Our dive club had two ( early) Northcrafts) - 5.5 and 5.9m.
BOTH suffered similar issues - flexing , cracking and delaminating decks, and hills splitting along the chines !!!
A couple of features - insufficiennt stringers ? in the build up - and a lot of wood unglassed ........ add water .......and ..... sponges
The hulls were particularly thin which I guess was a feature of the low cost build but in the end ( 2000) we scrapped them as unseaworthy
......... I am sure the latest ones are much better designed and built ????!! but I personally wouldn't ........