Stuart,
You've just put a smile on my face... because the true sign of a forum's success is when you start cross referencing older posts... and this is the first time we've ever done that on here!
Thanks!
So heres a relatively recent post with a reply I made:
http://www.heron-dinghy.org.uk/component/option,com_fireboard/Itemid,135/func,view/id,204/catid,1/#204
Lengths:
Main Sheet - needs to be sufficient to go round your blocks (config optional) with the boom hard out against the shroud, and then of course enough to reach your hand in the helming position. If you assume that the boom goes to right angles then roughly speaking you'd have a right angled triangle with two sides the length of the boom (2.4m roughly) - depending how you have set up your blocks you might have 2 or 3 loops - giving you 7.5m and then about6 another 1.2m to sail wiht. That gives about 10m - which is what Kevin Butler supply as a standard Heron Main.
Jib similar principle enough to allow the jib/genoa to be sheeted in tight to the port block, and then the starboard sheet to go round the mast and through the starboard block (plus stopper knot) If SH some people like to tie the two free ends together - so add an extra metre... then remember to double the length as that was just the starboard side of the sheet. i'm sure Kevin used to list a 6mm jib sheet but can't remember the length.
He also lists halyards as 24ft - I'm guessing as they are both the same length that is for a gaff rigged boat. Mast of a gaff rigger is 3.2m (10.5ft roughly) So 24ft gives enough to go up and back down the mast which is how you'll start off before pulling the gaff or jib up. If you are going bermuden you'll need longer I would think.
If you have the money dynema is incredibly strong - but the very thin stuff 2-3mm will take your fingers off if you hold it and it pulls through your hands... like cheese wire! It will possibly also eat into blocks! The average heron just uses a low stretch plait for halyards. Sheets - think comfort and low kink...