Bent rudder shaft?

[ggray]

I would think it would require a lot more than 500 pounds to permanently bend a 2.5 inch ss shaft with only 16 inches of leverage.

I know it's a pain, you will have to have your boat lifted to drop out the rudder and again to install it.

[Celestialsailor]

Originally Posted by ggray

I would think it would require a lot more than 500 pounds to permanently bend a 2.5 inch ss shaft with only 16 inches of leverage.

I know it's a pain, you will have to have your boat lifted to drop out the rudder and again to install it.

If the rudder was to be scrapped anyways, you could cut it off outside the boat and then drift the rest of the shaft up into the boat.

[Nord Sal]

Originally Posted by ggray

I would think it would require a lot more than 500 pounds to permanently bend a 2.5 inch ss shaft with only 16 inches of leverage.

I ran the numbers quick to see what kind of force it'd take. It's a simple cantilevered beam with a perpendicular load pulling on the end. Using 50,000 psi yield strength (Aqualoy 19), a 2.5 inch diameter shaft (Sect. Mod = 1.53in^3) gives a bending moment of 50,000 psi x 1.53 in^3 = 76,699 inch*lbs for the shaft to yield.

To get that kind of bending moment with a 16-inch lever arm, the applied force would need to be: 76,699 in*lbs /16 in. = 4,794 lbs.

If the shaft is 2" diameter instead of 3", this would drop to a little less than 2,500 lbs for the same length lever arm.

A bit less than I'd have guessed.

CelestialSailor's come-a-long hypothesis seems plausible.

[Celestialsailor]

I was thinking a come-a-long trying to pull the engine in and if it (the engine) was hooked on something, it may have produced that result. I've seen stranger things.

[erie]

Originally Posted by bunnins3

Thanks everyone for your replies. Lots of good options and ideas.

Update: Hauled out the boat and no damage to rudder or skeg below the water line.

Perhaps when installing engine it got hung up and swung into the shaft.
What ever did it it came from the top...

[Dieseldude]

Hard to imagine how a stout stainless steel rudder stock was so bent. Could the hydraulics really exert that much force? Any sign of damage to hydraulics? Seals leaking? Ram mountings weakened? One would expect that hydraulic relief valve would have opened and bypassed pressure before such damage could occur. Do linkages have any medical shock relief built in, or is over load relief reliant on hydraulic relief valve only?



Attacking this would require landing the boat high and dry. Is there sufficient overhead clearance to raise the stock after disconnecting from rudder? If obstructed, is it practical to cut a hole in above structure, and restore after completing work. Might be possible to have a machine shop that is skilled at shaft work straighten the stock. Best to bring them photos and discuss before starting job. Straightness tolerance would need to be determined by experienced steering expert.


Of course, condition of bearings will not be known until stock is removed. May need inspection scope for a good look.




I would check the hydraulic relief valve to insure that it opens at specified pressure. Would not use any data on the valve as reference. Somebody may have fitted an incorrect valve in past. Need the spec's from the boat builder or hydraulic plant supplier. Are the manuals aboard?



Might be a good preventative to fabricate an extra bearing arrangement that would fit just below the top of the shaft. This would shorten free span of shaft, reducing bending moment to shore it up against future stresses. Of course would need to find some structurally sound attachment points close by. Having a fabricator do the job could get expensive. If you have welding and fabrication skills, you can do it quite economically. Would require tacking parts in situ and probably safest to complete welds ashore. If you are not confident in you own welding, perhaps tack it yourself and have a welder lay the beads. A brass single piece bushing should be sufficient. Or possibly a high density plastic material. It will need grease ports and internal grease grooves. A good bearing supplier should be able to find an off the shelf bearing.



Good luck

[robertmfranklin]

Seems like a bit of overkill to me with a great deal of under-info.

Whoah, don't cut anything, just yet!

Looks like with some care the rudder may be extracted from its stuffing box. It is worth a determined effort even if it involves some temporary compromise of the sleeving structure. That damage if it happened could probably be fixed with some glass and epoxy DIY for a lot less than $40,000.

If the shaft bent, it can be bent back. The shaft is not spinning at 1500 RPM, so alignment perfection is not important, just "good enough" will do fine.

Weakness? Probably not because the force of steering is not that great in the circular direction. However, that is an opinion for someone competent in such things. Certainly not me.

Then there is always the possibility of picking up a rudder from a Marine Salvage yard and adapting it to fit.

This looks like a big problem, but it may not be.

[col50]

Originally Posted by Bowdrie

So far, your post has the most merit.
Looking at the pics for a while I'm wondering if the PO originally had the ram and arm mounted up near, or at the top of the shaft.
That tiller arm is really short, indicating a cylinder with a short stroke.
That leads to a very short "throw" from "hard-over to hard-over, and quite acute angles.
In the absence of positive stops, (relying upon the limits of piston stroke,) it is possible to get the rudder in a "dead center" position, where the ram pressure has more effort to push against the shaft instead of turning it.
As if the tiller arm and ram were in a straight line when pressure is applied.
Just thinking out loud,,,

I'm thinking the same thing. If that's what happened, then it might be possible to to straighten the shaft the same way, enough to get it out.

[Martinini]

Find another rudder. Cut the old one at or below the bent part with sawsall. You will have to raise the boat high enough to drop the existing rudder or do what I did and dig a hole under it and drop it into the hole to pull. Save all the parts in case you have to have a fiberglass shop fabricate a new rudder. If you can work with fiberglass you could do it yourself. It's not as hard as you think. But you need the old one for reference. Will need to cut in two to see the internal structure to replicate. Again sounds hard but not really.

[Dieseldude]

Robert and Col50 made good points. The rudder stock moves at low speed. So no need for perfect straightness. The hydraulic ram is free to flex a bit with a slight bend. That's why I suggested experienced steering expertise be consulted about straightness. You might get away with the straightness being out a couple of degrees. If bend extends to bearing supported region, and perfect straightness is desired, perhaps a light cut can be taken off by lathe work after straightening as best as possible. But that would require that bearings and tiller arm bore be compensated for the reduced diameter. Perhaps a bushings would could be fitted in tiller arm, or stock be sleeved. Under size bearings could be fitted. Removing too much material will weaken the stock though. This job seems to require some good marine steering expertise to make some critical judgements.



The cause of the bend ought to be determined. If it was caused by stresses against the rudder, there should be rudder damage, or at least surface marring. If internal, is there any surface deformation visible on the stock? Any scoring, or impact marks? How about the stock linkage? Any cracks or deformation? Is the joint keyed? If so what is the condition of key and key way. Perhaps the stock and linkage should be dye tested for cracks. Had the bearings been seized at one time, causing excessive force to try and turn the stock? Once dismantled, inspection of bearings may give some clues. It is unlikely that this dry end of the stock was weakened due to corrosion.


On a commercial vessel, I saw a stock overhauled by turning down on a lathe to get below corroded region. The stock was resurfaced by welding a continuous layer of weld. This was turned on lathe to restore surface. An expensive job but probably not necessary just to straighten a bend.



As said before, it would be wise to check that the hydraulic relief valve is bypassing at proper pressure to avoid excessive force.

[OneBoatman]

I tend to agree with the CelestialSailor suggestion that the ram actually bent the shaft. It looks as though the rudder post may have been replaced at some time done somewhat on the cheap. The clamp on lever arm doesn't look like anything I've seen on a production boat. There is also witness around the upper bearing/seal at the top of the tube where epoxy or other resin was applied that doesn't look original. The pivot connection where the ram joins the lever arm alos appears loose in the picture. As the other writer comments I see no stops thus if the lever arm assy spun at some time on the shaft it seems probable the ram pressure bent the shaft. For this to have happened the rudder itself's movement would have to be restricted and the autpilot attempting to steer. Such as a hard grounding with the autopilot on, also check the leading edge of the keel at its deepest point for evidence of damage. For fix start by removing the clamp-on steering arm and ram pivot assy and the slide the upper seal up and off. If you are on the hard (and it's not so hard) you will need to get permission to dig a temperary hole in their yard or otherwise pay to lift the boat enough to drop rudder and shaft down. It looks as though you might have to cut off the top the post so be prepared to do this as well but you may get lucky.

[col50]

Originally Posted by Dieseldude

Robert and Col50 made good points. The rudder stock moves at low speed. So no need for perfect straightness. The hydraulic ram is free to flex a bit with a slight bend. That's why I suggested experienced steering expertise be consulted about straightness. You might get away with the straightness being out a couple of degrees. If bend extends to bearing supported region, and perfect straightness is desired, perhaps a light cut can be taken off by lathe work after straightening as best as possible. But that would require that bearings and tiller arm bore be compensated for the reduced diameter. Perhaps a bushings would could be fitted in tiller arm, or stock be sleeved. Under size bearings could be fitted. Removing too much material will weaken the stock though. This job seems to require some good marine steering expertise to make some critical judgements.

The cause of the bend ought to be determined. If it was caused by stresses against the rudder, there should be rudder damage, or at least surface marring. If internal, is there any surface deformation visible on the stock? Any scoring, or impact marks? How about the stock linkage? Any cracks or deformation? Is the joint keyed? If so what is the condition of key and key way. Perhaps the stock and linkage should be dye tested for cracks. Had the bearings been seized at one time, causing excessive force to try and turn the stock? Once dismantled, inspection of bearings may give some clues. It is unlikely that this dry end of the stock was weakened due to corrosion.


On a commercial vessel, I saw a stock overhauled by turning down on a lathe to get below corroded region. The stock was resurfaced by welding a continuous layer of weld. This was turned on lathe to restore surface. An expensive job but probably not necessary just to straighten a bend.



As said before, it would be wise to check that the hydraulic relief valve is bypassing at proper pressure to avoid excessive force.

The rudder shaft (stock) is part off the rudder. There is no way to put that into a lathe.

[Dieseldude]

Originally Posted by col50

The rudder shaft (stock) is part off the rudder. There is no way to put that into a lathe.

Are you sure about that? Rudder stocks that I have seen are a single metal rod that is fixed to the rudder by a fastening arrangement that can be dismantled. We only have inboard photos of this one, no drawings or photos of outside stock and rudder arrangement. If rudder and stock were one integral structure, initial fitment would be quite difficult.

[billcrowley]

Foss Foam makes replacement rudders for popular sailboat models. Not sure if your Cooper 416 falls into that category - but it wouldn’t hurt to ask them if they can help you. Last time I checked with them (5 years ago) a replacement rudder for our Newport 30 was $1500.

[col50]

Originally Posted by Dieseldude

Are you sure about that? Rudder stocks that I have seen are a single metal rod that is fixed to the rudder by a fastening arrangement that can be dismantled. We only have inboard photos of this one, no drawings or photos of outside stock and rudder arrangement. If rudder and stock were one integral structure, initial fitment would be quite difficult.

Yes I am sure about that. Removal of the rudder on this boat is done by removing the bearing (support) at the bottom of the skeg. Look at the drawings on page one of this discussion and it will make sense.