Replacing Mast Tangs

[CPD]

The chainplates at deck level are being replaced (rust staining being the giveaway sign) and the mast is coming down to enable replacement of the upper furler bearing.

My question is whether or not there is any merit at all in replacing the tangs and through bolts. We are talking of a 1976 Cenatur with what I believe be to the original tangs and through botls at upper and mid level. They looked fine, no rusting, no sign of wear.

What would you do and why ?

Thanks as ever.

 

[roly_voya]

If it aint broke... Lots of boats including 2 of mine have mast tangs from this date that are fine. If all the mast fittings are origional then while the mast is down check everything with a magnifiyer. What you are looking for is signs of white powder indicating corrosion between mast and fitting. If you find it strip off the fitting and re-rivit with insulation to isolate mast from fitting (zinc cromate past or hard rubber) You are also looing for hire line cracks particularly at rivit hole and shroud fittings indicating fatigue. If you find any you may be able to get them welded but may need replacement - get specialist advice form a good rigging shop/spar maker.

 

[milfordman]

Thanks for your comments roly-voya. I am in the process of changing my standing rigging, and was unsure what to do about the tangs and through bolts, which incidentally look ok.

 

[William_H]

Usually the mast tangs and through bolts have a far greater strength (cross sectional area of load path) than the wire stays. As such you can usually expect the bolts and fittings to last for ever. Your chain plates may be OK with just a bit of rust treatment also.

However Stainless Steel has a habit of letting go at any time with little warning or crack progression.
So in the end it is all a matter of your own peace of mind when sailing and that is important. The same parts on my boat are 25 years old and I sometimes wonder when thrashing along in blow. But then I find there is so much choice of things to worry about.
good luck olewill

 

[roly_voya]

The other piont to remember when talking to people is that todays boats may well have several time the rig loads often with no heavier or even lighter wire and those silly ball joint things. Racing boats expect 3-5 years life from a rig, pilot cutters 30-50 years and you are somewher in between. Its an interesting piont that I have heard S/S ony work hardens and cracks if the cyclic loads exceed 10% tensile strength so I just calculated my rig loads to normally stay under that. Look at Brian Toss's book on rigging if you want to get into it.

 

[VicS]

[ QUOTE ]
I have heard S/S ony work hardens and cracks if the cyclic loads exceed 10% tensile strength so I just calculated my rig loads to normally stay under that

[/ QUOTE ] Unless you have exceptionally heavy rigging wire then the loads are going to exceed 10% UTS when you are sailing.

One can deduce from advice given in the Selden Masts Hints pdf that once the boat is heeling more than 15 - 20° the tension in the windward rigging will be about 15% UTS of the "normal" wire gauge for the boat, increasing further as stronger winds produce greater heel.

I cannot confirm your 10%UTS figure, is there a metallurgist in the house?, but basically you are right in as much that there is a certain stress below which fatigue failure will not occur.

 

[ean_p]

Is this to say then that if you slacken your rig while not using it then you will stop any fatigueing(?) within the wire ?