Building my own jet boat.

[Ricardo van Oudenhoven]

Hi, I am 14 years old and live in Holland,
I just became a member of Jetboaters.

I am planning on making a jet boat from scratch, something similar to a jet dinghy or a jon boat.
This would be the first boat I make, I have had 2 small fishing boats before, one of polyester and now one of aluminium, both under 5 meters. I would like to build the boat out of aluminium. I am not planning on fishing with the boat much, as the boat I have is ideal for fishing.

I was wondering,
What are some thing I should keep in mind when building the boat?
Where should I start? Should I start with the engine or with the boat?
What type of engine could I use instead of an engine designed for jet boats? Preferably something not to expensive. Could a motorcycle engine work?
How powerful should the engine be? I was thinking something around 50 hp.
Should I make a jon boat or more something like a jet dinghy?
What can I expect of the final cost of everything together?
If anyone has any suggestions please share.

Thanks in advance,
Ricardo.

 

[txav8r]

Hello Ricardo and welcome to Jetboaters! Let me first say that if you add your location in your profile, it will show your location on the member map, but more importantly, it will be in your profile that shows on each screen, and seen by anyone reading your posts, and gives an idea of how you might boat, what waters you boat in. You may be our first member from Holland!

Most of the membership here comes from the Yamaha Jetbiat line, but we have membership from the former seadoo boats and now chaparral and scarab boats. These are all production boats. We have had a few members that had build projects or restoration conversions discuss plans in the past. I don't remember anyone actually finishing one of these projects or posting about completion.

You will find that use of jet propulsion is critical to any given boat. And that the design of engine to pump needs to match the boat. By match, I mean that intake is critical as is pump output. Matching an engine to a pump will depend on either finding parts that will mate them or fabricating parts to mate them will be necessary. Costs generally dictate the use of engine pump combos that were designed to work together. Your cheapest approach may be a scrap jet ski, motor/pump combo. Depending on the performance your seeking, 50hp may not be enough but for a bare bones aluminum boat, it may be. We have a guy in the forum that loves speed mods and had some pretty good ideas on the dynamics of what it takes to drive a boat. @Speedling He may have plenty of ideas. As I said, intake and outflow are very important or you may just be building a water gun and not a propulsion system.

Once again, welcome aboard, good luck with the project, and keep us posted on your plans and progress!

 

[bronze_10]

Hi, I am 14 years old and live in Holland,
I just became a member of Jetboaters.

I am planning on making a jet boat from scratch, something similar to a jet dinghy or a jon boat.
This would be the first boat I make, I have had 2 small fishing boats before, one of polyester and now one of aluminium, both under 5 meters. I would like to build the boat out of aluminium. I am not planning on fishing with the boat much, as the boat I have is ideal for fishing.

I was wondering,
What are some thing I should keep in mind when building the boat?
Where should I start? Should I start with the engine or with the boat?
What type of engine could I use instead of an engine designed for jet boats? Preferably something not to expensive. Could a motorcycle engine work?
How powerful should the engine be? I was thinking something around 50 hp.
Should I make a jon boat or more something like a jet dinghy?
What can I expect of the final cost of everything together?
If anyone has any suggestions please share.

Thanks in advance,
Ricardo.

Welcome to the family!... I'm not sure about actually building the boats but if u need any information on jet boats u certainly came to the right place... ..... not..... not me but other know a lot of stuff..........m I just drive it and ask questions and I always get an answer here.

 

[Speedling]

Awesome idea kid!
I have started some plans but nothing as small as you have planned.
Let me get home from church and I can write more.

 

[Bruce]

Sounds like a fun project.

I am going to move your thread to General Discussion where it will get more attention.

I think I would start with a Jet Ski as it has all of the parts that you would need for propulsion.

 

[Wayloncle]

Let me get home from church and I can write more.

This makes think of a saying I used to see on a motorcycle forum I was a part of.
"I'd rather be sitting in my boat thinking about God than sitting in a pew thinking about my boat"

 

[robert843]

Welcome aboard! I actually have seen someone finish one of these projects. They took an aluminum jon boat and a donor Polaris 700 engine and pump from an old ski. The easiest way to do this project would be to get a donor engine and pump from a wrecked ski. converting a non marine engine to a marine engine would probably be fairly labor intensive especially to convert it to a jet drive but I'm not a mechanic by any stretch of the means so someone else may have better info here. I do have some pics from when the project was going on I just sent him a message asking if he had any finished pics as I know he has since finished it.

 

[tdonoughue]

Great idea for a project! And I think that @robert843 's photos are great. Only thing is that welding the aluminium would give me fits. But I like how they put the angled parts on the bottom to fit the angles of the donor boat. Good idea there.

Needs a bigger gas tank... Oh, wait. That is for my twin engines...

Welcome @Ricardo van Oudenhoven ! Keep us posted on the progress.

 

[Ricardo van Oudenhoven]

Thanks everyone for the extremely fast replies< I will look for a wrecked ski jet, I will definitely keep coming back to show the progress. If anyone has anything else to add please do.

 

[Speedling]

First of all, yes, find yourself a pump. Usually a wrecked ski can be found by looking online and such. I see old waverunners on auction sites but I'd go check out copart site because it is insurance stuff and I have seen the skis with 110 hp engines go for just a few hundred bucks because they are cracked.
Once you have that you need to determine the use of the boat. If you get a 110 hp engine and pump with it you will probably be building a planing boat so there is a bit of planning involved.

 

[Ricardo van Oudenhoven]

I found this online, I was planning on following this but making the bottom flat, kind of like the picture shared by robert843. What do you guys think?

 

[Ricardo van Oudenhoven]

http://www.speurders.nl/overzicht/w...i-550-motorblok-jetski-155711487.html?sr_ab=0
Sorry that it's in dutch, I found this engine online, I can get everything else I need from someone else. Would this be a smart choice? or is the engine not strong enough? I believe it's only 41 hp. Or would it be better if I find a complete jet ski?

 

[Speedling]

That boat you posted your own design? If it is, that's excellent!
A few pointers from a jet boat perspective however, if I may...
First, if you look at your drawing you have essentially a triangle section on the bottom. This is your running surface or pad. I don't like that design, and let me explain why. First, if you look at something like the Carolina style boats, you will notice they have something like a 12 degree rise but a V at the bottom where you have a pad. When they run slightly angled up they end up with the triangle that you show. For example:
So if you have a triangle shaped bottom with a pad, you are cutting down on actual running surface and the boat may have a very hard time getting on plane OR, will have a lot of bow steer making any sort of waves very hard to deal with.

Second. (and possibly your solution to that design) You created a flat section, so you aren't far off. You were thinking about the jet pump intake needing to be there I assume, which is perfect. However, again, you need more running surface there. 75% of your running surface is going to be the pump itself, or a big hole where the intake is. I would think you want to have that section straight for about 16" or 410mm or so. Another thing you can do to help is to make sure that the pump is as far back as possible, meaning, the intake is right at the back of that boat design, and the pump itself is more or less outside the boat. This would require you to make a bracket of some sort, possibly a swim platform, but would free up some good space inside the boat as well.

Below is a picture where he doesn't have a seperate running surface. This is probably EASIER to make and will ride better in rough water. See how it's a smooth transition to the sides? Your design will certainly work, but with the extra stuff you got going on, it may just be asking for more work with no benefit.




Thirdly, with this boat being 11-12' long it's going to weight a decent amount, even being out of aluminum. i would go with a little bit more HP than 50 if you can find it man. Like I said, the 110hp Yamaha engines are bullet proof 4 stroke engines that can be found cheap. As long as you make a decent setup in the hull, which I believe you already have with slight modification, you should be on plane and probably hit 35 mph.

Lastly, PLEASE post up pictures of the build!!!

 

[Speedling]

Another thought would be the Yamaha 2 smoke engines! 135 hp in a very light package! Would be amazing.

 

[Ricardo van Oudenhoven]

That is a stand up ski engine , I don't know what is available there but a real inexpensive engine that has the power and is very basic is the sea doo 720 . or the 650 sea doo engine keep in mind you will need everything , pump electronics , exhaust system , the old doos were pan engines, they actually sat on a pan so it is pretty easy to place them in another hull.

Will, do , thanks a lot

 

[Ricardo van Oudenhoven]

Speedling,
Thanks a lot for the ton of information. I didn't make the design myself but found it online, it was from someone that had made a jet boat himself. I will look for a stronger engine, I might ship it from Canada, as my brother lives there.

The main reason why I wanted to have a flat bottom was to make it more stable, as then it would be easy to climb in when swimming.

I will also somehow increase the running surface to 50 mm, just to be sure.

I was planning on making the pump as far back as possible,

something like this I was thinking.

I will also try making the running surface one piece.

Do you think it would be a good idea if I made the running surface completely flat, until it goes up? Or should I keep it at a V ish shape?

 

[Ricardo van Oudenhoven]

In a week I will have a break for a week, and will try doing as much as possible, I will most definitely post update pictures.

 

[GTBRMC]

@Ricardo van Oudenhoven

1) Welcome aboard! There is a lot of jetboat knowledge and wisdom here - the membership will do everything it can to help you.

2) I don't believe I have seen any comments about this above... if I missed some, apologies:

Cavitation (actually the lack of it) is critical to successful jetboat hull/pump/engine performance. A very small amount of cavitation will dramatically hurt performance, and a small-to-moderate amount could severely damage your pump, and do so surprisingly quickly. As you evaluate hull & pump combinations, it is absolutely critical that you have smoothly flowing water at the pump intake and plenty of it. Any aeration of that water flow - at all - will cause pump cavitation.

Practical example: This is the reason that even performance jetboats do not have stepped hulls... while the step(s) nicely reduced dynamic hull resistance, they also entrain a lot of air into the water flowing under the hull and would cause cavitation problems.

Good luck!

 

[Ricardo van Oudenhoven]

@Ricardo van Oudenhoven

1) Welcome aboard! There is a lot of jetboat knowledge and wisdom here - the membership will do everything it can to help you.

2) I don't believe I have seen any comments about this above... if I missed some, apologies:

Cavitation (actually the lack of it) is critical to successful jetboat hull/pump/engine performance. A very small amount of cavitation will dramatically hurt performance, and a small-to-moderate amount could severely damage your pump, and do so surprisingly quickly. As you evaluate hull & pump combinations, it is absolutely critical that you have smoothly flowing water at the pump intake and plenty of it. Any aeration of that water flow - at all - will cause pump cavitation.

Practical example: This is the reason that even performance jetboats do not have stepped hulls... while the step(s) nicely reduced dynamic hull resistance, they also entrain a lot of air into the water flowing under the hull and would cause cavitation problems.

Good luck!

Thanks for pointing out, will keep it in mind.

 

[Ricardo van Oudenhoven]

Does anyone know how much it would cost to ship a complete jetski from Canada to Holland?