In general, sailors are first superstitious and second almost ridiculously concerned with the appearance, upkeep and cleanliness of their ships. While not necessarily pristine in their individual persons, sailors have an obsession with making sure that their ship is. Nothing brings shame upon a crew like failing an inspection by their Captain or - worse still - by a visiting Commodore or Admiral.
Even pirates and privateers - mythically filthy if the literature is to be believed - were in fact careful, by and large, about keeping a clean ship. Accumulated filth outside and up in the tops makes a ship run sluggishly. On or below deck it makes simple sailing almost impossible, not to mention clearing for battle when preparing to take a prize. Logic in such a confined space dictates order.
To that end, the swab has become an iconic tool of seamen. The deck aboard naval and privateering vessels (and probably a good number of freebooters if we remember that many pirates were ex-navy) was scrubbed, washed and swabbed every morning of every day afloat. Even a ship in ordinary (at anchor in port with her masts and spares naked) would have been polished daily. Part of this is habit, part good manners (cleanliness is next to Godliness) and part wise husbanding. Like an expensive wood floor, a well kept deck will last for untold years.
The swab itself - essential a mop with a long handle and an end made from scrap pieces of what were referred to as "rope-yarns" - was not the first thing to hit the deck. In fact, it came last in the clean up. In the morning watch, sand was applied to the deck and then water. Next, it was down on your knees to apply the holy stones. These were pieces of sandstone used to scrub the sand and water mixture over the deck.
Why were they called holy stones? Ask any old salt and you'll probably get some variant on these three explanations. The stones were originally only used for the more detail oriented Sunday cleaning. In the early days of the Royal Navy, the stones were cut from grave markers in old churchyards. Since the men are on their knees, as if in prayer, holy was tacked on as a prefix to stones. Find one you like and go with it. Any - or none - are possible.
After the grit has done it's work, the deck is flushed with water and then the swabs come out. Getting the deck free of sand and relatively dry is vital to avoid men slipping and injuring themselves. There are enough hazards at sea without going ass-over-teakettle because some swab neglected his duty.
Swab, as with so many other words on the high seas, got tacked on to other words and morphed according to the situation. A swab could mean a drunk and, though now we tend to use the terms interchangeably, was neither a seaman nor a lubber out of hand. It was also the epaulet worn by officers of Lieutenant rank or above, as well as a hand towel used for wiping and drying dishes.
A swabber was a petty officer aboard a man of war in charge of keeping the decks clean. He might also be termed captain of the swabbers as was the case, interestingly, in smaller ships where the designated cleaning supervisor was not an officer at all. A swab-washer was the guy who cleaned out the head. Swab-wringers were sailors who cleaned the swabs after use so that they would be ready for the next predawn attack on grime and muck.
As anyone who keeps up a home knows, cleaning is a futile but necessary pursuit. That dust will settle there again, that pet hair is going to be in those corners next week and mopping that floor or scrubbing the toilet just means you can do it all over again sooner rather than later. Above discipline, the need for order and sheer, wanton pride must have kept our seagoing ancestors at the daily task of swabbing. And who would argue with the statement that a sailing ship gleaming in the sunlight as she hurries along before the wind is one of the most beautiful sights in all the world? Not I.