[PSUBS-MAILIST] Air compensating thrusters

[Jon Wallace via Personal_Submersibles]

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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