I never boil mine. Depending on the size of it, wrap in foil and roast until the meat is almost done. Remove from the oven, allow to cool slightly, the remove the rind and most of the fat. Then spread whatever kind of mustard you like over it, then press brown sugar onto the mustard. Turn the oven up as high as it will go, then return the gammon to the oven and cook for a further 30 mins. Delicious hot or cold
I put a gammon joint in the oven a couple of weeks back and fell asleep for 6 hours. The roast potatoes were, of course, carbonised. But when I took the foil off the gammon it was lovely.