[PSUBS-MAILIST] Minn Kota 101 - thread spec

Sat Jul 26 18:35:29 EDT 2014

Hi Jon,
I hadn't thought of the possibility of a fire inside a motor.
You would have heat, sparking potential, fuel in the form of greece, & plenty of oxygen.
Karl Stanley's air compensated motors have gone down to 2000 ft & regularly go to 1000
with his tourist operation, & no fires that I've heard of.
Now that you have brought this up I think I will look in to some sought of inflammable grease
to replace any existing grease in the motor, & make sure the motor is cleaned well on the inside.
As you say, it's too easy to just use the air supply you already have & you probably wouldn't look 
at other gasses unless you were going to have a dedicated tank for compensating.
Alan

________________________________
 From: Jon Eide Pettersen via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Sunday, July 27, 2014 9:18 AM
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec

Would it be a good idea to use an inert gas like nitrogen or argon instead of air to pressure compensate thrusters? This is because compressed air will have a high partial pressure of oxygen, making the atmosphere in the thrusters more flammable. Also, if there is water trapped inside the thrusters, a high pp of oxygen will greatly speed up the corrosion rate.

The downside is, of course, that air is readily available while an inert gas cost more. 

Regards, 
Jon E. Pettersen 

On 26 July 2014 22:27:49 CEST, Pete Niedermayr via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

>Hank, What is the story behind your magnetic coupler ? You were talking about them on the list and then you had one. Did you buy it ? If so where? Did you build it ? If so from what plans.
>
>Thanks Pete
>
>>________________________________
>
>On Mon, 7/21/14, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec
>To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
>Date: Monday, July 21, 2014, 6:20 PM
>
>there is a very nice
>solution here.  Magnetic couplers, it wouldn't take
>much to convert a minkota  to a magnetic coupled
>thruster.Hank
>
>
>On Monday, July 21, 2014 8:56:11 PM,
>Jon Wallace
>via Personal_Submersibles
><personal_submersibles at psubs.org> wrote:
>
>
>
>
>
>Dissipation of heat to the water environment via
>conduction with
>the motor housing would help temper overall thermal
>expansion. 
>The motors are essentially surrounded by an infinite
>sized water
>jacket and not typically operated at full speed for
>long periods
>of time.  I suspect actual thermal expansion of the
>oil in the
>motor housing during typical underwater operations is
>negligible.
>
>
>
>In regards to viscosity effect on the motors,
>JimK's GUPPY is oil
>compensated and three 101's in a K-boat
>configuration and had no
>problem moving that heavy (7 ton?) sub.  Check out
>http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720
>at
>0:20-0:28 where he just about stops the sub on a dime
>with two
>forward 101's.  Also in
>http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720
>at
>3:39 he pulls out of the boat lift with just one 101
>aft, and at
>4:02 he pulls out with two forward 101's.  Alec
>has smaller motors
>on SNOOPY but they still have enough power to move it
>around.  I'm
>sure viscosity effect on the motors are measurable but
>from
>practical application it doesn't appear to be much
>of an issue
>when two or more motors are used.  There's enough
>power to move
>the subs as desired even with any viscosity effect
>that is
>present.
>
>
>
>Jon
>
>
>
>
>
>On 7/21/2014 10:22 AM, Cliff Redus via
>Personal_Submersibles
>wrote:
>
>
>
>
>
>
>
>
> James, a couple of points.  First, to
>me the fewer
>the leak paths the better so I would not
>install the
>added plug.  The issue is how to get traped
>air out of
>the Md-101 when using oil compensation.  
>I like Alec
>and Hanks ideas for removing trapped air due
>to nipple
>protruding into body.  The other point is
>the wrap
>around tube volume can compensate for the
>small amount
>of air that remains trapped.  To deal with
>thermal
>expansion of the oil, first of all you are
>dealing with
>a small volume to start with so the
>tube/reservoir does
>not have to be all that large.  If you do a
>quick back
>of the envelope calc on the required volume
>to compensate for only thermal expansion of
>the oil you
>about need 3 US teaspoons for a MK 101 (
>Assume oil has
>a thermal expansion coefficient of 0.00056
>1/F and that
>there is one US pint of oil in the body of
>the 101 and
>that the temperature swing is 70F to 130F. 
>Delta volume
>is 0.125 gal * 0.00056 1/F * 60F = 0.0042
>gal*128 OZ/gal
>*6 US TSP/OZ = 3.2 teaspoons).  
>To me the design pressure inside the ME
>101 should be
>ambient pressure as they have lip seals on
>shafts.  Lip
>seals are design to take external
>pressure.  They re not
>designed to take internal pressure.  So a
>simple wrap
>around tube for oil compensation with say a
>volume of 5
>US teaspoons should work just fine as this
>would allow
>for thermal expansion of the oil and a small
>volume of
>trapped air and because the tube is
>flexible, the
>pressure inside the 101 is ambient which
>makes the lip
>seal happy.  As to Alan's suggestion on
>omitting all
>pressure compensation and only relaying on
>the lip seal
>without any pressure compensation, I am not
>wild about
>this idea unless the boat is only designed
>for shallow
>water.  MK designers when they speced the
>lip seals for
>MK were designing shallow submergence of a
>trolling
>motor with a factor of safety.  So as you
>get deeper and
>deeper, you are starting to expose these
>lips seals to a
>significant differential pressure which
>causes them to
>overheat and fail at some point.  Is this
>10ft or 50 ft
>or 100 ft.  Don't know but to me this
>exposes the boat
>to some risk particularly if use the
>101's for depth
>stability rather than a VBT and dive the
>boat negatively
>buoyant, i.e., vertical thruster fails,
>boat starts to descend and pilot is
>forced into dropping
>ballast.  
>
>
>
>To me a bigger question on air vs oil
>compensation is
>how much power are you giving up with oil
>compensation
>due to viscosity difference between oil and
>air.  
>
>
>
>As both Alec and Vance point out, there
>has been a
>lot of bottom time on MD-101s with oil
>compensation
>without a lot documented failures.  
>
>
>
>I have not decided in my own mind which
>compensation
>method I will use on my MD-101's for
>future boats.  
>
>
>
>Cliff
>
>
>
>
>
>
>
>
>
>
>
>
>
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