We actually don't know as much as we'd like about what N.A.M. Rodger referred to as "the female half" of the Royal Navy as we'd like -- there were some women aboard ship, and there were obviously many, ahem, casual carnal relations between men in port and sex workers, but we just don't know a ton about how many men were married, how many of those married men may have stepped out on their wives when they were at sea, and so forth.

The reason for that is pretty simple -- unlike our current militaries, which enlist men and women for a fixed number of years, other than some standing petty officers (the bosun, carpenter and gunner) any man who enlisted for a voyage enlisted for the duration of the voyage, and was paid off when the voyage ended. (By voyage, I don't necessarily mean a "there and back again" thing, but the length of a unit of service of the ship, which could range from a season to several years -- this would be at the discretion of the Admiralty.) So for our purposes that means a couple of things: first, for enlisted men, there was nothing like a universal RN roster that would track them and have overall statistics about them; and second, what details we have of pay are episodic. In Rodger's work cited above, he estimates that maybe 20% of men were married, but that's a very rough estimate.

But let's assume our hypothetical sailor does have a wife, and he's shipped off for a three-year voyage to the East Indies and back. How does she cash his pay while he's away?

She doesn't.

The reason for this is that sailors during the period I study would generally only be paid at the end of a voyage. If a ship were well-found in prize money, captains or pursers could distribute some cash at port stops, or pursers might have a supply of ready money to advance to seamen who had a need to spend it, but all that would be taken out of a seaman's wages that were generally just paid as a lump sum at the end of a commission. Given the hazards of maritime life, this made some economic sense, at least from the Admiralty's perspective -- no point in paying wages at home to the spouse of someone who might have been long dead by the time word reaches back to Britain. But the system put economic strain on the Treasury in times when many ships might be paying off at once, and during the Dutch wars of the 1650s/60s the Admiralty found a simple way to save money was to simply keep ships in commission, rather than paying them off in the fall as was usual. This expedient helped the Navy stay thrifty in terms of its spending, but created massive economic strain for the seamen and families involved in the Navy -- many of whom had also been impressed in this time period. On top of this, when men were paid, it was often in the form of tickets that would have to be cashed at the Admiralty in London, leading many men to have to sell them at sharp discounts to speculators rather than attempt to travel there themselves.

Rates of pay often stayed stagnant for quite some time -- one of the reasons for the great mutinies at Spithead and the Nore in 1797 was that seamen's wages had not been raised since 1700. Though inflation was rather low during the 18th century in Britain, prices had risen enough that discontent spilled over into a large portion of the fleet refusing to sail at a crisis in the struggle with France. Able seamen were paid £1 4s per lunar month (one pound, four shillings -- there were 20 shillings in a pound and 12 pence in a shilling) from 1700 to 1797, when their wages were raised to £1 9s 6d (one pound, nine shillings, six pence).

One interesting feature of the Navy was that it calculated wages on the theoretical basis of 13 lunar months plus one day per year (two days in leap years), though in practice the 13 months tended to be budgeted for and the day/s simply ignored.

Hopefully this answered your question. I have lots of other answers on my profile page:

https://www.reddit.com/r/AskHistorians/wiki/profiles/jschooltiger