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Re: Trolling Motors
Just to add some more to the general knowledge, but nothing really new.
I know Minnkota and I didn't know Evinrude (as trolling motors I mean). But I'm
dealing with MotorGuide which seems to have some more robust products than
Minnkota.
I also have all their technical specifications and drawings, about the shaft seal
they use a couple of cupped seals on the shaft. Two should be better than one, but
I agree that seal isn't the best for deep use.
I also have a Scubapro DPV which mounts Minnkota (Scubapro is part of the same JWA
group as Minnkota is) and there's another couple of small manufacturers which are
using the same motors.
I successfully dived the Scubapro Seashuttle to depths of 150/160 feet and it
never failed (it's rated to 180 feet).
There's another solution which should work much better, it's magneto-ceramic
coupled seals and it's widely used on ROVs thrusters as well on some DPVs. I know
this device as being really expensive (when purchased from the ROV market) but
it's also widely used on hi-pressure pumps running at very high speed and pressure
and it's a cheap spare part, even when using stainless steel spring and flange.
This is just a seal - however - and needs an appropriate housing to work, but if
you're building a life shell it should not be a problem to deal with a motor
housing.
I'm personally using MotorGuide for testing new DPVs design (the motor unit is
cheap and almost ready to go) but I'm designing my own propulsion unit.
Uh... and what about propellers? I don't really think the ones supplied on
trolling motors being very efficient for underwater propulsion... in fact, the
Scubapro is a pain (also due to its own design and mounting). I'm pretty sure the
pitch of those (trolling) propellers isn't that good, in fact it's designed for
high rotational speed. A variable pitch would work the best.
Dive deep and safely.
Paolo
--
Paolo Velcich
industrial designer
**********************
KORUM DESIGN
Viale Tricesimo 5/6
33100 - UDINE - ITALY
Tel. (+39)0432-603654
Fax (+39)0432-601213
e-mail: pavel@mail.nauta.it
http://www.x-plora.com
**********************
Subscuba@aol.com wrote:
> Albert,
>
> Is it possible that the motor seals did have some sort of pressure
> compensation across the motor shaft seal such that the actual differential
> pressure across the motor shaft seal was less than 700 feet of Sea Water?
>
> Ken Martindale
>
> PS On this site it is always possible to misinterpret people's comments in the
> wrong way. I try to assume the best or ignore what irritates me. I do find it
> interesting about the big discrepancy between what you have implied about the
> motor shaft seals and what I was told by Minnkota. I have also heard rumors
> about the seals being good past the vendors statements, but I have to be
> conservative for safety concerns and that I don't loose 3.5 years of work.
> Bear in mind my Sub is a wet Sub that I can bail out and not loose anything
> but the work and money. A 1 atmosphere Sub is a different story. If the motor
> seals leak do you run the risk of flooding and sinking? Can you bail out?
>
> Have fun.