[PSUBS-MAILIST] prop size

[Smyth, Alec]

Hank,

Although the calculations are in the propeller handbook and easy to do, there are significant guesstimates in them due things like the drag of your hull form being unknown.  You have an unusual advantage in that your sub is the first of a family that are, I think, all quite similar in shape and size. I'm not sure; I say that just based on seeing photos. They've been running around for so many years, I expect you would not be far off the mark if you could find out what prop and reduction is being used on the current Nektons.

Best,

Alec

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org] On Behalf Of hank pronk
Sent: Thursday, September 05, 2013 8:44 AM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] prop size

Hi Greg,
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.

From: greg cottrell <jgcottrell2002 at yahoo.com<mailto:jgcottrell2002 at yahoo.com>>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org<mailto:personal_submersibles at psubs.org>>
Sent: Thursday, September 5, 2013 6:20:01 AM
Subject: Re: [PSUBS-MAILIST] prop size

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<mailto:hanker_20032000 at yahoo.ca>>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org<mailto: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<mailto:jonw at psubs.org>>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org<mailto: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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