Is it just me or what? So far as I can see the pivoted spreaders on Seahawks do virtually nothing other than wear out mainsails. Mine flop about when tension comes off the leeward shroud so what on earth are they FOR? I've thought about replacing them with fixed spreaders but I can see no real point in having spreaders on a 21 foot mast. Any thoughts on this?
I don't rate myself as either a skilled sailor or an expert, so I'd welcome other views myself, but here's my understanding.
The function of spreaders are both to hold the mid section of the mast so it does not bow and to enable the the top of the shroud to meet the mast at a more efficient angle for holding it straight. On a design like the SeaHawk's, the triangle formed by the two shrouds rising from a common point on the cabin to either end of the spreader is an extremely effective method of stiffening the rather lightweight and somewhat flexible mast found on the boat.
Shrouds on the leeward side of the boat are largely redundant and it is quite permissible for them to go slack. However, excessive slack indicates that there is not enough tension on the windward side and it is the opposite side that needs tightening. But don't rush to tighten the shrouds!
As the SeaHawk has no backstay a major function of the shrouds is not only to stop the mast flexing sidewards but also to stop it bending forward when running and this backstay function is the reason the spreaders must be swept back. Obviously, tightening the shrouds excessively means the top of the mast begins to move further aft than John Bennett's drawings indicate it should be - 6" aft of the base of the mast.
So, to prevent lee side shrouds becoming excessively slack, it is quite likely that you should be tightening the forestay. Looked at from above the rig is essentially a triangular structure with the mast in the middle, though somewhat off-centre, and you should take up slack on one side by balancing the tension in both the other two.
As for pivoting spreaders, that's not just because it's a cheap and easy way to attach them. Because they are only doing their job when under tension there's no need to have them fixed. A fixed joint would not only be under a lot of strain, if not aligned absolutely correctly, it would also be more easily damaged when the mast is lowered for trailing or when in winter storage.
When it comes to damage to the main sail, I'd say there were two points. Consider altering course slightly when running to avoid going straight downwind and make sure everything on the tip of the spreader is as smooth as possible.
I understand that not going directly downwind is a standard technique for large yachts on ocean going cruises. The idea being, that once off the wind you are no longer in danger of an unexpected gybe, and the boat goes marginally faster as it moves to be on a broad reach. On a SeaHawk, with shrouds after of the mast, the main will never set properly when running directly downwind anyway.
On my original, almost 40 year old, mast I found that, after some thirty five years, the cap the end of the spreader through which the shroud passes had become firmly welded into the spreader tubing. I needed to replace the shrouds to keep the insurers happy - they looked fine! I ended up breaking off the sharp bits of the split pin that held the cap and just rubbing all the sharp bits smooth.
It was the rigger who came out from Jeckells, to assist me, suggested I do that. He was a guy who had worked for Jeckells since leaving school and claimed to have been sent out to Reedcraft to rig just about every SeaHawk built there. I took him to be a man who knew what he was doing.
I agree with all you say Greg and I've tensioned the rig so the leeward shroud still has tension on a reach (gives me 7" rake on the mast which is OK) but I am still not convinced the spreaders are doing what they should. They should have compression on them when on the windward side but it's not obvious. I wonder if they could be a couple of inches longer? I have some 19mm alloy tube so I'll make some longer ones as an experiment.
I've always sailed down wind in a series of broad reaches for exactly the reasons you state, but sometimes you can't do this (e.g. in confined areas like harbours and rivers). I use self amalgamating tape on the spreader ends to minimise sail damage. My end caps are, like yours, firmly welded by old age to the spreader. The pins are long gone.
BTW - I have now made a gasket from closed cell foam that fits on the underside of the keel plate handle, sealing the gap when the keel is down. Not a drop of Lyme Bay gets into the boat now :)
Have you been following our magnificent Lyme Regis ancient rowers, the Corinthians? They've just made it across the Atlantic http://www.taliskerwhiskyatlanticchallenge.com/ I reckon it's about time a Seahawk did this.........................