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Old 30 November 2005, 07:20   #41
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Just to prove I have no idea what I am talking about...........but what the hell.

Would the thrust of a jet will reduce as it gets lower in the water because the "water pressure" (hydrostatic head?) increases with depth? This will subtract from the nozzle pressure. I think it will would have to be quite deep for noticeable reduction.
Cant try a hose at the mo', because it has gone all stiff and the top of the bucket has some sort of hard film on it.

Props sort of cut a thread through the water (hence the term "screw") with the aid of the pressure differential across the blade.
Bigger diameter = more thrust (bigger surface area for Newton's theory to play with), and bigger pitch = more speed (distance per rev).
I am thinking about wood screws here . A No. 12 will pull something up good and tight but makes the wrist ache. A No. 4 will zip in nice and quick, but if you tighten it too much it will loose grip.

If you skip this reply, I don't blame you.
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Old 30 November 2005, 07:25   #42
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JW

I think the right hand arrow should still be there in the bottom pic, the removed end has now become the air or water outside the unit.

gArf. You are right. I can see a bit of blue sky outside.
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Old 30 November 2005, 07:30   #43
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Quote:
Originally Posted by Mark Halliday
.....Would the thrust of a jet will reduce as it gets lower in the water because the "water pressure" .....increases with depth? This will subtract from the nozzle pressure.....


If you skip this reply, I don't blame you.
Yeh but won’t the pressure at the intake end increase so equalling it out
I couldn’t skip your post so I printed it out and shredded it Des
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Old 30 November 2005, 07:31   #44
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Quote:
Originally Posted by Mollulnan
The amazing thing is how the hell you've managed to make a water jet sound so bloody complicated
ded rite molers yew scrowte.

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a couple of wines

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after 3/4 a bottle of wine!!
itts cuz orl de bastuds arr onn de pis an torkin bollix. wyne drinnkin wussis. reel menn drinnk beere.

fuk mee wots dis. anuvver wus


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I'm also into a bottle of wine
gArf
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Old 30 November 2005, 07:45   #45
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Quote:
Originally Posted by Mark Halliday
JW..I think the right hand arrow should still be there in the bottom pic, the removed end has now become the air or water outside the unit.
Yes, but I simplified the diagram. There seems to be a notion that the forward movement is caused by the jet stream rushing out of the open end and pushing on the air outside of the container. Whereas, I'm suggesting that it is the difference in pressure between the open end and the inside of the container. In reality it would be difficult to maintain a sufficiently high pressure in an open ended container so some form of restriction of the open end will be needed, hence, the nozzle.
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Old 30 November 2005, 07:51   #46
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Quote:
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Yeh but won’t the pressure at the intake end increase so equalling it out
Er........... yes.
Well..........no.
Ummmm........
Head x pump boost = thrust - head.
So ........... Only by head/boost...............
I think...................

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I couldn’t skip your post so I printed it out and shredded it Des
I hope its a heavy duty shredder, else you might wear it out.

Pass me a BEER someone, my fully adjustable yard arm says it time.
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Old 30 November 2005, 07:54   #47
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Yes, but I simplified the diagram. There seems to be a notion that the forward movement is caused by the jet stream rushing out of the open end and pushing on the air outside of the container. Whereas, I'm suggesting that it is the difference in pressure between the open end and the inside of the container. In reality it would be difficult to maintain a sufficiently high pressure in an open ended container so some form of restriction of the open end will be needed, hence, the nozzle.
Yeah. I get your point. Sorry, I thought you had "simplified" the nozzle out.
Detail omited for clarity and all that.
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Old 30 November 2005, 08:29   #48
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Pass me a BEER someone
ahh a reel mann att fkin lasst

dis mite saiv yew nobburs warin owt dem worlnutts yew corl a brayn

worterjett

gArf
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Old 30 November 2005, 08:34   #49
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wow diagrams as well.....

surely a water jet is a propellor shrouded with a collar, and that collar gets narrower at the rear
water is drawn in by the propellor which speeds it up and forces it rearwards, the converging collar or narrowing collar speeds up the water still further causing a fast stream of water to exit the hole giving thrust

isnt that all its about or did i miss something? i am sober at the mo so might not be on the right wavelength.
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Old 30 November 2005, 08:50   #50
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spot on
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