[PSUBS-MAILIST] Air compensating thrusters

Sun Jul 27 09:59:47 EDT 2014

Jon and all,

As to replacement, I'm planning to carry a spare, rigged out and ready to go. Any sign of failure and I change it out with the back up, then the replaced thruster goes into overhaul. As Jon says, $250 bucks is cheap insurance, and carrying the extra means an hour's work to save a long-planned dive week-end from ruin by a failed o-ring.

Vance

-----Original Message-----
From: Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sun, Jul 27, 2014 9:44 am
Subject: Re: [PSUBS-MAILIST] Air compensating thrusters

      Alan,

      Everyone is correct...about their own experience.  This is a Ford      vs Chevy debate with neither system being a perfect solution.       Primary use is likely going to dictate the best path to take, air      comp if you can't sacrifice power reduction or risk brush issues      in commercial operations, oil comp for simplicity in recreational      operations.

      Alec's experience is a pretty good story for recreational diving.       A 10 year life prorates to a cost of only $25/year for each MK101      and from a performance perspective he can't tell the difference      between air/oil comp on a small minn-kota.  JimK's 7-ton Bionic      Guppy gets muscled around easily with three oil comp'd MK 101's so      they obviously have plenty of power even if its less than it would      be with air comp.  That's enough evidence for me...no regulators,      no extra gas to carry, no extra plumbing, no overpressure valves      and no worries about maintenance or failure on all those small air      compensated components.  At $255 for a MK101 lower unit, I'll just      create a replace-one-motor-a-year budget.  No need to open the      can, replace brushes, turn the armature; just replace it with a      new one and I'll never have one motor that is more than four years      old.

      So you probably just want to toss a coin and pick a method.  Maybe      start with air comp first on a new build because if you don't like      it then converting to oil comp will potentially be easier than      vice-versa.

      Jon

      On 7/27/2014 3:42 AM, Alan James via Personal_Submersibles wrote:

Thanks Alec,

I was intending to also mention your            experience as a balance to the negatives

but got distracted.

The problem is that I am hearing a lot of            conflicting stories.

Even            with air compensation there are problems. Greg told me he            had a problem

with moisture getting in through the            exhaust valves of a second stage regulators.

I have put extension tubes around the            exhaust manifolods of my ambient sub's compensating

regulators to try & stop this.

I dive mostly in sea water, which is not            as forgiving as fresh, so want to get it right.

Emile was telling me about repeated            problems with one of his sub's thrusters, & he is now            using

expensive rim thrusters. I will leave it up to him if            he feels like sharing the details.

The guys at Fugu sub with 30 years            commercial experience are saying go with air, there are too            many hasles with oil. All commercial oil compensating units            have about 5psi overpressure which your system doesn't have. So who            is right? 

Cheers Alan

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