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Motor to boat length ratio

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wizbang

New member
"hi everyone, just joined. Mod

"hi everyone, just joined. Mod, i did read the posting rules, did a search, however didnt see anything that was close. so, i thought i would try this. thnx in adavance........
im looking at a few engines, trying to find a 35hp remote steer. year doesnt matter. i hear yami's are the best. so heres the delima.....
do i go for a 2stroke or 4. i will be pushing a 95 southern skimmer 14.5 ft skiff. the tag says max 35hp., and since ive been reading all the posts, ive now learned that the rating on the motor could be less than actual. the other delima.....
should i be looking for a less rated hp. engine that is actually a higher hp. ( model dependent ), and save the $? ill stop here....i ve got more engines questions. thnx to all that can give this a go

Wiz"
 
"Hello Troy and welcome to the

"Hello Troy and welcome to the forum.

Most of the commercial boat mfg's used the US Coast Guards formula to determine the max horsepower for a given boat.

The recommendation (which is all that it is) also considers the weight of the motor, and until about 2005 it was the weight of a "2 stroke" that was factored.

Around that time I noticed a particular model from Lund that I had been drooling over for a couple years changed from being rated at 150 horse to 115.

Everything else "spec wise" seemed to be the same, so I emailed Lund to ask WHY?

The response I got was basically, since the now popular 4 strokes weighed significantly more, they down rated the max horsepower to ensure that the boat would still handle in the manner it was designed.

I believe now that most boats are build "assuming" a 4 horse will be hung on the back so it's not an issue with a new model.

However, when dealing with an older one you need to consider the weight of the motor right along with the horsepower.

In 1995 a 35 horse motor fully rigged with trim/tilt would have weighed in just around 150 pounds.

My 2010 Yami catalog shows the 30/40 horse 4 stroke models @ 216 pounds (about 40% heavier - in 1995 a 60 horse 2S came in at 219 pounds).

On the lighter side, a 30 horse Merc tips the scales at 172 pounds (dry), so add the weight of oil and the prop to that.

As to the "actual" horsepower of the motor - since the mid 1980's, outboards have been rated in Shaft Horsepower, prior to that they were rated in Brake Horsepower which is (often) about 10% less than Shaft (so a 50 horse BHP is about 45 SHP).

Not a concern unless you are buying a motor built before about 1985, and with your boat being a 95 model, would have been rated by SHP.

If you are looking at a used 2 stroke, you can go with a 25, 30, or 35 horse - all would perform about the same (the 35 may get you 1 - 1.5 mph more wide open).

If used is your flavour, I would personally look for a 25 Merc. Yamaha built powerhead and gears with Merc's carb and ignition = probably the best built 25 horse 2 stroke ever on the water and an excellent motor your particular model boat.."
 
"Graham,
thnx for the info.

"Graham,
thnx for the info. what a wellspring you are.
ive got tons more to ask about engines and boats.
i know that this site is geared more towards engines and not boats. however the boat sites i visit seldom if ever give up the info in detail as this one does.
having said that....ill ask this...
any problem posting relative boat questions on this forum? if so which topic? thnx again for all your help and advice. which i WILL be following.

Wiz"
 
"This misc section is probably

"This misc section is probably your best bet.

Like you note, most of use here are "wrench benders" (either pro or the backyard type), but you will find a little bit of everything here.

Some, including myself, have just as much interest in rigging powerboats, so we have (other) boat related information laying around that has nothing to do with "fixin'" motors...."
 
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