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 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 (16 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)