Reinforcement for larger motor

[Mojo]

I just purchased a plan for 15' dinky and I want to put a 8 horsepower 4 stroke Honda. I would like to reinforce the transom and other areas of the boat. Any suggestions. Any ideas how fast this boat will run with 4 horse versus 8 hrs power.

[Boatplans.dk]

Thanks for your purchase of the plans.

I would suggest using a double transom, thus making it 18 mm [3/4"] instead of 9 mm [3/8"]. Then in order to ensure sufficient strength in the connection between the hull and transom apply extra glass tape e.g. 2-3 layers of 100 mm [4"] wide tape similar to the type described in the BoM.

The speed is dependent of the weight of the boat. So if the boat has a weight of 135 kg [298 lbs.], this include the hull, engine, gear, crew, etc. my calculations show that you would go 15 kn. with a 4 hp and 21 kn. with a 8 hp outboard.

[jem]

Wow 21 knots....that's kinda scarey fast for the Dingy 15.

You might want to think about changing the prop or something. Dingy 15 is a very sea worthy boat but it's no ski boat.

Maybe I'm just chicken.

[Boatplans.dk]

Yes, 21 kn. is fast, so be careful and look after yourself and your crew.

[banoe]

I would think the dingy 15' would get kind of scary with a 8hp the Dingy does not have very wide after planing sections it could get tippy at high speeds as more of the bottom wetted area gets lifted out of the water. I have put outboards on the side of regular canoes several times and they get tippy at speed with bigger motors. I fixed one canoe outboard setup by adding a Dole-fin to the cavitation plate it made the canoe ride much better. Should be plenty fast all though I don't think you would get 21kn I don't think the prop on a 8hp is capable of that kind of speed would be fun to try though.

[mojo]

Thanks for the feedback and suggestions. Wow!!! 21 knots on 300lbs of weight that is pretty good. I guess I'll never achieved that speed because between my son and I, we weight 310lbs. So, in my calculations: 310 lbs (son and I) + 55 lbs(motor) + 98lbs(boat) + 30 lbs(gear and beer) = 493 lbs. Oh I forgot to add 7 lbs of fish that we will catch that would put us in even at 500 lbs. At 500 lbs we will be cruising at 7 knots/hr which it will make a good trolling speed/hull speed. I guess we will forget about picking up some babes at the beach. Darn.....maybe 15 HP power will be ideal. Just kidding.
I just want to let you know that the design and the plan was great. I have been looking for this type of boat but could not find one that I like. It would be great to have a pattern. (it would make my life simple). So, it will a father and son project this summer here in sunny Florida. If the Nissan 8 HP 2 stroke will be to much for this dingy, I have a Yamaha 4 HP 4 stroke long shaft engine.

[Boatplans.dk]

Tanks mojo, I’m happy you like the design and plans.

With the displacement of 500 lbs and the speed of 7 kn. you would properly only need your 4 hp engine. This hull is extremely easy driven through the water and it doesn’t provide much resistance.

Patterns can be arranges. I have them almost finished, just a matter of lack of time that I haven't put them for sale yet. Drop me an email if you would be interested.

[Momo]

Verrry curious as to whether this worked or not.
I'm getting a great deal on a 10hp outboard 55-60lbs and would like to put it on the DK15 I'm going to build.
Also read the other post on keeping the same width of the boat from the middle to the back to hold the extra weight.
Looks like I shoulda bought the plans for the Garvey Flex 14.
(my second runner up)
Momo

[Boatplans.dk]

I haven't got any feedback on the large outboard, but I know that mojo ended up using a small Seagull. The dinghy has been going fine with that. You can see his dinghy on my website, it is the yellow one.

10 hp outboard would be fine for the 14' Garvey flex, but if it is the 15' Dinghy you like that's not much good