Re: [PSUBS-MAILIST] propulsion

["Joseph Perkel" <joeperkel@hotmail.com>]

Frank,

I guess efficiency is how you define it's use. The large slow wheel can't be 
beat for transits in wind and current. But, for precise station keeping, 
nothing would beat the thrusters.

A combination of the above would be a truly fantastic machine!

I would copy and improve upon PC- 14 if I had the technical experience and 
know-how. My scheme is a combination of pre-existing plans and a bit of 
imagination, but that one ( PC-14 ) would really have some serious 
potential!

Joe


> From: ShellyDalg@aol.com
> Reply-To: personal_submersibles@psubs.org
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] propulsion
> Date: Sun, 3 Dec 2006 16:46:15 EST
>
> Hi Vance. You're right. I'm using Madison Ave numbers for thrust and  won't
> really know how much until I get them wet.
> As for the low speed maneuvering from a big, single prop.....it is more
> efficient ( in power used ) but I would think also less precise.
> Another thing to consider is the ability to stop rotation and then reverse
> it. A larger prop will take more time to come to a stop, and require more 
> time
> and power to start. I think a short burst of power applied to a large prop
> would  be less efficient than the same power applied to a small one.
> My guess is that the efficiency ( thrust per watt ) on a larger prop is
> realized only after reaching the optimum level for that particular prop.
> Start-up and reversing to stop, or " bumping" the prop to move just a  
> little
> can't be efficient, and the larger the prop....the more energy is used to
> start it.
> Anything that spins has a gyro effect. The larger it is, the more power it
> takes to get it going.
> If we wanted to move just 6 inches and stop, and do that 20 times, it seems
> like it would be tough with a single big prop.
> A small prop could be bumped with much less power consumed.
> As for steering, you're right again. Trying to steer with just thrusters
> would be difficult to hold a straight heading, and the constant throttling 
> up
> and down would take lots more power and waste a lot. Air or hydraulic 
> rudder and
>  dive planes are the obvious power savers.
> Let me know what you think. Frank D.





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