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RE: [PSUBS-MAILIST] thrust vs displacement
Thanks Alec and Carsten,
Alec, We do have about the same ratio weight/thrust. I know that the shape
is really important but I just wanted to figure out if those motors where
enough for the sub before I buy them. Thanks for the info.
Carsten, The only place I can do that test now is in a public indoor pool.
It's -35C here today. There is no way that I'm showing up in a public pool
with my speedo and a toy sub, running along the pool. Sorry. Thanks for the
hint anyway!
Pierre Poulin
"Must keep a minimum of dignity"
>From: "Alec Smyth" <Asmyth@changepoint.com>
>Reply-To: personal_submersibles@psubs.org
>To: <personal_submersibles@psubs.org>
>Subject: RE: [PSUBS-MAILIST] thrust vs displacement
>Date: Sat, 15 Feb 2003 22:35:52 -0500
>
>Pierre,
>
>Solo's displacement will be 3,300 lbs, thrust 148 lbs. As for speed... I've
>really no idea! I remember toying around with some formula that gave me
>about 6 knots, but didn't even record it because my confidence level in the
>result was absolutely nil. As I recall it was based on displacement and
>ignored the shape of the boat altogether. I would think when you get to
>that sort of speed the shape would become much more important than things
>like displacement or wetted surface friction, and Solo ought to be
>exceptionally clean compared to a traditional manipulator-oriented boat.
>But frankly I don't know how to do real hydrodynamic modeling of vortexes
>and such. I chose my motors for their voltage and current draw, and speed
>is just the dependent variable for me. In any case, due to the density of
>water speed should be accomplished through shape and not horsepower. If
>Solo were to do 6 knots on two little trolling motors, I'd feel more than a
>little pleased. It sounds unrealistic.
>
>One important consideration is that stock trolling motors props are of very
>fine pitch. What that means is you could put 10 trolling motors on a
>surfboard and it still would not do more than a couple knots... certainly
>nowhere near 6 knots. I'm making variable pitch (statically variable) props
>so I can experiment and find the correct pitch to optimize speed.
>
>Sorry, I'm rambling.
>
>rgds,
>
>Alec
>
>-----Original Message-----
>From: Pierre Poulin [mailto:pipo305@hotmail.com]
>Sent: Sat 2/15/2003 8:56 PM
>To: personal_submersibles@psubs.org
>Cc:
>Subject: Re: [PSUBS-MAILIST] thrust vs displacement
>
>
>Hi!
>
>My sub have a displacement of 1092 lbs. It will have 2 motors of 28 lbs of
>thrust each (total: 56 lbs). What speed should I expect?
>
>Alec, what is the displacement, total thrust, estimated speed of Solo?
>
>Anybody else have a displacement/thrust/speed ratio that they now?
>
>Thanks a lot!
>
>Pierre Poulin
>
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