Mast and boom - rehabbing, finding corrosion and holes
So the mast is down, and I have removed ALL rigging for replacement. Some issues that are cropping up that are giving me pause are related to the stick itself, information appears to be sparse on this topic though.
The galvanic corrosion where dissimilar metals have been in contact has me concerned. I have lots of holes on the mast, both from prior items once installed and long ago removed, and also from stuff I am removing to replace/clean up the mast. I also have some white powder (not much, but some) when I remove some old stainless fasteners from the mast.
My concern is in the masts integrity. It is fairly "thick", but it has a fair amount of old screw holes throughout. I thought about possibly welding the holes in, but read something negative about that (again, regarding corrosion from dissimilar metals - even aluminum on aluminum). My obvious biggest concern is the mast itself deciding one day to fold it up and go swimming.
Can anyone recommend some options on how to go about remedying these holes, and also how to determine of the stick is unsafe for offshore work? My plan as of right now is to fill them in with fiberglass chop, smooth and fair the stick, and paint it with a high quality paint.
All the rigging is to be replaced, so disregard all of the old hardware seen in the pics. It's all being replaced. My hopes are that the mast is stronger than I think it is and can take more abuse than it has taken to date.
Anyone know about aluminum masts and when to consider replacement? How about how to possibly reinforce it somehow?
There are two large plates welded on both sides just below the spreaders (the rust stains are from a non ss washer rotting away on one spreader bolt):
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There are two large plates welded on both sides just below the spreaders (the rust stains are from a non ss washer rotting away on one spreader bolt):
I'm wondering if the spreaders were relocated at some point in time. I can't think of any other reason why 'filler' plates would be needed at that location (both sides, I'm assuming?)
The current spreader attachments look sturdy enough - how are they attached (don't see welds )
Generally mast failures are primarily due to rigging failures, I think it's exceeding rare for a properly supported mast to fail under normal sailing circumstances due to the stick itself.
__________________ ".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
I'm wondering if the spreaders were relocated at some point in time. I can't think of any other reason why 'filler' plates would be needed at that location (both sides, I'm assuming?)
The current spreader attachments look sturdy enough - how are they attached (don't see welds )
Generally mast failures are primarily due to rigging failures, I think it's exceeding rare for a properly supported mast to fail under normal sailing circumstances due to the stick itself.
They are attached by large bolts, they do seem very sturdy (I have stood on them many times, they don't even budge with my weight on them - no flex, no weirdness).
I am hoping all new, professionally fabricated rigging will suffice. My "worst case" is a rollover situation. That's what I am trying to discern - whether or not my mast would survive something like that. I realize there is no way to guarantee anything in a situation like that, but I'd like to mitigate the chances as much as possible of course.
(both sides regarding the plates by the way, probably old spreader points I'd imagine)
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I am not an expert on mast failures. I am going to make a few guesses that are better than nothing. I am thinking that undetected cracks are going to be the reason for failure. I am not counting the situation where the design limits are exceeded by loading the mast by a knock down or collision with a bridge. First off, a mast has to be designed to have some holes drilled in them. People are expected to drill holes for all sorts of attachments. I do not know how big these holes can be before weakening occurs, but there has to be a standard, probably in some book on rigging sailboat masts. I did notice a cut out in the mast for a halyard I think, but this is towards the top of the mast where I am thinking the forces are less. Check around the holes, welded plates, and cut outs for attachments looking for cracks. There is a special dye for aluminum that can be used to detect cracks. This can be with visual light or strong black light depending on the type of dye. The dye is applied by brushing or spraying then wiping off the excess dye and cracks can then be detected by visual inspection. This method can be surprisingly sensitive for detection of imperfections. You could even dye the whole mast.
You also said there was some white deposit, but not much. The question here is how much aluminum is left. If thin, then perhaps a patch could be welded. Obviously you can already see how well a welded patch worked on this mast. Looks like a nice job and I do not see anything that looks like electrolysis from dissimilar aluminum types. I am thinking if the correct type of aluminum plate and welding wire is used with proper welding technique, that a patch is not a problem. So, go looking for cracks and corrosion, see what you find, probably nothing, and then see about possible repairs if there is something. Myself I would ignore screw holes although these could be plugged for esthetic reasons.
Last edited by LakeSuperiorGeezer; 03-08-2011 at 09:41 PM.
As long as the holes are staggered there should be no problem. The lower halyard exits should not all be at the same height but at varying heights for example. I would also look for cracks. When attaching hardware to the mast use TefGel to isolate the dissimilar metals.
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Brian
Living aboard in Victoria Harbour
"So the mast is down, and I have removed ALL rigging for replacement. Some issues that are cropping up that are giving me pause are related to the stick itself, information appears to be sparse on this topic though.
The galvanic corrosion where dissimilar metals have been in contact has me concerned. I have lots of holes on the mast, both from prior items once installed and long ago removed, and also from stuff I am removing to replace/clean up the mast. I also have some white powder (not much, but some) when I remove some old stainless fasteners from the mast.
The white powder is simply oxidized aluminum. It is pretty normal for a stainless fastener to cause this when the threads aren't coated with something when they are installed. The fact that you were able to remove the screws without them shearing off tells me that it's not too bad.
Make sure that every fastener that you use is coated with something like Lanacote or Tuf gel or at least Locktite.
My concern is in the masts integrity. It is fairly "thick", but it has a fair amount of old screw holes throughout. I thought about possibly welding the holes in, but read something negative about that (again, regarding corrosion from dissimilar metals - even aluminum on aluminum). My obvious biggest concern is the mast itself deciding one day to fold it up and go swimming.
Can anyone recommend some options on how to go about remedying these holes, and also how to determine of the stick is unsafe for offshore work? My plan as of right now is to fill them in with fiberglass chop, smooth and fair the stick, and paint it with a high quality paint.
Extra holes are seldom a problem. You can fill them with various products like JB weld (which is nice because is sorta matches the color). You can also just pop aluminum rivets into the holes to close them up.
I would not worry about the integrity of the spar because of the extra holes.
All the rigging is to be replaced, so disregard all of the old hardware seen in the pics. It's all being replaced. My hopes are that the mast is stronger than I think it is and can take more abuse than it has taken to date.
I guess you mean that you are replacing the tangs and bolts. I would also take a really good look at the stainless strap that goes over the mast head and to which the headstay and backstay attach. I have seen these fail.
Anyone know about aluminum masts and when to consider replacement? How about how to possibly reinforce it somehow? "
If there is a reputable rigger in your area, it would be worth paying them for an hours time to do a really good inspection of the stick.
That said, I didn't see anything in the video that really causes me concern except the mast head strap.
As to when to replace the spar. They are usually replaced when they break. I've seen keel stepped mast that were so badly corroded at the base that I had to cut a foot off and we still used it again. Just had to make up a taller step.
Rig failures are usually caused by things like a bad chainplate giving way unexpectedly or neglected rigging that fails. I've can't remember a mast being lost because it failed from having too many holes in it. So I would rest easy.
Check with a good rigger just to be sure though.
My regular racing skipper drills holes in his boat all the time to accomodate gear upgrades and crew requests. He fills the old holes with small, threaded plugs with allen-heads. You can find these in stainless at any decent hardware store.
Just tap the holes, smear the plug with Lanacote and screw it in. In the future, if you ever find that a set of holes lines up with a piece of gear that you want to attach, simply unscrew the plugs and use the holes. The Lanacote will ensure that the stainless doesn't bond to the aluminum mast.
Enough small holes drilled in a concentrated area can affect the integrity of the mast. I doubt you have that problem, but I thought I'd mention it.
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S/V Old Shoes
1973 Pearson 30 #255
Small holes are a bigger problem than large holes because small diameter radii are stress risers. So, your best bet would be to slightly increase the size of the holes. This would also eliminate any stress cracks that are starting.
Small holes are a bigger problem than large holes because small diameter radii are stress risers. So, your best bet would be to slightly increase the size of the holes. This would also eliminate any stress cracks that are starting.
This is true if you are trying to stop an advancing crack by drilling a hole at the end of the crack to distribute the forces. For just a small hole itself, I am thinking there are not enough forces concentrated around the hole to be a problem. Check holes for cracks, maybe that's the reason the hole is there.
Last edited by LakeSuperiorGeezer; 03-09-2011 at 10:47 AM.
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