[PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation

Sat Feb 21 15:26:58 EST 2015

Thanks for the post Alec, with the hours you have had Snoopy in the water, this feedback is important.  

As to Kort nozzle, I designed the part to be machined out of Nylon from my local machine shop.  The shop has finished these parts and I am waiting on him to finish the support hubs as well as a support that screw into the exiting support boss on the MK-101s.   I used a Wageningen ducted propeller series 37 profile as a basis for the design.  I am anxious to get one of these into the water to an do some bollard thrust measurements. I have rewired all the ship systems to accommodate a 36V battery bank and the new MD motor controllers.  Works really nice on the bench.

________________________________
 From: Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
Sent: Saturday, February 21, 2015 12:39 PM
Subject: Re: [PSUBS-MAILIST] Lip Seals - Thruster Pressure compensation

Hi Cliff,

I agree 100% on all you just said. Snoopy uses oil compensation and the seals are in the standard orientation. No leaks until they eventually just wore out after years of use (and were easily replaced). I like your new aluminum piece, that should be good! Where was it you got the kort nozzles again? I have tried three times to contact the guy (George) who makes the Gavin scooter, to buy his nozzles, but have never managed to get hold of him or a response from him.

Thanks,

Alec

On Sat, Feb 21, 2015 at 10:31 AM, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

>
>
>Hank, thanks for posting your experience with this oil leak and your steps to mitigate.  I am interested in this thread as I am in the process of installing four MK-101 as thrusters for the R300.  I have been going back and forth on air vs. oil pressure compensation.   My current preference is oil.   It seems to me that the pressure compensation method you choose impacts the orientation you should choose for the lip seals.  For those of you that have not torn down a MK-101 lower unit, they have a two lip seals on the prop shaft. These seals are oriented such that as the housing is taken deeper, the outboard pressure increases due to ambient water pressure and causes the outer most seal to tighten down on the shaft.  These off the shelf seals can be reversed.  Factory assembly has both with cups facing outward.  These can be reversed and if you want to, you could even mix orientation of the seals.  If you choose air compensation, and plan to keep the
 regulated air pressure 1-2 psi above ambient, then it makes sense to reverse these lip seals as the pressure inside the housing is greater than the pressure outboard.  On the other hand, if you use oil for a pressure compensation, then it makes sense to leave the lip seals as originally oriented.  To me, if the lip seals have cups facings outboard, then a soft flexible external bladder for the oil makes sense so that as the lower unit heats up and oil wants to escape, it easily pushes into the bladder rather than out past the lip seals.  If you had a stiff bladder, then oil would take the path of least resistance and escape past the lip seals as they are not design to see much reverse pressure.  
>
>
>Hank, I might have missed it in one of your post but how are the lip seals oriented in your thrusters and are they MK-101's?  By the description from your post, it sounds like yours are oriented cups facing inward to benefit from a stiffer bladder.
>
>For those of you that have MK lower units, can you comments on lip seal orientation and any issues with seal leaks stiff vs. soft bladders, and small vs large bladders?  Did you stay with the factory orientation of the seals (cups facing outward) or did you reverse them?  Any experience with oil leaks past theses seals? 
>
>
>BTW,  I  have a machine shop working on an anodized T6-6061 aluminum replacement part for the MK101 part that has the external fin and the shaft  seal cavity. The modification I have made is to add material to the inside if this part so that three internal bosses are formed that have female threads.  Into these three holes will be threaded 316 SS support rods to hold the Nylon Kort nozzle.  Originally I was using a weldment consisting of a strap with the three supports to hold the Kort nozzle but  I was having trouble fabricating these accurately enough. I will post a picture of finished thruster with Kort nozzle when I get the parts back.
>
>Cliff
>
> 
> From: Alan James via Personal_Submersibles <personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
>Sent: Friday, February 20, 2015 8:29 PM
>Subject: Re: [PSUBS-MAILIST] calculation
>  
>
>
>That's easy, you shift houses don't you.
>Interesting about the compensation & the lip seal needing pressure.
>Alan
>
>
>
>
> From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
>To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
>Sent: Saturday, February 21, 2015 8:46 AM
>Subject: Re: [PSUBS-MAILIST] calculation
>  
>
>
>Alan,
>I would have to stand my sub up on the nose to do that :-)
>Hank--------------------------------------------
>On Fri, 2/20/15, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
>Subject: Re: [PSUBS-MAILIST] calculation
>To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
>Received: Friday, February 20, 2015, 2:04 PM
>
>Hank,if you
>have the dish there,
 you can pour water in to
>it&
>measure how much water, to get the internal
>volume.But
>you probably knew that already.Alan
>    
>    From: hank pronk via
>Personal_Submersibles
><personal_submersibles at psubs.org>
>
>To:
>personal_submersibles at psubs.org 
>  Sent: Saturday,
>February 21, 2015 5:50 AM
>  Subject:
>[PSUBS-MAILIST] calculation
>  
>
>Can someone calculate the volume of a dish for
>me please.  The dish is 34in dia and 5 in deep.
>Thank you 
>Hank
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>  
>  
>-----Inline Attachment Follows-----
>
>
>
>
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>   
>
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
>   
>_______________________________________________
>Personal_Submersibles mailing list
>Personal_Submersibles at psubs.org
>http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>

_______________________________________________
Personal_Submersibles mailing list
Personal_Submersibles at psubs.org
http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20150221/112477c6/attachment.html>