Nice monkey fist. The metal being smooth and entirely covered, unlikely to scratch delicate topsides, makes such a unit ideal for attachment to a throwing line for both rescue and boating use.

Hint, usually you will want to try to throw over your target. Bouncing a half-pound lump off a drowning person's skull tends to change the nature of the call. On the up side, they tend to make a lot less noise and thrash around less.

You might try a half-pound lead, or less toxic bismuth, sinker. Same weight but a little less pocket filling.

My favorite for weighted defense devices is a pair of discount store knee-high nylon socks, one inside the other, and a considerable weight of lead shot or BBs. An interesting variation is to substitute a pound of dried beans. Shot or beans have a knock-on effect because they don't rebound on impact.

You can wear the socks and make soup of the beans.

I once used a sock full of dried beans to true up a vertical mill when my usual hammer got left behind.