[PSUBS-MAILIST] T-Rex Thrusters & Cooling

[vbra676539 at aol.com]

Joe,

We once machined a 3/4 hp 120 volt thruster motor and a piece of steel pipe to matching OD and ID. The idea was to make the unit smaller and perhaps help it run cooler. It ran hotter! The loss of air circulation in there was apparently more important than what would appear to be an improved heat sink. When I say hotter, I mean hotter than you could touch (even in the water). Hot enough, we decided, to fry the motor under heavy usage, which meant that it didn't work at all as far as we were concerned.

The JSLs were the best example of on/off thrusters (no motor controls, only relays) I can think of, as they were used for main propulsion as well as for maneuvering. 1 1/4 hp/28 volt. The shaft end base plate of the motor was replaced with a machined aluminum section that serves as the bearing case on the motor side and as the housing for the planetary reduction gear on the prop side, and also as the mid-body of the thruster. The units are all aluminum (5000 series?). The motors fit fairly close in there, but with a distinctive air space. All the pieces were o-ring sealed (no welding) and held together with spring loaded flip clamps.

>From front to back you get the forward end plate with bulkhead connector, the motor sleeve, then the gear case, followed by the sand cast back bullet that contains a flex-shaft coupling, bearings, and the shaft seal, then the prop and nozzle. The props were/are 14/14 inch square tipped four blades running in a machined syntactic foam nozzle and maybe, I say again, maybe, put out a hundred pounds of thrust. Not small, and probably not very efficient by modern standards, but they were to all intents and purposes bulletproof, save the occasional shaft seal failure.

Cooling was never a problem with these things. They were designed and built in-house, and we carried a spare or two offshore. Each sub had eight of them (4 horizontal aft, 2 lateral fore and aft, and 2 vertical fore and aft). Not lightweight, but serviceable and (certainly by modern standards) cheap.

George and I talked a good bit about the thrusters we used offshore and the ones he built. His were built from available stock material and, except for the custom order extended shafts, were off-the-shelf. In his view, they worked fine. He didn't care for trolling motors. Not enough torque. Something that Alex proved once again in the Keys by choking one down with a piece of soft coral. Something to keep in mind.

Vance


-----Original Message-----
From: Joe Perkel <josephperkel at yahoo.com>
To: Psubbers Mailist <personal_submersibles at psubs.org>
Sent: Wed, Oct 9, 2013 5:49 pm
Subject: [PSUBS-MAILIST] T-Rex Thrusters & Cooling





I am trying to understand George's design intent reference his 1 ATM SCH40 pipe housings and cooling.
 
Where #8 SCH40 O.D. being 8.625" and your typical 2-3 HP DC enclosed fan cooled motor being roughly 6", was it his intent to have this airspace between the motor and inner wall for air circulation, or is this space simply incidental?
 
I am wondering if these housings can be slimmed down to a more snug or custom fit with a reliance on conduction for cooling? Perhaps even filling the 1 ATM housing with non-compensated oil for the sole purpose of efficient conduction?
 
I am also noting that the bow thruster industry likes to get the motor out of the props way with a 90 degree drive arrangement. This has interesting implications for potentially more efficient and downsized lateral thrusters.
 
Some musings.
 
Joe
 
 
 




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