newbie help plz....building a off the wall boat(s)

[Rick Willoughby]

John
This is more my style of boat:
http://www.youtube.com/watch?v=l2UOH65QOI4

I think Hamilton jets were the first jets. Here is some detail on operation:
http://www.hamjet.co.nz/index.cfm/Th...jet_Works.html
Basically it is an axial flow water pump or you could consider it an enclosed propeller. Very little chance of damage to the prop unless you operate in really trashy conditions. The axial flow bit is important from an efficiency perspective.

The thing about a jet boat is that they turn very quickly because the hull does not grip the water like a boat with an external prop and strut:
http://www.youtube.com/watch?v=pbN4tvQD3Jk

This might be a good place to start looking for bits:
http://www.sbtontheweb.com/Merchant2...egory_Code=P40
I suggest you get something tried and proven first. You are probably best picking up a second hand jetski and then looking for refurbished parts to suit the number you eventually make.

The jetski units are really neat compared to fiddling with a motorbike or mower engine. If you wanted to go a smaller scale then you could fiddle with a drive unit of your own manufacture but jetski size is serious power in a very compact form.

Rick W.

[Workinforwood]

I don't exactly know anything, but I do have a jet ski and the water sucks in to cool the engine right in front of the prop. There is a grate under the boat, the water goes up through the grate and the driveshaft and prop is in there which slams the water out a hole in the back where a tube directs the water direction. The coolant pipe is right in front of the prop on mine, and I don't know how it possibly sucks water in that tube at that location as it seems in my mind to be impossible, but it does it nonetheless. I have to climb under and inspect the grates periodically because the suction is powerfull and the grates can get clogged with weeds, in which case you loose speed and cooling abilities. It's safer than an open prop, but can still kill you. A lifejacket strap can get sucked up and wrap the shaft for instance and then you'd drown. I had a rope from a tube get sucked up and wind the shaft, then had to get a tow and pull the whole shaft out to unwrap it. But that's all off the topic...but that is where the cooling tube is.

Oh...motorbike motor, flip it over in water and you are done for. Jet ski motor has safety valves, so if motor is upside down, valves close, no water enters motor. You do have to re-flip the motor in the proper direction so the valves don't open up when the motor is only halfway back to normal position. Also, motorbike motor might be more prone to cracking the head if submerged due to hot engine being cooled super fast. Less likely on a jet ski, but still it does sometimes happen on jet-ski motors too. There was a guy up in town last year with a jet ski he was selling where he modified it to have a seat inside the hull with a regular steering wheel and an outboard motor off the back. I think he was using it for racing, but who knows.

Good luck with your project. Let me know when you test it so I'm not in the water or withing 500' of shore ! lol