40 h/p mercury and 18' pontoon

[jimmywayne]

I've asked this question before but I now have a few more things I was asked to include. I have a 40 h/p mercury pro and 18' pontoon and I can only get about 4700 rpms is this the correct prop? Going by the gps with 2 people in the boat it will only go about 15mph is this about right? The prop on the boat is 9" with a 13 pitch. On the prop it says #48 73136 A40 13P Measuring from the center of the hub to the bottom of the foot I measure 6 3/4" so technicaly I could use a prop about 13.5". I would love to get a little more speed and a little better gas mileage. Is it possible by changing the prop? Or since I only have a 40 h/p mercury tracker pro series am I asking for too much? Any help would be appreciated. Thanks Jimmy

 

[steelespike]

Re: 40 h/p mercury and 18' pontoon

I believe the rpm range on your motor is 5,000 to 5,500.
Assuming the motor is sound and well tuned it appears you should go to a 11" pitch.Should put you at about 5,100.You might try to find a pontoon dedicated prop.Usually 4 blade.If you have the patience a pontoon can get pretty good mileage at speeds about 6 to 9 mph. Careful motor trim,and weight distribution can improve speed and mileage. You might be able to get to 18 or 20 mph.with a light load and careful prop selection.
A pontoon doesn't plane, pushing one at planing speeds is a waste of fuel.
There are some pontoon forums you might pick a few brains over there.

 

[Silvertip]

Re: 40 h/p mercury and 18' pontoon

The diameter of the prop used on Mercury engines depends on whether or not you have a "BigFoor" lower unit. Those engines have s 2.33:1 gear set while the standard engine has a 1.83:1 and runs a smaller diameter prop. If you have the standard lower unit then you definitely DO NOT want a 13.5 inch prop as the engine is already struggling as it cannot reach its recommended RPM band. Next, regardless of diameter, even an 11 pitch prop is too much. Step down to a 9. I have a 40 HP Suzy four-stroke on my 18 foot pontoon and it will run 19 - 20 MPH with a light load at 5800 rpm. Of course, all of this moot unless you are absolutely sure the pontoons do not have any water in them, they are clean, the engine is running correctly, the throttle linkage is properly sync'ed and the throttle is actually opening the carbs fully.