Want to diy a speed boat and was hoping someone who knew thier stuff could tell me hell yea or no

[Chopperr007]

I’m thinking ide be better off choosing power source and then the drive train.Iwas going to go with a 1.8L naturally asperated with a surface drive speed prop and have the ability to move it up or down as needed I was thinking that ide like to put that in a 9 or10’vhull and locate the engine in front of me ,not too far forward.I don’t have a lot of money so I’ll have to get creative with making it a 2 speed so the prop doesn’t cavitation off the rip,and my diy trim will be easier to do.so I’m wondering or hoping that someone will look at this post and give me a heads up on whether I’m on track with something here thanx.

 

[gonzo]

If you don't have a lot of money, a used boat is a better idea. You can't choose a power source until there is a hull to go with it, total weight of the boat, target speed, operating conditions, etc.

 

[montero]

Front engine placement means you want use automotive 2 speed transfer case with driveshaft joint at the transom ?

 

[Chopperr007]

Front engine placement means you want use automotive 2 speed transfer case with driveshaft joint at the transom ?

Thanks ,that helps a lot .

 

[Chopperr007]

If you don't have a lot of money, a used boat is a better idea. You can't choose a power source until there is a hull to go with it, total weight of the boat, target speed, operating conditions, etc.

I don’t have a lot of money to throw at something all at once but building a boat takes time and that I have plenty of and with time comes a little money I can afford too invest,thanks

 

[montero]

Have you chosen a Yamaha engine?

 

[HelmutSheina]

Probably the simplest way to power a small boat with any suitable engine is a transom mounted Thai style longtail. There are safety considerations with this, so do good homework before the tools come out. Check out Thai racers, they move.

Also a 10' Vee hull would have to be extremely well designed to handle a four cylinder car engine. Here are some free plans for your perusal. If you want speed, check the hydroplane section. Most are from the pre-epoxy resin era, and are built accordingly with heavy timbers, resorcinol, and a lot of metal fasteners. That's what you get for free, there will be lots of ideas though.

Absolutely Free Boat Plans

 

[Chopperr007]

Probably the simplest way to power a small boat with any suitable engine is a transom mounted Thai style longtail. There are safety considerations with this, so do good homework before the tools come out. Check out Thai racers, they move.

Also a 10' Vee hull would have to be extremely well designed to handle a four cylinder car engine. Here are some free plans for your perusal. If you want speed, check the hydroplane section. Most are from the pre-epoxy resin era, and are built accordingly with heavy timbers, resorcinol, and a lot of metal fasteners. That's what you get for free, there will be lots of ideas though.

Absolutely Free Boat Plans

Very nice thanks for the planes .yes I’ve had my eye on the Thai racers as well ,from what I gather is that you lose a lot of hp in jet boats .thats why I wanted to go with the prop and these plans give me some ideas because from some of what I’m learning that I’ll need a transfer case but a couple of these boats are straight up direct drive,cool.im trying to maybe make some money ,i used to build houses sub contractor .i bought a 12 ton stinger with 18’ jib .they didn’t do that around here .people thought it was kool especially when it got hot because i made a flat umbrella out of aluminum safety rails for scaffolding and snap tie a big tarp to it .and with a 6 point pic my fellow worked in the shade.even after i got the rafters up ide stacke plywood on the roof and hang the umbrella and get to work sheeting it.in the shade anyway i think im gonna build molds for these boats and use very little wood in them if any ,then that would bring the price down .and if it was a winner then wall i can slap another together in half the time.well you help is greatly appreciated so ill keep posting my progress and y’all have and good day and a wonderful life.

 

[HelmutSheina]

Chop longtails use surfacing props not jets.

 

[Chopperr007]

Chop longtails use surfacing props not jets.

Yea and they are fast and I think the shaft is directly hooked up too the motor.and it’s wired that when I investigate it online it always talks about cavitation,saying I need to have a 2 or more speed ,and I don’t think those Thai boats have one.

 

[HelmutSheina]

there is no reason it can't.

 

[gonzo]

Yea and they are fast and I think the shaft is directly hooked up too the motor.and it’s wired that when I investigate it online it always talks about cavitation,saying I need to have a 2 or more speed ,and I don’t think those Thai boats have one.

Surface piercing propellers are designed to ventilate, therefore they don't cavitate.

 

[Jimboat]

looks like a fun project. you should decide on hull type, size, weight, target velocity, etc before considering engine spec.

 

[HelmutSheina]

Surface piercing propellers are designed to ventilate, therefore they don't cavitate.

Just to expand on what Gonzo says here. Cavitation and ventilation are frequently confused terms but the meaning is clear.

I'm using a phone, which I find fiddly to type on, so will use a website link to explain. There is plenty more info available on it.

Propeller Cavitation vs Ventilation: How to Tell the Difference and Fix It (2026)

Learn the difference between propeller cavitation and ventilation: symptoms, causes, diagnostic steps, and fixes. Stop power loss and protect your engine.

captainpropeller.com

 

[rnlock]

I'm sure a suitable plan already exists. I don't know if it's any good, or even if it's safe, but Glen-L has a 12 foot plan into which people have stuffed absurdly large engines. At some point, I should think enough power in a tiny boat risks it becoming an out-of-control airplane. Just how fast do you need to go? If 40 or maybe even 50 mph is enough, it might be cheaper to buy an existing boat. On the water, 40 or 50 mph is fast, especially if you hit a big wake. I just saw a listing for a used 16 foot deep-v boat with a 120 hp motor for $1000. And another similar boat for free. If you want to go 75 or 100 mph, I wonder if it wouldn't be safer to use a wing in ground effect craft. At least they are stable when they leave the water's surface. You might even just be able to bolt an air propeller on the end of the crankshaft. Just make sure, unless you have a pilot's license, that it isn't able to get very high. Plus you'd have to do a lot of homework to determine which designs are reputable.