Imagine you have made your plug and it's shiney ready to mould...use honey wax to wax it about 5 or 6 times then decide where your shuttering needs to be to allow removal from the plug....when shuttering sorted pva release using a sponge, let it dry then gel coat, leave this to go tacky..ie you can leave a finger print in it but nowt on yer finger then startlaying up...when you have got the layers needed take the shuttering off and lay up the other side to create your joint......simples really.

Grab someone from the boat yard and barter with a few pints you might even end watching him do it for you...