Re: [PSUBS-MAILIST] external Motors for depths of 1000ft

["Captain Nemo" <vulcania@hawaii.rr.com>]

Rob,

I don't have an exact number, but drag-induced RPM reduction on the armature
isn't much at all due to it's shape.  A guy to ask might be Dave at DC
Marine, or Casey at trollingmotorparts.com.

BTW: Casey is presently selling the complete MK Riptide 101# 36VDC unit for
about $550.  This is a saltwater motor, and for this price you get the
factory potentiometer, prop, the whole tamale.

MK's are factory rated to one additional atmosphere: 33FSW.  People have
been using them to 100 feet with a 95% success rate, but the company won't
cosign that.  One tech I know of is modifying the motors to work
uncompensated at 300 feet by polishing the shaft and matching it to a better
seal; I've got no info on the success / failure rate of those modifications,
but he says people have been using them for a while and didn't mention any
complaints.  One thing, though; if you open the case to modify the innards,
you need to reassemble it correctly: time the brushes and torque the covers
down properly.  Otherwise, she no runna so well.....

Regarding props: one problem MK had years back with the 4HP (just a name,
not a horsepower rating) occurred when they went from the plastic weedwacker
to the an aluminum prop.  Large numbers of burned out motors started coming
back the shop; MK finally returned to the original prop.  Something to keep
in mind when thinking about modifying the prop arrangement from what the
design engineers originally decided on.  Not saying it can't be done, but
possible overheating is something to be aware of.

The pressure compensation of any of these motors should make them
serviceable at homebuilt-sensible depths.  If in doubt about oil
compensation, you could always use air.

Pat


From: "Rob Innes" <innespace@jett.net>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, June 19, 2002 10:03 AM
Subject: Re: [PSUBS-MAILIST] external Motors for depths of 1000ft


> Does anyone know how much resistance is caused on the trolling motors by
> filling them with the oil? Approximately how much thrust could expect  to
be
> lost on a Motorguide 107lb thrust unit? Has anyone fitted one or more of
these
> motors to a sub or DPV?  I'd be very interested in the results
>
> Rob Innes
>
>
>