In the 16th and 17th centuries, everything was
transported by ship. It was also before commercial
fertilizer's invention, so large shipments of manure
were common. In dry form it weighed a lot less than
when wet, but once water (at sea) hit it, it not only
became heavier, but the process of fermentation began
again, of which a by-product is methane gas. As the
stuff was stored below decks in bundles you can see
what could (and did) happen. Methane began to build up
below decks and the first time someone came below at
night with a lantern, BOOOOM! Several ships were
destroyed in this manner before it was determined
just what was happening. After that, the bundles of
manure were always stamped with the term "S.H.I.T" on
them which meant to the sailors to "Ship High In
Transit." In other words, high enough off the lower
decks so that any water that came into the hold
would not touch this volatile cargo and start the
production of methane.
You probably did not know this true history of the
word. Neither did I.
I always thought it was a golf term.
