Glad you liked the videos. You can see them all by searching for www.sailingcatamarans.com or Woods Designs sailing catamarans in youtube. More clips will follow, especially of Tucanu sailing with the cuddy.
We changed Tucanu's beams to aluminum to save weight. Then we put that weight back on by fitting the deep mast beam.
Fortunately I was able to get some mast sections that had a very flat bottom (ie aft face when used as a mast) In fact most modern mast sections are that sort of shape.
Then I made some hardwood chocks to stop the beams twisting or moving in the boxes.
Finally I fitted the beam straps through U bolts bolted to the top of the beam. These prevent the beam twisting and also stop the hulls coming apart.
So far, after one season heavy use nothing seems to have moved. There is certainly no squeaking or visible flexing.:
I will put the photo back soon (I am not in my office right now so cannot do it)
Yes you can build Merlin in double diagonal plywood rather than strip plank. I send the Strider plan sheet as well as the Merlin one to help you. You need 2 layers 3mm ply.
You can also build Strider in strip plank instead of cold moulded, in which case I send you the Merlin build sheet
I hope this helps. BTW more boat photos are always welcome!