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."

Levers Increase Force and Torque

Winches use the principle of physics called "Levers" to increase force and torque. Two types of levers are used: one internal, the other external. The external is the lever arm (the winch handle) and the internal is the revolving sets of rotary levers called gear sets. Power and torque increase as speed decreases.

Power Ratio

Power ratio is the term we use to describe the ability of winches to pull a load. Harken uses a winch's power ratio as the winch name. For example, a 48 has a power ratio of 48:1 in the final gear. This means a kilo of handle input, generates 48 kilos (106 lbs) of power.

Calculating Power Ratio
Power ratio is calculated as follows: (Handle Length/Drum Diameter) x Gear Ratio = Power Ratio.

• Calculate power ratio using a 254 mm (10") winch handle
  (Shorter handles decrease power because they have shorter levers)
  (Drum rpm increases handle turns because they have a smaller radius)
• Measure drum diameter or find specifications in the Harken winch section.
• Gear ratio can be determined from the Harken specifications

Speed and Power Inversely Related

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.

• Low Power = Fast Trim (Light Loads)
• High Power = Slow Trim (High Loads)

Winch Speed
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 determining 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 = pi x diameter).

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 muscle men is a luxury most club racers can't afford.

• Wide Drum Diameter = High line speed; low power
• Short Winch Handle = High line speed; low power

Faster Speeds

Faster winch speeds can also be achieved with three- and four-speed winches. A typical smaller three-speed winch, like the 60.3ST 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

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.

Handle Length

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.

Winch Alignment is Key

Other factors that influence the final power of a winch include whether two people can grind the last few feet of sheet using a double-grip 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.

Line Entry Angle is Important

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.

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.

Alignment
Line entry at final drive gear location = decreased load on gear housing and drum bearings
Ls = Sheet load
Lgh = Gearing housing load
Ldp = Drive pinion load

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.

Article Courtesy of http://www.harken.com/article.aspx?id=15885