Just purchased a new set of shrouds for 3321, and was wondering about spreader lenghts.
old shrouds were fixed at the shortest lenght to the spreaders ( first hole in from the Wire was where the screw was) and I wondered if anyone had any thoughts on moving the spreader plate out a hole or two with a view to increasing the rig power. If I lenghten the distance from mast to spreader tip ( and therefore shroud) I straighten up the top section ???

That seems counter-intuitive to me.  Is the issue not the degree to which the shroud changes direction at the spreader tip, and therefore the extent to which the spreader transmits shroud tension to the mast?  If you had no spreaders, the shroud would probably hardly bend the mast at all, irrespective of how much tension you put on it.

See the articles in the library (GGGGG on setting up the mast) for a detailed overview on this.  There's a point where you will push the middle of the mast to leeward if you lengthen the spreaders.  You are looking to push the shroud out about 30-40mm from the straight line.  As shroud bases differ so much from boat to boat there are no golden figures for offset and angle for older boats.

You have to be a member to access the article, so if you are not, there's another example of what you get for your £20

Here's one of the links.

GGGG's article is good for new, stiff boats. On an older, softer boat the 'out of line' may have to be significantly more,- depends on what you're trying to achieve.

I have printed GGGG's guide out and the others. Having come from Lasers into the merlins the only thing I know about seting mast's up is plugging the two bits together.

i guess I am trying to get a little more power from the rig. It's a case stepped low bow tank boat from 1983, lowers but no strut with fixed jib tension ( jib hooks into mast, rig tension comes from throwing levers on shrouds) ans I realy was just loking for advice as to increasing the distance from spreader tip to mast with a view to powering up the rig more.
Guess i experiment and see what happens..

Does it not depend on sail cut, crew wieght etc.  I think that tuning guides are great for one designs, but with things like the merlin you need to get the right guide for the right boat .  Dick Batts guide is good for older merlins. Best thing to do hamish is try diferent settings.

Jib hooks directly into mast? Is that common?

It would apear to be rather unusual on merlins - certainly the only one i have seen. It means the rake is pretty much fixed - the only way to lenghten the forestay is to add shackles!

Pity you can't have the jib tension (and thus rake) adjustable from a purchase on the tack of the jib, led under the foredeck. But then of course the jib would rise off the deck as you raked.

Mags
This has been done - the jib needs to be converted into a stuff luff so that the bottom does not ride up the deck.

Crewcut 684 and Beat Nik 1523 both had adjustable jib tacks but the fashion then was for a low cut jib a bit off the deck anyway and a bit of wood with holes in it served as adjustable job fairleads! Crecuts wasa fearsome affair with bike chains and levers Beat Nicks just wire rope and purchases, there were lots of others. But then things moved on.

Aha! The stuff luff....of course!
Leading this purchase from the chute down to the kingpost (as low as possible) would reduce the stress on the hull a bit, and counteract the kicker...no?

Still pondering my plans for deck-stepping 3245 you see! I know I moan about DIY in the home, but with the boat its another matter entirely.

Mags I basically copies Lawries layout that he used on 'smart tart' on my NSM the photos youve posted are pretty clear, the only difference is that I used a couple of 15" harken mussle boxes which reduce the point loading & secondly were just sat in the shed!! It was more fun than decorating regards Barry.

Mags

On the one boat that I have seen with this (White Whale), the amount of rake allowed for the mast is not all that great and you would probably be better going down a more conventional route.