Yacht Repair on balsa core

[Brother D]

Not sure if this is the right place to ask... I follow many channels on YT but one I support is this guy who bought a hurricane damage cat and is the process of properly repairing it.

https://youtu.be/7xyybKdBgrk

So my question is why do the yacht builders use small blocks of balsa as the core material? Why wouldn't you use long planks or at least strips?
I get using the small blocks on compound curves, but for long straight areas why not use planks?

[Arnold Cunningham]

Because for the type of loads a panel will take, end grain is the right way round. If you had a "beam" of balsa in there, the structure would be an awful lot weaker.

Balsa in a boat is always a dilemma. It's incredibly good if done well, better than most, arguably even all, other core materials - but you absolutely must prevent water ingress or it just turns to mush. So when people start screwing in to it (which it's crap at), moisture gets in and it all turns to mush. So good structural and system design is a must - and then, when done well, nothing really beats it for taking a punch.

Edited by Arnold Cunningham on Thursday 24th October 09:22

[Brother D]

Thanks AC that makes sense. Recall building model planes it's pretty squishy along the grain. I just assumed it served the same purpose as foam (like in my windsurfing boards) but reading up, foam is no where near as good as end-grain balsa for point loads.