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Old 08-04-2014, 09:46   #1
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Filling Void in Rudder Shaft

The top half of my stainless steel rudder shaft, above the waterline, is hollow and collects condensation inside throughout the year. Is there a benefit to filling this void with pourable foam to prevent the collection of water? Would there be any detrimental effect in doing this?
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Old 08-04-2014, 11:53   #2
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Re: Filling Void in Rudder Shaft

Can you drill a small hole where the tube meets solid to let the water out? Can you cap it so that nothing gets in? I wouldn't fill it with foam due to the possibility of poultice corrosion. It is an interesting rudder stock design - is there a weld where the two types meet?

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Old 08-04-2014, 12:02   #3
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Re: Filling Void in Rudder Shaft

any foam that is not totally solid will only collect water or dampness and encourage the SS to corrode and break. It doesnt sound like a good situation as is though either. SS + enclosed water= failure. Drilling a hole at the joint betwen solid and hollow is a good idea, but also putting a stress riser at the highest stressed part of the assembly. Do you know if the tube is welded to the solid? that is an even worse situation. Is the bottom really solid or did they fill it with resin? Why would they do this? to save a few pounds for racing?
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Old 08-04-2014, 12:09   #4
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Re: Filling Void in Rudder Shaft

I am not sure drilling a hole in a rudder shaft even if it is above the water is a good idea. Know anyone with a lathe? a piece of nylon machined to an interference fit would be good once it is dry inside.

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Old 08-04-2014, 12:20   #5
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Re: Filling Void in Rudder Shaft

Just building my rudders now. The bottom is plugged with resin and was going to plug the top as well.
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Old 08-04-2014, 14:22   #6
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Re: Filling Void in Rudder Shaft

Many rudder shafts have a hole or two in them for quadrant and tiller arm mounting - no problems with that at all. A small round hole should not be a stress riser any more than a keyway.

Walking around the boatyard here, I see many rudders off boats and almost all of them have a hole in their shafts. Even the tube ones.

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Old 08-04-2014, 15:38   #7
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Re: Filling Void in Rudder Shaft

Thanks everyone for the pointed responses. Perhaps I didn't explain the construction of my rudder shaft properly. The shaft is a hollow stainless steel tube with the bottom half (inside the rudder) filled with resin and/or foam. I cannot determine what they used when it was originally constructed. The top half of the shaft (inside the boat) is hollow. There is no leaking in the rudder shaft. It is dry and rust free. The water inside is caused by condensation from two air columns inside and outside the shaft. It is not filled with water, but some does collect in the bottom. The shaft is drilled for a through bolt that connects the quadrant collar to the shaft. At the top of the rudder shaft(inside) are two welded bars perpendicular to the shaft where the slot for the emergency rudder is mounted. It is my understanding that when they make rudders today, the builder fills the entire rudder shaft with 20 lb. pourable foam. This is what they do at Foss Foam on their new rudder construction. Ergo, what negative impact could occur if I filled the top half of the rudder stock (below the weldments for the emergency rudder) with the pourable foam to eliminate the collection of moisture? I am in the final stages of a rebuild and want to address all relevant issues before I reassemble/re-install my rudder in the Spring. Also, isn't poulstice corrosion only on aluminum? Would this also effect stainless steel? All comments will be greatly appreciated.
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Old 08-04-2014, 16:12   #8
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Re: Filling Void in Rudder Shaft

Hi rog

Is the condensation causing corrosion in the hollow is that's the worry ? or is it that the condensation is causing damp around the area ( rudder position sensor etc ) that you are trying to protect.
I would be more worried about making things difficult for future removal / repair with foam everywhere, from what I understand, stainless is more corrosion resistant open to the air rather than being incapsultated , but I am no expert , just spouting my thoughts these pics May point to where I am coming from Click image for larger version

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Old 08-04-2014, 16:29   #9
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Re: Filling Void in Rudder Shaft

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Originally Posted by Hoofsmit View Post
Hi rog

Is the condensation causing corrosion in the hollow is that's the worry ? or is it that the condensation is causing damp around the area ( rudder position sensor etc ) that you are trying to protect.
I would be more worried about making things difficult for future removal / repair with foam everywhere, from what I understand, stainless is more corrosion resistant open to the air rather than being incapsultated , but I am no expert , just spouting my thoughts these pics May point to where I am coming from Attachment 79022Attachment 79023

Hoofsmit,
There is no corrosion in the interior/exterior of the shaft. There has never been any water in the rudder. However, I am trying to cover all my bases while the rudder is out of the boat and under rebuild. I suppose the idea of a small amount of standing water inside the hollow SS shaft is my concern and my question is should this really be a concern or am I shooting pink pigeons?
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Old 08-04-2014, 17:03   #10
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Re: Filling Void in Rudder Shaft

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Originally Posted by colemj View Post
Many rudder shafts have a hole or two in them for quadrant and tiller arm mounting - no problems with that at all. A small round hole should not be a stress riser any more than a keyway.

Walking around the boatyard here, I see many rudders off boats and almost all of them have a hole in their shafts. Even the tube ones.

Mark
Yeah, all mine have been solid shaft, and Ive seen those broken, snapped right off... who'da thunk it?. I'm kinda wary of tubular ones in the first place, but I thought he had a solid shaft joined to a tubular shaft (or line drilled) and if the hole was right at that interface, near the hull exit... seems like the highest stress place in the first place. It sounds now like it's completely hollow.
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Old 08-04-2014, 17:48   #11
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Re: Filling Void in Rudder Shaft

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Originally Posted by rognvald View Post
Hoofsmit,
There is no corrosion in the interior/exterior of the shaft. There has never been any water in the rudder. However, I am trying to cover all my bases while the rudder is out of the boat and under rebuild. I suppose the idea of a small amount of standing water inside the hollow SS shaft is my concern and my question is should this really be a concern or am I shooting pink pigeons?
So are you sure that the shaft is hollow?or Is it bored a few inches in to allow various designs of emergency tiller to be fitted?

The one in my pics was solid but bored, I think the stainless May we'll be heat treated after welding the cross members that are in the foil as well as any additional quadrant fittings to de -stress any heat induced weakening when manufactured
I personally would not worry about condensation having an affect on the shaft, but as I say I am no expert,
others on cf have loads more experience than me,
I have worked with metals most of my life and know drilling holes is not going to strengthen a shaft with laterial stress as it's function and non uniform cooling needs to be annealed to create tensile strength
I think the pink pigeon was in dick dastidles cartoon ?
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Old 08-04-2014, 17:48   #12
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Re: Filling Void in Rudder Shaft

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Originally Posted by Cheechako View Post
Yeah, all mine have been solid shaft, and Ive seen those broken, snapped right off... who'da thunk it?. I'm kinda wary of tubular ones in the first place, but I thought he had a solid shaft joined to a tubular shaft (or line drilled) and if the hole was right at that interface, near the hull exit... seems like the highest stress place in the first place. It sounds now like it's completely hollow.


Cheechako,
How would you weld a solid shaft(bottom) to a tubular shaft(top)? I would imagine a builder would use either a solid or tubular shaft since a weldment would provide no structural integrity and be a candidate for crevice corrosion and/or structural failure . . . especially on a rudder shaft with its high torsional loads. I would imagine mine is tubular(weight saving for a performance cruiser) with either epoxy or expandable hi-density foam as is the one BoatGuy is building. This is also the way they are built at Foss Foam. What do you think?
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Old 08-04-2014, 17:56   #13
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Re: Filling Void in Rudder Shaft

Fresh water condensation is not going to cause the crevice corrosion you are concerned with.
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Old 08-04-2014, 17:56   #14
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Re: Filling Void in Rudder Shaft

I dont think they would weld it... too much $ for boat builders! However... it seems like I have seen one with a circumferential weld on it. Maybe a repair? Anyone else seen one?
If it is dry inside, I guess it might be best to leave it, at least it can "breathe". Anything you fill it with, epoxy , plugs etc have the potential to not fit completely water tight (shrinkage etc) and then you have created a problem.
One type of rapid corrosion in SS is from oxygen depletion. I dont think it matters if from Salt or fresh water(?), although salt has other things that aid the corrosive process.
anyone ever have a fresh water tank leak?
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Old 08-04-2014, 18:14   #15
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Re: Filling Void in Rudder Shaft

If you wanna go top shelf, leave out the foam and pour it with Chockfast Orange.
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