# Jet boat

Discussion in 'Boat Design' started by Benjamin L., Oct 3, 2022.

1. Joined: Sep 2022
Posts: 6
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Location: Montreal

### Benjamin L.Junior Member

Dear members,

I’m trying to build a light jet boat (re enforced fiber glass) about 8’ long x 42 inches large. I have a 2T engine , 290cc, 36hp @7500 RPM. The maximum weight of the boat is 130kg including the captain. The shaft is direct and horizontal To maximize the output, please let me know:

-The shaft size and lenght
-The diameter of the jet
-Any other things that I should know…

If you guys can, please give me the answers and the way how to calculate them because I might have to change the boat size. I will be able to calculate by myself then.

I thank you in advance for any hints! Have a great day!

2. Joined: Oct 2007
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### bajansailorMarine Surveyor

Re how the maximum weight of the boat is 130 kg (how did you arrive at this figure?), and assuming that you are of average weight (say 80 kg?) then that only leaves 50 kg for the boat, the engine (how heavy is your 2T engine?), the drive shaft, the water jet and the fuel tank, not to mention a lifejacket and perhaps an anchor with a chain rope cable (?).

Re how you are 'trying' to build a light jet boat - how far have you got so far?
Do you have any drawings that you can scan or photograph, and post on here for reference please?

3. Joined: Sep 2022
Posts: 6
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Location: Montreal

### Benjamin L.Junior Member

Hi Bajansailor,

Thanks for your help! I weight about 60kg, the engine is 27kg without fuel. The boat is made of Pvc sheet and re enforced fiberglass and from what I heart on Youtube, the boat weights 32kg. So you’re probably right, the weight should be around 150kg.
What do you think about all this? Should I make the boat a bit longer, let’s say 110’’ to have more legs room?

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4. Joined: Oct 2007
Posts: 3,285
Likes: 1,314, Points: 113, Legacy Rep: 37