Sorry Guys

Do you know the clock face type scales with a hook on the bottom and a handle on top (you can buy them in the fishing sections of say, Kmart)

Tie that to the boom, get your mainsheet or another rope and make a sling that lifts off 4 points, so the boat can be lifted without rocking, somewhere around between the centrecases and mainbeam, two people one either side, or one standing at the mainbeam (between the hulls, the other at the rear beam, lift boom and boat, one of you should be able to see the scales clock face to get the weight.

It sounds complicated but its not, I wish I could show a picture of what I mean, I'll see if I can.

Regards