D2 Forward or D2 Aft?

[pandora25]

I own a 38' boat with a carbon rig and double aft swept spreaders.
The rigging is wire, a combination of dyform and regular wire.
Backstay only. No running backstays.
D2 are continuous and terminate at the deck. I have always terminated these aft of the caps.
A new and experienced crew member believes I should be doing the opposite, terminating them forward of the caps. That this effects rig tune in important ways, even how the backstay will be able to bend the mast.

This is news to me and the rest of the crew. Indeed, the distances between the wires at the spreader tips and on the deck termination are so small, it is difficult for me to believe that it makes a real difference.

The deck termination is one solid steel piece with the Caps, D1 & D2 all terminating within about 3 inches of each other (D1 inboard, Caps & D2 outboard). It all looks equally strong so either outboard termination could hold the cap load.

The top spreader has a generic tip with 2 holes, so the cap can be directed either forward or aft.

There is no information in the owners manual about this and the boat does not have a class tuning guide.

I’d appreciate hearing comments

[Brion Toss]

Hi,
I commend your deck crew for having an inkling, at least about how one can use swept spreaders to impose and control bend. It is true, in theory, that moving the intermediate to the forward position would make the wire behave more like a diamond stay -- or like a B&R rig --but I think that the effect of a change in position in this case would be hard to measure. We are talking about an angle of less than 1 degree, if my math is right; there just wouldn't be enough extra compression on the spreader to make a measurable difference.
It also seems likely that, by moving the upper shroud aft, you would in any event be undoing any compression gains for the intermediate.
So go with the principle, which is correct, that the angle over the spreader tips affects mast shape fore-and-aft, and tune accordingly. Get a rough shape in, then tune from the top down, leaving the D1 quite slack until the very end. For more on this, please see my tuning video.
Fair leads,
Brion Toss

[pandora25]

Thanks for the reply.