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RE: [PSUBS-MAILIST] Water nozzle propulsion

Yes it's exactly the same idea as a jetski, although modern jetski's use an axial "impeller" (if you can call it that...I'm not sure what the exact term is) and I suspect most subs would use a centrifugal type impeller (like in a bilge pump).  Also note, that some small home-made unmanned submersibles use bilge pumps as their propulsion device.  I've seen small projects where they mount four to six bilge pumps, each in a different direction, to provide all range of motion required.
I wonder though, is this type of design more complex and/or more expensive than pressure compensating the electric motors?  From a monetary and complexity perspective, how do they compare?
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Akins
Sent: Tuesday, April 11, 2006 9:35 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Water nozzle propulsion

Hi John.
Is your electric motor brushless or sparkless? Take care if you install it in your battery compartment without first isolating it from the batteries. Risk of hydrogen explosion.
Just an idea, but after you form the nozzles from wood, have you considered using that to make a mold and pour the nozzles out of brass? Brass would be more corrosion
resistant than aluminum or mild steel. You could go to a local foundry or even make the mold yourself.. You could also use wax to form the nozzles
and then pour the mold material over the wax, and then when the mold material had hardened and you drill a hole to pour your brass into the mold, the wax will evaporate and
the brass will fill the void where the wax was. Called the lost wax process for molding an object. Unfortunately the mold is only good for one usage because you destroy it when
you break it apart to get to the molded piece.  I am interested in these underwater water pumps for sub propulsion, but I know nothing about them. Is it something like the propulsion
used for a jetski but with an electric motor instead of a gas motor? Or is it more like an enlarged bilge pump in operation? Or is it more like a submersible in pipe well pump?
I only know about electric motors and propellers like on my wetsub. The water pump idea intrigues me because I like the idea of someone being able to install the electric part inside their sub
and the rest outside and therefore not need any pressure compensation like you would on an electric motor with a prop. It would be great to see some video of this in action underwater.
Bill Akins.