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Old 28 May 2014, 07:20   #1
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Do waterjets create as much turbulence as props...?

Slightly sciencey question I suppose, however:

I was just tootling around the estuary earlier and the big Condor ferry came past, I followed it out a little bit and sat in its nice a flat wake. It is an accepted fact that following directly in the turbulence of another prop makes yours less efficient, however does the style of the water jet (ie just a moving column of water as opposed to a rotating column of water) negate this effect?
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Old 28 May 2014, 08:04   #2
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Props are designed to work in "still" water not turbulent, any disturbance will affect the performance. Incidentally, your hull will be less efficient in any form of turbulent water
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Old 28 May 2014, 09:47   #3
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Incidentally, your hull will be less efficient in any form of turbulent water
Any form? Don't race boats have notches sculpted in to their hull to create a kind of foam/bubble turbulence so that it unsticks the hull from the water?
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Old 28 May 2014, 12:00   #4
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Any form? Don't race boats have notches sculpted in to their hull to create a kind of foam/bubble turbulence so that it un sticks the hull from the water?

I was talking about running in the wake of another boat,
I would venture that even stepped hulls are not optimized to run under these circumstances.

There is a difference between laminar flow, boundary layers and running in prop wash/jet wash.
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Old 28 May 2014, 15:52   #5
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water jet (ie just a moving column of water
I think you just hit the nail on the head - Is it any worse than motoring against a strong tide, regardless of how the water is moved past you?
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Old 28 May 2014, 16:00   #6
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I think you just hit the nail on the head - Is it any worse than motoring against a strong tide, regardless of how the water is moved past you?
That's what I was thinking, however surely that water has been through the impeller and a piping system so will be just as turbulent as water from a prop?
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Old 28 May 2014, 16:09   #7
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That's what I was thinking, however surely that water has been through the impeller and a piping system so will be just as turbulent as water from a prop?
the water is straightened in the out nozzle otherwise it would be wasted thrust.
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Old 28 May 2014, 16:21   #8
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That's what I was thinking, however surely that water has been through the impeller and a piping system so will be just as turbulent as water from a prop?
the water is straightened in the out nozzle otherwise it would be wasted thrust.
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Old 28 May 2014, 16:57   #9
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the water is straightened in the out nozzle otherwise it would be wasted thrust.
Very interesting, thanks for finding that video. He seems to call them "fixed stator veins". Why are these a benefit & therefore how come it would be wasted thrust without them?
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Old 28 May 2014, 18:24   #10
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Very interesting, thanks for finding that video. He seems to call them "fixed stator veins". Why are these a benefit & therefore how come it would be wasted thrust without them?
I'm no expert but I would posture any energy that is rotational in nature is not adding to the forward thrust, removing/reducing this will increase the forward thrust.
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