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Traditionally, before the popularity of roller reefing booms of the 1960's, the mainsheet attrached to the boom 10% to 25% forward of the end of the boom. It was typically attached with multiple bails with the forward most bail, or the heaviest loaded bail, directly over the traveller, or horse. End boom sheeting is the most efficient way of sheeting a sail in terms of requiring the least am out of line, force and boom size. It is generally a bad idea to have the mainsheet at the midpoint of the boom since this has the highest loadings on the boom and requires the most rope or else on a bigger boat a winch. That said it is often done on boats with cabin top mounted travellers and on small racing dinghies.
The reason that I say that mid-boom sheeting requires the most line has to do with the way that designers approach designing sail handling hardware. We start out by determining how much load that we think the sail handler can reasonably pull (say 30 lbs) and then we back into the amount of purchase required. So if we look at a boat with end boom sheeting that needed a 3:1 mainsheet, if we moved the mainsheet to a position 25% from the end of the mainsheet we would need to go to a 4:1 mainsheet. And if we went to the mid-point we would need a 6:1 mainsheet. Except that there are much higher frictional losses when we increase the mechanical advantage and typically the mechanical advantage is further increases so in the example above the 25% position might be increased to a 5:1 and the mid-boom position to a 8:1 (or put on a winch with a stopper). In other words not only are you dealing with a lot more line but also a lot greater frictional losses.
Jeff
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