Carbon Mast - Spreader bar slot

[Delfini]

My C Spars carbon mast of 15 years is down whilst the boat (Swan 48R) has a bit of work done and I asked the yard to check the rig - they reported the spreaders roots are a bit wobbly at the mast. After checking and confirming a few mm of wobble (mostly up and down) Ive removed the bottom spreaders and what’s left is a solid lump of aluminium (spreader bar) with fixing holes for the lower stay/s and the spreader itself and this bar just slides through the mast via slots each side. The spreader base seems to rest against the side of the mast via a stainless spacer shaped to fit the spreader base section

Over time the slots in the mast have worn a bit and it looks like the spreader bar is the primary cause which has mild corrosion in the area of the slot and acting as an abrasive

Does anyone have an idea of a fix - can I just make up the wear in the mast slot with epoxy filler or should I square off the slot and consider some sort of insert - if so what material would be best with a carbon mast and aluminium spreader bar ?

I would be grateful for any first hand experience of this problem or advice from any with Carbon rig knowledge

Thanks

 

[anoccasionalyachtsman]

Any chance of some pictures? I think I can visualise it, but best be sure.

@vyv_cox could be handy here.

 

[Delfini]

Hi - a picture of the spreader 'in situ' and also the mast slot with spreader and spreader bar removed - you can see the outline of the spreader base plate on the mast

 

[anoccasionalyachtsman]

If I couldn't pick the brains of someone who's done this repair before I'd be thinking of picking out all the compromised material and overfilling before filing back for a nice snug fit on the insert. I've got my doubts about normal filler additives being appropriate though, and would probably mix epoxy and chopped carbon.

What I'd like to hear from that someone though is whether that's just wear through movement/stress cycles or if there's an bit of galvanic corrosion there too. Knowing which flavour of stainless it is would help decide the latter. If there is corrosion because the ss is not suitable I'd then reconsider the filler so that there's less carbon nearby. They might also offer guidance on whether something like duralac would be worth using.

Have you tried contacting C Spar?

 

[TernVI]

Galvanic corrosion is probably a big part of the story, but it will be the aluminium which is the problem more than the stainless.
Carbon and aluminium often cause problems together.

 

[anoccasionalyachtsman]

You could be right, as I understood it the stainless root acted as a spacer between the CF and Aluminium.

 

[Delfini]

If I couldn't pick the brains of someone who's done this repair before I'd be thinking of picking out all the compromised material and overfilling before filing back for a nice snug fit on the insert. I've got my doubts about normal filler additives being appropriate though, and would probably mix epoxy and chopped carbon.

What I'd like to hear from that someone though is whether that's just wear through movement/stress cycles or if there's an bit of galvanic corrosion there too. Knowing which flavour of stainless it is would help decide the latter. If there is corrosion because the ss is not suitable I'd then reconsider the filler so that there's less carbon nearby. They might also offer guidance on whether something like duralac would be worth using.

Have you tried contacting C Spar?

..... as far as I know C spar are no more ?

 

[Delfini]

Thanks all - as far as I am concerned there is no question the cause is galvanic corrosion of the aluminium spreader bar which has fizzed up at the joint with the mast and caused what looks like an abrasive action on the slot - given the rig has been raced hard over the past 10 years the wear could easily have been anticipated - its the fix I am searching for - fill the small wear gap in the slot (its no more than 0,5mm) to make it rectangular again or fabricate some sort of insert and also removing the fizzed bit of aluminium and maybe laying in aluminium weld (or filler) and machining flat again

As ever your guidance much appreciated

 

[Seriola Dumerili]

Hi, same problem here! Unfortunately after just 3 and a half years... I suppose your spreaders are also carbon?
I am expecting an answer from the manufacturer. If the gap between spreader and the mast is uniform, titanium maybe?
(English is not my native language)

 

[anoccasionalyachtsman]

Replacing the through bar with stainless (if you can bear the weight...), or carbon with stainless inserts for the terminals - titanium lovely if the budget will cover it, would seem to give a useful life extension. 3 1/2 years, ouch.

 

[Seriola Dumerili]

I was thinking at Ti just to fill (and isolate) the gap between the spreader and the mast

 

[Delfini]

..... just to close this out - the boatyard couldn’t come upon with a fix they were prepared to stand behind with any sort of warranty but they were happy to recommend aluminium loaded epoxy filler for the spreader bar and chopped carbon loaded epoxy for the mast slot/s - the consensus on cause was galvanic action between the carbon and aluminium and salt - the stainless spacers seemed pretty much brand new and unaffected

I took one of the bars to a long standing friend who makes his living in metal fabrications and he said no problem to sandblast and then lay aluminium weld into the areas of corrosion on the spreader bar, machine back to flat and then anodise -the only slight concern for me was weakening of the base component in the welding process but the spreader bar itself is mostly in compression from the shrouds and its action on the mast the same - so I reckon the risk is low

Im going with that and will ask the yard to fill the gaps between the new spreader bar and the slot with chopped mat epoxy when the bar/s are fixed

 

[anoccasionalyachtsman]

..... just to close this out - the boatyard couldn’t come upon with a fix they were prepared to stand behind with any sort of warranty but they were happy to recommend aluminium loaded epoxy filler for the spreader bar and chopped carbon loaded epoxy for the mast slot/s - the consensus on cause was galvanic action between the carbon and aluminium and salt - the stainless spacers seemed pretty much brand new and unaffected

I took one of the bars to a long standing friend who makes his living in metal fabrications and he said no problem to sandblast and then lay aluminium weld into the areas of corrosion on the spreader bar, machine back to flat and then anodise -the only slight concern for me was weakening of the base component in the welding process but the spreader bar itself is mostly in compression from the shrouds and its action on the mast the same - so I reckon the risk is low

Im going with that and will ask the yard to fill the gaps between the new spreader bar and the slot with chopped mat epoxy when the bar/s are fixed

Sounds very pragmatic, but I'd suggest having a word with West or Gurit (SP Systems) about the epoxy filler. Chopped carbon won't do much for compressive strength, but it will play a part in future corrosion and so I'd be looking at a high density filler or glass instead. (I believe that pure epoxy would be even better, but applying it would be awkward). Do ask them though - I've never worked on a carbon mast.

 

[savageseadog]

Our carbon Hall spars spreader root ‘holes’ are stainless lined tubes. Best described like a fixed tube through the mast. Our spreader bar is similar bar to yours but machined stainless from a solid bar I guess. the middle bit of it is a solid cylinder which is a perfect fit in the root. so without the stays on each set of spreaders rotate slightly like a aircraft flap helping the rods align with the chain plate I guess and stopping any rub / wear on the carbon. Our spreader bars are covered in Teflon grease. (38ft yacht / double spreader rig). Last time we had them out there wasn’t a micron Of wear apparent. You could fit something similar to your rig - the beauty of round linings and round cylinders, if there a tight fit, the load is well distributed, like the Clevis pin. you don’t get stress points like a more box section hole.

 

[Delfini]

A solid round spreader bar and round tubes locating the spreader root sounds like a great idea but I'm not ready to replace my spreaders (48ft yacht/triple spreader rig) this time around - I will fix the spreaders and straighten up the carbon mast slots with a bit of epoxy and make the bar/s a nice sliding fit - the bar/s were smothered in teflon (or similar) grease by whoever fitted them last as they slid out of the mast slots quite nicely - here are the spreader bar/s nearly complete - the corrosion/erosion has been sand blasted out, the resulting void/s filled with 5356 filler rod (recommended for the marine grade 5083 base material) and machined flush to the original - off to the local anodiser tomorrow and with a bit of luck back to the yard on Tuesday - Im very pleased with the result and grateful for the advice here