Panel or Not to Panel?

Isnt the top battened part of the sail meant to be almost flat anyway i thought this was the point of the square head?

 

Depends on the wind strength and what means you have to control it. On my boats there is an upper outhaul that makes a huge difference in sail shape in different conditions. Look closely at the sail in the picture; you can see the shape it has at the very top....

 

Alex, I guess you'll be disappointed that the schools Strathclyde 70 competition has been cancelled for this year - so were we. But hopefully you'll be keeping at it and planning to race next year!

So here are a couple of comments aimed especially at Strathclyde 70s.

There haven't been any gaff-rigged ones so far but "Loki", no 9 in the attached picture won the 2007 Students' races with a slightly different arrangement. The tip of the mast is bent back but it doesn't swing like a gaff. So you don't have the problem of the head of the sail falling away to leeward, and in fact the mainsail set very nicely to windward. But it didn't look at all good when sheeted out downwind.

I would also reiterate what's already been said about fin sections. If you don't learn any other bits of science, learn about foil sections. Nothing else is more important when it comes to designing a boat that will go to windward.
If I can add something of my own on this...

Choosing the right section depends on you having first made the right choice about fin area, and this is a difficult one. I don't think there's a good explanation out there of why you need proportionately bigger fins on smaller boats. I have puzzled a bit over performace at very low Reynolds numbers but I think maybe it's something much simpler. The sideways parts of the lift generated by the rig and by the foils have to balance one another. Each will depend on the area and the air or water speed. Wind speed isn't much different for a Strathclyde 70 or a sixty-foot ocean racer, but the ocean racer will be going about 10 times as fast through the water. So proportionate to its sail area, the ocean racer can manage with much less keel area.

Strathclyde 70s aren't very highly developed boats and even an International One-metre will go through the water at nearly twice their speed to windward. So it follows that a Strathclyde 70 is going to need a lot of fin area. I suspect many of the existing boats have too little. If your fin is too small you will need to make it quite thick, with the maximum thickness well forward, to get as much lift as possible out of it and stop it stalling at low speeds. But there will be a price to pay in drag.