“By and large” now means: on the whole; generally speaking; all things considered.
The phrase is nautical in origin, used as far back as the 1500s, and meant sailing “alternately close-hauled and not close-hauled.” The earliest known reference to “by and large” in print is from Samuel Sturmy, in The Mariners Magazine, 1669.
When the wind is blowing from behind a ship’s direction of travel, it is said to be “large.” As you can imagine, that is the most favorable wind and, with the biggest square sails, a ship could travel fast in the downwind direction.
In simplified terms, “by” means “in the general direction of.” Sailors would say that to be “by the wind” is to face into the wind or within six compass points of it.
Sailing “by and large” required the ability to sail not only downwind, but also against the wind. It may seem impossible that a sailing ship could progress against the wind, but they can. Doing so involves the use of triangular sails, which act like aeroplane wings and provide a force that drags the ship sideways against the wind. With this dragging, and by correct angling of the rudder, the ship can sail “into” the wind.
The 1800s windjammers like Cutty Sark were able to maintain progress “by and large” even in bad wind conditions by the use of many such aerodynamic triangular sails and large crews of able seamen.
A ship could either sail “large” or it could sail “by the wind,” but never both at the same time. Therefore, in sailors’ parlance, the phrase “by and large” meant “in all possible circumstances.”
I’ve sailed on motor-driven ships, though never on a sailing vessel. By and large, I’d rather walk.