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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
"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 |
Coupling for split Rudder Post
Jim
The torque forces from the tiller are pretty low in engineering terms. You don't have to match the strength of the shaft, you only have to match the torque the tiller and the person on the other end can develop. And you can only pull so much before you fall over ... You can develop much more torque from a wheel because of pulley ratios, also because you can pull a spoke up wit ha lot more force than you can pull a tiller sideways. Don't know how long your tiller is going to be, or it's dimensions, but I'd bet any coupling that looked like it was big enough would be plenty oversized when looked at in engineering terms. Whist I am with Steve in that screws have their issues, it's possible to design them out. There is a thing called a Ringfedder ( or something similar) coupling which requires no keyway in either shaft, and will take all the torque and end loads you could possibly throw at it with a person on the end of a couple of feet of wood. They are not cheap, but neither is one-off machining of a split coupling if you have to pay for it. I had one made recently to replace my engine to output shaft coupling, the "real"price was around $600 Aust. It cost me about half that, but there was no material or profit margin in that figure. I'd try to work out the loads and shaft sizes, and then start talking to someone in industrial transmission supplies. If you can figure out how to do it with a commercially made item, you will have some guarantee that it's appropriately sized. I'm not a mechanical engineer so I won't do the calcs for you, but I know the principles and can point you to some relevant suppliers in Melbourne. David Flew "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 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
On Wed, 14 Apr 2004 10:06:21 -0700, "Evan Gatehouse"
wrote: "jimthom" wrote in message . com... 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 Evan's point should not be hard to grasp in the context of a tiller/rudder post. A determined push from Jimthom's hand on a three foot tiller could wring off a one inch rudder post entirely. Think of it as a 3 foot wrench on a big bolt. Ah, the power of the lever. But in this thread, the traditional fixing for the bicycle crank keeps coming to mind. The old-fashioned pedal crank fixing seems to have no trouble handling a repetitious, cyclic load of up to 240 pounds at an arm of 10 inches, 60 rpm for 20 years plus on a 3/4 inch shaft. All done with smooth round holes, and a single flat worked on the shaft..... The cotter bolt is what works the magic: its tapered flat of less than 1/12 slope will hold the shaft tight, even without its fixing nut and lock washer.... Brian Whatcott Altus OK |
Coupling for split Rudder Post
Thanks for your offer, David. I'm confident that yours and other
contributors to this thread have put the problem in perspective for me and I can go forward from here. Cheers, jimthom |
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