As all of these were wooden sailing vessels, either converted cargo ships or, primarily after the abolishion of slavery in the US and UK, fast sailing vessels. A wooden ship has a natural life span of a couple of decades in most cases, depeding on conditions, role and maintenance. While it is possible to keep a wooden vessel in good condition for a long time (Like the USS Constitution for example) it is *enormously* costly to do so.

A "normal" lifespan for a cargo ship might be something like this (and I am generalizing wildly here, I know):

- Launched for a merchant company in England and taken for sea trials. Given to a popular, experienced or well connected captain and competent crew. She's a new ship. Probably relatively fast compared to her peers and in good shape. Used for a decade or two on a high priority route, perhaps passengers, mail and cargo on the transatlantic route. She's among the fastests and newest ships out there.

- A few decades old but still a solid old girl. Sold to help finance construction of a new ship and bought by another merchant company. Perhaps slightly refitted to suit whatever purpose the new owner have for her and given to a less experienced captain. She is put on some less prestigeous but probably also less demanding route. Pig Iron from Gothemburg to Amsterdam for example. New ships are faster but pig iron is in no hurry and she's still solid.

- After another decade or two of this she's old and starting to suffer for it. Newer ships are faster, carry more and require less crew. Technology is moving forward after all, even in the age of sail. She's replaced on her original route and left in port for a year or two. Failing to find another task for her she is sold to a less scrupulous merchant for cheap. He outfits her with an equally cheap crew and has her hauling timber from Luleå to Lübeck. Until the owner forfeits payment to the crew. They wait for a few months in Lübeck until it becomes apparent that he screwed them out of the their payment for their last few trips and find new employment. The city sells the old ship for scraps. She is towed up to Timmensdorfer Strand and chopped up.

Now, Guineamen (slave ships on the trans atlantic trade) were rarely the finest ships available to begin with. Slave trading was considered a dirty business even back then. It was dangerous for the crew and poorly paid. Discipline was harsh, borderline brutal, and conditions often required the crew to sleep on deck in the open. Added to this there was always the risk of an uprising. So you're not going to put the finest ship you have on a slave route, now, you're going to use an older ship, one you can afford to lose and a crew you can also afford to lose. You find a very hard captain and have him recruit a few equally hard officers, give them a whole lot of guns, maybe even swivelguns to aim at the half deck. They find a few sailors who can find *no* other work. Former prisoners, men in poor standing, men in deep debt and the like. Even then they may actually trick them about the nature of the journey. This ship, this is not the kind of ship anyone is going to invest vast sums of moeny restoring. She'll likely end up aground, ablaze, sunk or abandoned within a few years.

The fast ships used to smuggle slaves after the abolishion were a little different. Quick and light they were often used for naval service if captured by the major naval powers or piracy and smuggling if caputred by someone of a more... enterprising nature. Many of these ships were Barks built in the 1850's when the California boom created a massive demand for shipping. By the time many of these ships were finished the boom was over and merchants were left with an abundance of fast ships and no route. At the same time demand for Cuban sugar (extremely labour intensive) was at an all time high, slavery was still legal in Cuba and slaves were still sold in africa at vastly reduced prices (due to UK and US patrols). Here was a chance to make a lot of money and many took it. Ships were bought, crewed (well paid crews too, this was risky but profitable business) and sailed on the West Africa - Caribbean route. It was a race between smugglers and naval patrols with high stakes and high profits.

Anyway, if you have follow-ups, feel free.

EDIT: Spelling and formating