Lifespan of aluminum mast

[Hardhead]

My C22 mast is 30 years old, and doesn't show any obvious stress defects. However, I did notice last weekend that the mast seems to have a "natural" lateral bend of maybe 1" over the top 10 feet, standing, but with very loose shrouds. With the starboard upper shroud about 22 on a Loos PT-1 scale, and the port upper about 21, it straightens out. Seems okay to me.

Is there any concern that normal sailing and rigging stresses eventually add up to a weakened aluminum mast?

 

[pclarksurf]

Full disclosure-- I'm not qualified in any way shape and form to spout metallurgical theory but my mast is now 45 years old and shows no discernible signs of weakness nor stress.

Now -- add a freakshow PO with a penchance for hole drilling or some other version of abuse (improper rig tension-- defunct standing rigging) and the equation changes rapidly. But for my .02 the test of time is speaking loudly.

 

[Hardhead]

Thanks pclarksurf - there certainly does seem to be a lot of older masts in regular use. I haven't often heard of masts being replaced, unless they happen to come down on their own. Considering how flexible they are, and how easy it is to put pre-bend in, etc., I was just assuming there has to be a cumulative effect at some point. Aluminum aircraft seem to fly forever though, and they certainly have a lot of stress.

 

[pclarksurf]

good stuff here: essentially flexibility is your friend, but only to a point:

Below a certain stress level, the steel alloy will never fail due to cyclic loading alone. On the other hand, aluminum does not have a true endurance limit. It will always fail if tested to a sufficient number of cycles. Therefore, the fatigue strength of aluminum is usually reported as the stress level it can survive at a large total number of cycles, usually 5 · 108 cycles. It should be noted that there is a considerable amount of scatter in fatigue test results. It is therefore important to test a sufficient number of specimens to obtain statistically meaningful results.

Math and mechanical wizardry in the attachment

 

[greg_m]

Could then bend be from the mast not being secured/supported correctly for traveling/storage?

 

[Hardhead]

Could then bend be from the mast not being secured/supported correctly for traveling/storage?

That's my guess. I get the sense the boat sat unused for about 10 years for a period before I owned it, and it probably relates to how it was supported. There doesn't seem to be too much concern to mast age though.

 

[gdudik]

I’m in the same boat (heh) as @pclarksurf. 45 year old OVAL style mast, which means its for sure original. POs have drilled holes all over the place. Mine has a little bit of a bow in the middle from being trailered with no center support over the years. Both most recent PO and I raced this boat at least some. I don’t see any signs of impending doom. I just adjust the shrouds to keep the mast in column and then as per the tech manual. Works fine!

 

[Hardhead]

I'm no engineer, but thinking about it a little further, most of the stress on the mast would seem to be straight down compression, directed from the shrouds. Given that, it would seem difficult to collapse a mast absent a shroud failure. Probably not much to worry about really.

Of course, I've just cursed myself by ever making that statement..

 

[Benny17441]

It is one of those things that I would not worry about until it breaks. The shrouds and fittings on the other hand should be inspected every six months. Lost a mast years ago for a simple cotter pin.