Use pressurized water as manuevering thruster?

If the pump operates at rated conditions the inverter will be a monster - maybe USD1000+. Going from 12V down to 240V is obviously 20 times so the current is 20 times higher. It will need to be a big battery to hold up for a minute or so of operation.

When you do your pump test on 240V you could also take a current reading. The 12V current will be roughly 20X for the same result.

Will be interested in you results.

Rick W

 

Although this thread is a bit dated I am interested in the subject and would like some feedback on my idea.

I am looking at installing this pump http://www.catpumps.com/select/pdfs/333.pdf or one very much like it for a water maker. My thought was to utilize to also power a bow thruster and fresh water deck wash.

If I install a deck fitting I will have a supply of water at 800psi @ 10 lpm give or take or if you like a high pressure salt water gerni. Now if I use two solenoids one for each port and starboard clamped to a pole on the bow with each nozzle pointed in the appropriate direction I am thinking I should have an effective bow thruster (not that it is really needed) for a 36 foot boat.

I have attached a rough sketch.

Parts list:
Clamp
Pole
High pressure flexible hose
Some fittings
2 x solenoids
Cable and switches

 

Ratch
The link does not produce anything for me.

If you run at 800psi and 10lpm you will get about 1.7kgf - not a lot. You can measure this with a small Gerni. You can certainly feel the thrust but it is not tiring to restrain. I cannot see it doing a lot on a 36' boat against a bit of a breeze.

You will also have quite a weapon. The nozzle velocity will be around 100m/s. That will throw a long way when exiting a streamline nozzle. Would not want it pointed at me.

Rick W

 

Hi Ratch, looks okay, i would be a bit worried about the alli body in the pump as it would need a good rinse after the salt water use. If you were to try it just below the water line you would move the bow at its pivitol point as i have tried this with a similair set up. I used a 24ft boat and a deck wash pump 11 bar max. it did indeed move the boats bow. Only good for manovers and not propulsion. However small moves at slow speed is what is recommended in berthing. I am considering a good pump myself on a sale or return basis, if i can find a good supplier. good luck, regards TF

 

Hi guys i managed to do a successful test today and have been able to move the boat with the small pump 100lmin. the movement is very slow and in a reverse or aft direction as well as port or starboard, I think this is due to the outlets being in the tip of the bow as it curves round. I am getting a 240v swimming pool pump 500lm 6 bar. I will be trying it next week. keep you updated. TF

 

Hello,
Under the jet propulsion forum I have a recent thread where a spreadsheet is posted by another gentleman.
In it is a spreadsheet which converts horsepower (and hence watts) to thrust force given speed of the boat and size of the discharge nozzle.

For low speeds such as a thruster would have, I would suggest you use a large flow per minute at a very low pressure to maximize thrust.

Further, if there is an engine on board, I would suggest a hydraulic pump mounted to the engine, combined with a water pump mounted to a hydraulic motor near where you needed the thruster. It might be cheaper and more convenient then an all electric system.

 

Rick W, thanks for your clear and professional explanations.
I'd like to look at the Willdo combi jet thruster (ie stern and bow) for a 48 ft heavy sailboat ..guess 80-100kgf is about right.
On the point that you get more thrust if discharging into air vs underwater....You said you could not calculate how much more but would you hazard a guess?.
My thinking is that by having the nozzles just above the waterline aimed slightly downwards you'd reduce the number of underwater hull fittings and get a higher thrust that would offset the negative effect of the downward angle? it might be a bit noisy but would not be any risk to nearby boaters.
I presume Willdo realise that thrust is higher above water but have traded off more safety and quietness against a higher power requirement.
The boat has a 100hp Volvo engine so a direct connected waterpump via a toothed belt and magnetic clutch as Willdo proposes would give plenty of power ... and one would only generally only use the thrusters in neutral. A concern could be the transverse force applied to the engine main bearings by the toothed belt drive.
Would you have any comments?

 

I have Googled long and hard for something that gives me the back pressure on a nozzle. It is a process of entrainment and is a function of nozzle velocity of course. I have not been successful in finding data on it or the physics involved. I know it was a fundamental step in making modern high speed water jets efficient. You can do a simple test with a hose and a bucket of water to get an indication. At the relatively high velocities of these thrusters I expect you would lose 20 to 30% of the thrust by submerging it - that is a guess.

I also have a severe dislike for underwater fittings so I agree with with your approach. Actually it is not the fitting but more often what is connected to it. A slight downward angled jet will lose very little in the side thrust and should be safe to other boats.

I doubt that a properly tensioned toothed belt tension would cause any concern for a motor shaft for the sort of power take-off required.

Rick W

 

Thanks Rick

 

Belt fly planes used for reduction mainly
No worry !

 

hi Kistinie
Your reply was a bit cryptic...could you explain please

 

I think that this pump will do the job. Run it off of the engine while in neutral.
http://www.catpumps.com/pumpdetail.cfm?PumpID=251&link=1
Don't know the price, but I'm sure that it's up there.

Just thinking out loud here, but what about hydraulic rams with a plate that may come off of the sides of the hull on a hinge. Kinda use them like a fish tail, or a whale tail to................ Nevermind. Paddlewheel thrusters?......Naaaaaa.

I like the idea of a reversible inline pump in the middle of a pipe that runs from starboard to port. Sucks on one side and pushes from the other. Need a high volume pump.

Pressure losses would not be very great through full port valves and fittings. I can run some pressure drop calcs, but pretty much what ever the head pressure is, It will be maybe 10 psi less at the outlet, depending on line size and pipe material. Fiberglass or PVC has a far lower Delta P than steel pipe.

 

mudman ... "idea of a reversible inline pump in the middle of a pipe that runs from starboard to port." would't work unless you had big diameter suction pipe on one side and small diameter nozzle on other with pump in between. I suppose you could do it with a reversing pump and some non return valves ie a big suction opening on each side as well as a nozzle on each side.......might as well just go for a conventional tunnel thruster.

the flap idea...whale tail .....is interesting....

 

Oups...Sorry for delay

Toothed belt have more than 95% efficiency and some amateur planes use these belts for reduction on engine pulling more than 150 HP.
Harley davidson use belt too
So i do not see why it couldn't drive a pump safely.
Just think to have a protection as theses belts are extremely dangerous for hands, clothes...

 

So you are in agreement with what I stated in post #98?

Rick W