The white bulkheads are polypropylene as it was the most material I had when rebuilding Kaizer, and it was a bit stronger than the previous HDPE bulkheads. But it is prone to cracking/shattering upon large impacts (just look at Carcinus) so that would explain why the supporting bolt would have ripped it off.

It's also a matter of how things are mounted; bolt placement and distance from edges etc can alter the levels of localised stresses, leaving some areas more prone to cracking/shattering than others. I just put bolts in where I thought to be the best areas.

If you were to replace that with Nylon (especially if you go to 20mm Nylon like the wedge triangles - there's definitely enough weight for it) you wouldn't suffer that problem to the same degree. I'm not saying that it would eradicate the problem completely but the likelihood of a repeat scenario would be greatly reduced.

Out of interest, did any of the wedge triangles take hits? How did they hold up if they did?