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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.
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