From: vbra676539@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] propulsion
Date: Sun, 03 Dec 2006 15:19:46 -0500
Frank,
What are you using that makes 100# of thrust at speed? The Minn-Kota 101s
make that on calculated static thrust or bollard pull tests, but will
probably show something substantially less underway. I like them for the
use, but am skeptical about the madison avenue claims until I can get one
on the boat and see what's what.
And just to fine tune your answer on big props, what they REALLY do best is
provide good thrust at low speeds, which makes them more efficient in close
maneuvering as well as transits, never mind applying some bias to hold
things steady while fooling around in currents. Maneuvering thrusters
compliment that power very substantially, making life easy for the pilot.
I am watching with interest how things work out for those who are using
those same maneuvering thrusters as main propulsion. Keep in mind here that
George Kittredge started with trolling motors and gave up on them for lack
of thrust--building his own at much greater expense. There was a good
reason for that at the time, and I'm wondering if the more powerful
trolling motors available today will supercede the effort.
It would be interesting to spend some time with Karl Stanley and see what
the limitations have turned out to be on Idabel. It sure is a lot simpler
to do what he did than to build all this other stuff, especially if it's
just for a few percent difference.
Vance
-----Original Message-----
From: ShellyDalg@aol.com
To: personal_submersibles@psubs.org
Sent: Sun, 3 Dec 2006 1:57 PM
Subject: Re: [PSUBS-MAILIST] payload
There was a thread on this a short time ago. A single, large propeller
turning slowly gives more thrust (speed) while smaller, faster props give
you more precise control in close maneuvers.
Multiple thrusters can act as a back-up system if one fails.
It would seem logical that a combination of the two would be best.
It depends on what purpose your sub is designed for.
If you want to motor over a long distance, moving quickly, a large
propeller and a sleek torpedo shaped hull is best.
On the other hand, if you can tow, carry, or otherwise transport your sub
to the dive site, and want to see something close-up, work, photograph,
salvage, etc. then small multiple thrusters will be needed for the fine
adjustments needed for that.
If, for instance, you want to attach a cable to a sunken boat, or move
vertically along a wall to photograph the life, or anything that requires
precise control, a single large prop wouldn't work at all.
I'm building my sub with two thrusters in the back with a rudder/dive plane
mechanism for main forward/reverse propulsion.
Additionally, the two reversible side mounted thrusters can pivot 90
degrees from horizontal to vertical so up/down, forward/reverse,
left/right, or spin without moving can be done.
With all four in the forward position, at full speed, the total thrust is
400+ pounds.
A little extra thrust might come in handy when I need to push against a
current or push the sub to the surface.
Some of the main things to consider would include: purpose, complexity,
cost, reliability, replacement/maintenance, power consumption, and maybe
entanglement.
I'll be watching for answers from the other guys on this to see what else
is important.
Frank D.
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