<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:12pt"><div><span>Hi Pete,</span></div><div style="color: rgb(0, 0, 0); font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px; font-style: normal; background-color: transparent;"><span>I went through all the usual steps to get a magnetic coupler for Gamma. The cost was in the 2K range for all the parts, two magnet assemblies and a barrier. I went to my best resource, ebay, and found a brand new surplus hydraulic pump with a magnetic coupler. Based on the pump specs, port sizes etc, I new the magnetic coupler was sufficient in size for Gamma. I bought the pump complete for about 200 dollars, amazing! It was a simple machining job to make it work with Gamma's existing set up. Magnetic couplers are really a great
set up. Guess that is why Nuytco uses them. It would be nice to make a kit to fit the minkota motors. A small pump conversion is all it would take. If the end cap were replaced in the kit, I am sure sufficient depths could be achieved with them.</span></div><div style="color: rgb(0, 0, 0); font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px; font-style: normal; background-color: transparent;"><span>Hank</span></div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 12pt;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 12pt;"> <div dir="ltr"> <font face="Arial" size="2"> On Saturday, July 26, 2014 5:19:05 PM, Jon Eide Pettersen via Personal_Submersibles
<personal_submersibles@psubs.org> wrote:<br> </font> </div> <br><br> <div class="y_msg_container"><div id="yiv2586516062"><div>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.<br clear="none">
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The downside is, of course, that air is readily available while an inert gas cost more. <br clear="none">
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Regards, <br clear="none">
Jon E. Pettersen <br clear="none"><br clear="none"><div class="yiv2586516062yqt4205053554" id="yiv2586516062yqtfd74730"><div class="yiv2586516062gmail_quote">On 26 July 2014 22:27:49 CEST, Pete Niedermayr via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="yiv2586516062gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex; border-left-color: rgb(204, 204, 204); border-left-width: 1px; border-left-style: solid;">
<pre class="yiv2586516062k9mail"><br clear="none">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.<br clear="none"><br clear="none">Thanks Pete<br clear="none"><br clear="none"></pre><div class="hr" style="margin: 5px 0px; padding: 0px; border: 1px solid rgb(204, 204, 204); border-image: none; height: 0px; line-height: 0; font-size: 0px;" contenteditable="false" readonly="true"></div><br clear="none">On Mon, 7/21/14, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br clear="none"><br clear="none"> Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec<br clear="none"> To: "Personal Submersibles General Discussion" <personal_submersibles@psubs.org><br clear="none"> Date: Monday, July 21, 2014, 6:20 PM<br clear="none"> <br clear="none"> there is a very nice<br clear="none">
solution here. Magnetic couplers, it wouldn't take<br clear="none"> much to convert a minkota to a magnetic coupled<br clear="none"> thruster.Hank<br clear="none"> <br clear="none"> <br clear="none"> On Monday, July 21, 2014 8:56:11 PM,<br clear="none"> Jon Wallace<br clear="none"> via Personal_Submersibles<br clear="none"> <personal_submersibles@psubs.org> wrote:<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> Dissipation of heat to the water environment via<br clear="none"> conduction with<br clear="none"> the motor housing would help temper overall thermal<br clear="none"> expansion. <br clear="none"> The motors are essentially surrounded by an infinite<br clear="none"> sized water<br clear="none"> jacket and not typically operated at full speed for<br clear="none"> long periods<br clear="none"> of time. I suspect
actual thermal expansion of the<br clear="none"> oil in the<br clear="none"> motor housing during typical underwater operations is<br clear="none"> negligible.<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> In regards to viscosity effect on the motors,<br clear="none"> JimK's GUPPY is oil<br clear="none"> compensated and three 101's in a K-boat<br clear="none"> configuration and had no<br clear="none"> problem moving that heavy (7 ton?) sub. Check out<br clear="none"> <a href="http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720" target="_blank" rel="nofollow" shape="rect">http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720</a><br clear="none"> at<br clear="none"> 0:20-0:28 where he just about stops the sub on a dime<br clear="none"> with two<br clear="none"> forward 101's. Also in<br clear="none"> <a
href="http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720" target="_blank" rel="nofollow" shape="rect">http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720</a><br clear="none"> at<br clear="none"> 3:39 he pulls out of the boat lift with just one 101<br clear="none"> aft, and at<br clear="none"> 4:02 he pulls out with two forward 101's. Alec<br clear="none"> has smaller motors<br clear="none"> on SNOOPY but they still have enough power to move it<br clear="none"> around. I'm<br clear="none"> sure viscosity effect on the motors are measurable but<br clear="none"> from<br clear="none"> practical application it doesn't appear to be much<br clear="none"> of an issue<br clear="none"> when two or more motors are used. There's enough<br clear="none"> power to move<br clear="none"> the subs as desired even with any viscosity effect<br clear="none"> that is<br clear="none">
present.<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> Jon<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> On 7/21/2014 10:22 AM, Cliff Redus via<br clear="none"> Personal_Submersibles<br clear="none"> wrote:<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> James, a couple of points. First, to<br clear="none"> me the fewer<br clear="none"> the leak paths the better so I would not<br clear="none"> install the<br clear="none"> added plug. The issue is how to get traped<br clear="none"> air out of<br clear="none"> the Md-101 when using oil compensation. <br clear="none"> I like
Alec<br clear="none"> and Hanks ideas for removing trapped air due<br clear="none"> to nipple<br clear="none"> protruding into body. The other point is<br clear="none"> the wrap<br clear="none"> around tube volume can compensate for the<br clear="none"> small amount<br clear="none"> of air that remains trapped. To deal with<br clear="none"> thermal<br clear="none"> expansion of the oil, first of all you are<br clear="none"> dealing with<br clear="none"> a small volume to start with so the<br clear="none"> tube/reservoir does<br clear="none"> not have to be all that large. If you do a<br clear="none"> quick back<br clear="none"> of the envelope calc on the required volume<br clear="none"> to compensate for only thermal expansion of<br clear="none"> the oil you<br clear="none">
about need 3 US teaspoons for a MK 101 (<br clear="none"> Assume oil has<br clear="none"> a thermal expansion coefficient of 0.00056<br clear="none"> 1/F and that<br clear="none"> there is one US pint of oil in the body of<br clear="none"> the 101 and<br clear="none"> that the temperature swing is 70F to 130F. <br clear="none"> Delta volume<br clear="none"> is 0.125 gal * 0.00056 1/F * 60F = 0.0042<br clear="none"> gal*128 OZ/gal<br clear="none"> *6 US TSP/OZ = 3.2 teaspoons). <br clear="none"> To me the design pressure inside the ME<br clear="none"> 101 should be<br clear="none"> ambient pressure as they have lip seals on<br clear="none"> shafts. Lip<br clear="none"> seals are design to take external<br clear="none"> pressure. They re not<br clear="none"> designed to take
internal pressure. So a<br clear="none"> simple wrap<br clear="none"> around tube for oil compensation with say a<br clear="none"> volume of 5<br clear="none"> US teaspoons should work just fine as this<br clear="none"> would allow<br clear="none"> for thermal expansion of the oil and a small<br clear="none"> volume of<br clear="none"> trapped air and because the tube is<br clear="none"> flexible, the<br clear="none"> pressure inside the 101 is ambient which<br clear="none"> makes the lip<br clear="none"> seal happy. As to Alan's suggestion on<br clear="none"> omitting all<br clear="none"> pressure compensation and only relaying on<br clear="none"> the lip seal<br clear="none"> without any pressure compensation, I am not<br clear="none"> wild about<br clear="none"> this idea unless the boat is
only designed<br clear="none"> for shallow<br clear="none"> water. MK designers when they speced the<br clear="none"> lip seals for<br clear="none"> MK were designing shallow submergence of a<br clear="none"> trolling<br clear="none"> motor with a factor of safety. So as you<br clear="none"> get deeper and<br clear="none"> deeper, you are starting to expose these<br clear="none"> lips seals to a<br clear="none"> significant differential pressure which<br clear="none"> causes them to<br clear="none"> overheat and fail at some point. Is this<br clear="none"> 10ft or 50 ft<br clear="none"> or 100 ft. Don't know but to me this<br clear="none"> exposes the boat<br clear="none"> to some risk particularly if use the<br clear="none"> 101's for depth<br clear="none"> stability rather than a VBT
and dive the<br clear="none"> boat negatively<br clear="none"> buoyant, i.e., vertical thruster fails,<br clear="none"> boat starts to descend and pilot is<br clear="none"> forced into dropping<br clear="none"> ballast. <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> To me a bigger question on air vs oil<br clear="none"> compensation is<br clear="none"> how much power are you giving up with oil<br clear="none"> compensation<br clear="none"> due to viscosity difference between oil and<br clear="none"> air. <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> As both Alec and Vance point out, there<br clear="none"> has been a<br clear="none"> lot of bottom time on MD-101s with oil<br clear="none">
compensation<br clear="none"> without a lot documented failures. <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> I have not decided in my own mind which<br clear="none"> compensation<br clear="none"> method I will use on my MD-101's for<br clear="none"> future boats. <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> Cliff<br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"> <br clear="none"><div class="hr" style="margin: 5px 0px; padding: 0px; border: 1px solid rgb(204, 204, 204); border-image: none; height: 0px;
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