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Landfall-Learning > Science > Mechanical Systems

Mechanical Systems

There are several important mechanical systems on the boat. All of the sails, ropes, winches, pulleys, rigging and hardware make up the bulk of the mechanical systems. These systems are the basic tools we need to operate the boat. Basically, we are taking tough, heavy tasks and using mechanical devices to make them easier and more efficient.

The sails are quite heavy and difficult to raise and lower without mechanical help. Also, when the wind is blowing hard, a great deal of pressure is placed on the sails, making it very hard to adjust or "trim" the sails without mechanical help.

Breaking the heavy anchor out of the bottom mud, sand or rocks and then hauling it and the long chain rode back onto the deck would be difficult if not impossible without the help of our mechanical systems.

The lines (ropes) we use to raise or lower the sails are called "halyards." A halyard runs from the base of the mast up to the top, then through a pulley and back down to the base of the mast. At the base of the mast is a winch. The winch is a metal drum driven by a series of gears within the winch drum. If we wrap the free end of the halyard around the winch drum one time, we can reduce the effort required to lift the sail by one-half, so it would take only 50 pounds of effort to raise a 100-pound sail. This is called "mechanical advantage.

On the top of the drum is a winch handle socket. By inserting the handle in the winch handle socket and cranking the winch, the gear train inside the drum is used to reduce the load even more. The power of the winch when using the handle is expressed as a ratio. A 5:1 ratio means that the effort required to lift any given load is reduced or divided by 5. Put another way, 5 pounds of weight can be lifted with only 1 pound of effort. In our current configuration on Landfall, we can crank up the 100-pound sail using only 10 pounds of effort. Through the principle of mechanical advantage we have made a tough, heavy job very simple and easy to accomplish.

The lines used to adjust the sails in and out (or "trim" the sails) are called "sheets". The sheets on the headsails attach to the aft end of each sail (called the clew) and run back to the cockpit, where we usually sit. With the sheets run back to the cockpit, we can make adjustments to the sails as the winds change when we are underway.

Just before the sheets enter the cockpit, they are run through a pulley to lighten the load and reduce the effort required to haul in the sails when the wind is pressing against them. Additionally, there is a winch on each side of the cockpit that we can wrap the sheet around, to reduce the effort even more.

On both the mainsail and the mizzen main there is a "boom" attached to the mast by a "gooseneck." The boom is kept horizontal by a line called a "topping lift" attached to the top of the mast and the end of the boom. The main sheet and the mizzen sheet are attached to the respective booms. Because there are no winches to help handle these loads, a "block and tackle" is used instead.

A block and tackle is made up of a system of pulleys. The pulleys are combined into a pair with an upper and a lower set of pulleys each running through an axle. The upper set of pulleys is attached to the boom and the lower set is attached to the cabin top of the boat. The sheet is then threaded through all of the pulleys, back and forth, top to bottom. Each respective turn through each set of the top and bottom pulleys reduces the load by one half. Therefore, if there are two pulleys in the top set and two pulleys on the bottom set, we have a 4:1 mechanical advantage and we can manage a 200-pound load with only 50-pounds of effort. However, to move that load for 10 feet, we must pull 40 feet of sheet through the block and tackle.