Tar can resist salt water reasonably well as a traditional protective coating, but salt, abrasion, sun, and constant wetting make marine exposure much harder than ordinary rain.
Salt water is more demanding than fresh rain. It wets, dries, leaves crystals, encourages abrasion, and is often paired with wind, sunlight, movement, and biological growth. Tar was useful at sea because it helped protect rope and timber from that harsh cycle, not because it created a perfect permanent barrier.
On boats and maritime gear, tar helps shed water and gives a sacrificial coating that can be renewed. Rope, seams, spars, and exposed wood could be treated repeatedly. The regular smell of tar around old harbours came from maintenance as much as from new construction.
Salt can make ageing more uneven. As water evaporates, salt remains in cracks, fibres, and surface texture. This can leave pale deposits, hold moisture locally, and add physical stress. Movement from waves or rigging can then wear the coating faster than on a static fence.
Tar in salt-water settings should be understood as a maintainable defence. It can be very useful, especially in traditional maritime contexts, but it needs inspection, renewal, and compatibility with the material beneath it.