I am glad I asked this question. Thank you all for your replies and ideas.

Is it required that a throwable have a line attached?

The reason I wanted to throw it was because I wanted all the other boats in the area to see the bright red thing going thru the air and then floating in the water, hopefully altering them that something was wrong. My son was just floating there barking orders about getting the spiny down and telling us to gybe.

This might turn into a good place to stow my polypro tow-line. Hmmm . . . to tie it off to the boat…?