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not ******
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Discussion Starter #1
i remember some thread on hot boat about the discusion of jet drives making the boat go foward by the force of sucking or pushing the water. Lets hear your thoughts!
 

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mo balls than $cents$
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the jet doesn't suck itself along:p it may have suction at 0 mph, but as soon as the boat is moving, there's positive pressure in the intake, which means the sux theory can sux it:D
 

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Its all thrust. If it were suction, in theory we would suck the boats underwater.
 

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go by your local f.d. and ask them if you can have ahold of one of their 2 1/2" nozzles, and ask them to open it up wide. then you'll figure out what thrust, or "nozzle reaction" is all about. and thats putting out nowhere near the amount of water that a jet is
 

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not ******
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Discussion Starter #6
Its all thrust. If it were suction, in theory we would suck the boats underwater.

ok, maybe stupid question then, or i just dont realize something simple here......when we ride with the diverter all the way up and the nozzle spray is going up in the air........wait a min i think i just figured it out...like jets4fun said, i guess if i strapped on a pair of roller skates and opened up that fire hose, i would be zinged across the parking lot.......so its the motion of water passing through the nozzle creating the thrust?
 

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bingo

you wouldnt need a pair of skates. in the fire service its referred to as nozzle reaction. and if you're not paying attention it will knock you on your ass
 

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The short and simple;

The jet drive is a powerful, engine-driven water pump that sucks in great quantities of water through the bottom of the boat and shoots it out through a nozzle at the stern. Operating on the principle of physics that, "for every action there is an equal and opposite reaction", the boat is propelled forward. ;)
 

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jetboataholic
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All thrust!:)devil

No suction at all after you get up to speed. It just scoops it up and shoots it out once you get moving a little.
 

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....like warm apple pie
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ok, maybe stupid question then, or i just dont realize something simple here......when we ride with the diverter all the way up and the nozzle spray is going up in the air........wait a min i think i just figured it out...like jets4fun said, i guess if i strapped on a pair of roller skates and opened up that fire hose, i would be zinged across the parking lot.......so its the motion of water passing through the nozzle creating the thrust?
So my guess is you never owned a 'stand up' Jet Ski and blasted yourself in the NADS trying to get going in deep water! Its a quick education on how a jet works. LOL! :D
 

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Guess the short and simple wasn't Simple enough! lol

The Impeller--Like a compressor--PULLS IN water and PUSHES it out through the nozzle! Just that simple! :D

If it don't suck! you don't go!!---cuz, Thats how an IMPELLER Works!! :D
 

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Its all thrust. If it were suction, in theory we would suck the boats underwater.
Well, not really. The boats buoyancy is greater than the suction of the pump. When under way the pressure of water being fed into the pump might be slightly greater/less what's being expelled Too much water charged at the suction housing passes under the "suction" housing and the term over stuffing the pump is at play. Either way, the forward momentum of the boat and the hulls buoyancy and ability to get on plane over comes the impellers ability to "suck the boat down". At idle in shallow water it can suck debris up from the bottom. Now if the pump by itself was to magically spin somehow by itself then it would indeed suck itself into the water...but...with the pressure of thrust exiting the other end would still move forward.
Soooo in short...yes...the pump does suck.
See, I'm not just a pretty face:)sphss
 

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not ******
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Discussion Starter #13
Yea understand how a jet works as far as pulling in water and shooting it out, had a couple, just never thought of the physics part rather than mechanical part.
 

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Yes and no. At idle, the impeller is replacing water that has been displaced at the nozzle. As speed increases, the impeller is not sucking, it is using and compressing water that is being forced into it.

If the impeller were sucking through the rpm range, the intake would always be at negative pressure, which its not.
 

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Hammer got it. I was typing as he replied. In theory, was my key word. If the boat were small enough to barely float a pump and motor and you fired it up, the pump would (should) pull it down.
 

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Someone on HB had a chart of when his intake went from negative to positive pressure. The was a definate area where suction was a factor, and someone else had a cracked intake due to the stress created.
 

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... As speed increases, the impeller is not sucking, it is using and compressing water that is being forced into it.
...
Well to a point sure it is, no matter how much water is infront of the impeller it's still sucking it in via the blades...but, if the intake is "overcharged" by water being "forced" into it, the excess it can't ingest simply blows under the suction housing.
*Imagine this...lets say you stood in front of a fire hose with you mouth wide open and you're inhaling through your mouth (follow me)? Even though your mouth is over charged/powered by the force of water being directed at it, you're (still) sucking it in by inhaling. What you can't suck in or ingest because of over stuffing/pressure is forced away from your pie hole.
What I'm talking about above is the "sucking" aspect of the pump...not how thrust is produced.
 

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How thrust is produced...?
On the backside of the impeller, is it the impeller blades that (force/pressurize) the water into the shrinking veins of the bowl that try to compress it (remember you can't compress water) that then causes it to exit the nozzle at a high velocity...OR...is it the (speed) of the water accelerated by the rear of the impeller that is building pressure trying to compress it into the narrowing bowl veins that causing it to exit at a high velocity?
I gotta lay down :)sphss
 

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here we go again ... :D



this thrust thing has been beaten to death ...
LOL, that's thrust not "suction".:)sphss
PS, during last weeks colonoscopy it felt like one of those traffic cones was jammed up my donut! But that's on another thread.
 
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