HI John, and everyone
Given the comments and some more history about mast failures at deck level, I took a look at my mast which is on sawhorses in my yard at the moment… and I am concerned about what appears to be ‘pitting’ in that area adjacent the deck partners, along with some abrasions (from getting knocked during 40 years of stepping/unstepping I presume?). Also where you see the red arrow pointing there are some ‘imprints’ of perfect circles about 6mm in diameter which are puzzling. You will have to really enlarge this pic to see these little circle outlines.
I’m interested to hear from you, and anyone else, if this pitting looks like serious corrosion. My first mate thinks it might be a good idea - if its even possible - to insert a tight-fitting aluminum spline inside the mast in this area to reinforce it?
Thanks for any input!
Greg Silver,
Misty Cat N26C #121
St. Peter’s, Cape Breton
You should contact Mike Quill about it. He advised me on repairs when I found pitting beneath my tack collar. There are specifications for how deep the pits can be and still be safe, but you should ask him because the spec might be different for the area right next to the deck, it being right at the fulcrum. Mine was well within spec and I followed his instructions on repair. You are lucky your mast is on sawhorses! The prep involves sand blasting which is very difficult to do in a nice marina.
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I would also suggest talking to Mike about the details of how to do reinforcement with a spline.
I only know enough to know a few of the questions and none of the answers. I’m guessing that if the spline is merely a tube with flat ends, it may create stress points at its top and bottom where the mast suddenly flexes differently where it suddenly becomes thinner again. So, I’m guessing any kind of a spline has to be designed carefully to avoid that.
The questions are: is that correct and, if so, how should the spline be designed to avoid that problem?
Thank you for this photo. While I am VERY sorry about your mast failure, I have to say that it is very comforting to me to see how much corrosion it takes before it actually fails. If that black is accumulated oxidation within an existing crack, then it looks like about 40% of it was already gone for quite a while. I think my semi-annual tack collar removal and inspection should ensure that the minor corrosion repairs that I did last year will be adequate.
According to Mike Quill there is an acceptable depth of a corrosion pit. I think it was 25% of the tubing thickness, but I am not sure and you should ask him. Especially because you have a different size mast than I do.
If your pits are safe, then you need to sandblast any aluminum oxide out of them - but don’t overdo it. Stop as soon as you get to shiny aluminum. Then fill with a dedicated aluminum epoxy (like this one). You should do the epoxy filling immediately after sandblasting because aluminum will re-oxidize very quickly. Then sand the whole area with 40 grit paper, paint with a dedicated aluminum primer, and then with a good quality paint system. Interlux has a brief outline of the painting process here. I have done this and sandblasting while in the water in a marina was the hardest part. If you’ve got your mast on sawhorses, you’ve got a much easier fix ahead of you.
Those mystery dents look superficial and harmless to me. No idea what could have caused them, but if your mast comes in and out every year, it might have happened in the process or in the yard. Now that you know about them, you can keep an eye out and maybe you’ll figure it out eventually. Or maybe it happened on a previous owner’s watch and you’ll never know.
Please report back what Mike says and how this turns out for you.
