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Re: Trolling Motors
I agree with you Ken! Why would evinrude use such a high quality,
pressure proof, "expensive" shaft seal for a motor thats not meant to be
more than 3 feet under the water???
Steve McColman, Vancouver Island
>I use on my Sub a Minnkota 70 pound thrust 24 volt Trolling Motor ($169
each).
>I examined the shaft seal and found it is a simple "Cup" seal in which
the
>shaft rotates in a rubber seal. Thus the shaft does abrade the rubber.
This
>degradation is a function of differential pressure across the seal and
for low
>pressures is long lasting.
>
>When I was talking to Minnkota, they stated the seal wasn't good for
much more
>than about 30 feet of fresh water before it could leak. I believe his
response
>was conservative but their seal certainly would not work at 700 feet
and if it
>did it wouldn't last long. I ended up pressure compensating my motor
with a
>somewhat simple SCUBA regulator such that the differential pressure
across the
>shaft seal was less than 2 feet of seawater and was positive. This
means that
>any leaks would leak air out and not corrosive seawater in. At least I
hope
>so, I still have not made sea trials yet although the my Wet Sub is
ready.
>
>The point of this is that since the Evinrude Trolling Motor is in the
same
>competitive market I personally doubt that their shaft seal will
reliably
>operate with 700 feet of sea water differential pressure. Pressure
>compensation, I believe, will be required.
>
>If someone is planning to use the Evinrude Trolling Motor, it would be
>critical to call the vendor and get real data on their shaft seals. I
know I
>did on the Minnkota Trolling Motor. I spent about $20 on the phone
calls. I
>also got design information on the Motor Controller I designed. High
surge
>currents can demagnetize the Trolling motors permanent magnet stator.
>
>Good Luck,
>
>Ken Martindale
>
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