Hi, Can anyone tell me when the rules allowing the bow-tanks to extend further aft came in? I suspect this makes a difference boat stiffnes and hence to performance on open water

If my memory is correct Gringo 3213 was the first low bow tank and was also the first Omega / Rowsell boat. This was in 1980 so boats around that time and number could be either - you would need to ask. As far as I am aware from 1981 onwards all were low tank configutations.