Thanks for all the advise, a lot to mull over!
I think I will contact Shetland to find out what the boat should weigh, and then get the boat weighed. My Alaska 500 has a cream coloured hull, think that means it was made by Shetland prior to selling the design to Seahog in 1988 when hull colour was changed to white?
Sounds like I'll just have to cut some inspection hatches to have a look if weights don't match.
Thanks again for all your help.
Cheers Ruairi