Philip,
I have info on two Superseal 26 boat IRC forms (Lesa and Knave), though they are quite old circa 2008 to 2011.
These are basic empty weights without any gear. They are 6437lb and 5996lb. Lesa has a Yammer 1gm10 and Knave a Beta 10hp. they work out as 2.87tons and 2.66tons respectively. If you start weighing your gear you will be supprised how much it weighs. I did some quick calls on Memo weighting fuel, water, tools, kedge anchor, fenders and all the other paraphernalia I could find and it was a substantial amount, probably 1/2 ton +, so your crane weight may not be so far out.
Out of interest was the crane load direct from a hook sensor or from the crane as the radius of lift will affect the crane jib load seen at the crane base.