I'd be prone to using thrusters of the same size, and carrying a spare that
could replace any of them. The JSLs use them pointed athwartships, vertically
and fore and aft for main propulsion and they're about as good as it gets for
close work (considering the weight). However, it's power heavy for transits, as
you're steering with the maneuvering motors all the time. Their motors are on
and off (1 1/4 hp 28VDC through a planetary gear turning 14" props in a Kort
nozzle).
Rudders and planes are nice for transits. You could build the thrusters
into the things and operate them mechanically from inside (the same as our side
units now). Then a fixed lateral on the bow--four thrusters in all. Mind
you, the most successful builder these days is Phil Nuytton, and he mounts
verticals fixed and steers with the motor controls on his side thrusters (2 or 4
units), also fixed. It's simple, doesn't require anything but cable
penetrations, and saves a lot of fuss and bother with rotating shafts through
the hull.
The bigger Minn-Kotas all have speed controls and lots of other tasty
options, including battery condition meters, solid state chargers that could go
INSIDE the sub, rather than be toted around, and even a built in auto-pilot on
some models. In fact, they have a dual motor unit designed to mount to the
topside of an outboard's cavitation plate, and I don't see why that couldn't be
adapted to fit them on either side of a rudder, and wouldn't THAT be a kick in
the tail!!! We'll see what they say, and then look at the price.
Vance,
Snoopy came with the side thrusters and I added the stern
thruster. I'm not certain how many pounds thrust I have on the sides, but I'd
guess they're about 40 lbs. Those appear very nicely sized, but I'd
encourage you to go with variable speed as opposed to my simple on/off. As you
might have seen in the cable collision video, Snoopy goes a bit too fast for
limited visibility. I wouldn't want them any smaller because they're just right
for maneuvering on the surface, but for UW use variable speed would be
a worthwhile improvement.
The stern thruster is tiny, just 28 lbs. My reasoning for
that was that I was envisioning using it UW and wanted something small to go
slowly. That turned out to be a mistake. The problem is if I'm cruising UW on
the stern thruster alone I have no vertical control, so the main use of the
stern thruster is on the surface, and it's way too small for that. The
side thrusters, because they rotate, are the ones to use submerged unless you
were also putting in a fixed vertical thruster.
Bottom line, I'd go with side thrusters in the 40-50 lb range and
a stern thruster in the 75-100 lbs range.
Ah, and the question about currents. Unfortunately in the sorts of
tidal currents you have down there in South FL, all of the above are
useless!
:)
Alec
I remembered the conversation after sending the email, but didn't hear how
you had actually done the job. Excellent. Just as plain-dumb-simple as can
be. I just wrote Minn-Kota about this. They've got the 101# saltwater 36
volters, plus a new electric outboard that is 48 volts. I'll have to
see whether I can afford a box full, as will take at least four motors to
do what I want. Which model did you use for Snoopy, and how are they in a
current?
Vance
-----Original Message-----
From:
Alec.Smyth@compuware.com
To: personal_submersibles@psubs.org
Sent: Thu, 16
Nov 2006 10:38 AM
Subject: RE: [PSUBS-MAILIST] Oil Compensated
Thursters
That's funny Vance, because you were the guy who gave me
instructions on how to do it!
Each trolling motor has two little plastic elbows screwed into the
casing, one on top and one below. I have about a foot of clear plastic tubing
that is wrapped around the can and ends in each elbow. The tubing being flexible
will compress if there are any small air bubbles left in the motor (I've found
it impossible to eliminate ALL bubbles, there's always a small one that shows up
in the tube). The reason the elbows are on the top and bottom, as opposed to say
the sides, is to make it easier to fill with oil. I disconnect the tube from the
top elbow, raise the open end of the tube above the level of the motor, and
add oil through the tube until it flows out the top
elbow.
Obviously to install the elbows you need to take the motor apart,
because drilling and tapping the holes creates metal chips that would ruin
the motor in short order. You also need to make sure you're drilling in
between the magnets, which come glued to the inside of the motor can.
I hope that description is clear. If you see the actual HW it's
ridiculously simple.
thanks,
Alec
Alec, How do you compensate the oil? I'd love to try some of those 36 volt
Minn-Kotas. They've got a ton of umph, and might get me back a couple of
hundred pounds of payload from George's Model-T Rex style thruster cans. And it
would be cheap, too. Vance
-----Original Message-----
From:
Alec.Smyth@compuware.com
To: personal_submersibles@psubs.org
Sent: Thu, 16
Nov 2006 9:39 AM
Subject: RE: [PSUBS-MAILIST] Oil Compensated
Thursters
I had an email conversation with Carl about a year ago on that
topic. They're just straight air compensated, with Swagelok SS fittings tapped
into the trolling motor casings. The reason I'd contacted him was to ask whether
he was using air, because some on here maintained that at his depths, the
partial pressure of O2 in air would be a fire hazard. I think his sub
demonstrates it's not.
BTW Snoopy's trolling motors started out air compensated and are
now in their second season with oil compensation. I have nothing at all against
air compensation, and would go with that if my air bottles were outside the
hull. But the way it was implemented on Snoopy the air was passed through the
shafts from the cabin, and there just wasn't space to do it properly along with
the cables. What's been interesting about the switch to oil is I can't notice
ANY difference. The motors seem to pull just as strong, and even sound exactly
the same as before.
cheers,
Alec
Oil compensated DC motors work just fine at moderate depths. Alvin had
problems originally with brushes arcing, but he Hymak 5 hp motor used
by Hyco on nearly everything they built was a serious workhorse. You get to tear
it down and change brushes periodically as they wear faster, and they'll
get the oil dirty, so you'll have to watch that. I was on Karl Stanley's web
page last night and it looks to me like his Idabel is using about a case of
trolling motors, and they must be compensated, as the sub is rated for 3000 foot
service. Maybe we ought to ask him what the secret is, if any.
Vance
-----Original Message-----
From:
DJACKSON99@aol.com
To: personal_submersibles@psubs.org
Sent: Wed, 15 Nov
2006 10:35 PM
Subject: [PSUBS-MAILIST] Oil Compensated Thursters
Can anyone support this statement: "Scripps has tried to fill the DC
motors with oil, but the oil gets between the brushes and the commutator, where
the insulation properties of the oil causes problems. Although it would be
possible to use high voltage to break through the oil film, the high voltage is
a safety hazard for the divers."
I was thinking about 24 or 36 volt oil compensated brushed trolling motors,
but after reading the above I looked and could not find any examples of oil
compensated brushed motors under 100 volts.
What are your experiences and thoughts?
Thanks
--Doug J
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