Most catamaran bowtubes are alum. or carbon mast sections. Some builders are getting shocking quotes to get these built, so they are considering ply/epoxy bow tubes.
I do urge using the best plywood and do not skimp on construction as this is a mission critical part of your cat.
One thing, ideally the tube end bolt would be not 90 degrees but parallel to the hull. I am assuming the hulls are rigid enough that the delta is not significant enough to upset that pin.
Corners are biaxial roving. The red is biaxial bushing. Blue is triaxial. Yellow is the stainless. There will be cross laminate to hold the triaxial onto to the box.