<font color='black' size='3' face='Arial, Helvetica, sans-serif'><font class="Apple-style-span" size="3">Cliff,</font>
<div><font class="Apple-style-span" size="3">Messy, not hard.</font></div>
<div><font class="Apple-style-span" size="3">Vance<br>
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<div style="font-family: helvetica, arial; font-size: 10pt; color: black; ">-----Original Message-----<br>
From: Cliff Redus via Personal_Submersibles <personal_submersibles@psubs.org><br>
To: Personal Submersibles General Discussion <personal_submersibles@psubs.org><br>
Sent: Mon, Jul 21, 2014 9:47 pm<br>
Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec<br>
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<div>Concur Jon that water will act as thermal sink and that the duty cycle on the thrusters are not severe but I don't agree that the thermal expansion in negligible. If you assume that the temperature change I estimated was high by a factor of two, then you would still end up with 3 teaspoons of oil that would be forced into the ambient tube. Small but not negligible. There will be a change in the internal temperature of the motor from the off position to on and given the amount of oil in the 101 body, there will be oil that has to escape. </div>
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<div>Granted, the primary purpose of the compensation is to keep from exposing the housing to a high differential pressure but thermal expansion still
has to be accounted for in sizing the ambient reservoir.</div>
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<div>These MK 101 are powerful at almost 1.8 HP at 47 amps when air filled but there has to be some degradation in power when filled with oil due to the viscosity difference with air. At 75F, light oil is over 1800 times as viscous as air. IS there enough power to push a psub about, sure. I am just trying to come up with what kind of HP loss you get with oil compensation. </div>
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<div>Does anyone know what rpm these motors max out at in the water?</div>
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<div>Good point Vance on trying to make the armature as hydraulically smooth as possible to maximize power when oil compensated. I wonder how hard this would be to do?</div>
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<div>Cliff</div>
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<font face="Arial" size="2"> <b><span style="font-weight: bold;">From:</span></b> Jon Wallace via Personal_Submersibles <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>><br>
<b><span style="font-weight: bold;">To:</span></b> Personal Submersibles General Discussion <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>> <br>
<b><span style="font-weight: bold;">Sent:</span></b> Monday, July 21, 2014 7:55 PM<br>
<b><span style="font-weight: bold;">Subject:</span></b> Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec<br>
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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.<br clear="none">
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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
<a class="yiv2776807261moz-txt-link-freetext" target="_blank" href="http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720" rel="nofollow" shape="rect">http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720</a> at
0:20-0:28 where he just about stops the sub on a dime with two
forward 101's. Also in
<a class="yiv2776807261moz-txt-link-freetext" target="_blank" href="http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720" rel="nofollow" shape="rect">http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720</a> 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.<br clear="none">
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Jon<br clear="none">
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On 7/21/2014 10:22 AM, Cliff Redus via Personal_Submersibles
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<div> 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). </div>
<div>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. </div>
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<div>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. </div>
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<div>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. </div>
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<div>I have not decided in my own mind which compensation
method I will use on my MD-101's for future boats. </div>
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<div id="yiv2776807261yui_3_16_0_7_1405949616767_12">Cliff</div>
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