Re: 2005 Merc 15hp questions
All the Mercury props for your motor end in "A12". Try looking at the hub, mine has the diameter and pitch stamped there.<br /><br />I have a 2002 Mercury 4-stroke 9.9 with a 15hp carb and a 9x9 prop. I just put on the new carb, so I don't have a lot of performance numbers yet. On my boat (12' flat-bottomed, 5' beam), I've had up to a total displacement of 750 pounds and it will achieve 18.5 mph (gps) at 5500 rpms (with extra throttle left over). I'd guess that it could push around 900 pounds at 5500 rpms. With the 9.9 carb, at 750 pounds, it would achieve 11 mph at 4300 rpms (so if the carburetor switch didn't make it a 15hp, it's close). <br /><br />When you say your boat weighs 1200 pounds, is that your total displacement (boat, motor, gear, people) or just the boat's weight? If you're talking about total displacement, I'd think you should be able to run in the mid teens. I'd go for a 9x8 prop. If it's 1200 pounds before you start adding passenger weight, you might not have enough power to plane. In which case, I'd try the 9.25x7 prop or just keep the one you have and only run at displacement speed. <br /><br />If you can't plane, don't always push it. You'll probably run around 5 mph at displacement speed (which would be an easy-on-the-motor 2500 or so rpms), versus an engine-killing 4500 rpms at 8 mph.
