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Today when I was preparing my mast for stepping tomorrow, I was lucky to notice a major crack in the ball-and-stem fitting at the masthead that the forestay attaches to. Unless this fitting were replaced, this could lead to a serious rigging failure on the water. This would most likely occur under extreme conditions when I was least able to cope with the mast coming down. I took the fitting to a rigger (at Fogh Marine in Toronto) and he said that the crack looked like it had been developing for a while and was probably enlarged each winter by water freezing and expanding in the crack. From now on I intend to do a much more careful inspection of all the standing rigging each spring. I advise any owners who have been assuming that fresh water boats don't need such careful attention, to take this issue more seriously.
Bob, S/V Heatwave
Bob's photos of the swage are available in Black Arts >> Cracked Swage. –Admin
Last edited by (2004-04-30 00:42:39)
I was checking my mast on Saturday and found the exact same
crack. Sounds like too much of a coincidence that both boats had the
same failure. Parts must have some defect or maximum expected life.
Thanks for the tip Bob. I would have checked it over, but perhaps
not as carefully if you hadn't pointed it out.
John, yes this is a very interesting coincidence. I can't believe that this crack could have developed under normal conditions -- the breaking strength of this part should be over 20,000 lbs. The part looks rugged enough for a 40' boat, let alone a 26' boat weighing under 5000 lbs. I assume that your boat is also a Mark V. Would you mind telling me where you sail (salt/fresh/heavy air/light air, etc.)? Also, how did you replace the fitting. My findings (Toronto area) were that an exact replacement was not available ("no longer made"). I had to go to a size smaller and drill out the eye from 3/8" to 7/16" to accomodate the headstay toggle pin. Fortunately, the "mushroom" end of the new part is exactly the same as the original, so there was no problem at the masthead end. The part distributor, a rigger, and a sailmaker all assured me that the smaller part is plenty strong enough for the boat, but I am a little concerned that, if a heavier part failed, how long will a lighter part survive?
I sail out of Mimico and the boat is also a Mk V. As far as I know, the boat has always been in fresh water.
I only found the problem on Saturday afternoon, so I don't have a new fitting yet. Unless someone else has found a better supplier, I suspect I may also have to go with the smaller part, which isn't very comforting.
If you can send me your e-mail, I'd like to discuss further how you went about fixing it.
John Ferreira
<A href="mailto:ferreira@algorithmics.com">ferreira@algorithmics.com</A>
About 2 months ago I had a rigger assist me in inspecting my 1972 MkI, as I was concerned with the original rig which had been used in salt water environment since delivery. After a lot of polishing, we were able to detect some minor cracks in 3 of the 5 lower swedgings (I have a babystay as opposed to two forward lowers). A strong magnifying glass showed the cracks.
I chose to replace all of the lowers on the advice of two riggers who both indicated the upward facing lower swedgings are the common failures with the uppers almost never give a problem, even with this age rig in salt water in this tropical environment. Freezing is not an issue for us.
The long Navlok fittings allow you to cut the shrouds and replace the lower fittings while retaining the original wire rigging. This seemed to be a prudent approach although I will remove the mast on the next haul and inspect all fittings very closly.Warren Smith
Serendipity
I looked at the same fitting on my MKV over very carefully last weekend - couldn't find a problem. But I am interested in finding a replacement part - I'll replace it next winter even withoiut finding a crack.
Jim W
Distant Thunder
An analysis of the cracked forestay fitting is coming along, but is not complete yet. Some interesting results are turning up. The fitting has been sectioned crosswise and lengthwise to reveal the internal structure. It is composed of three pieces -- a hollow "eye" part, a hollow "ball" part, and a bridge piece that connects the two other pieces. The hollow parts are internally threaded, and are connected by a short piece of threaded rod. The threaded rod seems to contribute most of the strength. It looks like a 1/4" x 20 threaded rod. The welding probably just closes the joint between the eye and ball part, and keeps them from unscrewing.
I now believe that this fitting design would not be likely to fail in service, contrary to my original guess.
It looks as though the crack in the weld between the two outer pieces could actually propagate all the way around, creating the impression of a complete failure, but the threaded rod would continue to contribute enough strength. The crack would not be likely to propagate into the rod, since it is a separate piece of metal.
Disclaimer - I am not an engineer and this opinion carries no legal responsibility.
A metallurgical analysis of the parts shows the SS to be composed of 12% chromium, 19% Nickel, trace amounts of manganese sulphide, and the rest iron. While chemically this sounds like a good grade of stainless steel, the unofficial opinion of the anayst is that the outer pieces are of poor quality, with too many impurity inclusions and long manganese sulfide "stringers" in the metal. The purpose of including manganese sulfide in SS is to make it more easily machinable, but apparently the regions should be smaller and better distributed than in this sample. The threaded rod part appears to be of higher quality metal.
Bob.
Last edited by (2004-05-13 13:06:57)
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