Just reviving this thread now that I've calculated my boat weight.
I used the method quoted on another thread which involved weighing the jockey/nose weight, then shifting the boat back a few inches and re-weighing before a few calculations based on distance to axle etc. I did this a few times with different positions of the hull and they all came out at about 1150-1200kg. Add to that the trailer weight of 420kg (as stated on design plate)and we are at about 1600kg +/-.
The trailer axle is specced at 1500kg so it's safe to say the trailer is not really the right one

. I assume the self-weight of the axle could be deducted but I doubt that's going to be anything like 100kgs+ so it'll still be over. If i'd bought the boat fully rigged from Osprey I'd be having words. As it was part home built, I will accept responsibility for not checking. However, it would have been nice to have been advised when trailers were discussed.