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Old 29 November 2005, 18:23   #21
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Voith Schneider drives as seen on googlio

http://www.heatherk.com/images/Panam.../OtherTugs.htm

missus
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Happy New Resolutions!!! : RIBbing for the craic!!!
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Old 29 November 2005, 18:28   #22
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That's a lot nicer than the Fkkrs I have to work on!
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Old 29 November 2005, 18:30   #23
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Quote:
Originally Posted by Hugh Jardon
.. tugs use large props and move large volumes of water to get the required thrust for the work they do..
Sorry Hugh, I not singling you out for comment. I don't believe this is what is required. Surely the object is to get the propeller to advance through the water not for the propeller to move the water backwards. An analogy is a car with its wheels either spinning or gripping.
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Old 29 November 2005, 18:31   #24
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Well done Kathleen, 100% for that.

All tugs with voith schieder drives are known as tractor tugs, this means they can react the same in all direstions.
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Old 29 November 2005, 18:40   #25
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Quote:
Originally Posted by jwalker
Sorry Hugh, I not singling you out for comment. I don't believe this is what is required. Surely the object is to get the propeller to advance through the water not for the propeller to move the water backwards. An analogy is a car with its wheels either spinning or gripping.
mmm not sure, will have to have a think about that one, ideally the prop wants to move thru the water but if it is trying to push a large boat and it is just starting off then a lot of water will be expelled rearwards until the forward motion matchs the prop forces. Is a tricky subject to get your head round after 3/4 a bottle of wine!! time for bed said zebedee!!
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Old 29 November 2005, 18:46   #26
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Quote:
Originally Posted by Hugh Jardon
.. ideally the prop wants to move thru the water but if it is trying to push a large boat and it is just starting off then a lot of water will be expelled rearwards until the forward motion matchs the prop forces.
I agree with that. A bit like a car spinning its wheels while accelerating.
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Old 29 November 2005, 19:31   #27
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I do understand both props and jets, but I'm also into a bottle of wine and can't be arsed to explain the differences. But, having operated both, I think thet a jet is a quirky, inefficient pile of crap that is only fit for frightening the shit out of people in New Zealand!
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Old 29 November 2005, 22:06   #28
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Quote:
Originally Posted by pressman
One for CODPRAWN.

Tugs also use Voith Schrieder drives, but then I suppose you know about those aswell.

Compass units are, another one, kitchener gear, there are many, best you read up on these!!
Yes I do as a matter of fact - when I was a kid spent a lot of time visiting BP tankers and the tugs etc. Also spent some time sorting out computers at various dry docks - more interested in the ships than what I was supposed to be doing!!!
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Old 30 November 2005, 03:07   #29
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My twopenneth (as I understand it)
Taking water as a constant volume noncompressable liquid (which it's not, but it is close)
A propeller mostly drags itself through the water by creating low pressure on the front of the blade which is why cavitation (lowering water pressure below vapor pressure) destroys drive.
A jet takes in low velocity water and raises it's pressure and speeds it up by restricting it's area, ejecting it out the back producing drive via the inertia of the column of water behind it, put the column under water and most of the drive is lost, which is partly the reason jets can lose in the rough. (try it with a hose pipe in a bucket of water. End of the hose in the air it will push, end of the hose in the water it don’t so much)
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Old 30 November 2005, 03:22   #30
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We have a Voith Schneider tug at work - only a small single unit one, but it's a superb little tug. You can go to any direction of thrust very very quickly - to learn about how it works, goto the Voith website and get some of the PDF files they have there.
Since we dry docked her earlier on this year, the top end speed has gone from around 6knots with the whole vessel shaking to about 8.5knots - it's not fast, but it makes up for that in great handling.
When we had her out the dock, we had to check everything was ok, including the hook release on the back
http://files.ribseadrive.co.uk/lilah_small.wmv

-Alex
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