Hi,

I have another shaft seal question:

What type of seal could I use to seal
a trolling motor shaft for use under
higher pressure?

I am thinking of diver propulsion, so
it should hold up to 5 bar, or down
to 150 ft depth.

Thanks a lot,

Chris

On Mon, 17 Nov 2003 00:34:42 +0100, Chris wrote:


Hi,

I have another shaft seal question:

What type of seal could I use to seal
a trolling motor shaft for use under
higher pressure?

I am thinking of diver propulsion, so
it should hold up to 5 bar, or down
to 150 ft depth.

Thanks a lot,

Chris

Consult a seal dealer. The regular lip seals, effective though they
are might be too fragile for this service. o rings in appropriately
grooved housings can handle this pressure - they can be arranged to
seal better under pressure, in fact.

Brian W Altus OK

O-rings are not well suited to constant or high speed shaft rotation.. (by
high speed I mean motor shaft).

I worked on the Navy deep submersable program and we overhauled all of this
type of equipment.. There are seals available that are well suited for motor
shafts. A vendor that specializes in high pressure pumps will have something
for this job.

BTW.. The best way to deal with the compression forces in electrical cables
is to intentionally flood them with mineral oil in Tygone tubing. Just be
sure you purge all the air pockets by applying a vacuum before sealing the
ends. (old saying, "you can't compress a liquid"). This method works to the
deepest ocean depth.

--
My opinion and experience. FWIW

Steve
s/v Good Intentions

How would a motor handle the increased turning resistance
caused by the oil filling? Do you think a trolling
motor would survive being oil filled?

I was thinking about converting one into a diver propulsion
vehicle, (DPV, basically a small torpedo that slowly tows
a diver) because they are available much cheaper than DPVs.

Are there any brands/Models you would recommend or warn
against, and does anyone have ideas for such a conversion?

I was thinking of housing lead batteries in a PVC tube
(air filled) and mounting the oil filled or otherwise
pressure proofed motor behind it.

Thanks for your comments,

Chris


Steve wrote:

O-rings are not well suited to constant or high speed shaft rotation.. (by
high speed I mean motor shaft).

I worked on the Navy deep submersable program and we overhauled all of this
type of equipment.. There are seals available that are well suited for motor
shafts. A vendor that specializes in high pressure pumps will have something
for this job.

BTW.. The best way to deal with the compression forces in electrical cables
is to intentionally flood them with mineral oil in Tygone tubing. Just be
sure you purge all the air pockets by applying a vacuum before sealing the
ends. (old saying, "you can't compress a liquid"). This method works to the
deepest ocean depth.

--
My opinion and experience. FWIW

Steve
s/v Good Intentions

Chris says:

snip

I was thinking about converting one into a diver propulsion
vehicle, (DPV, basically a small torpedo that slowly tows
a diver) because they are available much cheaper than DPVs.

snip

By the time you buy all the parts, oil fill what needs to be oil filled,
fabricate your casing, buy your high-pressure bearings, etc, and assemble the
brute, you will have spent more than if you bought the finished product from an
assembly-line with DPV stencilled on the side. Chances are the innards will be
exactly what you are putting in yours, but with the economies of scale built
into the pricing.

HTH ;-)

Steve

Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

Well,

uh, reality check. Ok, this is the budget:

Rough estimate was
$200 for batteries and charger,
$100 for Battery housing (large PVC tube or similar)

I don't know what model of trolling motor I'd have
to use, and the pressure proofing is the other unknown.
I thought it would be doable, as they are already designed
for submersion, the only possible problem at depth being the
shaft seal.

DPVs start at around $1000, $3500 for good ones. Do you
think I would have to spend $700 on the trolling motor
and shaft seals or oil filling?

Thanks again,

Chris


Stephen Baker wrote:

Chris says:

snip

I was thinking about converting one into a diver propulsion
vehicle, (DPV, basically a small torpedo that slowly tows
a diver) because they are available much cheaper than DPVs.

snip

By the time you buy all the parts, oil fill what needs to be oil filled,
fabricate your casing, buy your high-pressure bearings, etc, and assemble the
brute, you will have spent more than if you bought the finished product from an
assembly-line with DPV stencilled on the side. Chances are the innards will be
exactly what you are putting in yours, but with the economies of scale built
into the pricing.

HTH ;-)

Steve

Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

Chris says:

uh, reality check. Ok, this is the budget:

snip

DPVs start at around $1000, $3500 for good ones. Do you
think I would have to spend $700 on the trolling motor
and shaft seals or oil filling?

Ouch! I didn't think they were THAT expensive! Well, if nothing else, you've
been and gone and checked...

;-)

Steve

I like Rick's suggestion in the parallel thread.

He suggested a compensating chamber for the motor,
to keep the seal differential pressure low at any depth.
You could implement it like this:
Regular trolling motor. Low, low viscosity liquid.
A hole in the motor case, for a tube and small bronze bellows,
biassed to the closed position, and slightly "inflated " with light
fluid. Another screw in the motor case to pressurize slightly with
fluid. Seal the screw with an o-ring. put a guard cover around the
bellows.
How expensive could that be?

Brian Whatcott Altus OK

On Sat, 22 Nov 2003 22:27:59 +0100, Chris wrote:


Well,

uh, reality check. Ok, this is the budget:

Rough estimate was
$200 for batteries and charger,
$100 for Battery housing (large PVC tube or similar)

I don't know what model of trolling motor I'd have
to use, and the pressure proofing is the other unknown.
I thought it would be doable, as they are already designed
for submersion, the only possible problem at depth being the
shaft seal.

DPVs start at around $1000, $3500 for good ones. Do you
think I would have to spend $700 on the trolling motor
and shaft seals or oil filling?

Thanks again,

Chris


Stephen Baker wrote:

Chris says:

snip

I was thinking about converting one into a diver propulsion
vehicle, (DPV, basically a small torpedo that slowly tows
a diver) because they are available much cheaper than DPVs.

snip

By the time you buy all the parts, oil fill what needs to be oil filled,
fabricate your casing, buy your high-pressure bearings, etc, and assemble the
brute, you will have spent more than if you bought the finished product from an
assembly-line with DPV stencilled on the side. Chances are the innards will be
exactly what you are putting in yours, but with the economies of scale built
into the pricing.

HTH ;-)

Steve

Stephen C. Baker - Yacht Designer
http://members.aol.com/SailDesign/pr...cbweb/home.htm

Brian Whatcott wrote:

A hole in the motor case, for a tube and small bronze bellows,

Don't even need that complication. The existing seal should be adequate
for a compensated system. Drill and tap the casing for a tube fitting
and attach a foot long piece of surgical tubing. Fill the motor with
light biodegradable hydraulic oil, and top off through the tubing. Stick
a rubber plug in the tubing end to seal it and it's done.

Rick

On Sun, 30 Nov 2003 03:43:07 GMT, Rick
wrote:

Brian Whatcott wrote:

A hole in the motor case, for a tube and small bronze bellows,

Don't even need that complication. The existing seal should be adequate
for a compensated system. Drill and tap the casing for a tube fitting
and attach a foot long piece of surgical tubing. Fill the motor with
light biodegradable hydraulic oil, and top off through the tubing. Stick
a rubber plug in the tubing end to seal it and it's done.

Rick

Delightfully simple. Not sure about the long-term compatibility of
latex and hydraulic oil though.

Brian W