Yes, people have used various surplus parachutes as sea anchors. However, the current commercial
versions are already set up for boating
use with things like appropriate swivels, launching containers, attachment points for a float, etc. I'm sure you could get a surplus chute to work, but you'd have to do some study and work to duplicate the effectiveness of the boating-specific ones. You have to really think about launching the thing--picture yourself on deck
, at night, in a gale, trying to launch a pile of light nylon and strings into the sea without getting tangled in the whole mess. The boating
companies have worked out how to do it safely.