Two- versus one-part tangs

[S/V Liberty]

Are two-part tangs (i.e. tangs which accept eyes) superior to one-part tangs (i.e. tangs which accept forks)?

It seems to me the one-part tang has the big advantage of guaranteeing fair loading of the clevis pin provided only that the angle the tang makes with the mast provides a fair lead and that the clevis pin hole is drilled at a right angle to the tang itself. With two-part tangs, particularly those in which one part is bent twice to accommodate the eye thickness, you have to get both the angle with the mast correct AND drill the holes in the two parts in just the right places in order to get fair loading.

I have seen one boat where one part of the two-part tang broke, and the second part lasted long enough to get the boat to port for repairs. But perhaps a thicker one-part tang wouldn't have broken in the first place?

Perhaps the reason is that the two-part tangs can be made adequately strong using less metal and are thus lighter? Or provide more space between the inner tang surface and the mast so that a single-part tang would have to be longer (and thus heavier) to provide the pin and cotter enough room to clear the mast?

I must be missing something.

Seth

[Ian McColgin]

Since what you call one and two part and others know as eye and fork must always be paired, eye to fork, never eye to eye or fork to fork, I can't understand your question. It it's eye on the tang it's fork on the cable and visa versa.

It's more normal for the forks to be on the cable rather than the chain plate or mast tang for simplicity of manufactoring but hardly always, especially with the large number of fork mast tangs one finds made up from, as your terminology correctly puts it, two parts.

G'luck

[S/V Liberty]

Originally Posted by Ian McColgin

It's more normal for the forks to be on the cable rather than the chain plate or mast tang for simplicity of manufactoring but hardly always, especially with the large number of fork mast tangs one finds made up from, as your terminology correctly puts it, two parts.
G'luck

Yes that was my question ... In fact the majority of mast tangs I've seen are made up of two parts (a "fork tang"?), mating to an eye at the top of the shroud. Yet it seems to me that a one-part tang (an "eye tang"?) is superior because it's easier to ensure fair loading of the clevis pin. The only critical parameter in an eye tang is the angle made with the mast whereas with a fork tang you need to get at least two if not three angles right and then get two holes lined up properly.

So why aren't one-part tangs more commonly seen?

Seth

[Bob Pingel]

I think the reason that most mast tangs are configured a "forks" is because fork terminals on wire are not real practical. You could use an aircraft fork, but they are suboptimal in marine applications. You could use a marine eye toggle but they are expensive (twice the cost of an eye) and toggle action is typically not necessary.

Yes, the tangs are a bit of a bother to fabricate, but it seems to give the best and most economical solution.

Bob Pingel

[S/V Liberty]

Ah OK. Hayn seems to make some nice swaged "marine" forks that don't have the smaller clevis pin hole that the aircraft forks do, but, yes, they are way more expensive than an eye of similar strength. But you're right. It makes more sense to put extra effort into the mast hardware (rarely changed) rather than extra expense in wire terminals (changed more often). Thank you for setting me straight!

Seth

[Ian McColgin]

I must be missing something.

If you have a fork it must go to an eye. I can't imagine a reason, except ease of building, why it matters which is which. Chainplates are usually a single tang and very robust, filling the space in the stay's fork. Mast tangs can be either but it's often easier to work with two pieces of thinner stainless to make a fork than to work with one to make a tang - depending on where. An over-the-truck tang that holds both headstay and backstay might be more readily made of one piece with forks on the stays. Shroud tangs, especially lowers, might be forks but might be eyes if made up Herreshoff style for screwing to a wooden mast.

Assuming they are matched - and manufactorers seem to be wonderfully consistant in pin and hole sizes and matching for a give wire size - you will have a fair load. Forks and eyes are ubiquitous in the marine industry.

I could see some unfair loading if the fork is really made of two tangs coming out from some bolts into the mast. Unlike a forged fork that you'd find in a stay terminal it is easiy to imagine that one could have a little misalignment. As it happens, most people drill the hold-down holes in the outer tang first, then put the pin in both and clam them to the bench while drilling through to the inner tang. Or pin, clamp and drill them bother. Either way, it's hard to go wrong and it's hard to fit the correctly sized pin through misaligned holes.

G'luck