What hp motor to use for 15ft fiberglass

[neil271978]

Hello everyone,

I am trying to go as cheap as possible because I don't have that much money and I had bad experience with buying a used motor. Anyway my boat is 15 feet and weighs approximately 550 pounds. I had a 25 hp on it and was going about 30mph. I don't need to go fast. I just want to go. 10 mph would be fine for me for now. So what hp would I need to reach that speed?

 

[mjbrueck]

Re: What hp motor to use for 15ft fiberglass

I'm assuming from your post that you're buying new. You probably don't want to go much under 25 hp. Was the 30 mph an estimate or based on GPS? It sounds a little high for a 550# boat with 25hp.

10 mph is a bad speed for a 15' planing hull, you'll use more gas than you will going 30 mph and you'll kill your motor faster. To plane, you might be able to get away with something like the 18 hp Tohatsu/Nissan - you may need a smaller pitch than stock prop. If you just need displacement speed (about 5 mph for your boat) for ponds or small lakes, a 5hp would be plenty. It's between 5 mph and 12-14 mph where you'll be running in a very inefficient range.

 

[Kev]

Re: What hp motor to use for 15ft fiberglass

mj makes some good points to be sure. If you go for a very small motor though, try to at least get a 2 cylinder, usually about 8-9.9 HP nowadays. The 2-cylinders are smoother and a lot ballsier than the smaller one cylinder outboards.

I'd agree that an 18 will probably plane your boat, but not really easily. It will depend a lot on how many people and what load you expect to carry. Also on how you distribute the weight.

The Tohatsus seem like nice motors. I'm looking at one myself.

Good Luck,
Kev

 

[Texasmark]

Re: What hp motor to use for 15ft fiberglass

I agree with mj also. Decide what you want to do; go slow, like slow or get on top (plane out) and get on with it. 25 mph is not high speed, by any means, but it is a nice comfortable speed, efficient (probably the most efficient for most boats), and you get a good dry ride.

Just noticed in the '97 Merc catalog that their 2 cyl 30 hp has 39 cu in pushing a 2:1 gearbox and doesn't mention the standard prop. I'd go for that sucker if you can find one. You ought to be very pleased with the performance from that engine and it's new enough to run on todays gas.

I know the old '50's OMC 25 was a pushing dude. Figured out why.....35 cu in. It turned a 10 1/2 x 12 prop but was running a 1.75:1 gearbox but was rated at 4000 rpm.

Current Merc/mariner 25 hp's are only 24 cu in, but sporting a 2.25 gearbox and turning a 10 1/2 x 13 wheel and rated to 6000. I think that makes them pretty competetive with the old 25 and being new they can run on today's fuels.

So, if you can't find a 30, grab yourself a 25.

Can't comment on OMC as i don't have any sales brochures on them.

My 2c,

Mark

 

[neil271978]

Re: What hp motor to use for 15ft fiberglass

I know this probably sounds really dumb but i am new to boating and still learning. Can someone describe exactly what plane means. Anyway I have priced everywhere around here and there is a place with a 18hp Nissan 4 stroke electric start for $2700. That seems to be the best deal I can find. One place had a 25hp manual start 2 stroke for $2500 but I really don't like pull starting so I would much rather have an electric start. Which do ya'll think would be better?

 

[Texasmark]

Re: What hp motor to use for 15ft fiberglass

Plane means that the boat gets out of the water and on top of the water......you have displacement hulls and planing hulls. Ships are displacement hulls; most recreational smaller boats (less than say 30 feet) are planing hulls. By getting out of the water and on top you get much more economy because the hull drag is significantly reduced................but if you have 100,000# of cargo to move, you will do it by displacement, not planing. 8)

Get your $2700 Nissan. Gotta do what you gotta do. An 18 is no slouch and you can have a lot of fun with one on a light, small boat. When I was a kid, I had a 13' wooden boat with a '57 18hp Evinrude....go to www.old-omc .de site and you can see one. Coluld barely ski with it, but I could and without skiing it ran the boat fast enough for me at the time. Had a lot of fun.

HTH.

Mark

 

[neil271978]

Re: What hp motor to use for 15ft fiberglass

Well I found a 25hp electric start four stroke EFI for $2880 from Bass Pro Shops which is by far the best deal. Only problem is they are on recall and they dont know when I could actually get one. But it looks like that will be my best bet. Only 200 more than the 18. I think I'll be patient and wait for the 25 and see if anything else better comes along in the meantime

 

[neil271978]

Re: What hp motor to use for 15ft fiberglass

By the way MJ the 30mph was just a guess it might have been slower