Re: Chain plate or impact.
That looks like impact from the INSIDE. A hit from outside that could cause that sort of crazing would be unlikely to have totally missed the teak rails. I would think there would also be a more distinct primary impact point - down to the glass - instead of just crazed gelcoat.
Could be caused by the expansion of corrosion inside those miserable glassed in chains.
Either way, happy grinding.
I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.