<html><body><div style="color:#000; background-color:#fff; font-family:tahoma, new york, times, serif;font-size:12pt"><div style="RIGHT: auto"><SPAN style="RIGHT: auto">Hi Greg,</SPAN></div>
<div style="FONT-SIZE: 16px; FONT-FAMILY: tahoma, new york, times, serif; RIGHT: auto; COLOR: rgb(0,0,0); FONT-STYLE: normal; BACKGROUND-COLOR: transparent"><SPAN style="RIGHT: auto">thanks' for the input. Reducing the shaft speed is not the only goal, but a very attractive benefit. I hadn't considered the extra entanglement threat. There is the cool factor, are we allowed to include that? :-) I need to replace my motor and I am missing the key mounting brackets. I have a new motor with a gear reduction on it. It seems like a good time to make the change if it makes sense. I will loose about 5% with gearing and one bearing. I just wonder if I will gain 5% with the larger prop. If it were even, there is still the shaft speed to consider.<VAR id=yui-ie-cursor></VAR></SPAN></div>
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<DIV class=hr style="FONT-SIZE: 0px; BORDER-TOP: #ccc 1px solid; HEIGHT: 0px; BORDER-RIGHT: #ccc 1px solid; BORDER-BOTTOM: #ccc 1px solid; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 5px 0px; BORDER-LEFT: #ccc 1px solid; LINE-HEIGHT: 0; PADDING-RIGHT: 0px" readonly="true" contenteditable="false"></DIV><FONT size=2 face=Arial><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> greg cottrell <jgcottrell2002@yahoo.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 6:20:01 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> Re: [PSUBS-MAILIST] prop size<BR></FONT></DIV>
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<DIV><SPAN>Hank,</SPAN></DIV>
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<DIV><SPAN>I was standing in Frank Busby's kitchen one day many years ago discussing this same question. He had returned from Finland on a mission to carefully document two deep diving subs being built there for the Soviets (Finland agreed under threat of economic sanctions to allow the inspection). The two subs in question had very large stern props driven by hydraulics that turned very slowly. They were later named Mir 1 & 2. Frank compared the concept to ice breaking ships that use huge props that turn very slowly. It's quite efficient because there is little energy wasted on turbulence and cavitation.</SPAN></DIV>
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<DIV style="FONT-SIZE: 16px; FONT-FAMILY: arial, helvetica, sans-serif; COLOR: rgb(0,0,0); FONT-STYLE: normal; BACKGROUND-COLOR: transparent"><SPAN>Also, in the realm of human powered subs, the winners have all had large diameter low aspect ratio props that look for like aircraft props. </SPAN></DIV>
<DIV class=yiv1694287964ms__id5838 style="FONT-SIZE: 16px; FONT-FAMILY: arial, helvetica, sans-serif; COLOR: rgb(0,0,0); FONT-STYLE: normal; BACKGROUND-COLOR: transparent"><SPAN></SPAN> </DIV>
<DIV class=yiv1694287964ms__id5838 style="FONT-SIZE: 16px; FONT-FAMILY: arial, helvetica, sans-serif; COLOR: rgb(0,0,0); FONT-STYLE: normal; BACKGROUND-COLOR: transparent"><SPAN>But there are trade offs- gear reduction will use a little power. Belt reduction a little less. There is more drag on a big prop when it is not turning (unless you feather it).</SPAN><SPAN>Fouling a big prop is more likely unless you put it in a big cage. But if the goal is lower shaft speed then it can be a good way to go.<VAR id=yiv1694287964yui-ie-cursor></VAR></SPAN></DIV>
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<DIV class=yiv1694287964hr style="FONT-SIZE: 0px; BORDER-TOP: #ccc 1px solid; HEIGHT: 0px; BORDER-RIGHT: #ccc 1px solid; BORDER-BOTTOM: #ccc 1px solid; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 5px 0px; BORDER-LEFT: #ccc 1px solid; LINE-HEIGHT: 0; PADDING-RIGHT: 0px"></DIV><FONT size=2 face=Arial><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> hank pronk <hanker_20032000@yahoo.ca><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> Wednesday, September 4, 2013 6:58 PM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> [PSUBS-MAILIST] prop size<BR></FONT></DIV>
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<DIV style="FONT-SIZE: 16px; FONT-FAMILY: tahoma, new york, times, serif; COLOR: rgb(0,0,0); FONT-STYLE: normal; BACKGROUND-COLOR: transparent">I have a two part question,</DIV>
<DIV>Is it beneficial to increase my propeller size to increase efficiency. I was under the impression from my boating days that a large slow prop is more fuel efficient. It should increase battery range and slow down the shaft speed, helping the seal.</DIV>
<DIV>I have a much larger prop left over from boating and I am thinking of using it on Gamma</DIV>
<DIV>The next question is,,, is there anyone here with the ability to calculate the new rpm for my given prop size and motor hp.</DIV>
<DIV>Hank<VAR id=yiv1694287964yui-ie-cursor></VAR><BR></DIV>
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<DIV class=yiv1694287964hr style="FONT-SIZE: 0px; BORDER-TOP: #ccc 1px solid; HEIGHT: 0px; BORDER-RIGHT: #ccc 1px solid; BORDER-BOTTOM: #ccc 1px solid; PADDING-BOTTOM: 0px; PADDING-TOP: 0px; PADDING-LEFT: 0px; MARGIN: 5px 0px; BORDER-LEFT: #ccc 1px solid; LINE-HEIGHT: 0; PADDING-RIGHT: 0px"></DIV><FONT size=2 face=Arial><B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> Jon Wallace <jonw@psubs.org><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> Wednesday, September 4, 2013 6:18:15 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> [PSUBS-MAILIST] There's gold in them-thar waters<BR></FONT></DIV>
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