lower shrouds angle

[benz]

I'm in the throes of designing a gaff rig for my Cape George 31' , and was advised by a master rigger to attach the lower shrouds higher up the mast than what I had drawn, so that the gaff should have more room to swing. Moving them higher, however, decreases their angle from the mast centerline to less than the 12 degrees suggested as a minimum by the "Rigger's Apprentice". It has occurred to me to bolt a plank to the hull where the chainplates are to go and bend them around the outside of that, to give more width down there, but this doesn't seem to widen the angle all that much, at least on paper.
Any suggestions?

[Brion Toss]

Hi there,
Boy, did you get some dumb advice. What kind of an idiot would tell you to decrease shroud angles? Oh, it was me? In that case I'll rationalize the heck out of that advice.
This is a fundamental problem with gaffers, and it is even worse on sloops and ketches, where the main tends to be further forward, where the beam is even narrower. You're lucky if you can get 10°.
But that gaff has to be able to swing. The "bolting a plank on" course that you mentioned is one possibility. The resulting extensions are called "channels", and they need to be quite thick, usually with the longer dimension being horizontal, to increase the span enough to make a difference.
Another possibility is to shorten the throat of the sail. This raises the peak angle, limiting the radius of rotation, so the gaff hits the wire later, under lower loads, and gets the jaws altogether away from the wire, which is supremely important. And by the way, a higher peak angle is in general a good thing, within limits, for improved sailing efficiency.
But the only way to avoid the problem altogether is to run the gaff on a track, letting you put the shrouds where you wish. Major design can of variables here, however, along with some cost-intensive hardware.
So I'd work to optimize the traditional setup by whatever means available, and reconcile myself to the fact that you aren't going to get as generous an angle as you might want.
Fair leads,
Brion Toss

[benz]

Thanks Brion,
I figured my plank idea had to have a nautical name. Channels...I like it. I've certainly considered using a standard mast section with a track, but yet another reason I'm going with a gaffer (a pretty small reason among many others, though) is that I dislike track slides and cars and all that paraphenalia. And mast sections are expensive. I made a full-size model of the bit of mast where the shrouds attach and the gaff sits, out of a bit of stovepipe and some ropes, and put a model gaff jaw against it to see about the swing (I have to do things that way; not good at scaling or theorizing), and I'll dust it off and try it some more with different peak angles.
Ben