G’day,

I’ve just built my first boat, A glen l minimaxxed which is 8ft long and 4ft wide. Basically 3 sheets of 6mm plywood cobbled together with a 15 hp motor clamped to it. Which is a 1997 mercury 15hp 2 stroke I borrowed off my fishing boat.

Took it out to Copeton Dam in North NSW for a run and had a bloke on a jet ski drive along beside me to see how fast she goes and he says i’m doing 50 km/hr.

I have read about the old 15hp racing outboards getting 50 or more mph and this has me scratching my head how they get those speeds. I’m running a 9.25x12 pitch solas prop 8 spline and dont have a tacho but by ear it sounds about 6,000 or so. Tried the original 9x9 and it was clearly over revving.

I’ve never opened up an outboard motor to see inside one other than taking the gearbox off to change a water pump so other than that im a outboard noob. I have mucked about with 2 stroke bikes changing port timing and comp and managed to get an old 2 tonne dual cab 4x4 farm hilux down the 1/8 mile in 8 seconds with a home made turbo setup on a holden v8 I’d welded in there years ago so I can handle a spanner and a die grinder a bit. I’m keen to learn how a bloke might do a bit of modifying on a merc 15 to get it going faster than 50km/hr like she’s running now.

Can any of you fellas steer me to some info or books or first hand ideas that can get more power out of this old merc 15 ? Looking at the motor I cant even see how the heads come off.... looks like barrel and head is 1 piece not sure. I’m not sure how to post pictures here either but theres 1 of the boat in my profile page.

Thanks