Coupling for split Rudder Post
 

I'm planning to add a third bearing on deck for my skeg rudder post,
whcih means I have to make it in two pieces so that I can have
clearance to remove the rudder without elevating the boat. Is there a
prefered method for making a coupling for a 2-piece rudder stock (i.e
splined sleeve), or is there another solution to the problem of
removing a very long rudder post? (rudder stock is solid 1 1/4" ss).

Thank You, jimthom

Coupling for split Rudder Post
 

I have seen split rudder posts on commercial and fish boats before, where a
flange type shaft coupling is used. This would be much stronger than using a
keyed or splined shaft coupling i would imagine. I'd consult with a NA to find
out what the proper sizing would be.

I'm planning to add a third bearing on deck for my skeg rudder post,
whcih means I have to make it in two pieces so that I can have
clearance to remove the rudder without elevating the boat


Jared Crane

Coupling for split Rudder Post
 

"jimthom" wrote in message
om...
splined sleeve), or is there another solution to the problem of
removing a very long rudder post? (rudder stock is solid 1 1/4" ss).


You don't say if you are wheel or tiller steering.. A two piece rudder would
tend loosen up from constant torsion with a tiller or quadrant above the
shaft coupling.

A coupling would work but in addtion to the splines or key, your coupling
should be split so that several bolt will apply camping force around the
shaft.

Also there should be a bolt going through both the upper and lower so the
weight of the rudder doesn't pull it out of the coupling. This can
accomplished by the clamping bolts passing through a notches in the side of
the shaft.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions

Coupling for split Rudder Post
 

Thank you for your views. I will have a steering quardrant for
hydraulic steering (wheel inside) below the coupling (with a shunt
valve) and tiller in the cockpit. The lower skeg bearing will prevent
the rudderpost from exiting the coupling and the bottom of the hull. I
can't use a flange for the coupling since I will need to cut it off to
remove the rudder post from the stuffing box, but you have givin me
some food for thought - Thank You
jimthom


"Steve" wrote in message ...
"jimthom" wrote in message
om...
splined sleeve), or is there another solution to the problem of
removing a very long rudder post? (rudder stock is solid 1 1/4" ss).


You don't say if you are wheel or tiller steering.. A two piece rudder would
tend loosen up from constant torsion with a tiller or quadrant above the
shaft coupling.

A coupling would work but in addtion to the splines or key, your coupling
should be split so that several bolt will apply camping force around the
shaft.

Also there should be a bolt going through both the upper and lower so the
weight of the rudder doesn't pull it out of the coupling. This can
accomplished by the clamping bolts passing through a notches in the side of
the shaft.

Coupling for split Rudder Post
 

Jim
It's a little hard to imagine this from the words, ( I'm a scribble it on
the floor person ... ) but I can't see why a coupling would not work. I
think you have a rudder on a shaft which has a lower ( skeg ) bearing and an
upper ( stuffing box ) bearing. The steering quadrant is above the stuffing
box, and there will be some shaft free above the quadrant. So the shaft is
stiff enough to take the steering forces on the overhung section above the
stuffing box.. You need the upper bearing because the extended shaft is not
stiff enough to take the forces from the tiller as an overhung load.

If you mount one half of a standard engineering type split coupling to the
protruding shaft, and the other half of the coupling has the bottom of the
"extension " shaft --- the top end of the "extension " shaft goes through
the upper bearing. And the tiller connects somehow to the extension
shaft - I'm assuming above the upper bearing.

I'm assuming this is all done with standard shafting, with torque
transmitted by keys in keyways, and the couplings held in place by locking
screws.

So to remove everything, you disconnect the tiller and it's attachment,
loosen the collar on the upper bearing, ( the one which stops the shaft from
riding up, because the keyway locking screws won't ) loosen the locking
screws on the upper half coupling key, and the shaft just pulls straight up.
Then loosen the locking screws on the lower half coupling, and pull the
coupling off the lower shaft. I can't comment on how the rest of the stuff
goes, but it should be along the same lines.

I've left out the bits about everything being corroded together, dropping
keys and screws into the bilges, and getting nickel anti-seize all over
everything ... but it's a boat, right?

I would probably use a split coupling if I had the space, because if the
coupling halves are stuck to their respective shafts, you can use a bearing
puller to help remove the coupling. You could use a one-off split coupling,
but it's going to be dearer because you will have to design it and have it
machined. But if nicely designed the keys will be captive in both the
coupling and shafting, so there is no need for locking collar on the upper
bearing........

Now someone who really knows what they are doing can tell me where I'm
wrong. The above is how I'd do it industrially, it's not necessarily going
to translate to the boat situation.

Regards
David

"jimthom" wrote in message
om...
Thank you for your views. I will have a steering quardrant for
hydraulic steering (wheel inside) below the coupling (with a shunt
valve) and tiller in the cockpit. The lower skeg bearing will prevent
the rudderpost from exiting the coupling and the bottom of the hull. I
can't use a flange for the coupling since I will need to cut it off to
remove the rudder post from the stuffing box, but you have givin me
some food for thought - Thank You
jimthom


"Steve" wrote in message
...
"jimthom" wrote in message
om...
splined sleeve), or is there another solution to the problem of
removing a very long rudder post? (rudder stock is solid 1 1/4" ss).


You don't say if you are wheel or tiller steering.. A two piece rudder
would
tend loosen up from constant torsion with a tiller or quadrant above the
shaft coupling.

A coupling would work but in addtion to the splines or key, your
coupling
should be split so that several bolt will apply camping force around the
shaft.

Also there should be a bolt going through both the upper and lower so
the
weight of the rudder doesn't pull it out of the coupling. This can
accomplished by the clamping bolts passing through a notches in the side
of
the shaft.

Coupling for split Rudder Post
 

"David Flew" wrote in message
...
Now someone who really knows what they are doing can tell me where I'm
wrong. The above is how I'd do it industrially, it's not necessarily
going
to translate to the boat situation.

All sounds good, until I get to the set screw.. I'm from the old school of
belt and suspenders, I don't trust set scews in prop shafts or rudder posts.
If anything will come loose it will when you steering with the tiller in an
emergency situation.

I'll restate my recommendations to use the clamping bolts in a coupling that
is split lengthwise, one side only. Then these clamp bolts pass through the
very edge of the coupling bore and once the coupling is fitted to the shaft,
you pass a drill bit, then reamer, through the bolt hole and it cuts a notch
in the shaft. So the clamping force of the bolts prevent any rotation
movement while the bolt notch prevents the coupling from pulling off.. A set
screw would just walk up the shaft, over time and under alternate tiller
torque.

Regarding the coupling. These should be purchased blank and let them machine
shop bore them and broach the key way to suit the shaft. This way you get a
very acturate bore and key fit while you also can have the shop mill and
drill for the tiller head fitting.. He can also drill/ream for the clamping
bolts and this would then be a 'registered fit' so your assembly will always
be exactly in line with the rudder blade.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions

Coupling for split Rudder Post
 

"jimthom" wrote in message
om...
Thanks again for your ideas.

The problem is really what type of coupling to use to resist the
torque forces of the tiller. If I could use flanges, the total
x-section area of the bolts that hold the flanges together should be
the equivalent to the x-section area of the rudder post, so there is
the potential for a lot of torque. As you said, splines may losen and

Uh I don't think so. The polar moment of inertia should be the same
shouldn't it rather than cross sectional area?

So a few little bolts on a very large diameter flange would have the same J
as a rudder stock that is very close to centerline.


--
Evan Gatehouse

you'll have to rewrite my email address to get to me
ceilydh AT 3web dot net
(fools the spammers)

Coupling for split Rudder Post
 

Thanks again for your ideas.

The problem is really what type of coupling to use to resist the
torque forces of the tiller. If I could use flanges, the total
x-section area of the bolts that hold the flanges together should be
the equivalent to the x-section area of the rudder post, so there is
the potential for a lot of torque. As you said, splines may losen and
wear, set screws may wonder, and even the bolting method that you
describe may not be stong enough. Once a little movement occurs there
is accelerated wear and eventual failure.

I did a search for mechanical couplings and found a wealth of
resources; now it is a matter of sifting through them to see what I
can come up with. There is even have one device that resists torque
forces by heat-shrinking the coupling to the shaft!

Cheers, Jim

Coupling for split Rudder Post
 

PS Steve, I missed the bit about the keyway on my original reading of
your post when you describe the coupling device; this looks promising.
Cheers

Coupling for split Rudder Post
 

"jimthom" wrote in message
om...
Thanks again for your ideas.

can come up with. There is even have one device that resists torque
forces by heat-shrinking the coupling to the shaft!


I would recommend against heat shrinking the coupling on since your whole
objective is to be able to drop the rudder. Usually a heat shrink can only
be removed with a hylraulic press or a lot of heat.

If you looking at flanged couplings, then just get a propellor shaft ridgid
coupling. In these the bolt a fitted and you won't have any problem with
torque movement.

Steve
s/v Good Intentions