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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The contents of this e-mail are intended for the named addressee only. It contains information that may be confidential. Unless you are the named addressee or an authorized designee, you may not copy or use it, or disclose it to anyone else. If you received it in error please notify us immediately and then destroy it.