Engine size for old speedboat plans (Skeeto)

[brownsoft]

I'm thinking about building from old plans for a skiboat called 'Skeeto' but the plans don't provide suggestions for the outboard motor size. The boat is just under 15 ft in length. I used a method of calculation described on a website, but this gave me a maximum 'safe' horsepower rating of 85. I'd like to know what is the optimum size, what is the minimum size etc.. Any thoughts?
Here's a piccy

[mmd]

This is utterly un-calculated, un-researched, and un-professional (I haven't had my morning coffee yet), but I have a 60's vintage wood speedboat about the same size & layout as yours. The "old fellahs" who have used boats like mine have told me that the boat will get up on plane with a 25 hp motor, will zip along comfortably and economically with a 40 hp, and it will get a bit difficult to handle with anything above 60 hp. If your hull has a bit of vee at the transom (mine is virtually flat) it will take a bit more power to plane and will track better, so add 10 hp to the above comments. Good luck, it's a nice looking boat.

[WWheeler]

Recently seen in the local buy & sell paper:

"For sale wooden boat for restoration project. (needs new transom). Also included, 90 Hp. Johnson."

Draw your own conclusions.

[Mr. Know It All]

I have a 1961 Lyman 16 footer outboard. The original outboard motor was a smokey,loud and powerfull 1961 Johnson 75HP 4-stroke (weighs 400 lbs.). I've heard it pulled 2 Adult water skiers real fast. I myself would be happier with a Lighter, smaller, newer, more fuel efficient and reliable 35HP motor. The boat is 41 years old and I'm older than the boat so I guess that accounts for my taste. I want a motor that 2 people could humanly lift on and off the transom also. If you want to add more HP to the boat think seriously about beefing the transom when building and buying one of those backbraces. Just check the price difference between a 25HP and a 50HP,that will help you make your mind up too. That Skeeto looks like a fast boat and has nice lines but I'll bet a 40HP would be plenty of power. Good Luck.
Peace-----> Kevin in Ohio

[Bryan Mehus]

brownsoft,
In the short description of the plans in the back of Spring, 1971 Boat Builder, it says "use motors up to 60 hp."

Probably would be plenty given that current motors are considerably lighter than those of the late '60s and early '70s.

Bryan

[brad9798]

Forget weight, 85 hp on that boat will push you 60+. (guesstimating, of course).

I've got a 15-foot center console running a 65-horse, and I push 45-50mph! And that's fast when you hit wake/chop/etc.

If it were my boat, I'd look in the 50hp range. Upper 30's to low 40's is awefully fast on the water in the type of boat pictured.

Glen-L sells many similar models, and have researched power. Their typical 15-foot runnies are rated from 60-85hp.

Good luck.

Brad

[jeff pierce]

Speaking of Glen-L, they have a curve on their website that gives an estimate of speed as a function of gross weight divided by horsepower for a "typical" planing hull. Since we have established that the design was for up to 60 hp and you probably have a feel for a minimum speed you would like to be able to achieve, I think you can pretty much bound the problem.

Nice little boat.

[bainbridgeisland]

As mentioned by others, weight is not really the problem. New outboards are lighter than they used to be.

I doubt the transom is a problem either. If concerned about it, a small increase in the size of the transom knees would make it much stronger.

I am concerned about the stiffness and strength of the bottom. High speed power boats have very high loads on the bottom of the hull. The bottom loading goes up as the speed squared. Thus, 43 knots develops 50% more bottom loading than 35 knots.

Remember in the early 1960's, a 35 hp motor on a 15' boat was a reasonable ski setup. A 45 hp motor was probably an average ski boat power plant. If your engine is too big, the bottom of the hull may not be strong enough.

[brownsoft]

Thanks for all the advice. I love the look of the boat but the cost of larger outboard motors is huge over here in Australia and I would like to get away with the minimum. A 40 hp motor costs near $6000 (or close to $12,000 american) here.

I should have mentioned that the plans for skeeto (and many others) are available free at Boat plans