Ed Minch wrote:
"I have also used it [redwood] on our tall ship for mast tops - platforms at the
top of the large lower masts that were used as sniper locations in the 17th c.

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"This is where we learned it is not rot resistant"

I think the point about  redwood is that it is pest resistant, not rot
resistant. The same chemicals that make a redwood splinter in your finger
fester, do a real trip on bug bodies. I'd be willing to bet---you may have rot
in your mastheads, but I'll bet you don't have termites, do you?
Tom Conroy 

[ducking and running]