Re: [PSUBS-MAILIST] Through Hulls

[jbarlow@bjservices.ca]

     I believe that an excellent bushing choice is an I-Glide bushing from
igus.  It is a polymer bush and so insulates the shaft from the housing
mitigating the .  It is also self lubricating and also is excellent for use
in water environments.  They also make thrust bushings but you mould have
to check the loading as they may not have enough capacity for a main prop
thrust bearing.

www.igus.com

I have used T-500 and M-250 bushings both types in water and sea water
environments successfully.
 They also make spherical self aligning bushings which may help alleviate
some problems.

Again you have to weigh the advantages and disadvantages of any systems as
Gary suggests.  Any method has its own disadvantages.

For instance the manual method of moving Vindicator's weight would have the
disadvantage of being much slower than a hydraulic method.

Jay.

The will ship you free samples of their product from the web site, perhaps
also satisfying STORM's (and mine) requirements.


Jay.






|--------+------------------------------------->
|        |          "Gary R. Boucher"          |
|        |          <engineer@sport.rr.com>    |
|        |          Sent by:                   |
|        |          owner-personal_submersibles|
|        |          @psubs.org                 |
|        |                                     |
|        |                                     |
|        |          21/11/2002 08:35 AM        |
|        |          Please respond to          |
|        |          personal_submersibles      |
|        |                                     |
|--------+------------------------------------->
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  |                                                                                                                                            |
  |      To:     personal_submersibles@psubs.org                                                                                               |
  |      cc:                                                                                                                                   |
  |      Subject:     Re: [PSUBS-MAILIST] Through Hulls                                                                                        |
  >--------------------------------------------------------------------------------------------------------------------------------------------|




At 08:00 AM 11/21/2002, you wrote:
>And Gary    Although I'm not propelling my sub with a through hull
>shaft, I can't see the complexities of a straight shaft design.  It
>seems that a good face seal, with maybe a backup seal as a safety
>measure, would be simple, cheep and safe.

Thru-hull shafts are a viable approach.  But, you will have some
engineering problems to overcome.  Much of this depends on your design.  Do

you have ballast tanks located where they shaft will have to run?  If the
shaft is of low diameter and/or runs over a foot or so, you will have to
use some form of shaft support.  This support will probably be required
both inside and outside the hull.  Allowing the shaft to go through the
seals at an angle other than 90 deg can cause problems.  Outside shaft
supports will almost assuredly have to be employed.  These supports must
include bearings of some type which must be protected against corrosive
elements while remaining lubricated.  Many propeller shafts are stainless
steel.  Many bearings or bushings are not.  This can cause dissimilar metal

problems in the water electrolyte.  Since propellers generate thrust, this
thrust must pass up the shaft where it can be loaded into the hull.  This
will require a thrust bearing of some type.  If the thrust bearing is
placed close to the propeller it will probably be in the water and must
conform to the requirements stated above.
     All of these supports, bearings, and seals will have to be nearly
perfect in their alignment.  That means that the motor will also have to
have its shaft in direct alignment or else a flexible coupling or U-joint
will have to be used to couple the motor to the shaft.  Shaft alignment
will probably require adjustment points at all support locations.  The
shaft will probably pass through the hull at an angle other than 90
degrees.  This may require a design effort to make sure that the shaft
passes through the seals correctly.
     If the motor is located far to the aft end of the sub, you may have
access problems.
     If you find that the line of thrust is above or below the center of
drag of your boat, too bad.  No adjustment is possible as with hydraulic
motors (in my case) or motor pods that can be raised or lowered.  This is
not a major problem in general but may require a small adjustment in planes

or ballast weight at full speed as compared to being stationary in the
water.
     Any approach to solving propulsion has advantages and
disadvantages.  Weigh them all carefully.  I did not list the advantages
but most of these are obvious.

I hope this answered your question.

Gary Boucher


>   My sub is using motor pods
>with HP shaft seals and are not pressure compensated.  I have three
>motor pods, each with a shaft seal.  I like this design but do think
>that one straight shaft would have been much easier and just as safe
>although not offering the same control.  Why is a straight shaft
>something to be avoided?  Your thoughts please.
>
>Thanks guys,
>Dan H.