Re: Nozzles?

["Sean Walinga" <sean.walinga@home.com>]

> << I intend on keeping it to a minimal volume to minimize air volume,
>  mass, ballast, increase strength, etc, etc. I've already found some DC
>  motors, 96-140vdc, 15 HP units, which should really make the unit fly.
>  Unfortunately, I'm looking at controllers, relays, etc, which you really
>  need for high output units like this, ie, not your typical trolling
motor.
>  With those high voltages and currents, I can't afford a short. Also I'm
>  looking at a Kort nozzle configuration for the inlet. I haven't figured
out
>  all the physics yet for an optimum high velocity, low pressure imbedded
>  nozzle, so I'm still doing the research on this. If I can find some good
>  engineering calcs on Kort nozzles, I'll be happy. >>
>
> Have you thought about a jet ski nozzle?   They might work fine for the
high
> output you want.  But I also remember someone a year or so ago saying that
> they work on very high rpm and don't work at depth because.... something
> about air bubbles in the water under the jetski make them really kick the
> power out... and there are no air bubbles at depth.  As I recall, this
person
> was speaking from emperical experience.   (Are you out there yet)
> Gene Seus

I may have been one that was discussing it last year. I don't think I'm the
experienced one you speak of though... :)
>From my understanding, jet-ski nozzles need a measured amount of air to
create a vacuum as the mixture of air and water reaches the impellor. This
measured amount of air changes with the speed of the boat which forces
manufacturers to compete to find the optimum mixture of air and water.
Presently, the intake on jet-ski's will alter to increase or decrease air
intake as needed to maximize the thrust generated. Without this vacuum, the
jet-ski's performance deteriorates rapidly and feels to the rider as though
the jet-ski has stalled. Also, the high output you speak of is only truely
efficient when the boat is traveling at a speed close to the speed of the
water being ejected. If the sub speed will not be even close to the speed of
the water being ejected then a propellor would be more efficient (although
the impellor would be more safe for sub launchers).

One thing that I have considered in the past is the mounting of a gasoline
engine with the exhaust being injected into the intake area of the water
jet. This would solve the exhaust issue and also solve the air requirement
for the water jet. The right mixture would be very difficult to obtain I'm
sure. With the power of a gasoline engine  (bionic dolphin) and this type of
water jet set up, a very interesting sub would result. Any fishermen on the
surface would see only a long stream of tiny bubbles rising to the
surface...

Sean