Because sailboats depend on human power
to perform such tasks as sail trimming, rig adjustment, steering and sail changing, a wide
variety of mechanical devices have evolved to allow relatively weak people to control
highly-loaded systems. Block and tackles, hydraulics, and winches are the most common
devices to magnify "people power."
Winches use two basic principles of
physics to increase force: those of the lever and those of reduction gears. The handle is
the lever as well as the input device used to drive the winch. the internal gears magnify
power by reducing the speed of rotation.
Power
Handle Length/Drum
Radius x Gear Ratio
Low Power = Fast Trim (Light Loads)
High Power = Slow Trim (High Loads)
Power ratio is the term we use to describe the ability of winches to pull a load.
Most manufacturers use power ratio as the name of the winch. For example, a 48 is a winch
with a theoretical power ratio of 48:1 in the final gear. This means that for every kilo
of handle input, theoretically 48 kilos of power is generated. Since a normal adult is
capable of handling loads of 25 kilos, hypothetically, the winch can pull 1,200 kilos of
sheet or halyards.
Power ratio is calculated as follows:
(handle Length/Drum Radius) x Gear Ratio.
Power ratio is traditionally calculated
using a 10" (254 mm) handle length. Shorter handles decrease power. Drum radius can
either be measured or found in the manufacturer's specifications. Gear ratio can be
determined from the manufacturer's specifications.
In winches, as in any simple machine,
speed and power are inversely related. If you want fast trimming, you will have lower
power. If you want high power, you will have slow trimming. This is the reason that all
moderate and large winches are offered with two or three speeds. For light loads, you can
use a fast speed that doesn't offer much power, and as the load increases, shift to a
higher power and trim the last few feet at lower speed.
Speed
Drum Circumference (2Pi x
Radius) x Gear Ratio
Wide Drum Diameter = High Line Speed = Low Power
Short Winch Handle = High Line Speed = Low Power
When we talk about speed in a winch, we mean the amount of line that is pulled for
each revolution of the handle. The primary considerations in determing winch speed are the
gear ratio and the drum circumference. since the line is wrapped on the drum, each
revolution of the winch will pull in an amount of line equal to the circumference of the
drum (Circumference=2 pi radius).
When you are looking for a
"fast" winch, you will use a wide body winch with a large diameter drum.
Unfortunately, since the drum diameter is also a function of the power ratio, the wide
body winch will offer less power for the same gear ratio. The average racing boat that
uses wide body winches compensates for this loss of power by simply cranking harder,
though a crew of musclemen is a luxury most club racers can't afford!
Faster winch speeds can also be achieved
with three-and four-speed winches. A typical smaller three-speed winch, like the 48.3
offers direct drive in first speed. The drum turns one revolution for each revolution of
the handle, so under low loads, sheets can be trimmed very fast. While this speed is not
geared, there is a slight mechanical advantage obtained from the relationship between the
lever (handle) and the drum diameter. Larger three-speed winches, from the 56.3 up,
typically have a geared first speed because even under low loads, some additional
mechanical advantage is required.
Four-speed winches are typically
three-speed winches which offer a choice of a direct drive first speed or a geared first
speed. The crew selects the appropriate first gear and then uses the three speeds
available. For example, in light air upwind, or for most spinnaker trimming, they might
well choose a direct drive speed for very fast trimming, while for tacking in a breeze
they would use the geared first speed.
Another way to increase the speed of a
winch is to use a shorter handle, typically an 8" (203 mm) handle. The 8" handle
is faster because it swings in a smaller arc and a crew can rotate the handle faster. The
same power problem is experienced, though, as handle length is a part of the power ratio
calculation and decreasing the handle length 20% reduces power by 20%. Still, the 8"
handle is a very effective and inexpensive means of increasing winch speed in light and
moderate conditions.
Alignment
Line Entry at Final Drive
Gear Location = Decrease Load on Gear Housing and Drum Bearings
Other factors that influence the final power of a winch include whether two people
can grind the last few feet of sheet using a doublegrip handle and even the placement of
the winch on the deck. Many winches are positioned on coaming, which forces the crew to
lean across seats or otherwise assume uncomfortable and inefficient postures. Runner
winches are often difficult to grind because they are to windward where the crew is
reaching up, rather than leaning over the winch.
Winches are further affected by how they
are mounted on the boat. The most important factor is to ensure a proper line entry angle.
Lines must lead up to a winch at about a 5-to 8-degree angle to prevent overrides of the
sheet on the drum. If lead blocks are too high to allow this angle up to the drum, the
winch must be raised slightly, or you will have serious problems preventing overrides.
Using a knife to release a fouled sheet is dangerous, expensive, slow, and unnecessary.
It is also important to mount the winch
so the line is properly aligned to the final drive gear pinion. Improper alignment
dramatically increases the load on the gear housing resulting in inefficient operations,
and in severe cases, in winch failure. Let's look at two examples: one with the load
aligned properly and one with the opposite situation. In case A, with the proper
alignment, the load on the gear housing is minimized since Ls and Ldp are in opposite
directions. In case B, where the load is improperly aligned, the load on the drive gear is
maximized - Lgh+L1+Ldp - but this time the loads are in the same direction and adding up.
Marty Rieck –
Reprinted Sailing World Magazine
All new first gear ratios provide faster
sail handling. Designed to optimize human biomechanical factors and reduce fatigue.
