Winches are a fairly recent development in sailing. I believe the first winches for small boats appeared in the 1920ís. Before then it was all block and tackle. Even the big sailing ships didnít get large Jarvis winches until the latter half of the 19th century. Block and tackle takes somewhat more muscle power, which is why winches eventually were developed.
One problem with block and tackle is the amount of line needed for each sail. For example, with a four part tackle a Genoa
trimmed for a broad reach, you will need four times as much line for trimming and control compared to a sail trimmed via winch. And keep in mind that that multiple applies for each sheet and halyard
and possibly traveler on on your boat
If you examine photos of sailing vessels from back when, you will note the large coils of line around mast
bases and on racks where the sheets
On a typical cruising boat
or side decks is where the line will likely be resting. Do you have room for four times as much line as you now have? On our boat the total length of the jib sheets
is 80 feet, both sides. A four part block-and-tackle rig would be 320 feet. Thatís a lot of line in the cockpit
., and a lot of weight on the sail that light air has to lift
. And imagine the tangles when sailing with guests. We have a 3-part arrangement on the main sail. Itís about 350 feet. It is too big to trim without a winch in all but the lightest air.
Next is the matter of blocks. Assuming youíre sailing something in the cruising size, the afore-mentioned four part system with require either sets of fiddle blocks or (more traditional) double blocks. I believe if you price
them, youíll be close to the cost of a winch for each control line by the time you figure in the cost of a quadruple sheet system. Blocks will last a long time, sheets and halyards not so much. By the time you figure in line replacement cost I doubt there will be much economy. One of the factors of operating costs the old sailing ships contended with was chafe- it required constant line mending and replacement.
I realize your question was about physics. I canít help there much,but youíll be calculating force exerted in pounds at a given wind
speed on a given sail area, then dividing by the a mechanical advantage of your block and tackle, depending on two part, for part, six part, whatever. The answer is the physical force in pounds required to trim a particular sail at a given wind
speed. Sailors have been able to control and handle sails
for centuries without winches, but as the breeze turns into wind, it begins to require real muscle power.
If youíre still into the idea, I would suggest referring to Howard Chappelleís books
on American small sailing craft and the fishing
schooners. He may have notes on rigging