In sailing ship days, sea serpents often attacked ships in search of prey. Sometimes the monster washed men off the decks and into the sea by surfacing alongside and spouting a hose-like jet of water. More often, it simply snatched them with its huge jaws. On rare occasions it totally destroyed small ships by wrapping its coils around them.
The only certain defence against sea serpents is a gum resin known as asafoetida, obrained from the plant Ferula foetida which grows in Persia and Afghanistan. This reddish-brown resin with its acrid taste and strong onion-like odour, should be ground into powder and scattered on the water around the boat or ship. Sea serpents abhor supsivion of the substance keeps them away.
Sea serpents sightings are so well documented that one may ignore suggestions that the monsters are no more than schools of dophins, giant squids, or other commonplace maritime occurrences.
Taken from "Encyclopedia of THINGS THAT NEVER WERE" by Michael Page and Robert Ingpen