The word scurvy may make you think of pirates and sailors on long sea voyages, but "land scurvy" affected many European Crusaders who spent months trudging through the Middle East. In 1747, Scottish physician James Lind found that oranges and lemons could cure scurvy, but that didn't help all sailors.
Read more about how gradual advances gave us the real cure for scurvy at Atlas Obscura. Link
The British establishment grasped onto the concept of citrus, and then did it really really wrong. First, they substituted cheap and easy to get limes - readily available from British holdings in the Caribbean - for the more effective lemons or oranges. Then they further boiled the limes in copper vessels, which had the non-helpful side effect of reducing the (thus far unknown) Vitamin C content even further.
People began to suspect that maaaaybe this whole citrus thing was not as effective as it had been claimed. Of course by then steam engines in ships brought the age of sail and voyages of longer than 6 weeks to an end. Semi-success-via-roundabout-ways!
Read more about how gradual advances gave us the real cure for scurvy at Atlas Obscura. Link
And of course many steam powered merchantmen were built during the war meaning that there was a supply of powered shipping to replace the sailing vessels which had been laid up.
Today it may be possible to build a sailing vessel requiring a smaller crew, particularly using kites rather than masts and sails, but nobody seems to be interested in doing so. Since Jones and Merry invented the Flexifoil there have been several ideas put forward for large kite powered vessels, but none seem to have made it to production. The beauty of kite power is of course that it can be applied to a powered vessel. So that it can be used to supplement or replace the normal propulsion when wind conditions are right. This may become popular as fuel prices rise further.
Long sail voyages in square-riggers continued long after the steam-ships came.
Their economic advantage remained until the second-world war, and on some routes, with some cargoes, they were cheaper to run.
Most of the sailing ships involved in ocean trade were seized, interned, confined to port during the war,and received little or no maintenance during that period. Afterwards, the capital cost of re-equipping and repairing was just too great, the last grain-race took place in 1949, and then the long-distance, Cape-Horn voyages ceased.
The winners of the Grain Race, from the Spencer Gulf in Australia to Europe, came in at anything between 83 and 110 days sailing, far greater than the six weeks (42 days) quoted.
Scurvy, by then, was virtually unknown.
Hence the name "tree of life".