[PSUBS-MAILIST] Drive shaft alignment & sopport.

["Walter Starck" <wstarck@ozemail.com.au>]

Every inboard power boat from tiny dories to supertankers faces the
drive shaft problem.  Alignment is normally achieved by adjustable
engine mounts or with  brass shims using a feeler gage at the shaft to
motor coupling to measure alignment.  The coupling is disconnected and
the gauge used to measure alignment adjustment until it is even between
the two faces at all points.

In a low power applications such as a Psub it's even easier.  You can
simply set up the motor mount with reasonably close alignment and use a
self aligning coupling to eliminate the need for fine adjustment.  These
couplings are typically of rubber and since exact alignment of the motor
is unnecessary it can also be mounted on rubber shocks.  This approach
makes for much quieter operation..

The outer propeller shaft bearing is normally water lubricated and of
rubber, composite material or lignum vitae wood.  The inboard end of the
shaft can use a conventional thrust bearing.

Dive scooters have solved all these problems for depths up to several
hundred feet with thrust comparable to trolling motors.

If you enjoy problems and complicated expensive solutions complete with
all sorts of reasons why what works in practice is no good in theory and
should be ignored consult an engineer..  They can  solve problems that
don't even exist and create new ones no one else has encountered before.

The essence of elegance is simplicity.

Walter Starck
Golden Dolphin Video CD Magazine
The premiere publication of diving and the ocean world.
www.goldendolphin.com





----- Original Message -----
From: "Dan h" <machine@epix.net>
To: <personal_submersibles@psubs.org>
Sent: Friday, November 22, 2002 1:20 PM
Subject: Re: [PSUBS-MAILIST] Through Hulls


> Gary
>
> I've heard several people say that straight shaft drives with the
motor located
> inside the hull wasn't a good way to go but none ever said why.
Alignment could
> be a problem, I guess, but with sound planning that could be dealt
with.  The
> need for bearings in sea water is an issue I didn't consider but as
Jay points
> out, a non metallic bushing could be used on the prop side of the
seal.  True,
> thrust would be transmitted through the shaft but a properly sized
ball bearing
> flange block inside the hull would be adequate to carry that load.
>
> I guess it mainly boils down to how a straight shaft fits your hull
design and do
> you want a fixed prop and a rudder or a prop that is directional.
>
> Thanks for the explanation.
> Dan H.
>
> "Gary R. Boucher" wrote:
>
> > 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.
>
>