mast repairs

Taking off the mast of an old boat this is what we found, a lot of corrosion at the partners and at the step.
The step doesn't look so bad, but at the partners corrosion and a couple of 1/2 " holes are pretty scary ....
What would be the best way ti fix this??

 

My first thought is to replace it, that is some pretty rough looking corrosion. Secondly you could cut out the corroded section, and fit an internal sleeve in the mast, or add an external sleeve.

There are some people on here who know a lot more about mast repairs than I do so I would hold off until they respond.

 

I'm assuming from your piccies that it is an aluminium mast.

That said, don't repair it. Replace it.

The mast would be a 6000 series extrusion. Once you weld it you've lost half your strength. Once in a sea spray environment and when taking fatigue into account you can loose as much as 90% of its static yield/proof stress.

Unless you're willing to perform structural calculations to satisfy yourself that the structural integrity of the mast in bending and buckling is not compromised post repair, i would replace it. No question.

 

unfortunately replacement is not an option due to cost and location ..i'm in costa rica so even if i could find a deal for a second hand mast .. transport to here would be too expensive anyway.
And welding aluminum is not a good ....
I like the idea of the internal or external sleeve after cutting off the damaged area......
but I would like to hear more opinions on this ......

 

It looks like the amount of removal would be extensive.

You would need to find a sleeve that is a perfect tight fight internally and then additionally another, over the affected region. Then to rivet or mono bolt the two together. This is not as easy as it sounds. You also need to ensure that the rivets and plate thickness can transmit the same or better loads as the original. I would strongly urge you to consider getting a NA to look at the size/thickness of plate and also size number off rivets.

You also need to take into consideration that aluminium does not like being against bare aluminium, this is also another source of corrosion, thus you need to protect both surfaces prior to attempting this method.

Finally, I would add that this is only a temporary repair and should not be considered as permanent. At some stage you must replace the mast. Otherwise a bodged or cheap repair will seriously affect the performance of the mast further than it already has been by the removal of sections of the mast.

 

Wow, that is a challenge. I think if it was mine I would cut off the bottom and live with a shorter mast. the other alternative is to sand blast off all the corrosion and than weld on a doubler over the whole area. You would have to form it to fit tight against the shape of the mast.

After it is back together I would also apply corrosion inhibiting compound regularly like LPS or Corrosion-X. It is used in AL aircraft to prevent corrosion on the think lightweight structures.

IT might be possible to add a heavy doubler without welding, using blind fasteners ("pop" rivets) or sheet metal screws, but unless it is all sealed up with sealant between the surfaces it will only create more places to trap moisture and it will corrode away again.

 

yes I know it is going to be temporary, but by now it is the only option ...
now i understand the repair at the partners with the internal/external sleeve ...
what about the bottom?
corrosion there is not very deep ... and there is a sort of plug that i've been trying to remove but it looks frozen ...
any suggestion on how to remove it and check the interior?
should i also use the double in/out sleeve there?

 

The corrosion looks bad. sleave and repair is possible but not ideal.

Perhaps you could chop off the tube at the partners, then re engineer for a deck stepped mast ?

Is there corrosion under the main boom goose neck ? Spreader roots ?

How big is the boat ? Nothing wrong with a wooden box or birdsmouth mast .

in central American you have suitable woods.

 

try soaking the frozen parts with Automatic Transmission Fluid (AFT), the stuff used in automobile transmissions. It is a powerful penetrate and detergent, as well as a lubricant. Soak it for a few days repeatedly, heat gently with heat gun to warm the outer sleeve (makes it larger) and than you should be able to knock it off with a large mallet (repeated small blows should break it loose). That is presuming there is no welding, fastness or adhesive holding it place. The mild heat should soften adhesive if there is any.

I have done this on many corroded parts on both old cars and boats, works amazingly well.

Good luck.

 

I'm not sure of the laminating schedule necessary, but you might consider a composite repair. I'm sure you could wrap it with carbon fiber, say 1 meter in each direction and vacuum bag it to achieve a layup as thick of carbon as the aluminum extrusion and it would be very strong at that point. I'm not sure how it would handle compression, but it might get you to a place where you can have the mast replaced. And it's something that can be done with relatively limited tooling.

Good luck.

Edit: maybe not vacuum bag. Would be hard if not impossible to do on a mast due to the bolt rope slot. So possibly wrap in an elastic material with holes to allow the excess to seep out like they do for home-built custom carbon bicycles.

 

A quiet word: IF you're considering a patch up job using composites, do not, do not, lay carbon directly onto the alloy - you'll have another rat gnawing problem otherwise ... from electrolysis - grind rough/smooth, lay glass, then carbon. The perfectionists will be horrified.
We did this to an eaten away alloy mast for a Piver Nugget trimaran; it has lasted near 20 years.

 

It doesn't look all that bad. Do an external doubler riveted and glued for the area at the spreaders. The bottom doesn't look as badly corroded but it's easy to do the same there. If you want to get that plug out of the bottom likely you'll have to cut it out. Drill the biggest hole you can through it then saw cut out to the mast wall, tap chunks into the mast until you can pull the rest out.

 

Yes, the spreaders holes will also have to be insulated by an enlarged area of hard epoxy (glue mix and cut glass), no carbon or the same troubles will reoccur, then drill. Any carbon to metal anywhere is a no, no, imo.
I've just remembered, we didn't even use uni directional carbon, just uni glass tows then finished with box weave glass - and that was 25 years ago, couldn't get carbon in those days. Here's the boat, Marguerite Star.
But the same was done to the tuned up Crowther B24 here, but using glass/carbon; that job is also a couple of decades old.

 

I'd look at the step. I might consider raising the height of the step by making a slope-sided shape out of solid wood and glass. The new raised flat-top step would allow a few inches of height to be cut from anywhere on the mast such as the partners area and/or the heel. It might be necessary to replace the heel casting and the appropriate sleeve for the partner area, which you could have shipped to you.
To have to modify the mast to make it shorter above the deck would require a lot of drilling and refastening and would be quite a lot of work, which you might want to avoid.

 

I like this idea of composite repair
no bolt rope slot on this mast, so no problem for the laminations and vacuum bagging. ...
this idea suonds interesting ....also because i can taper the repair and avoid a hard spot.