Transmission-free surface drive? (jet pump reverse bucket)

[srimes]

Hey that's cool. Do you have a picture?

[Lt. Holden]

Originally Posted by srimes

blowing totally beats sucking for creating thrust. As far as thrust is concerned, sucking sucks.

So that's why it's called a 'Blow Job'

[dccd]

The original concept is a great idea, surface props are really bad when run backwards due to thier highly skewed angle and trailing blade flat edge. And since when running at speed only the bottom half is in the water you would not have to completly draw the "bucket" up over the prop. That would help keep it compact. Anything you can do the eliminate the useless wieght of that 1:1 gearbox is going to give you better performance. Also, I can't believe the remarks made about how it could not work, its moving mass (water) for thrust and your redirecting it aft, the boat turns when you re-direct the flow to the side yes?. Send me a message as I have some ideas that may make it really light if its for a pleasure craft.

[srimes]

thanks for your input. I don't mind if you post your ideas here, but if you'd rather message them to me I'd still be interested. Any ideas about stearing in reverse with a fixed prop shaft? I had an idea about a reverse bucket where each half angles the thrust slightly sideways and the bucket would slide left and right to bias the thrust. This seams like it may be more simple that if it pivoted on 2 axis, 1 to engage and 1 to turn. Of course, on a boat this small and simple turning in reverse may be an unnecessary luxury . That's what paddles are for.

[brunello]

Originally Posted by PetterM

There is no reason what this should not work, in fact I think Renato Sony Levi tested a similar arrangment at some point....I think it was quite difficult to control though...

Correct, Sonny Levi already did it and perhaps it was even patented. There was one boat actually built with the device, which was a reversing bucket actuated by twin hydraulic rams. The boat was one of the FC155 built by STAIN in Turin, in aluminium alloy, powered by diesels (Isotta's?).

The drive system was Mr. Levi's step drive and had (as far as I can remember) an angled transom (like a 45° or so big chamfer between the step and the transom), clearly to help reversing.

There were long testing sessions (on a smaller boat) on a lake nearby Turin and of course the reversing worked fine and the bucket posed no problem at all at high speed. To my knowledge, the trickiest at the time was 'neutral', which was an almost impossible position to achieve. The conclusion was that, probably, you need a clutch for that. Also, especially on some kind of boats and considering that the prop is exposed, you really might want to stop prop rotation (people at sea, ropes, weeds, grounding etc.), so the clutch might be a must.

With high speed diesels (and petrols), then, the current design trend is to reduce propeller speed and increase diameter: i.e., you most probably do need a reduction gear ratio box as well.

Once you fit a reduction gearbox and a clutch, you might as well avoid all the cost, weight and engineering efforts (structural loads are not light) of the reversing bucket and just buy an off the shelf reversing gearbox, with a built in reduction.

This is probably why Mr. Levi did not replicate his reversing bucket on any of his drives later on. Certainly this was our reasoning for not emplyoing such a device on our Flexidrive systems.

As far as reversing is concerned with surface propellers, Levi patented his 'diamond back' surface propeller blade section; others added a small reversing 'nose' on the back of the wedged section; and in general, the trend towards bigger wheels turning slower (even in reverse) does not pose any more problems in backing with semisubmerged systems.

Regards, Brunello