Mast Corrosion

Hi all,

I pulled the mast our of my old girl last week so that i could replace all the lights and rewire as anything electrical had long given up. We got the rewire and the lights installed , that's all good .

Then today I was back at it installing a new Windex after the last one fell off. That's all ready to go.

I then set about cleaning up the mast step and it's here i need your input. There is quite a bit of corrosion in the area where the end plug fits into the base of the mast section (see pics). It looks concerning to me, but how worried should I be? If I am right to be concerned what do people suggest is the best way to deal with this?

I had thought one solution would be to cut off the base where the corrosion has occurred (about 200mm would probably do it) and weld a 200mm section onto the bottom. The catch with this would be finding a mast section that was the same profile (I doubt that would be easy). I have also read that welding aluminium may not be such a good thing when you are talking about an extrusion like a mast. Is this the case?

So perhaps some sort of sleeve job (if something is required)? This would also require a new end cap as the sleeve would make the internal diameter of the mast section smaller. Again finding the correct shaped mast section would be the challenge.

I'm keen to hear peoples thoughts on this and also solutions that doesn't involve replacing the mast as this is not really an option for me at present.

Select to expand quote

riverider said..
If it's keel stepped you can cut it at deck height, put in a compression post between the keel and deck and step it on the deck.

Thanks riverrider, Yes I had thought that might be an option but bit of an operation to pull off.

The other idea I had whilst pondering this today would be to cut off the offending end then have a welder add an addition to the base of what is currently the end cap equivalent to the length cut off the mast section. That way it does not change the overall length of the mast whilst removing the corroded section.

Does anybody have any thoughts on this solution?

Select to expand quote

MattM14 said..

riverider said..
If it's keel stepped you can cut it at deck height, put in a compression post between the keel and deck and step it on the deck.

Thanks riverrider, Yes I had thought that might be an option but bit of an operation to pull off.

The other idea I had whilst pondering this today would be to cut off the offending end then have a welder add an addition to the base of what is currently the end cap equivalent to the length cut off the mast section. That way it does not change the overall length of the mast whilst removing the corroded section.

Does anybody have any thoughts on this solution?

With out seeing the mast step, it would to me seem like the simple solution to lift the step. Have you got a pic of that ?

The mast base has been sitting in bilge water.
I would chop off the corroded section and build a wooden mast step that is built up high enough to compensate for the lost section as well as to lift the mast base out of the bilge water.

Jarrah is quite rot resistant and it is readily available. I could be treated with epoxy for added longevity.
I am sure that some one will come along with a better or alternative wood selection.

The advantage of using wood is that you can make it up cheaply with basic tools.
Also, it could look very sweet if well made.

gary

Select to expand quote

Ramona said..
If it was mine I would leave the track area alone and cut out the sections that are corroded. Cut pieces to size with the appropriate curve and weld in with a mig welder. "Splatter" weld like in this video.

This is a particularly fast weld and dumps heaps of material on the job. Grind the weld flush on the outside and inside so it clears the cap. 36 grit flapper wheel will have it looking like new.
You may need to build a screen to keep the wind from blowing the argon gas away. Caution: the aluminium shows no indication of how hot it is and it's easy to get burns!

Would be very careful welding at the mast base - have to check if the aluminium alloy used in the mast extrusion suffers HAZ strength reduction when welded - see here the typical strength reduction can be around 60%.

www.esabna.com/us/en/education/blog/the-haz-in-aluminum-welds.cfm

Select to expand quote

garymalmgren said..
The mast base has been sitting in bilge water.
I would chop off the corroded section and build a wooden mast step that is built up high enough to compensate for the lost section as well as to lift the mast base out of the bilge water.

Jarrah is quite rot resistant and it is readily available. I could be treated with epoxy for added longevity.
I am sure that some one will come along with a better or alternative wood selection.

The advantage of using wood is that you can make it up cheaply with basic tools.
Also, it could look very sweet if well made.

gary

Thanks Gary - Yes I had thought of this also as a way that I could possibly / probably pull off a fix myself with the tools I have available. I am much more comfortable working with wood than metal.

I had wondered about the need to attach the base cap to the block of hardwood. The current set up has the mast sitting on the mast step which has a "lip" built up around it so the base of the mast rests in a indentation. I guess this is to ensure that it sits in the right position and can't move around laterally or forward / aft. With the base of the mast sitting on a block of hardwood it would be above the level of this surrounding lip so theoretically could slip sideways / forward / aft off the block of wood.

I could screw through the mast end cap into the block of wood but that is introducing a different metal to the aluminium end cap (in the form of a stainless steel screws) which could result in a repeat of the current issue. Could it not? I might be able to create a recess in the top face of the wood block that the mast sat in or screw some aluminium plate onto the sides of the wood block the protruded above the top edge to create a retaining lip without actually needing to attach it to the mast itself.

Thoughts?

So one question I have is about cutting the corroded end off the mast. Is there a more accurate and precise way of doing this than just using an angle grinder? I'm concerned about getting a straight cut through the mast section so it sits flush on the end cap all the way around and ensuring that this cut is at right angles to the vertical aspect of the mast so the mast sits perpendicular to the boat.

I'm limited by the location. The mast is currently sitting on the yacht club marina, so it's not like I can wheel it into a workshop somewhere. Is there another tool I should be using or just ensure I mark it out accurately and then be very careful with an angle grinder?

Best idea for me is to go the jarrah and epoxy route. Nice and strong and it gets it out of the bilge - it is now a feature.

My mast is held onto the flat mast base by two large stainless coach style bolts that go through the alloy. Lots of yellow stuff over the bolts and it is all good. Only put yellow stuff or whatever we use now near the head of the bolt, push it through the mast base and then put some epoxy on the threads. Screw it all down. It has held this way on my boat for a couple of decades.

As for cutting square, I have done this a bit and my fav way is to get some paper and wrap it round the section. Line it so it lies upon itself and then trace with sharp pencil. Always get a nice cut. Also don't only epoxy the base in. Remember that epoxy glue is strong but doesn't like shock loads, glass handles shock loads but isn't great at gluing. But put them both together and you will need a sledgey to get it out. So cut a nice hard wood (any hardwood will do but lay the grain flat) so that it fits in the bilge. Then remove block, put on mask and grind all gelcoat off area and surrounds for 10cm. Then mix up peanut butter consistency epoxy glue and smush down. (YOu can have up to about 5mm gaps in your grinding and cutting and epoxy will cater for the gaps fine). Then go around with rounded over coving tool and clean up epoxy coves. When set, sand and then cover it two layers of 400gm double bias. Don't use any other fabric, double bias is a wonder at conforming to crazy shapes, just keep on tapping at it with your brush and it will eventually lie down. Then the thing will be super strong and ready for the mast base. DON"T USE POLYESTER!

Select to expand quote

MattM14 said..
So one question I have is about cutting the corroded end off the mast. Is there a more accurate and precise way of doing this than just using an angle grinder? I'm concerned about getting a straight cut through the mast section so it sits flush on the end cap all the way around and ensuring that this cut is at right angles to the vertical aspect of the mast so the mast sits perpendicular to the boat.

I'm limited by the location. The mast is currently sitting on the yacht club marina, so it's not like I can wheel it into a workshop somewhere. Is there another tool I should be using or just ensure I mark it out accurately and then be very careful with an angle grinder?

Use a wrap around, can make one out of paper then cut it with the grinder using a 1mm disc. Make a few cuts in the corroded section to practice before cutting it where it needs to be done if you need the practice.
I was a welder until retired but I wouldn't weld anything to mast extrusion, IF I had no choice I'd use a Tig welder and made sure the inside was sealed and filled with Argon gas. But to attach another length to mast I'd use a sleeve and rivet it with Monel rivets after cleaning all the corrosion I could and spray it with a few coats of Penetrol at 5 min intervals. If the fit is not perfect fill let the Penetrol dry a few days before joining the pieces and fill any gaps with epoxy/silica mix or something like JB Weld putty.
In your case if the mast was sitting in water I'd go with the wood option as previous posters suggested and apply multiple coats of wet on wet epoxy using a heat gun for the first 2-3 coats to make sure the epoxy penetrates the wood grain as deep as possible.

Select to expand quote

MattM14 said..

r13 said..

MattM14 said..

riverider said..
If it's keel stepped you can cut it at deck height, put in a compression post between the keel and deck and step it on the deck.

Thanks riverrider, Yes I had thought that might be an option but bit of an operation to pull off.

The other idea I had whilst pondering this today would be to cut off the offending end then have a welder add an addition to the base of what is currently the end cap equivalent to the length cut off the mast section. That way it does not change the overall length of the mast whilst removing the corroded section.

Does anybody have any thoughts on this solution?

Sorry to say but this is probably not going to work unless the mast section is considerably over sized for the yacht. Usually deck stepped masts compared to keel stepped masts need their lower panel stiffened with internal doublers to increase the section modulus to an acceptable stiffness to account for the structural support differences keel stepped and deck stepped. What yacht manufacturer / designer and model is it? For a fractional rig 2 spreader deck stepped mast we did recently the doubler went in up to about 300mm above the lower spreader.

Thanks r13
I'm probably not leaning towards cutting the mast off at the deck. That seems a bit too radical at this point in time given that the corrosion is only effecting the last 200mm or so of the mast. Some of the other solutions seem simple and less involved at this stage.

Good to know it might be a possibility if required but beyond my skills / knowledge.

Am sure you have this in mind but check the fore and aft angle of the bottom of the mast cut off plane - if you have some rake in the mast set up and this is not allowed for in the mast step mounted on top of the keelson, onto which your alum mast step/plug sits and is screwed to, then the mast lower end cut would have a slight angle to it fore and aft.
If you are building up this hull keelson mounted mast step structure by 200mm make sure it is stiff and strong enough in both directions. Decent ply gussets each side laterally, and each end fore and aft, could be needed. Epoxy sealed.
Tefgel is a far better corrosion isolator than Duralac which I assume "yellow stuff" is referring to.

Just a tip when cutting aluminium with a grinder get a candle & push it on cutting disc as a bit of lube now & then otherwise disc loads up & it's heaps faster & colder cut & it really takes the load off if you're using a cordless grinder

A quick update on this.

I have found a metal fabrication guy who will have a go at welding the addition onto the mast end cap. Turns out my initial guess without having either the mast or the end cap in front of me was way off and it is only an addition of 80mm. The end cap is an aluminium cast so he acknowledges that the weld may not take but he is keen to give it a go. If that is unsuccessful he will fabricate the addition and bolt it onto the end cap along with a lip around the top edge so the end of the mast sits square on the new addition.

When I have the new piece I will post some photos so you can see what it turns out like.

Select to expand quote

Am sure you have this in mind but check the fore and aft angle of the bottom of the mast cut off plane - if you have some rake in the mast set up and this is not allowed for in the mast step mounted on top of the keelson, onto which your alum mast step/plug sits and is screwed to, then the mast lower end cut would have a slight angle to it fore and aft.

We will mark out the cut off line as a measurement from the existing base of the mast all the way around so that it maintains the same angle as it currently has.

Well after numerous delays due to a case of Covid, deliveries going astray and the Christmas shut down I'm finally able to give an update. The fabricator was able to successfully add the necessary addition to the end cap so whilst it is a bit heavier than it used to be it should do the job nicely ????. Mast due to go back in the boat tomorrow once we have cut off the corroded section and put it all back together. in order to prevent this happening in the future I have painted the end cap (it's just the primer in the pic). I was not thinking of using any fastenings holding the cap in place given that it fits into the end of the mast so it can't slip off the cap even with the new addition. I don't want to have any other metals in contact with the aluminium. Thoughts?
Any suggestions for anything (if any) to cover the inside of he mast with? Perhaps Duralac or lanolin grease? Recommendations welcome. I did manage to get some paint on the inside of the mast also but not certain it covers the whole area as the new cap is a little higher than I had asked for so more will be cut off.

The yellow Duralac gets everywhere and stains stuff yellow (don't ask me how I know). Tefgel is white, it still gets everywhere, but it does not stain in the same way.