Submersible Motor Design

[gypsycoder]

Hi y'all. As I have already done the work of converting my boat to use
the E-Pod I have been hoping that I might find a submersible motor I
can use to replace the E-Pod motor. As it turns out designing and
manufacturing a reliable submersible motor is a real challenge. The
following information is part of an email exchange I had with a sales
engineer at a company called Empire Magnetics.

"We make submersible step motors and BLDC for a number of companies,
universities, and the Navy. Whether you are submerged a few feet or
to the bottom of the ocean, you must have an oil filled pressure
compensator or your motor will leak.

There are 3 very obvious techniques that most people think of to make
a motor water-proof. There are also 3 theoretical things you must
do or the motor will leak. It may take 1 to 6 months but it WILL leak
water and be destroyed. The OFP (oiled filled piston) pressure
compensator is absolutely needed. If a motor is not oil filled, water
will get inside the motor quickly. If it is oil filled without a
pressure compensator, within minutes, the motor starts running and the
windings get hot. This heat expands the oil, pressure builds up
(hydraulic effect) and oil will leak out at the front motor shaft
seal. The pressure compensator solves this problem.

Fresh water will demand that you make the housing out of 304 stainless
steel. If the water is salt water, the housing must be 316 stainless
steel. O-rings must be used at every joint and the wires must be
properly potted when they exit the housing. You could specify a
Seacon waterproof connector. Each half of the connector is over $1000
for both the connector and the socket. None of these materials are
inexpensive.

This type of design absolutely does work and nothing short of this
will. Empire Magnetics is the leader in this area – there is no other
company that we know who’s unit is really water proof that we are
aware of. We typically get calls from unhappy customers where a motor
company thought that these under-water motors are easy. It took us a
great deal of time and effort back in 1987 to figure all these thing
out and get it right.

Our motors do work – they are not inexpensive. In the long run they
will give you the results that you want."

Basically a motor like this is a special product for them and requires
an engineering charge. Prices on their web site for similar motors are
in the $8000 - $9000 range.

Personally I am going to convert my boat back to shaft drive and use a
Mars 3000 motor mounted inside the boat. I estimate the cost of doing
this to be about $2000.

Here are links to the Empire Magnetics web site and technical
articles.

www.EmpireMagnetics.com
http://www.empiremagnetics.com/articles/deep_sea.htm
http://www.empiremagnetics.com/articles_indx.htm


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