40 h/p mercury pro and 18' pontoon

[jimmywayne]

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?

 

[mthieme]

Re: 40 h/p mercury pro and 18' pontoon

I wouldn't expect too much in the way of speed.
Usually toons require a flatter prop - less pitch.
This is supported by your low WOT rpm.
Judging by the info so far (which is minimal), you could easily go 4-6 less on your pitch. You'll have to check the numbers on your prop to see what you have now. I think a 13P-15P is fairly standard on a Merc.
What year is the motor?

 

[jimmywayne]

Re: 40 h/p mercury pro and 18' pontoon

it's a 1996

 

[steelespike]

Re: 40 h/p mercury pro and 18' pontoon

As suggested get your prop size.Without prop size rpm means nothing.If the motor is sound and properly trimmed
carefull weight distribution ,right prop you might see 18-20.