Following up on the "what brand boat" thread, I thought I'd pass on my
(admittedly limited) understanding of rot. Wood is pretty durable stuff.
I've heard it called "nature's composite" and that's not a bad description.
The bulk of a wood cell is cellulose, which by itself wouldn't last long at
all, but it's encapsulated in a tough natural polymer coating that gives it
its strength.

Rot is caused by fungi that feed on the cellulose in wood cells. In addition
to the polymer coating that protects the creamy nougat center of the cells,
wood also contains compounds that are toxic to rot-causing fungi. The
effectiveness varies from one species to another, with cedar and redwood
being examples of woods with a high degree of natural rot-resistance.
Treated lumber gets its rot resistance from being artificially infused with
fungi-toxic compounds.

For rot-producing fungi to take hold, you need both air and water, in
addition to wood. Wood is never completely dry (if it was it would become
brittle and unusable), but its normal moisture content is rarely sufficient
to promote rot. You generally need a fairly generous external supply of
water over a relatively long period of time to get rot started. The air
component is important, too. For example, I replaced the rotted front motor
mount in my boat last year. Due to a rather poorly implemented design, the
timbers that made up that mount had been sitting in an enclosed pool of
water for about 27 years, but the rot was confined to the top section where
the mounting screws penetrated the wood, where air was available. The
submerged part showed no signs of rot at all.

If you can succeed in denying rot-producing fungi air and water you can
avoid wood rot indefinitely. Air is just about everywhere we are, so water
is the logical part of the equation to subtract. In wooden buildings, we
concentrate mainly on keeping water from getting to where the unprotected
wood is. And when it does find its way in, we dry it out as quickly as
possible. In a boat, water comes with the territory, so we use coatings to
keep water away from our wood. Our success in maintaining this barrier
varies.