I died twice to a sea serpent while rafting across narrow ocean strips (so far).

First time, I could approach the gravebuoy by paddling backwards, ready to flee full sail in the wind. I couldn't retrieve my corpse, but I could lure the serpent to the coast. I launched a few arrows, and waited for it to return to its spawn location, which allowed me to finally get to the buoy (still seing the beast in the distance).

Second time, I hadn't enough material to build another raft, but I had anticipated better and my gravebuoy was closer to the coast. I could swim to the buoy, take things from it, and sink closer to the coast, at a distance allowing a go-and-return swim.

In both cases, I died several times while adjusting the "strategy", sometimes with another death penalties, sometimes without.