MacGregorSailors.com

When is too big, too big?

My 83 M25 came with an Evinrude 2 stroke 15 HP. Looks to be a engine that is about 20 years old. The marina that I serviced it at today, says it is the exact same size engine as the 9.9, with a larger air intake? Something like that.

Is this OK for a rusty sailor that has never operated a boat motor in his life?

I am not going to replace something that works because it is a little out of specs, but what should I watch for, so I do not end up in trouble?

Do I put some sort of safety line on the engine, in case it falls off?

A lot of different questions here;
- motor size & weight
-transom thickness
-motor mount
-location
As for motor size, to each his own. I know lots of people with 3,4, or 5 hp motors who seem very happy. As for me, I like to sail in weather and places where I'm very glad to have a little more. Merc 9.9 for me. (But it won't go any faster than hull speed no matter what.)
My Mac 25 came to me with a mount bracket that may be on the light side, but had a long throw, which I like. And a new one for a 100# motor was about $350, so I kept it and beefed up the spring. Then I glassed 2 layers of 3/4" plywood to the transom way wider than I probably needed, because I do trailer with the motor on. Lot of work, no problems. Satisfied. Bear in mind you also need to find a way to strap your tank down. Mine is in the lazarette where I can get to it. Also at least give some thought to ventilation for fumes.
As for the foam, just take the blocks out, do what you want, put em back in. But reinstall the hatch. It not only helps keep gas fumes out of the cabin, It will keep that foam in place if you should ever need it. It won't help much if it's floating around the cabin.
You'll have a blast with that 25.

You should have a line on the motor to stop it from submerging. I am the Board expert on that, btw, Captain Dunk.

I think the 25 is a non-planing hull, which means that extra HP above 8-9 wont make you go any faster. Hull speed for your boat is about 7 mph, so dont try to go over that.

A lot of marine engines are based on the same short block and head, and changes in induction (either carbs or EFI) determine the HP the motor will develop. Its a bit more complicated than just a larger air intake (thats probably telling you not to have your carb serviced by this guy btw).

On the Nissan line, the 4- 5-6 HP line are the same motor, with a slightly different carb and camshaft - you could buy the parts and convert a 4HP to a 6HP in your garage.

I doubt any manufacturer jumps from 9.9 to 25 HP with just induction changes - my guess is its a bigger bore motor and maybe even more cylinders to more than double the power. In the Nissan line the 10 to 25 HP jump is from 300cc to 500cc displacement.

Catigale wrote:You should have a line on the motor to stop it from submerging. I am the Board expert on that, btw, Captain Dunk.

I think the 25 is a non-planing hull, which means that extra HP above 8-9 wont make you go any faster. Hull speed for your boat is about 7 mph, so dont try to go over that.

A lot of marine engines are based on the same short block and head, and changes in induction (either carbs or EFI) determine the HP the motor will develop. Its a bit more complicated than just a larger air intake (thats probably telling you not to have your carb serviced by this guy btw).

On the Nissan line, the 4- 5-6 HP line are the same motor, with a slightly different carb and camshaft - you could buy the parts and convert a 4HP to a 6HP in your garage.

I doubt any manufacturer jumps from 9.9 to 25 HP with just induction changes - my guess is its a bigger bore motor and maybe even more cylinders to more than double the power

Thanks for safety line recommendation, I seemed to remember having one was a good idea, but I have not rigged it up yet. Would be a shame to have it go under and loose it, because something got loose or broke free.