<html><head></head><body>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>
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The downside is, of course, that air is readily available while an inert gas cost more. <br>
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Regards, <br>
Jon E. Pettersen <br><br><div class="gmail_quote">On 26 July 2014 22:27:49 CEST, Pete Niedermayr via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail"><br />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 /><br />Thanks Pete<br /><br /><hr /><br />On Mon, 7/21/14, hank pronk via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br /><br /> Subject: Re: [PSUBS-MAILIST] Minn Kota 101 - thread spec<br /> To: "Personal Submersibles General Discussion" <personal_submersibles@psubs.org><br /> Date: Monday, July 21, 2014, 6:20 PM<br /> <br /> there is a very nice<br /> solution here. Magnetic couplers, it wouldn't take<br /> much to convert a minkota to a magnetic coupled<br /> thruster.Hank<br /> <br /> <br /> On Monday, July 21, 2014 8:56:11 PM,<br /> Jon Wallace<br /> via Personal_Submersibles<br /> <personal_submersibles@psubs.org> wrote:<br /> <br /> <br /> <br /> <br /> <br /> Dissipation of heat to the water environment via<br /> conduction with<br /> the motor housing would help temper overall thermal<br /> expansion. <br /> The motors are essentially surrounded by an infinite<br /> sized water<br /> jacket and not typically operated at full speed for<br /> long periods<br /> of time. I suspect actual thermal expansion of the<br /> oil in the<br /> motor housing during typical underwater operations is<br /> negligible.<br /> <br /> <br /> <br /> In regards to viscosity effect on the motors,<br /> JimK's GUPPY is oil<br /> compensated and three 101's in a K-boat<br /> configuration and had no<br /> problem moving that heavy (7 ton?) sub. Check out<br /> <a href="http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720">http://www.youtube.com/embed/u0b7NjxttL4?rel=0&vq=hd720</a><br /> at<br /> 0:20-0:28 where he just about stops the sub on a dime<br /> with two<br /> forward 101's. Also in<br /> <a href="http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720">http://www.youtube.com/embed/9Vaq4JK9wVs?rel=0&vq=hd720</a><br /> at<br /> 3:39 he pulls out of the boat lift with just one 101<br /> aft, and at<br /> 4:02 he pulls out with two forward 101's. Alec<br /> has smaller motors<br /> on SNOOPY but they still have enough power to move it<br /> around. I'm<br /> sure viscosity effect on the motors are measurable but<br /> from<br /> practical application it doesn't appear to be much<br /> of an issue<br /> when two or more motors are used. There's enough<br /> power to move<br /> the subs as desired even with any viscosity effect<br /> that is<br /> present.<br /> <br /> <br /> <br /> Jon<br /> <br /> <br /> <br /> <br /> <br /> On 7/21/2014 10:22 AM, Cliff Redus via<br /> Personal_Submersibles<br /> wrote:<br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> James, a couple of points. First, to<br /> me the fewer<br /> the leak paths the better so I would not<br /> install the<br /> added plug. The issue is how to get traped<br /> air out of<br /> the Md-101 when using oil compensation. <br /> I like Alec<br /> and Hanks ideas for removing trapped air due<br /> to nipple<br /> protruding into body. The other point is<br /> the wrap<br /> around tube volume can compensate for the<br /> small amount<br /> of air that remains trapped. To deal with<br /> thermal<br /> expansion of the oil, first of all you are<br /> dealing with<br /> a small volume to start with so the<br /> tube/reservoir does<br /> not have to be all that large. If you do a<br /> quick back<br /> of the envelope calc on the required volume<br /> to compensate for only thermal expansion of<br /> the oil you<br /> about need 3 US teaspoons for a MK 101 (<br /> Assume oil has<br /> a thermal expansion coefficient of 0.00056<br /> 1/F and that<br /> there is one US pint of oil in the body of<br /> the 101 and<br /> that the temperature swing is 70F to 130F. <br /> Delta volume<br /> is 0.125 gal * 0.00056 1/F * 60F = 0.0042<br /> gal*128 OZ/gal<br /> *6 US TSP/OZ = 3.2 teaspoons). <br /> To me the design pressure inside the ME<br /> 101 should be<br /> ambient pressure as they have lip seals on<br /> shafts. Lip<br /> seals are design to take external<br /> pressure. They re not<br /> designed to take internal pressure. So a<br /> simple wrap<br /> around tube for oil compensation with say a<br /> volume of 5<br /> US teaspoons should work just fine as this<br /> would allow<br /> for thermal expansion of the oil and a small<br /> volume of<br /> trapped air and because the tube is<br /> flexible, the<br /> pressure inside the 101 is ambient which<br /> makes the lip<br /> seal happy. As to Alan's suggestion on<br /> omitting all<br /> pressure compensation and only relaying on<br /> the lip seal<br /> without any pressure compensation, I am not<br /> wild about<br /> this idea unless the boat is only designed<br /> for shallow<br /> water. MK designers when they speced the<br /> lip seals for<br /> MK were designing shallow submergence of a<br /> trolling<br /> motor with a factor of safety. So as you<br /> get deeper and<br /> deeper, you are starting to expose these<br /> lips seals to a<br /> significant differential pressure which<br /> causes them to<br /> overheat and fail at some point. Is this<br /> 10ft or 50 ft<br /> or 100 ft. Don't know but to me this<br /> exposes the boat<br /> to some risk particularly if use the<br /> 101's for depth<br /> stability rather than a VBT and dive the<br /> boat negatively<br /> buoyant, i.e., vertical thruster fails,<br /> boat starts to descend and pilot is<br /> forced into dropping<br /> ballast. <br /> <br /> <br /> <br /> To me a bigger question on air vs oil<br /> compensation is<br /> how much power are you giving up with oil<br /> compensation<br /> due to viscosity difference between oil and<br /> air. <br /> <br /> <br /> <br /> As both Alec and Vance point out, there<br /> has been a<br /> lot of bottom time on MD-101s with oil<br /> compensation<br /> without a lot documented failures. <br /> <br /> <br /> <br /> I have not decided in my own mind which<br /> compensation<br /> method I will use on my MD-101's for<br /> future boats. <br /> <br /> <br /> <br /> Cliff<br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /><hr /><br /> Personal_Submersibles mailing list<br /> Personal_Submersibles@psubs.org<br /> <a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /> <br /> <br /> <br /> <br /> -----Inline Attachment Follows-----<br /> <br /><hr /><br /> Personal_Submersibles mailing list<br /> Personal_Submersibles@psubs.org<br /> <a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /> <br /><br /><hr /><br />Personal_Submersibles mailing list<br />Personal_Submersibles@psubs.org<br /><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /></pre></blockquote></div><br>
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