pontoon with motor transplant

[the454assassian]

Hey everyone I got a 24 foot pontoon at the end of last summer. I had to replace the floor on it so I didn't get to use it to much. It had a motor swap by the last owner. It is running a johnson 150 fast strike. It has a 14x24 prop on it and I am pretty sure that is not what I need for my pontoon. I have not hooked up the tube for the speedo yet but my RPMs is 3k at WOT. It is not fast enough for me and seems to use way to much gas. We like tubing so looking for something to help move this big beast.

 

[steelespike]

As a starting point a 13" pitch should work.Try to find a pontoon specific prop.A 4 blade may help. A 150 will use about 15 gallons per hour at wot,regardless of the size or type of boat.
Your mpg will depend on the speed achieved.Your mpg should have a vast improvement.

 

[the454assassian]

Thank you sir, I was thinking about a 14 pitch but I will go with your advice and use a 13. Any idea what kind of speed I should expect out it?

 

[steelespike]

Being a starting point the 13 may be slightly undersized but your better of there than over propped because you can control the rpm. while you decide if you need a change.
Pontoon speeds are allo over the place for boats that appear to be about the same. 30-35 is a reasonable number.

 

[the454assassian]

So i am getting 25 mph @5000 rpm. I am going to hook up the tilt/trim switch on the throttle and see if i can't get it a little better while underway. Currently i have to stop the boat and lay over the back and adjust it with the switches on the motor

 

[steelespike]

Is your speed by gps? The Only accurate numbers.Lightly loaded?
Trim may help.You may also raise or lower the motor a hole at a time
whatever seems appropriate.Weight distribution is important you don't want to be dragging the underside of the boat in the water.
​ Your rpm seems right on.I think the 150 is rated at 5000 rpm.Using a 1.86 ratio slip is about 24% in range for a pontoon.