Newbie needs help please!!

Hello,

I was doing research for a very small jet drive for a boat I was building and came across this forum. I have a delimma and need some help. I'm building a very small boat (about 7 1/2' total length) for my daughter. I would like to install a jet drive in it with a 3-6hp range... may be able to handle a 10hp.... I have about 24x40 inches of working space in the rear of the boat to install the jet unit. Is there anyone who makes a unit this small? If not, does anyone have or has seen plans for one that I could build myself. I'm not an engineer or machinist, but I will figure it out if I need to... I read an article where a guy used a trash pump and 5.5 hp motor to make one... not sure if this is really a good application for it though. Any help would be greatly appreciated! Oh, a quick note: I haven't started building the boat yet, any design mods that need to be done wont interfere,as long as they aren't too drastic... Thanks again.

Neil

 

Dont worry newbie,---Neil, we all started like this.

If you hav'nt built the boat yet that is a good position to start !!!.

Everybody makes the same mistake, they build a boat and then look for some thing to drive it, limiting themselves to space and all kinds of restrictions.

My advice would be to find a power unit appropriate for your expected speed.

Then think about the boat. If you do it this way --you will be in control.

So may people do it the other way round then go and ask a prop manufacturer to get them out of the----trouble.

Oh,-- and welcome to the forum.

 

Thanks Jack for your suggestions and enouragement. Problem is, I don't know of anyone that makes a jet unit small enough for my appication. I guess that's what info I'm asking for. I know of one company only and they absolutely won't sell just the jet drive. You have to buy the complete craft, which costs $3500! Not quite practical for me... Any other info or suggestions? Thanks again!

 

Well wouldnt you be better off just buying a usable Sea doo or some other little jet boat thats has a smash or something then cut the top off it and re arrange the interior???

At least you would know that its going to work when its finished.

And Itlle be a lot cheaper.

 

I've already researched that possibility. The smallest jet ski made was a kawasaki 300. They were rated for about 30hp. That's still too much power. Also, it's too large physically. I'm looking for something about 10hp. Just wondered if anyone has ever seen a unit this small.

 

Check out North American MArine Jet. They are prototyping a little jet and are looking for applications.

 

I've already tried to contact them... Still waiting for an answer... Any other suggestions? Is it possible to take the jet drive off a larger model, shorten the shaft, and replace the engine with a smaller one? Maybe a 6 hp Honda horizontal engine or similar? Would it be enough power is my concern....

 

Mokai makes something exactly what you are talking about, but they are expensive considering they only have a 5hp Honda (about 3500) and a jet unit inside an 8' kayak.

 

I've already contacted them as well. They will sell me a complete drive unt ($1000!!!), but only if I have a boat already. They require a serial number to confirm it.... another dead end.

 

Have you developed a budget for this project? It kinda sounds like you're going pretty "high tech" if this is just going to be a little home-built putt-putt for your daughter. You may want to consider other easier access drive system options, inboard lawn mower engine with prop and shaft drive w/ tiller steering, or a little old outboard, or even an electric trolling motor. Jet drive inherently reads "high performance" - a "go faster" kind of boat. If that's what you have in mind, then the propulsion systems you've been looking at and finding are likely what's available, and the pricing is probably quite reasonable.

Waterjets are "simple", but only in principle / theory. To make one yourself, you would need access to some pretty sophisticated machinery and need metalworking skills that are generally beyond those of the "home-tinkerer". The materals alone for a "one-off" waterjet of your own making will be difficult to access and expensive. Quite simply, to make your own waterjet you're goint to need the same kind of equipment and skills that the manufacturers use. "CNC" cutting machines, large lathes, some parts will need to be TIG welded, some parts may even need to be castings, which will involve modelling, mold making, and all the stuff that goes along with that.

So... what's the objective here? What are you really trying to achieve?

 

Swan,

I'm not looking to 'engineer' one myself. You're right, the cost and resources necessary to do that are out of my budget at this time. My goal for the boat is to get away from props altogether if possible. I feel it would be safer. Plus, no one has put a jet drive in this boat before, so the 'wow' factor is there as well. I have already considered the suggestions you mentioned..... Even considered buying a kit to adapt an outboard engine to a jet type and grafting the kit to the boat, but it would extend below the bottom of the boat and I would like to keep from doing that if possible.

I have done quite a bit of research on all my options. I'm still committed (thinking maybe I should be committed for trying this! ), to find a jet drive system that will work. I'm just looking to see if anyone has any knowledge of one small enough for my application. I do appreciate all of the suggestions so far! I hope that they will keep coming. There may be an idea that I haven't thought of yet and I'm always open to suggestions....

Neil

 

okay heres a long shot, well not really. I dont know how fast you want to go, but you could use a model boat jet drive. There are several companies that make up to 60mm pumps, very well made and under 400$ a piece. I'd take two, put them on a belt drive to a motor, so not only will it have a jet it'll have two Jet skis only use something like a 80mm pump anyway. It wont break speed records, but it would work. If you dont want to use much power, these pumps can use 26cc weed wacker motors. Your talking about 100lbs of thrust. I would think two pumps would move a 7' boat pretty good, if shes light. Heck make it radio controlled too.........you control the fun lol.

http://206.206.85.209/xtdoc/Details.aspx?ProductCode=m-1723&store=mhzusa

http://www.swashdrive.com.au/

 

Thanks for the info Quicksilver. I had briefly thought about this earlier, but didn't know if there would be enough power. I wonder how you would translate the specs on the those two drives into horsepower? Are there any drives larger than that? The boad hull will weigh approx. 70lbs total with a payload of probably another 150lbs max. So... that means I will have a total weight over 200lbs. Just sounds like alot for rc jet drives (even if I had two). I will admit though I don't have any experience with them, so any help would be appreciated.......

 

well most of these 26cc zenoahs push like 5 hp. You might just want to go with two of them, or a 10hp motor hooked up to a belt driving two of them. I think that would be a really neat project, if you build it you better take pictures and video.

You know if your pushing 200 lbs, maybe 15hp would be good, but its got to be hooked up neatly, cant be torquing on those drives with all that power. I figure if it meant for for like 40lbs, and would go 45mph, then 15hp would get going around 15mph. maybe I'm wrong, but I dont see why this shouldnt work. I would also suggest, dont skimp on the drives, get the best ones, swash drives, I've seen video of a 2ft long rc boat with one, pull a knee boarder like 20ft, before losing steam. That isnt easy......at all. would be cool, whats the boat look like? ideally you'd want a shallow vee with a flat spot by the transom for the drive, but if your using two drives, they can be on the vee.

Whatever you do, dont resort to using trash pumps and such, its really not the same thing, nor nearly as efficent.

p.s. heres the latest incarnation of my rc jet boat, mind you this is only a 29mm pump, you'd be using two 54mm drives, there a bunch of videos.
http://www.youtube.com/watch?v=82xlH6UGQDE

I am currently building another.

 

Thanks again Quicksilver. What do mean by hooking up a 15 hp motor 'neatly'? What type of engine could I use. Don't these jet drives run at very high rpm's? Any suggestions as to what motors will work? The more economical the better... I would like to have an electric start if possible also. How much hp do you think the drives could take? I sent Swashdrives an email asking for specs and suggestions, but haven't heard back from them yet. They may not be taking me seriously.... lol