in 1.5 hours, maybe 1 hour would be ideal. but then I'd have to getting upwards of 15 mph to pull that off and I just don't see it, but I don't know - figured I'd see what others might know, maybe there is a way to pull it off.

 

[jlh3rd]

24', twin 25" diameter toons...
'05 60 hp merc 4 stroke bigfoot, one driver, ....20-21 mph@6000 rpm(max)
'21 115hp merc CT, one driver...........................26-27 mph@5800 rpm (max)

I rented an 18' pontoon a few years back..( posted here somewhere). had a 9.9 ? hp honda on it?..two people, my phone gps said about 10mph if I recall.....

 

[JohnSz]

That 25hp wasn't made for high thrust, which is what is needed on a pontoon. The Merc Bigfoot/Command Thrust have a larger gearcase to deal with that. You would also need to find the lowest pitch prop available to even try it. Most will be rubber hubbed, and will fail quickly in very high thrust applications.

I'd recommend an open Mod-V jon boat, like a 1648, for that motor. You will be over 20mph with two people.

 

[Scott Danforth]

Buddy has a 18' pontoon, 35hp motor. moves same as it did with a 25hp 30 years ago. all of 14-15mph.... on a 7 mile long lake, would take 30 minutes to get to the other end.

I have in mind, that this might be a way to just run the lake, 7 miles long, end to end, and maybe be able to do that in 1.5 hours, maybe 1 hour would be ideal. but then I'd have to getting upwards of 15 mph to pull that off and I just don't see it, but I don't know -

you may want to check your math there. to do 7 miles in 1.5 hrs is needing to be running 4.67mph to do it in 1 hour would be 7mph. to move 7 miles at 15mph would be about 28 minutes


an no, a 20hp wont plane any kind of pontoon boat.

 

[film495]

I think I may keep it on a skiff and switch the skiff back to a tiller. It is an Indian River Skiff I put together from kit plans. I put a console on it, becuase the tiller handle seemed to really pull too much, but I think I can fix that by raising the motor mount and getting the cavitation plate up an inch or two to align better with the bottom of the boat. The original plan was tiller motor and oars, and I think I might just go back that route, and get rid of the steering wheel and remote cable controls, and simplify it. Then at the end of the year, I can just pull the motor and put it on a stand in a garage, and flip the boat over and just leave it until spring.

I was thinking of downsizing the motor for that, or just having it as a row boat, but - hmmm ... maybe I should mess with it again with what I have. That skiff is kind of a neat runabout for small/medium lakes.