Aluminium mast corrosion fixes

[andyj301]

I removed a stainless fitting (whisker pole attachment) from near the base of my mast, revealing some worrying corrosion.

Thumb for scale.

It's worse that it looks, I can feel deformation on the inside of the mast.

Could this have a plate or collar welded or are there any other fixes?

 

[William_H]

The corrosion area will be near the bottom of the mast. Not an area of real stress (concern) unlike areas between the cap shrouds and intermediate shrouds or between intermediate and base. The stress will be one of mostly compression where you are concerned. (under the snotter) (spin pole attachment)
So you are looking for percentage of material lost in a cross section of that part of mast.
I think you will find it is not such a great concern. Consider loss of cross sectional area where halyards might exit the mast.
As a matter of comparison one of my masts (21 fter) (had a few) had cut outs near the bottom for turning blocks about 3cms by 2 cms one each side. Plus holes on each corner for screws. Lots of corrosion. The mast actually crumpled under load with bulging outwards in places. Not a total failure but of concern. I did get it all reinforced. (only to blow the mast on contact with a marker post)
In would suggest a coat of epoxy over corrosion. To flatten it. Larger screws in to tapped thread with lots of duralac.
If you are still concerned find a section of mast or boom that can make a large patch over the area and attach with rivets or screws. With again epoxy under neath.
The weld repair you envisage will damage the heat treatment of the mast material and possibly end up less strong than original. ol'will

 

[Rum Run]

I think the significance of the corrosion and it's remedy depends on the structural design of the mast: Old masts were basically a fairly thick-wall round tube with some holes and designed by experience + rule of thumb, which should have plenty of safety factor. A modern race-oriented design will be lighter for the stiffness but less safety-factor.
So far as I know, an ally mast will have age-hardened, which will be affected by welding but with an old pole mast with 4mm thick walls I think that won't matter. Modern thin-wall tube could be a problem and I'd plate and closely rivet that using Duralac and monel rivets!
More info about the age of the rig and the type of boat would be useful.
A pal of mine with an Elizabethan 30 had corrosion at the mast foot and plated it and that's been fine for over 20 years in offshore conditions.

 

[doug748]

Manufacturers of finished masts are usually very good at doing the job properly but even would be professionals attaching after market fittings can be hopeless.
I would either get a bigger fitting or re bed the old one the with proper galvanic protection and probably a plastic gasket of some sort. Give it a wire brush and a coat of aluminium primer first. I agree with William H, highly unlikely that the mast has lost any necessary strength.

.

 

[andyj301]

Thank you all. Your advice and experience is very much appreciated, especially with all the other jobs on the hard this year.

The boat is a 1979 Halmatic 30 with original mast (Kemp I think). So clean up, treat and plate with rivets should be the belt and braces.

 

[bluerm166]

If the area has been corroded substantially then a small plate won't restore the full structural integrity .A longer 'splint' is the answer and a long inner rivetted sleeve is the full job.Most easily achieved with a piece of the same mast section with a split.

 

[BobnLesley]

Thank you all. Your advice and experience is very much appreciated, especially with all the other jobs on the hard this year.

The boat is a 1979 Halmatic 30 with original mast (Kemp I think). So clean up, treat and plate with rivets should be the belt and braces.

Based on the photo I wouldn't bother to over-plate it, though if it worries you, get a larger s/steel backplate welded onto the fitting (not the mast itself) and as advised by others, install a separating membrane between that and the mast along with LOTS of duralac on the fixing threads.

 

[Keith 66]

From experience with several old masts they dont just corrode at the bottom but can corrode under any fitting.
Many manufacters including Kemp used Triangular crosstree bases with two big rivets at the top & one at the bottom, when the crosstrees droop downwards as they often tend to do the fitting tends to bend away from the mast between the top two rivets, this leaves a handy pocket for dirt & water & ice to collect & corrosion will follow.
I have seen this happen on several boats including our Sabre 27 & several Westerlys, Remedy for our boat was a much larger stainless steel crosstree base in a diamond shape extending well beyond the original. Kicking strap attachment points on booms also corrode & i recently had to replace our boom for this reason, It had been plated over before but was on the way out!

 

[andyj301]

Thank you again for replies. I'm on the hunt for a suitable section of mast. Looking at masts that have been extended or joined, the inner sleeve would give more reassurance. Could a sheet of aluminium be used, treated with primer or epoxy?