So my mast on the H2 is one of those lovely carbon super spar things, we have an adjustable forestay but no lowers. I picked up an idea that if you are at the top end of the weight range you might want to make the spreaders longer and angle them more forward (less sweep). Can I ask why?

Where the mast sit further down within the pyramid is determined by the spreader rake. They push the mast about relative to the shrouds (and the hounds and the mast step).   

The other important thing to mention is rake. Raking the mast back will create more mast bend assuming you keep everything else the same. I find it better to set spreaders for what I generally think is good, then use rake to depower the rig before a race (but in the 200 we have to go in to iron to adjust rake on the water). Rake is usually far easier to adjust on the day and I feel has a larger impact. But that depends how easy all these things are to adjust on your boat though. 

Got it - but I will try not go that far and besides the mast is very good at bending in gusts and depowering already so I would rather trade some downside for more power especially as I am built like an ape and love hiking my nuts off!

I suspect that I would concentrate on keeping the lower mast pretty straight athwartships by lengthening the spreaders, since it is not like a two sail boat where you are trying to open the slot In the gusts.  That way you could concentrate on calibrating the fore and aft bend for a given wind strength.  

One thing that I did not quite get is the absence of any control of the lower bend, but I guess that all H2s have the same set up.

If I had one I am sure that I would get great reward from buddy tuning, to help with set up and calibration.

It might also be worth talking to HD to establish how they envisaged the mast/spreader/forestay setup.

One thing I will add, is I've always been a believer that you can override a 'too straight' mast set up by pulling sail controls to de-power. However, downwind you can't make the mast any straighter once your down-haul / kicker is fully off. It's always easier to rake a mast too which is often adjustable on the water, or as least without dropping the mast.

In the 200, for example, it gets to the point where the kicker is off so much you lose any leech control. I've found it better to run a straighter mast, so I can still keep a little so kicker tension and have nice depth. Then just kicker the hell out of it upwind (and not run too much rig tension). 

Obviously if you're not in a SMOD you could get a differently cut sail or different sectioned mast too... Just be glad you don't have caps and lowers and weight on trapeze wires to worry about too!

Spice has two wires, and TBH I should work out how to maximise power with just one trapezing as I'm not the best at helming off the wire and don't have a regular crew who can compensate for my shortfalls.......

I did have a graphic demonstration a few weeks ago, a blasting day with my mate in his Blaze and me and irregular crew in the Spice, the difference between t'crew wiring and not was dramatic (should be obvious but we were just having fun reaching up and down......).

So, yes in principle the more lowers the straighter the bottom section. This will help create a bit of grunt down low. However, we never really measure tension for lowers, we just went on how the sail looked, where the starvation creases developed when increasing kicker. So, my feeling was it was more about balancing and distributing kicker forces so there is a nice even bend in the mast. 

Similarly for caps, they just really supported the huge kite downwind. Upwind you'd want them pretty loose to allow the rig to work, maybe a bit more on in the light to open up the top of the sail and let it breath. 

Simply put, spreader rake will control the static bend in the rig, or the amount of pre-bend that the mast gets for a given forestay tension. Once this is decided the length of the spreaders will dictate the stiffness of the mast in changing conditions, so essentially gust response. The only concern with overly long spreaders, particularly when you have no lowers at all is that the mast will sag in the middle and the tip will actually move to windward. This is particularly true when the rig is set up very slack, less of an issue when there is still plenty of residual shroud tension on the leeward side. 

I think the first thing to decide is whether the rig likes to be slack or tight, I would imagine without lower mast control or support that it would be safer to have it on the tight side. When I first got my RS100 when they were brand new I turned up at the nationals having only sailed the boat for a week, the only way I could make it feel right was for the rig to be so slack that upwind the shrouds were both slack, it was rocket ship fast but that boat has good support at deck level. In that case I just wound the spreaders back as far as they would go to help prevent the mast inverting downwind. 

I agree that playing around too much with the rig on the water can often be more a distraction than good. But spending time off the water on getting a decent set up seems like a good use of none sailing time at almost all levels. 

It's usually something which can be done over couple of sails to get a workable set up, then after that it's just set and forget. Most classes have a tuning guide, so with very little thinking you can just copy a setting out of their then focus on sail controls and what you do on the water. 

I think it's harder in the new classes, like H2's hadron where there is less likely to be accepted ballpark settings so you have to work out more for yourself by putting in to practice the theory. .