[PSUBS-MAILIST] Water jets

Sun Oct 26 15:11:26 EDT 2014

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
>>   #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
>>
>>   -----Inline Attachment Follows-----
>>
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>>
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