I have a 1981 50 hp Mercury (4 cyl) on a 15.5' fiberglass runabout. When lightly loaded (1 or 2 people) the motor seems well matched to the boat. It planes at about 3800 RPM and, at WOT, it revs at 5300 RPM (24.0 knots). I normally cruise at about 4200 - 4400 RPM (17 - 18 knots). Mercury recommends 5000 - 5500 RPM at WOT for this motor.<br /><br />This past weekend I carried 4 adults (myself included) and the boat had a real problem climbing out of the hole. At WOT the motor was at 3800 rpm and the boat was stuck at 9.5 knots. After a minute (or maybe 2) it would eventually climb up onto plane, the RPM would rise and things were pretty much normal. It got easier to climb onto plane as the day went on. I think it was because the boat was getting lighter as we used up fuel.<br /><br />My belief is that the motor is overpropped for carrying this heavy of a load. In reading through the archives of the board it sounds like this is not uncommon for a motor of this size. The motor is 50 hp (powerhead) and, in later years, was re-rated to a 45 hp (propellor shaft) before going out of production.<br /><br />The motor currently has a Quicksilver 14 pitch prop (new this season). I am thinking of getting a 12 pitch to use when I anticipate carrying a heavier load. Is this enough of a change in pitch to solve my problem? I realize that I will have to be careful not to exceed max RPM when lightly loaded.<br /><br />Thanks in advance,<br />Russell McPherson
