Cunningham question

[Chatham Sailor]

What’s the advantage of attaching the Cunningham primary to the vang area and running it up to the tack as opposed to using the gooseneck or the gooseneck hole for tying off? Would have fewer lines and bowlines crowding up the vang area and the primary wouldn’t get pinched in the gooseneck (as it sometimes does).

 

[LaLi]

I have mine tied with a bowline around the mast below the gooseneck. Works fine and uses a bit less rope. It pulls slightly more forward so it’s not the best possible angle but so what.
My gooseneck holes are filled with outhaul-related equipment...

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[Chatham Sailor]

Mast tie off is a new one for me but it makes sense.
Sometimes I just wonder what a (slightly corroded) vang junction can be expected to take in terms of stress. I wonder if that’s ever been measured. You don’t really hear about people ripping them off the mast so I guess it’s plenty strong.

 

[AlanD]

Without knowing exactly how corroded the fitting is, you can't tell how strong it is. My suggesting is to replace the fitting. Over the years I've seen many broken vang tang fittings.

Personally I use a loop of shock cord to retain the mast (though both deck eyelets and over the tang fitting), as it reduces the shock loading if the line is ever really needed.

It's also worth checking out that the line will restrain the mast from falling out, see if you can pull the rig out with it on and no Cunningham. I've rejected way too many when measuring, it's there for a purpose and it's meant to work.

 

[LaLi]

the gooseneck hole

Tested this, too, a long time ago. It's clean and simple, but the hole edge is just sharp enough that the line needs to be repositioned/replaced quite often. It's better to use the holes to attach outhaul blocks!

Sometimes I just wonder what a (slightly corroded) vang junction can be expected to take in terms of stress. I wonder if that’s ever been measured. You don’t really hear about people ripping them off the mast so I guess it’s plenty strong.

There was some talk a few months ago how much "extra" load the cunningham exerts on the vang tang and how it should be attached. Some thought there's a huge difference in different cunningham setups in this sense, but I remain skeptical. Of course, no one ever actually measures these things... The original vang blocks are rated at 300 kg, they've never broken (I believe), so the real loads are likely much lower.

I have broken one vang tang myself, it cracked on one side at the "corner" right next to the mast. I think there's a built-in weakness in the system in that as the mast overrotates just a little, the vang pulls at the tang at a slightly different angle on each tack, and this causes extra stress.

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[Emilio Castelli]

There was some talk a few months ago how much "extra" load the cunningham exerts on the vang tang and how it should be attached. Some thought there's a huge difference in different cunningham setups in this sense, but I remain skeptical. Of course, no one ever actually measures these things... The original vang blocks are rated at 300 kg, they've never broken (I believe), so the real loads are likely much lower.

I have broken one vang tang myself, it cracked on one side at the "corner" right next to the mast. I think there's a built-in weakness in the system in that as the mast overrotates just a little, the vang pulls at the tang at a slightly different angle on each tack, and this causes extra stress.

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Assuming we pull with 15kg of force (? probably more) the vang load on the tang is going to be 225kg; if you attach the entire cunnibham load to it, you'll add another 120kg (so about 50% more).
The vang tang can break when you release the vang because force is applied at an angle, at a point distant from the tang.
When the vang is on, the mast is not going to over or under rotate.
With a radial sail you want to be able to pull the cunningham past the boom; attaching it below the gooseneck might work, on the gooseneck probably not.
E

 

[LaLi]

Assuming we pull with 15kg of force (? probably more) the vang load on the tang is going to be 225kg; if you attach the entire cunnibham load to it, you'll add another 120kg (so about 50% more).

I'm assuming you assume a 15:1 vang and an 8:1 cunningham, feel a force of 15 kg at the tail of both, and no friction?
Whatever the cunningham load is, it pulls along the mast, and therefore can't be added directly to the vang load at 45°.
(These things should really be measured. There has to be some reasonably cheap and easy way that doesn't require load cells...)

The vang tang can break when you release the vang because force is applied at an angle, at a point distant from the tang.

Theoretically the pulling angle doesn't matter, but I think you're thinking about the whole vang cleating fitting acting like a lever when you pull the vang at a 90°-ish angle to the boom?
The distance doesn't mean a thing. Or do you mean the distance from the tang to the cleat swivel?

When the vang is on, the mast is not going to over or under rotate.

The vang won't affect this only if the tang (which the vang pulls) and the gooseneck (which the vang pushes) project the same amount from the mast, so that those levers cancel one another. I'll come back after making some measurements

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