[PSUBS-MAILIST] Water jets
Alan James via Personal_Submersibles
personal_submersibles at psubs.org
Mon Oct 27 00:30:27 EDT 2014
Marc,didn't want to have to Google again.Wiki..... Classic prop-drives are generally more efficient and economical at low speeds, up to about 20 knots (37 km/h; 23 mph), but as boat speed increases beyond this, the extra hull resistance generated by struts, rudders, shafts (etc.) means waterjets are more efficient in the 20-50 knot range (up to 90 km/h; 60 mph). Alan
From: Marc de Piolenc via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Monday, October 27, 2014 1:24 PM
Subject: Re: [PSUBS-MAILIST] Water jets
A blythe generalization that is essentially meaningless.
As Pazmany used to say: poot some nombers to it!
Marc
On 10/27/2014 3:50 AM, Alan James via Personal_Submersibles wrote:
> 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
> <mailto: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
> <mailto:personal_submersibles at psubs.org>> wrote:
>
> Subject: [PSUBS-MAILIST] (no subject)
> To: "'Personal Submersibles General Discussion'"
> <personal_submersibles at psubs.__org
> <mailto:personal_submersibles at psubs.org>>
> Received: Sunday, October 26, 2014, 7:39 AM
>
> #yiv9417249292
> #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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