trick is with deep water, if you are fishing more than 1 on a string, is to make sure the length of rope between pots is greater than the depth, so the first pot is on the boat whilst the second one is still on the seabed... otherwise your hauling a lot of weight up at once!
there's a curious little loop hole in fishery law for boats under 10 metres....
if you've got no engine (sails or oars) you can legally sell your catch, fish or shellfish without a licence or commercial registration