Hairline Crack in Mast

[ean_p]

Sleeving the mast is quite simple, finding the appropriate shelve might be more difficult. We sleeved a mast once, the forestay toggle failed after a life of 3 years. We had the mast maker supply the sleeve, we told him where the mast had failed, keel stepped and failed at the deck, and then sailed the yacht back from Manilla to Hong Kong (and then replaced the mast). So - mast makers are source of sleeves but you might find scrap masts at you local boatyard and be able to recycle a portion.

Jonathan

To be clear Neeves, did you have your mast sleeved at the deck penetration and did it require any further 'heat treatment' because of the welding heat? I ask as i have some corrosion behind a gooseneck and welding on a 6mm plate to remount the goose neck seems the easiest solution though I hear conflicting stories of the pre and post weld treatment required!

 

[Laminar Flow]

What's that supposed to mean, seeing as you repeated what I said?

Just that you beat me to it and were more concise. No snub meant at all.

 

[Laminar Flow]

Never mind .... as in, "never mind what I said as Vyv already said it".

Richard

Indeed, just me being (too) slow.

 

[Laminar Flow]

Thanks! Picture now attached further down thread. What size hole approx.. and should I fill the hole with sealant?

I think 3/16th would be fine.
As others have pointed out, it might have been caused by corrosion in which case drain holes would be appropriate as well as backing out the SS screws and isolating them with a suitable coating.

 

[vyv_cox]

Just that you beat me to it and were more concise. No snub meant at all.

Your wording was confusing. Sorry if I misunderstood.

 

[lw395]

Once the crack is there, you have to worry a little if the compression on the mast is spreading the crack under load, i.e. wedging the base casting into the extrusion.
I would be concerned if the heel casting moves at all in the extrusion.
The screws can help, in stopping the extrusion being wedged apart. Make sure they are not slack. I would consider taking the screws out and putting them back in nice and tight with plenty of Duralac to prevent (more) corrosion. If they are stripping in the casting, I'd probably drill and tap and replace them with machine screws. Maybe add extra screws. Or big monel rivets.
Ideally you'd take the mast down and get rid of any corrosion inside the mast extrusion, reassemble with Duralac.
Sleeving the mast is great, if you can get a sleeve to fit.
An ugly solution is to put a jubilee clip around the extrusion so it cannot open up. Put plastic of some sort to isolate the stainless from the ali.

 

[Neeves]

To be clear Neeves, did you have your mast sleeved at the deck penetration and did it require any further 'heat treatment' because of the welding heat? I ask as i have some corrosion behind a gooseneck and welding on a 6mm plate to remount the goose neck seems the easiest solution though I hear conflicting stories of the pre and post weld treatment required!

ean,

Our mast 'broke at the deck, keel stepped mast. We were competing in a RORC race from HK to San Fernando and the mast failed in very large swells with winds of 35/40 knots. We kept the mast up and lashed it at the base.

We had the yacht towed from San Fernando to Manilla

I ordered up the sleeve from the mast builder. It was slightly bigger than the inside of the mast but was 'U' shaped, same as the mast but open where the track would be. We simply hammered, wooden mallet, the sleeve into the top part of the mast and then hammered the bottom part, which was about 6' long, into the protruding part of the sleeve. The whole was then riveted together. I don't recall what rivets were used but the 'pattern' was irregular - so there was no 'line' of rivets (along which another crack could develop). There was no welding. We did not cut the mast down where the break was (to make it neat) as then the rigging would not have fitted. Effectively the repaired mast was the same height as the original, maybe a couple of mm higher and a bit stiffer, no bad thing.

This is a common method of building masts, or was then - sleeve and rivet

The repaired mast took us safely to HK and was used in a number of local races until the new mast arrived.

Jonathan

 

[Birdseye]

Thanks everyone for your all your comments, as you probably gathered I am a novice! Re the cause, I will check the rig tension as I have not done this yet, will also look at the screw and drainage for the ice theory, but as moored up permanently in a NW UK marina I am not sure this would be a frequent occurrence. As shes an old boat the long term corrosion of dissimilar metals plus salt maybe a distinct possibility. Sleeving sounds like a belt and braces solution and, but I presume a big job and a major expense my NHS salary wont stretch to at the moment! So drilling a small hole to stop crack propagation and see what happens seems like best short term solution, what would be the diameter of hole people would suggest and would you fill the hole with flexible marine sealant?

It looks like a fairly old mast and an old crack - I never know why people think that stainless rigging has a lifespan but masts dont. They too suffer corrosion and stress and ultimately require replacement. But usually people find that out in a stiff breeze when the old mast collapses. I appreciate your comment about the NHS salary ( you cant be a consultant ) but thats a crack that would leave me nervous. I certainly wouldnt try sleeving because that might cure the bottom of the mast but what about other stress areas like the spreader roots and mast head, so you risk spending money on a patch up not a cure.

Drilling a hole to stop propagation works and within reason the bigger the hole the better from a propagation POV. But any hole weakens the structure so I would go for maybe 3mm. But thats a guess not advice

It all depends on finances, value of the boat etc, but I did see when I last visited Allspars that they had some second hand good condition masts in stock. Worth checking before you consider sleeving.

 

[Laminar Flow]

Drilling a hole to stop propagation works and within reason the bigger the hole the better from a propagation POV. But any hole weakens the structure so I would go for maybe 3mm. But thats a guess not advice

Drilling a hole in a mast really all depends on where it is. Within the first 10% of an unsupported section you can cut quite a few perforations without causing any harm. NB all those 1" by 4" slots for the halyard ports etc. (I have at times wondered about those on some boats, but none the less, dismastings are a rather rare occurrence)

With what appears to be in the OP's case a crack right at the foot of the deck stepped base, you could drill a whopping big hole without any impact on the compressive loading ability.

The most important thing would be to arrest any further propagation of the crack even if you make it 1/2" and use it as the "new cable port" for the mast head light.

A simple collar made of aluminum flat bar around the base would arrest any chance of the mast profile buckling out. It could be riveted, screwed, bolted or welded.

Corrosion on aluminum spars generally happens where dissimilar metals are in contact with one another without insulation or where you have standing water due to lack of drainage.

On the average "cruising" boat spars are comfortingly over-specked.

 

[easton]

I had a similar, but worse problem (more cracks) about 4 years ago when we bought our boat. There were a series of hairline cracks running from the base for (I think, from memory) about 40-50mm up the mast.

We toyed with the idea of sleeving (internal or external, bonding, riveting etc) but the deciding factor was our inability to get the plug out of the bottom.

I used a dye penetrant kit to check where they all terminated, moved about 10mm up from there and cut the bottom of the mast off. I was pretty certain that I had got all the cracks.

The plug was replaced and a block of iroko cut to go under the mast plate, (with suitable hole sunk 15mm into it to house the coin ). Overall the boom and standing rigging height was unchanged, as it's a pain to make everything else lower to compensate (bimini etc) Longer bolts to go through the plate, iroko, compression post etc were needed.

I believe the corrosion causing mine may have been made worse as the mast was used as a return line/earth for the electrics at the top but can't be certain and might be clutching at straws.

It's been fine for four years now (taken us to Russia and back) but I do keep an eye on it with a close visual inspection every start and end of the season. It will get another non-destructive test (dye penetrant) probably at the end of this year just to check (and I've got some on the shelf now...)

I would have probably got away with drilling but getting rid of the worst corroded part at the base was an added benefit of cutting.

Andrew

 

[Poignard]

I had a similar, but worse problem (more cracks) about 4 years ago when we bought our boat. There were a series of hairline cracks running from the base for (I think, from memory) about 40-50mm up the mast.

We toyed with the idea of sleeving (internal or external, bonding, riveting etc) but the deciding factor was our inability to get the plug out of the bottom.

I used a dye penetrant kit to check where they all terminated, moved about 10mm up from there and cut the bottom of the mast off. I was pretty certain that I had got all the cracks.

The plug was replaced and a block of iroko cut to go under the mast plate, (with suitable hole sunk 15mm into it to house the coin ). Overall the boom and standing rigging height was unchanged, as it's a pain to make everything else lower to compensate (bimini etc) Longer bolts to go through the plate, iroko, compression post etc were needed.

I believe the corrosion causing mine may have been made worse as the mast was used as a return line/earth for the electrics at the top but can't be certain and might be clutching at straws.

It's been fine for four years now (taken us to Russia and back) but I do keep an eye on it with a close visual inspection every start and end of the season. It will get another non-destructive test (dye penetrant) probably at the end of this year just to check (and I've got some on the shelf now...)

I would have probably got away with drilling but getting rid of the worst corroded part at the base was an added benefit of cutting.

Andrew

That's what I considered doing with mine. The cracks extended not more than 30mm up from the base. But I was able to get it sleeved at a reasonable price so I opted for that instead.