Originally Posted by TeddyDiver
That's just stupid engineering to think ply core to spread loads, ... aluminum is best to leave for aluminum boats, nothing to do inside the composite layup
I'd just like to clear up some obvious misunderstandings here.
Extending a backing plate beyond load area is an inefficient method of supporting and transferring the concentrated loads from heavily loaded fittings. Just as a cored deck
fails when the core breaks down and allows outer layers to slide and flex independently, so it is with a large backing plate (except directly in way of bolts): the plate outer edges can move independently of the next layer, so much of the stiffness is lost. A better engineered solution is to build in that backing (whether aluminum or plywood) within the last few bottom layers, so they become an integral part of structure, increasing stiffness without increasing thickness/weight.
Muckle's fear of ply or timber core is sometimes well justified: because the ply is supposedly encapsulated, some builders will use inferior plywoods, they may skimp on sealing the bolt holes against water
ingress, and may use the wrong resins (most resins adhere well to end-grain but only epoxy
holds permanently to timber or ply). So timber/ply core used anywhere demands quality build. But then so does balsa (think of the number of boats with failed balsa-core decks) and any other core material creates equally serious issues over time, if quality of build/maintenance is lacking.
Let me know if you find someone offering solid glass hulls built entirely with epoxy - except for hi-tec, weight-saving, one-off racing
machines (never designed for longevity, and more likely to be cored), they must be rare as hen's teeth. Not sure it offers much advantage in strength either (unless you want to minimize thickness - never a great idea in a non-cored cruising hull). Only the water absorption is prevented, and that can be done with epoxy outer layers alone.
I think that's a fair assessment but feel free to correct anything I missed.