In the US, it's called a personal flotation device, or "PFD".
BALLS
scarcity
Leif probably encountered some storms while sailing.
Variable
Ferdinand Magellan died in 1520 while sailing around the world. Magellan was killed in a battle with the inhabitants of the Philippine isles.
Yes
Lief Ericson
He absolutely did. There had to be a storm or two while he was sailing which caused waves. Anyway, I have NEVER heard of any ocean to be wave-less.
he study finches on his way back
It didn't. It struck an iceberg and sank while sailing to America.
Radio and flares
A lot. It sunk while it was sailing in April of 1912.