Impervious Ships (spoilers RWC)

[Farseer]

in the midst of that re-read of CoD, these beings got the inklings of a theory on these ships...

It was apparently a formula, so its probably some coating.
Apparently it was a pirate isles concoction.
Maybe, in good old style of the convoluted interconnection you love Farseer, it could be that Winthrow is involved somehow? He's more a pirate Islander than a Bingtowner by the time of CoD.

...

Even if Winthrow isn't behind the formula, he no doubt knows of it.

What of Reyn and Malta's reaction to the boat that followed them? I'm not sure if that would fit with the theory that Wintrow is involved. Surely, if it were Wintrow, those two would have known of his plans for the making of the formula and then any later use for it? Wintrow would surely share such things with those two, of all people? Would let them know that he, or someone else, was making his/their way up the Rain River? Surely either he would go out on deck or, if some delegate of his was on board, they would make sure to make themselves known? Especially to a crew aboard a liveship?