Hi,, I got this '79 120 merc inboard with a 17P 15" prop,,, WOT 4500RMP only 27MPH is that correct? 18'fiberglass Glasspar boat! Or what should it do? Thanks
wiserboy <br /><br />30-35 MPH is about all you can expect with the 120 and an 18'er. I would try a prop size of 15-1/4 X 19 and see if you gain a little speed. Bear in mind this will lower your RPM's to about 4100 and reduce hole shot. I don't know the correct RPM range for your engine. Maybe others will chime in and help. Also, this post will probably get moved to the I/O section where more help is likely.
