Discussion Groups / English Usage / January 2009

It's only the sloops that have the c and s or the decimal notation.

Sloops were lightly armed, so your guess sounds good to me.

I have a book, "The History of the American Sailing Navy", which
obviously does not extend back to the early 18th century, but does have
this, on page 156:

"The British sloops of war built on a similar plan between 1795 and
1798 ... will serve to illustrate the point.  [The author is arguing
that the Americans tended to over-gun their ships.]  The /Cyane/ later
fell into American hands and was taken into the United States Navy.  
The British ships ... originally carried 16 6-pdrs. on the gun deck, 6
12-pdr. carronades on the quarterdeck, and 2 12-pdr. carronades on the
forecastle---24 guns all told against the Americans' 26 guns of heavier
weight."

Sloops and their armament might have grown, in the 60 years between the
OP's table and the 1790s, from 6 or 8 cannons and 10 or 12 swivel guns
(total 16 to 20 guns) to 16 cannons and 8 carronades (total 24).  The
carronade was invented in 1759, which would explain the replacement of
swivels with carronades. <http://en.wikipedia.org/wiki/Carronade>