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• 1807, Robert Fulton's Clermont the first ship to demonstrate the feasibility of steam propulsion for commercial use, but it also carried sail.




• 1819, The first steamship to cross the Atlantic was the American City of Savannah, but it also carried sail.




• 1837, Britain's steam-powered Great Western established regular transatlantic passenger service, but it also carried sail.




• 1838, SS Archimedes was the first steamship to be driven by a screw propeller, but it also carried sail.




• 1871, The first British Navy ship not to carry masts or expensive sails the H.M.S. Devastation..




• Commercial steam ships regularly carried masts and auxiliary sails into the 20th century (1900s).

Question:

IF steam power was superior to sail, Why did it take so long to abandon sail after steamships were demonstrated?.

I think it comes down to a few basic factors:

1. Early steam engines weren't very efficient or reliable. So it made sense to retain sails as a backup should the steam engine(s) breakdown or should the ship run out of fuel (especially on longer oceanic voyages were replenishment was uncertain).




2. Wind-power is essentially free (once you've invested in the masts & sails in the first place), whereas you had to keep buying coal. As the steam engines were inefficient it made sense to have sails to supplement steam. This could be in the form of using them both together to add a few knots to the ship's speed or using one or the other as circumstances demanded (i.e. steam into the wind, sail down wind).




3. Sailors are a superstitious and conservative folk, they knew sails and sailing, and it took some time to wean them off.




4. The transition was dependent on a number of later technological changes, such as improvements in boiler design (to improve power, reliability and efficiency), the introduction of iron hulls and the introduction of the screw propeller, to make steam power capable of replacing sail.

Steam was introduced into naval service when it could improve an existing system, or provide a new method of carrying out essential business. It did not revolutionise the conduct of operations at sea overnight. Early steam engines were expensive, heavy, uneconomic and ill balanced. They were far from ideal power plants for wooden ships.

...

The 1840s witnessed a number of vital technological developments, of which the screw and the iron ship were the most obvious. Equally important breakthroughs in iron production, boiler design, bearings, lubricants, manufacturing and control systems were essential to the development of modern warships. Many of these technologies were drawn from other engineering sectors. By 1850 steam ships were effective and reliable enough to be used globally, while fuel supplies. engineering back-up and vital docking accommodation were spreading to meet the need. Although a few key commercial routes already carried steam shipping, this was a luxury market, catering for passengers and mail, not bulk produce.

…

[For a warship] it made sense to fit a square rig so the ship could cruise under sail, saving the coal for tactical demands, and emergencies.

^{The Sail and Steam Navy List, R. Winfield (2004), pg.17}

You can't completely replace sail with coal until you are 100% sure that you are going to have access to coal everywhere you need to go.

This is basically an extension of Steve Bird's #1 and #2. It's beyond the economics and into the availability.

Do you have reliably supplied coaling stations all the way to, say, Australia? If it's a military operation, will all the ports be friendly? If not you need to keep sails on hand.

As an example the famous Clipper Ship Cutty Sark was one of the fastest trading ships in the world when she launched (1869) and was used for the China tea trade. But coal quickly covered that route so then she was diverted to trade with Australia.

Even when the infrastructure was in place, why abandon a sunk asset which can still produce some revenue?

Eric Newby wrote The Last Great Grain Race about his 1938 voyage as crew from Port Lincoln, South Australia to Glasgow, Scotland. These tall ships were carrying wheat grown on the plains of South Australia to the UK market. It did not matter to the wheat that the voyage was slower and less comfortable than a steamship. It was cheaper, which mattered to the purchasers of the wheat.

Conversely, migrants from the UK to Australia would book a steamship berth. The South Australian Maritime Museum has a hands-on display of the berths of the sailing era, the early steamship era, and the later liner era. Each has a substantial rise in comfort: from a hay-filled mattress shared with others, to a dormitory room of 6-8, to a twin-share room. The displays also note the fall in voyage duration; and the fall in mortality with each era (especially as the abundant power available in steamships allowed frozen food to be kept refrigerated).

I realise this answer is about the final years of sail. But I hope you find it useful to know how those last years were played out in far-away South Australia, home of last of the working sail ports.

Evolution is slow

You have fleets over fleets of sailing ships, and then someone, somewhere begins to build steamers. First, the steamer-wharf capacity needs time to ramp-up; then, the steamers need to gain superiority over the sailing ships; and finally the sailing ships need to be phased out. You simply just don't scrap sailing ship just because steamers are available.

For comparison, even in World War 2 plenty of horses have been used for various tasks. And WW2 is several decades later than the motor-car had been invented.

1- Reliability. The first steam engines were prone to breakdown. That's not particularly nice in a mine or in a factory but outright dangerous on a ship. It took time before engines were reliable enough for ocean journeys.

2- Sufficient range. You can't bunker coal in the middle of the Atlantic. Ships need sufficient bunker capacity to cross an ocean and still be able to operate economically. In other words, ships had to be large enough to carry both coal, cargo and make a profit. When the first steam engines appeared, ships lacked the capacity for both. That also took time.

3- Infrastructure. One harbor on each end of the Atlantic with enough bunker capacity is not enough. You need coaling stations everywhere. And again, it took time to develop a workable coaling network.

Developing all of the above took time.