billskip
Well-Known Member
It's quite possible that any repair will cost close to replacement iff not more.
Repairing spreader brackets
- Thread starter sailoppopotamus
- Start date
rogerthebodger
Well-Known Member
It could be fbricated from stainless steel very simply and fitted with an insulated pad between the bracket and the mast
mikegunn
Well-Known Member
The cracking depicted in the images occurred a very long time ago. I suspect the result of stress, either inherent within the casting or induced when the brackets were initially riveted to the mast. There is no obvious evidence of insidious progression and if the brackets were going to fail they would have done so long ago. The crack interfaces are showing signs of material loss through corrosion, possibly because they do not have the benefit of an anodised finish.
I would suggest that the repair be limited to routing out the cracks to remove any evidence of corroded material and then, as soon as possible filling the voids with an epoxy filler, to offer some protection from further corrosion. Yes, it is effectively only a cosmetic repair but in my opinion that is all that is necessary. After all, the brackets have already shown that their strength has not been unduly compromised by doing their job for fourty odd years.
I certainly wouldn’t advise attempting a repair by welding as that will only serve to induce further stresses, which may lead to further cracking.
Mike
I would suggest that the repair be limited to routing out the cracks to remove any evidence of corroded material and then, as soon as possible filling the voids with an epoxy filler, to offer some protection from further corrosion. Yes, it is effectively only a cosmetic repair but in my opinion that is all that is necessary. After all, the brackets have already shown that their strength has not been unduly compromised by doing their job for fourty odd years.
I certainly wouldn’t advise attempting a repair by welding as that will only serve to induce further stresses, which may lead to further cracking.
Mike
sailoppopotamus
Well-Known Member
Thanks Mike. I hear your argument, but I admit that I'm a bit uncomfortable leaving it like that. I'm going into the trouble of replacing shrouds, pulling chainplates, and actively trying to hunt down potential cracks by dye testing stuff, yet here is a glaring crack in a critical part of the rigging that I'm just going to ignore? Assuming this is a type of aluminium that lends itself to welding (heat treated ones I understand do not), would a weld performed by a specialist necessarily weaken the part?
A few people have suggested getting a stainless part made. I''ll ask around to see if if I can find somebody to do this at a reasonable price. I had initially thought this was too complex a part, but I'm all too keen to be proven wrong.
William_H
Well-Known Member
Assuming the spreaders are all "in line" ie the stays come down to chain plates abeam the mast then all loads on the spreader should be compression inwards. It does seem strange to me that the base is designed to give freedom of movement in one direction up and down. I would have thought that if any freedom of movement is needed it would be fore and aft. However I don't believe freedom of movement is desirable. Usually the stay slide on the end of the spreader but are on larger rigs attached at spreader end. (which does OP have)
I note OP says the stay wire also attaches to this bracket. This dictates the orientation of the bracket. I would feel more concerned re the integrity of the stay attachment rather than the spreader base integrity.
I would like to see a base made similar to the photo by Boathook but with a socket for the spreader all fabricated in SS. Tangs on the through bolt taking the stay load. The existing system is taking the stay load via 4 pop rivets that hold the bracket on. Not so reliable IMHO.
I note OP says the stay wire also attaches to this bracket. This dictates the orientation of the bracket. I would feel more concerned re the integrity of the stay attachment rather than the spreader base integrity.
I would like to see a base made similar to the photo by Boathook but with a socket for the spreader all fabricated in SS. Tangs on the through bolt taking the stay load. The existing system is taking the stay load via 4 pop rivets that hold the bracket on. Not so reliable IMHO.
mikegunn
Well-Known Member
I would certainly refrain from attempting repair of the brackets by welding. Stresses will be induced which may or may not result in a failure. Too many unknown unknowns in such a critical item.
If you don’t wish to adopt my suggestion I fully understand. In which case I would lean towards William H’s solution of stainless steel fabrications to replace the castings and the important addition of a through bolt to transfer the stay loads to the mast. The existing pop rivet arrangement is probably the weakest link in the arrangement. Should you ultimately add a through bolt I would suggest that it is installed with a spacer to prevent the mast being crushed during its installation.
Mike
If you don’t wish to adopt my suggestion I fully understand. In which case I would lean towards William H’s solution of stainless steel fabrications to replace the castings and the important addition of a through bolt to transfer the stay loads to the mast. The existing pop rivet arrangement is probably the weakest link in the arrangement. Should you ultimately add a through bolt I would suggest that it is installed with a spacer to prevent the mast being crushed during its installation.
Mike
Daydream believer
Well-Known Member
In their defence --Pop rivets have lasted 40 years & only removed due to failure of another component. So why do you feel that they would not last another 40, if not properly applied?
How do you get 4 spacers half way down inside the mast? Or are you proposing to drill extra large holes in the mast & putting the spacers on the bolts from outside so that they only provide shear & do not rely on any compression force?
My rigging fittings are all pop riveted & have been for 21 years. My shrouds are tensioned to 24%
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sailoppopotamus
Well-Known Member
I concede that something through bolted would probably be stronger. ZSpars have changed the design of their spreader system since my mast was made and it looks like the design has a spar going through the mast to take compressive loads. Having said that, I'm not an engineer so I wouldn't feel comfortable undertaking a structural modification to a design that has held fine for decades on who knows how many boats. After all, the engineers behind this design certainly took into account the various forces involved. A single 6.4mm monel rivet has a shear strength of around 540kg, and the bracket is attached to the mast by five such rivets. This roughly adds up to slightly more than the breaking strength of 5mm wire, so it looks like the rivets are not the weak point in the design.
Boathook
Well-Known Member
The original spreaders were round tube fitted into a fitting on the stainless steel plate along with the stays. The plate was removed, spreader fittings removed, etc and plate refitted for the baby / inner stays. The new spreaders and brackets were "off the shelf" from Kemps / Selden.
This was all done over 25 years ago.
Most rigging is in shear and pop rivets are ideal for this. The ones holding the stainless steel bracket on are 6mm so difficult to set !
Blueboatman
Well-Known Member
Notwithstanding your communications with Z spars uk..
I seem to remember that Z Spars called themselves something else in France.
It is - just - possible that a phone call to their French factory might unearth something useable ?
Z-Spar Main Page
With French phone number
I seem to remember that Z Spars called themselves something else in France.
It is - just - possible that a phone call to their French factory might unearth something useable ?
Z-Spar Main Page
With French phone number
billskip
Well-Known Member
Of course with cost cutting and weight consideration, it's possible the new design masts are made of thiner material
so an inner stay would be more necessary.
As you say its worked for years, and probably failed due to incorrect rigging tension as opposed to faulty component.
mikegunn
Well-Known Member
Perhaps I didn’t describe my proposal in sufficient detail, for which I apologise. I was not advocating replacement of the rivets. You’re quite right, they’ve served well up to now and in all probability could continue to do so for many years to come. Instead, I was suggesting that, should the OP decide to fabricate new brackets that provision be made to introduce a through bolt to which the shrouds could be attached. Rivets could continue to be used to retain the brackets. A sort of belt ‘n braces approach.
Incidentally, my noted response was in recognition of the fact that the OP would seem unwilling to heed my earlier advice i.e do very little. I fully respect the OP’s decision. It is after all, his boat.
Mike
Daydream believer
Well-Known Member
I think that the OP is right to deal with the situation whilst he can. A full repair/replacement, or whatever. It is the sort of thing that plays on the mind in F8
sailoppopotamus
Well-Known Member
Thanks. I've sent them and a couple of other ZSpars distributors an e-mail.
Your post and several hours of googling thereafter definitely put me off welding, that's for sure. My main issue is that welding may or may not weaken the part, but other than the welder's word for it I have no way of knowing for sure that I haven't made matters worse. If I can't find a replacement part, and if I'm unable to get a copy of reasonable quality cast, it seems safer to make some aluminium reinforcing plates and glue them on with the strongest adhesive I can find on either side of the crack. Sure, it's a bodge, but I certainly won't be making matters any worse strength-wise. As a minimum, this might prevent against further corrosion as your suggested epoxy repair.
Daydream believer
Well-Known Member
To me that would be the worse option. You do not know how good your glue is & you cannot see how the crack is developing underneath. definately a no no. Bodge is the right word.
Boathook
Well-Known Member
Are you able to get spreader brackets that fit the mast section and do the same as mine in post 11 ?
I can't see that raising a bracket a few inches would make any difference to the rig security as the existing brackets are still supporting the stays.
billskip
Well-Known Member
I tend to agree, I doubt any diy "glueing"
will be a success especially in a hot climate with big difference between hot day and cold night, and if it doesn't fail it can't be determined it was a success, however if it fails it's positive it didn't work and that to me is a risk I would not take.
Respect for concerns regarding welding, but I certainly wouldn't dismiss the idea without consulting a professional aluminium welder, as said possible in the motor industry or propeller repair.
Replacement would obviously be best.
This mast has 2x spreaders so would indicate a tall mast which carries a lot of rag = a lot of energy.
Snowgoose-1
Well-Known Member
The good news is that you have identified a problem that could have resulted in a very unpleasant experience. It might be worthwhile considering using a reliable rigger to offer some options.
Beneteau381
Well-Known Member
Clean it up and get it welded by a coded welder. Then as a back up make a U shaped strap with feet on and attach to the outside of the casting to “support” the casting with pop rivets or drill through the mast bit and mast, tap threads and bolt the strap over the repair. Use aluminium or preferably a strip of staineless
mikegunn
Well-Known Member
Sorry to be a wet blanket but no matter how competent the welder, he will be unable to ensure a stress free weld. It’s the physics! In any case, on such a critical item there should be a detailed post weld inspection for surface breaking flaws and a radiological examination to ensure freedom from shrinkage cracking at the internal weld/ casting/interface. Even then there will remain stresses of unknown magnitude which could “pop” at any time.
In my opinion covering the existing cracks with any form of reinforcement would be imprudent. It is important to be able to monitor the cracks to identify any progression. Introducing stainless steel into the mix with the need to take anti-corrosion practices into consideration would further complicate matters.
I feel that the OP has two options. The first, as I previously advocated, do nothing other than inhibit any further corrosion occurring on the crack interfaces or, have a complete reassessment of the spreader and shroud arrangement and have fittings manufactured from stainless steel. Obviously taking care to insulate the s/s from the aluminium mast during fitment.
What would I do? Probably the latter, but with the recognition that the time it would take to design and manufacture new brackets may eat into the 2025 sailing season. In which case I’d live with the existing “cracked” brackets until the new ones be ready for fitment. Then, probably no more than a day’s work.
Mike
