The Abyssal Razor is basically the iron-tier knife. The harpoon attaches whatever (non-tamed) creature you hit with it to you. At that point, your stamina will start draining at a rate dependent on the distant between you and your target. So if you hook a serpent and then drop sails and haul a** for dry land your stamina will disappear before you even realize it's low. I suggest going at half sail or even rowing speed if you think your boat will last long enough. Also you can chug stamina mead to give yourself a boost while fighting the serpent.

So why do you want to drag the serpent to dry land instead of just shooting them? Well the serpent has two guaranteed drops and one possible drop. Only the meat will float on top of the water. If you kill a serpent in the water their scales and head trophy will sink immediately and you won't be able to get them. The serpent trophy looks very cool, and the scales can be used to make an ok but very stylish shield.