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NicoDC said..
Very interesting topic.
Amongst shapers, there's a lot of discussion as to what is the best construction.
It is generally accepted that you need a pvc cassette for the tracks to go it.
You have some shapers that use PU pouring foam, but the final result can be unstable or remain to soft so this is not common practice.
connecting from hull to deck: some go from deck to hull with pvc only (so 1 super thick block) at the cost of weight, some use a couple of pvc sheets as beams to connect them with top and bottom, some use only a +- 3,5cm pvc block for the tracks (some put fibre under this block, some don't).
then there's the carbon-fibreglass discussion.
in my experience, I've only seen boards that failed because they didn't have any pvc cassette. Full-block, carbon,. seems to be less important.
For heavy duty (massive jumps and putting the foil in the extreme ends), a full pvc would be best suited imo. Carbon is overaten (fibreglass simply is stronger!! Carbon is stiffer, not stronger and only a couple of grams lighter).
i use a 3.5cm hull pvc block with a strong fibre patch under and over. So far so good.
Common practice in windsurfing that is relevant for foils are mast tracks. Construction is this: eps, strong fibre (glass or carbon) big pvc or PU block, strong fibre, mast track.
I've seen more wingboards fail in other areas.
IMO, shapers tend to use the HD cassettes because they work AND are easy....one router template and they're done. They aren't perfect though, the straight edges and bonding of vertical surfaces of very hard and very soft foam set them up for shear and hinging unless the area outside of the boxes a very stiff....ie multiple layers of differently biased carbon.
I use pour foam, very dense... again pros and cons.
Pros would be that you can expand the footprint of the "cassette" and engineer the shape to be round, have legs or whatever you want so as to spread the stress a bit. You can pour into undercuts. Can even pour it around stringers etc. Ditto with deck anchoring pillars.
Cons, it's not as easy to mix and pour consistently as one would hope. If multiple pours happen, it can striate horizontally and that gives the foam a weaker layer of stuck together foam to break along. It exotherms too, and in sufficient volume it's hot enough to bugger up the touching edges of EPS...which you'll never see until you dig it out.
To be really sure you need to layer fibre (hopefully carbon) in 0*, 45* and 90* orientation to get the most stiffness possible, some distance outside the perimeter of the foam and feather the edges or use a roundish footprint so it doesn't leave a hinge. If you're using carbon, probably best to bag it as that gets the best from the material and stops pooling of resin around the foil tracks.
I've only broken one, that was from a nuclear hit on a sandbar at speed..but it didn't come out, took a couple of months to get sloppy.