[PSUBS-MAILIST] prop size

[greg cottrell]

Hank,
 
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.
 
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. 
 
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).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.
 
Greg
 
 
 
 


________________________________
From: hank pronk <hanker_20032000 at yahoo.ca>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Wednesday, September 4, 2013 6:58 PM
Subject: [PSUBS-MAILIST] prop size





I have a two part question,
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.
I have a much larger prop left over from boating and I am thinking of using it on Gamma
The next question is,,, is there anyone here with the ability to calculate the new rpm for my given prop size and motor hp.
Hank


________________________________
From: Jon Wallace <jonw at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Wednesday, September 4, 2013 6:18:15 AM
Subject: [PSUBS-MAILIST] There's gold in them-thar waters



http://www.usatoday.com/story/news/nation/2013/09/03/florida-family-gold/2757357/
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