<html><body><div style="color:#000; background-color:#fff; font-family:arial, helvetica, sans-serif;font-size:12pt"><div style="RIGHT: auto"><SPAN style="RIGHT: auto">I'll be sure to tell the human powered sub guys.<VAR style="RIGHT: auto" id=yui-ie-cursor></VAR><BR style="RIGHT: auto" class=yui-cursor></SPAN></div>
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<DIV style="BORDER-BOTTOM: #ccc 1px solid; BORDER-LEFT: #ccc 1px solid; PADDING-BOTTOM: 0px; LINE-HEIGHT: 0; MARGIN: 5px 0px; PADDING-LEFT: 0px; PADDING-RIGHT: 0px; HEIGHT: 0px; FONT-SIZE: 0px; BORDER-TOP: #ccc 1px solid; BORDER-RIGHT: #ccc 1px solid; PADDING-TOP: 0px" class=hr contentEditable=false readonly="true"></DIV><FONT size=2 face=Arial><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> Marc de Piolenc <piolenc@archivale.com><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> Personal Submersibles General Discussion <personal_submersibles@psubs.org> <BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Thursday, September 5, 2013 8:42 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [PSUBS-MAILIST] prop size<BR></FONT></DIV>
<DIV class=y_msg_container><BR>It's not the low speed, but the large diameter of the propeller that <BR>gives better STATIC thrust per horsepower. The advantage of a larger <BR>prop is less under cruise conditions where the mass flow through the <BR>propeller is larger due to forward motion and it has only the drag of <BR>the sub to overcome. In fact, you really need to go through detailed <BR>calculation to make sure that a larger propeller is really of any use in <BR>your application.<BR><BR>Low rotation speed is NOT an advantage, though it may be dictated by the <BR>propulsion machinery. Low speed, high torque propeller drive gives high <BR>swirl loss in the wake, while higher speed and lower torque minimize swirl.<BR><BR>Best,<BR>Marc de Piolenc<BR><BR>On 9/5/2013 8:20 PM, greg cottrell wrote:<BR><BR>> I was standing in Frank Busby's kitchen one day many years ago<BR>> discussing this same question. He had returned from Finland on
a<BR>> mission to carefully document two deep diving subs being built there for<BR>> the Soviets (Finland agreed under threat of economic sanctions to allow<BR>> the inspection). The two subs in question had very large stern props<BR>> driven by hydraulics that turned very slowly. They were later named Mir<BR>> 1 & 2. Frank compared the concept to ice breaking ships that use huge<BR>> props that turn very slowly. It's quite efficient because there is<BR>> little energy wasted on turbulence and cavitation.<BR>> Also, in the realm of human powered subs, the winners have all had large<BR>> diameter low aspect ratio props that look for like aircraft props.<BR>> But there are trade offs- gear reduction will use a little power. Belt<BR>> reduction a little less. There is more drag on a big prop when it is not<BR>> turning (unless you feather it).Fouling a big prop is more likely<BR>> unless you put it in
a big cage. But if the goal is lower shaft speed<BR>> then it can be a good way to go.<BR>> Greg<BR>><BR>> *From:* hank pronk <<A href="mailto:hanker_20032000@yahoo.ca" ymailto="mailto:hanker_20032000@yahoo.ca">hanker_20032000@yahoo.ca</A>><BR>> *To:* Personal Submersibles General Discussion<BR>> <<A href="mailto:personal_submersibles@psubs.org" ymailto="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</A>><BR>> *Sent:* Wednesday, September 4, 2013 6:58 PM<BR>> *Subject:* [PSUBS-MAILIST] prop size<BR>><BR>><BR>> I have a two part question,<BR>> Is it beneficial to increase my propeller size to increase efficiency.<BR>> I was under the impression from my boating days that a large slow prop<BR>> is more fuel efficient. It should increase battery range and slow down<BR>> the shaft speed, helping the seal.<BR>> I have a much larger prop left over from boating and I am
thinking of<BR>> using it on Gamma<BR>> The next question is,,, is there anyone here with the ability to<BR>> calculate the new rpm for my given prop size and motor hp.<BR>> Hank<BR>> *From:* Jon Wallace <<A href="mailto:jonw@psubs.org" ymailto="mailto:jonw@psubs.org">jonw@psubs.org</A>><BR>> *To:* Personal Submersibles General Discussion<BR>> <<A href="mailto:personal_submersibles@psubs.org" ymailto="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</A>><BR>> *Sent:* Wednesday, September 4, 2013 6:18:15 AM<BR>> *Subject:* [PSUBS-MAILIST] There's gold in them-thar waters<BR>><BR>><BR>> <A href="http://www.usatoday.com/story/news/nation/2013/09/03/florida-family-gold/2757357/" target=_blank>http://www.usatoday.com/story/news/nation/2013/09/03/florida-family-gold/2757357/</A><BR>> _______________________________________________<BR>> Personal_Submersibles mailing list<BR>> <A
href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A> <mailto:<A href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A>><BR>> <A href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target=_blank>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</A><BR>><BR>><BR>><BR>> _______________________________________________<BR>> Personal_Submersibles mailing list<BR>> <A href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A> <mailto:<A href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A>><BR>> <A href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles"
target=_blank>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</A><BR>><BR>><BR>><BR>><BR>> _______________________________________________<BR>> Personal_Submersibles mailing list<BR>> <A href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A><BR>> <A href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target=_blank>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</A><BR>><BR><BR>-- <BR>Archivale catalog: <A href="http://www.archivale.com/catalog" target=_blank>http://www.archivale.com/catalog</A><BR>Polymath weblog: <A href="http://www.archivale.com/weblog" target=_blank>http://www.archivale.com/weblog</A><BR>Translations (ProZ profile): <A href="http://www.proz.com/profile/639380" target=_blank>http://www.proz.com/profile/639380</A><BR>Translations (BeWords profile): <A
href="http://www.bewords.com/Marc-dePiolenc" target=_blank>http://www.bewords.com/Marc-dePiolenc</A><BR>Ducted fans: <A href="http://massflow.archivale.com/" target=_blank>http://massflow.archivale.com/</A><BR>_______________________________________________<BR>Personal_Submersibles mailing list<BR><A href="mailto:Personal_Submersibles@psubs.org" ymailto="mailto:Personal_Submersibles@psubs.org">Personal_Submersibles@psubs.org</A><BR><A href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles" target=_blank>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</A><BR><BR><BR></DIV></DIV></DIV></div></body></html>