Water Jet on a sailboat?

[Polarity]

Just to round off the thread I thought I would post an informative reply I got from Mike the MD at Ultrajet. (with his permission I might add!)

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Dear Paul,

Thank you for your interest in our Ultrajet range of waterjet drives.

Waterjets would probably not be the best solution as they are installed on the transom of the boat with the reverse deflector normally clear of the water. The efficiency of the waterjet system at these low boat speeds would be considerably lower than a propeller and to obtain a static thrust of around 900 kgs would require in the region of 200 horsepower using our smallest waterjet model the Ultrajet 251.

The other point that effects waterjet performance badly is the presence of a keel. We normally advise that even small keels be removed for about 1 / 1,5 metres in front of the jet intake. The sort of keel normally present on large sailing craft would cause serious disturbance to the water flow into the jet intake.

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I guess you could split the intake eitherside but where would I put a 200hp engine!!

I guess its a boring old prop then!

Cheers

Paul






Ulradynamics web site here

[Stephen Ditmore]

On the subject of "boring old props" I would still urge you to check out variable pitch props, especially the Autoprop, which varies it's pitch continually and automatically (for powerboaters, the nearest equivalent for planing boats is the torque-shift propeller from Land & Sea or the equivalent product from Quicksilver accessories for Mercury/MerCruiser). This is a worthwhile innovation applicable to your boat.

[Bob Ames]

We tried putting in a waterjet into a Cheetah 30. I was able to design the drive such that there were no drive elements exposed during sailing (i.e the hull was flush and fair because the "nozzle"
retracted flush).
We abandoned the project due to the introduction of the boats
time schedule. There were problems with ventilation into the
cavity as this had to be primed and stay primed because the thruster/reverser exited below waterline.

I think the concept could have worked had the research been done independently of the boat and done in a very controlled environment.

Have you ever seen the web site of the Brazilian Amyr Klink who has built a couple of boats, Parity and Parity2 that are similar to your desgn brief.
ie Aluminium, Swing Keel, Aero rig for ease of handling and spent a lot of time having adventures in the Antarctic. He once spent a year stuck in the ice and once sailed round the world singlehanded in the southern ocean. His book descibes the detail and thorough planning that went into build and design that resulted in a very ribust boat.
Also you could look at the META (strongall) site as they built a budget boat for antarctic cruising recently.

Great site!

[CDBarry]

One of the local (Seattle) hydraulics sales reps had made himself a hydraulic outboard, complete with a huge prop in a Kort nozzle, that was powered off the front end of the generator on his sailboat. It had great thrust and efficiency, could swing 360 degrees and was seriously weather proof, and could be pulled up and put away. You could probably do something like it with some fiberglass, foam and the Northern Hydraulics catalog for not a lot of money.