Regarding distortion , i would definatly have a practise first on similar material to what you weld before starting proper . This is good sense on any job , to set up the machine so you don't use excessive power and cause distortion. Its good practice to mark out were your going to weld with a marker pen /chalk etc , so that you can have the tacks or stich weld equaly spaced . This way you can do a burst on one area , then move to another , allowing the welds to cool before you continue.
Practise is everything with welding , so get hold of as much scrap to practise on before you attack your boat !
Good luck!!