RE: [PSUBS-MAILIST] How to do external electric thrusters?

[Hugo Marrero <HMarrero@HBOI.edu>]

Marten,

Being a "newbie" I think that is very important that you aquaint yourself
with submersible design and operation before you embark in your building
endeavour. I am not trying to quench your enthusiasm, however, if you do
this it will save you a lot of headaches and frustrations. Submarines have
been around for a long time and the design and fabrication methods out there
are not only proven in the field, but they are also safe and sound.

Now to answer your questions,

1-How do you seal the hull with the electrical connections?

These connectors use o-ring seals, just plain old orings, that's it. Our
subs go to 3000 ft and these connectors perform flawlessly. The only thing
you want to be careful about these connectors is their physical location.
You want them to be protected from getting banged up as they can break
easily if not protected.

I do not reccomend neither endorse the use of home-made penetrators or
connectors not approved for underwater use unless they are properly
engineered and tested, in which case it will probably be much more expensive
and labor intensive than buying something off the shelf. Why re-invent the
wheel? ... right?

2- Do you just leave the wires exposed?

NEVER! All the electrical conductors should be rated for underwater use. The
most common cables for underwater use are Neoprene SO type or better cable.
They come in all kinds of sizes and conductors. They have to be potted to
the connector or you have to have them custom made by seacon brantner.
Inside the sub all the wires should be of a fire retardant material, and
should be smoke free / halogen free (safety). All the connections should be
inside an approved electrical junction box.

All this information is available in the "Rules for Building & Classing
Underwater Vehicles, Systems and Hyperbaric Facilities" Published by the
American Bureau of Shipping. 

Their website is:

www.eagle.org/

3-How do you enclose the motor to make it water tight?

You have to design and build a proper housing for the motor. This is not
something that you are going to learn by email. You will need to get
informed and do your research through engineering articles, books and
online. 

Again, this can be an expensive proposition. Our motors are being designed
and built by us and is costing us roughly $20K per motor not including the
engineering costs.

Something off the shelf may work if you are not planning to go to deep, like
a trolling motor, and even hydraulic motors will need to be enclosed in a
housing as sea water will damage them very quickly.

4-Will pressure have an adverse affect on the motor? If so, do you need to
compensate for the pressure?

The pressure affects not the motor but the shaft interface and the dynamic
load on the bearings. This in turn affects the motor performance. Brushless
DC motors and Variable speed AC motors can be totally submerged in oil to
make the housing design easier and cheaper as the housing will be "preasure
compensated". Regular brush DC motors must be in a pressure housing, and the
costs shift from the electronics to the engineering and fabrication involved
in the design and the depth rating of the motor. These require more
maintenance than preasure compensated systems.

I hope this helps a bit. Now is time for you to do your homework... ;o)   
 
 
Hugo,