[PSUBS-MAILIST] Water jets

Sun Oct 26 15:50:58 EDT 2014

One problem I can see is that if you have your Jet suckingwater in from the front & you pivot your outlets to get verticalmotion, then you will get forward movement from the suction ofthe inlet at a similar rate.Also I did a bit of research on jet propulsion a couple of weeks back& what I read said it was inefficient compared to conventional propulsion.Alan
      From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Monday, October 27, 2014 8:11 AM
 Subject: Re: [PSUBS-MAILIST] Water jets

I don't think water jets are necessarily inefficient, but if there is considerable piping around of the water before it exits through the jets, that's what I was referring to. However, even that was not meant as criticism, it is just a normal trade-off. It is surely less efficient than a conventional direct-coupled prop, but you also get entanglement-resistance and maneuverability.  

On Sun, Oct 26, 2014 at 10:11 AM, Marc de Piolenc via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

There is nothing inherently inefficient about waterjets. There are commercial fast ferries using them and getting very good thrust per horsepower - better than any supercavitating propeller could do at the same speed, certainly.

Lousy design will of course produce poor results, and jets are much less amenable to rule-of-thumb construction than open propellers. But whether it is "well known" or not, good design will produce good results.

Marc de Piolenc

On 10/26/2014 8:41 PM, hank pronk via Personal_Submersibles wrote:

Graham,
In the world of marine jet drive it is well known that jet drive takes two times the horse power to do the same job.  Jet drive is well suited to a craft that needs a shallow draft.  I think you will find it very complicated to control and it will be very inefficient. I have been down this road, I love the concept but abandoned it.  If you go forward may I suggest you start with a jet drive.  It is not a simple part to replicate.  The impeller tolerances are critical.  I have a jet unit on the shelf I could donate to your project.  The jet is from a jet ski. I would consider a single rear motor on a full gimbal.
Hank --------------------------------------------
On Sun, 10/26/14, Graham Bayliss via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

  Subject: [PSUBS-MAILIST] (no subject)
  To: "'Personal Submersibles General Discussion'" <personal_submersibles at psubs.org>
  Received: Sunday, October 26, 2014, 7:39 AM

  #yiv9417249292
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  #yiv9417249292  Hi   I am near the end of my build
  of my k350 and have started to look at new designs I am
  interested in building a flyer sub and have come up with a
  design which will include a vectored motor drive this will
  enable my flyer to hover and stop where ever I want. I have
  designed a motor unit which will drive a fan type propeller
  as an intake this will force water to the rear of the unit
   where it is compressed  then it is forced into ducting
  which will take  the water to four nozzles on the side of
  the craft. The nozzles are able to turn three hundred and
  sixty degrees  both side are independent of one another so
  rolls will be achievable. The reason for a vectored motor is
  you only need one motor source and one power pack this will
  ease the maintenance and increase the enjoyment of using
  your sub. I am interested in the clubs thought of this kind
  of design.  Graham

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