Jack Tar Englishman's name for the sailors of the Royal Navy during the time of the British Empire. There are three plausible etymologies for this name.

In the age of wooden sailing vessels, a ship's waterline was “painted” with tar (much as later telephone poles were soaked in and roofs lined of). The tar was long known as an oil product and would therefore resist water's damage. Today, some traditionally built wooden ships still prefer tar over the plastic coatings of the present as tar has a natural bonding with wood, where plastic's foreign molecule structure does not bind with wood. Even houses today are covered from basement floor to the first floor with tar inorder to keep the dampness from entering the home.

Also During the same period, a ship's rigging was rope made of hemp, which would rot quickly in such a damp environment. To avoid this, the ropes and cables were soaked in tar. Since it was a routine part of a sailor's day to “clap on to” and “heave” these ropes, his hands would be stained with tar, and thus earned the nickname “tar”.

Remember that Tar was such a common adhesive aboard ship that when sailors were advanced to Petty Officer (especially in the United States Navy), tar was used to adhere the new rank insignia to their clothing. The Navy Petty Officer ranking system is a series of chevrons placed under the symbol of an eagle or “crow.” As each rank was achieved (third, second, first, and chief petty officer), the insignia was “tacked” on by the senior enlisted by punching said insignia onto the shirt/arm of the newly-decorated petty officer. Even though a sailor's chevron/crow is an iron-on these days, ceremonies onboard U.S. Navy vessels still include the “tacking on” of the new rank. . . . to the amusement of senior enlisted and the bruising of the advancee!

Another explanation is that sailors frequently wore coats and hats made from a waterproof fabric called tarpaulin. This may have been shortened to “tar” at some point.

Also it was common amongst seamen to weave their long hair into a pigtail and smear it with high grade tar to prevent it getting caught in the ship's equipment. This practice continued until the early 20th century.