Thread: Power boat for the young fulla

So I know this question would be better posted on a boating forum but to save me signing up for one question I thought I might as well post it here in case anybody knows something about boating.

I have recently acquired a 15hp Yamaha 2 stroke with the intention of building a small hull to mount the motor on for the kids to burn around the lakes on.

Now I don't want to build the boat over 2.5m long and its only guna be carrying a child up to 40-50kg, is the 15hp motor going to be to much an back flip the little suckers if they give it to much juice or is that about right?

I've considered offering the 15hp on TM to swap for something round 7-10hp but I want them to be able to get up on the plane.

Any advise would be greatly appreciated, once I get the motor sorted I can get started building the hull on AutoCad

I can get a plane in a small smartwave with a 4hp so 15hp should be plently. Maybe just limit how much power they can take it to. My nephews motorbike is limited to how much gas he can give it

yeah I'm worried about the weight bogging the ass at low speed so the trade-in might be the option. Haha chuck her in reverse an it might turn into a submarine!

Yeah, better safe then sorry too.

I've got a 5HP on the back of my 3.1m ali dinghy. The previous owner had 15HP on the back but had to weight the front down a fair bit. Have only used it about 4 times with the outboard on.

Does the 5HP get you up on the plane?

My 15hp merc gets 3 adults up to 25knots on my 3.6 m inflatable so yea I think it might give you greif.

B F I've had a few boats , Had a 15hp on a 12 ft alloy dingy that planed with 3 adults in it . Don't worry too much about the weight as it is normal that a 15 hp is same as 10 hp just bigger boar. I'd say6 to 8 hp would be perfect but not essential .

25 odd years ago the family had a 12 foot alloy dingy with Im sure it was a 9 horse on it. It wouldn't quite plane no matter where i sat my skinny white Arse. Then it got a tohatsu 15 on it and was stupid fast with just me in it.
I heard older motors were crank rated power and new ones are prop rated? Perhaps why that 9 wouldn't make it plane. Maybe if it was a 10 foot it would have.

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Originally Posted by big_foot

Does the 5HP get you up on the plane?

Haven't had in anywhere that I could yet. Most of the time I just pull the thing around Ellesmere during duck season.

My brother has a 15 hp on a 2.5m inflatable (rigid hull) and it will tow a wakeboard and have even towed a 16ft fiberglass boat with 3 people on it on the plane (when they broke down.)
a lot will depend on the prop pitch wether you want top speed and slow takeoff or quick takeoff and less top speed.
Im thinking a 4 hp is plenty on a light boat... but this depend on how old your kids are and how safe they play and how heavy the boat is.

Cheers for the info guys yea I think the 15 might be a bit of an overkill but I got it at a sweet price.

Next question, anybody have a 4-8HP they looking to upgrade to 15?

I have a 9.9 that used to plain with a 12ft tinny with 2 pob and all the nets and fish etc....

what type of boat are you looking at building? If it has a pontoon type construction 15 would be fun. down the pitch will up the take off but drop the speed but also let the motor over rev if they hold it hard open... if it was me I would keep the 15....but for my son 6-8hp as he would hold it pinned given half the chance


I have a mate that has a 40 on a deeper V 12ft tinny and its great but you wouldn't want to put that in the hands of someone who way want to use full throttle all the time as you could get in to trouble....big time as it gets rigth out of the water at speed.

If the young fulla is quite mature about speed it may be OK but ...... if not mmm not the best I guess

Can you throw a pic of the motor on please.... what age is it?

Some of the modern motors are rated at the prop ,where the older type was rated at the motor. I would think 15 horses at the prop on a 2.5m is crazy.Even if its rated at the motor its way to much. I'd look at 10' - 12' for that motor.
Another thing to consider is the motor a long or short shaft ?