Prop for Homemade Pontoon

[WhatsUpDoc]

I believe back in 2006-09 this man where I live actually build this pontoon from the ground up. He was a retired engineer and to be honest this is the heaviest pontoons I've ever sat in.
Attach is a photo of the pontoon boat. As you can see it as these square/rectangle logs (if you can call them logs). I know the largest pontoon boat in the word I see on youtube as these types of logs. What he did was stuff the logs with white styrofoam. The boat was so heavy I actually had to add drain plugs on the back of each log because I wanted to see if they were leaking and no they are not. At least I have drain plugs like they should but it means he did a great job. The floor is aluminum and well its sits excellent in the water.

The problem I am having is he originally installed a 2002 Yamaha 50hp four stroke on this pontoon. I am telling you with 4 grown men it wouldn't get past 8mph topped out. So, I took off the 50hp and installed my Evinrude 150 HP. I set the motor on the very top hole and realized after taking it out to test I had to adjust it because it sat way too low in the water. Then I decided to try some things and moved it up to the very bottom hole on the motor, that was too high. I believe I have it properly set.

I cannot tell you what prop is on the motor as it was on my old bass boat and there are no numbers whatsoever anywhere on the prop. Its a stainless steel prop and I don't know why there isn't any numbers on the prop anywhere to show the size and pitch.

My question is, do pontoons normally use a different type of prop such as a high thrust prop? This pontoon is 18 feet long and just heavy as all get out.

What do you guys recommend for a prop for my 1995 Evinrude 150 HP and this pontoon? I am not looking to go 40 MPH but hopefully get up to at least 25-30mph. Going too slow well I believe that takes away my fishing time and if there is an emergency I don't want to be going 8 mph back to the boat ramp. Just something for 4 large men to be able to get from point A to Point B in a lot quicker time than 8 mph.

Thank you in Advance.

 

[Scott Danforth]

here is an anology. a houseboat with twin 454 big blocks moves at 8mph. the same houseboat with a 50hp motor moves at 8mph. that is the displacement speed of the hull

even with the 150hp motor, I do not see that pontoon getting to 25-30 on the water.

at a minimum, you would need lifting strakes, etc to get the boat from displacing water to sitting on top the water.

yes, pontoons normally use a different gear ratio and a high-thrust prop.

 

[flashback]

You need to know what the rpm is with the current prop in order to determine the size of the new one. Most likely will need less pitch.

 

[WhatsUpDoc]

here is an anology. a houseboat with twin 454 big blocks moves at 8mph. the same houseboat with a 50hp motor moves at 8mph. that is the displacement speed of the hull

even with the 150hp motor, I do not see that pontoon getting to 25-30 on the water.

at a minimum, you would need lifting strakes, etc to get the boat from displacing water to sitting on top the water.

yes, pontoons normally use a different gear ratio and a high-thrust prop.

I was thinking about those lifting strakes, I guess they can weld them on these rectangle logs/block or whatever they are called. Thanks you for reply will do a little more research.

 

[airshot]

Back in my younger days, working at a marina next to our cottage, they had a pontoon with rectangle logs. The idea was to carry weight. You see the marina had a derrick/ winch on the front to do dock maintenence and stack up large concrete rectangles to make a breakwall. The nearby town replaced their sidewalks and was kooking for a olace to dump the old slabs. The marina took all of them that were in rectangle form. You woukd be surprised how much weight that derick could pickup with those square logs !! A round log would have went under with half the weight. They didn't allow you to go fast whether we had the 25 hp or the 10 hp motor on it, 10 mph was it, top speed no matter if we had two people or six people. Not a smooth ride in any type of waves either !! Used that old barge for ten years then sold it after all those sidewalk slabs were installed.