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Old 02 December 2005, 10:42   #161
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Sounds plausible there seems to be very little restriction and little in the way of head so pressure would not be high. With the previously posted monster food pumps if we get a blockage there's not that much pressure or flow it doesnt ramp up and bust the pump - the impellor simply spins and the motor goes out on over speed (if invertor controlled) When the whole system is running tickety boo the motor is working really hard so high current is drawn. This equates to speed as it's volume shifted per minute.

Our veg oil is pumped in a similar way but its a tiny pump only does 400 -600 cubic metres and hour.
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Old 02 December 2005, 10:45   #162
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Quote:
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only does 400 -600 cubic metres and hour.
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Old 02 December 2005, 11:38   #163
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And, I don't think velocity is the key word, I think it's the shere weight of water that you grab hold of, and throw back quickly (accelerate) that gives the thrust.
If that was the case, you could have a big tube open at the rear and a fekkin great impeller shoving the water back. You're back to a tube with a propeller inside it. Tricky init?
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Old 02 December 2005, 11:47   #164
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Were back to KORT KNOZZLES now!!
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Old 02 December 2005, 12:00   #165
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If that was the case, you could have a big tube open at the rear and a fekkin great impeller shoving the water back. You're back to a tube with a propeller inside it. Tricky init?
Well I think that if I were trying to pull a ship into harbour, thats the setup i'd have, this is what I mean about the ballance of mass, and velocity being correct for a given purpose, if your jetsprinter needs to do 80mph, you'd engineer the pump to move water considerably quicker than 80mph, but that pump wouldn't be right for a 30 knt ferry.
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Old 02 December 2005, 12:03   #166
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Question:

when does a prop in a tube, become a waterjet drive?

ie, if your bowthruster had a huge motor, nice efficient impeller, and stators, but no constriction, and you mounted it at the stern, with a through-hull intake, would it be a low speed water jet?

I think it would, better at slow hard pushing than tearing along at 80 maybe, but still doing the same basic job.
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Old 02 December 2005, 12:15   #167
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... if your bowthruster had a huge motor, nice efficient impeller, and stators, but no constriction, and you mounted it at the stern, with a through-hull intake, would it be a low speed water jet?
Nah, I don't think it would. But I do think that it would be good for low speed pulling because it would constrain the water which would otherwise be thrown out of the blades by centrifugal force and the water which is trying to escape over the blade tips because of the pressure difference front to rear. I guess the propellers which have a ring around them work in a similar way.
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Old 02 December 2005, 12:33   #168
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Oh well, that was fun, but I still think it rather unlikely I'll ever own one.
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Old 02 December 2005, 13:35   #169
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Oh well, that was fun...
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Old 02 December 2005, 14:26   #170
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Can I just say inertia (again)
Also as I understand potetial energy is stored, and kinetic energy is in motion and not stored.
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