Drogue

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This article describes a device used in the marine environment. For the type of parachute used in aeronautics, see drogue parachute.

A drogue is a device to slow a boat down in a storm so that it does not speed excessively down the slope of a wave and crash into the next one. By slowing the vessel in heavy weather, the drogue can make it easier to control. A drogue is usually constructed to provide substantial resistance when dragged through the water, and is trailed behind the vessel on a long line.

Most drogues are best deployed out of sync with the boat by one-half of the length of the prevailing waves, so that the drogue climbs a wave as the boat slides down a wave. Nylon rope is widely use for hauling drogues as it absorbs the shock loading best by stretching.

Drogues come in several varieties, with the parachute drogue probably the most familiar, but also the most tedious to maintain, as the length of the tow line must be adjusted as the distance between the waves changes. There is also another type of drogue that uses hundreds of small fabric cones spread several feet apart along a rope that create drag on the water without needing to be tended to maintain synchronization with the waves. This type of drogue is more difficult to retrieve.

Makeshift drogues have also been created by dragging automotive tires, lengths of anchor chain, or very long lengths of line behind the vessel. Studies measuring the drag force created by dragging old tires behind the boat have concluded that compared to drogues, the force generated by even 8 old tires and 100 pounds of anchor chain is small and offers false security. The tires are also susceptible to skimming on top of the water, generating almost no force.

A sea anchor is somewhat similar to a drogue, but is usually much larger, and is intended to prevent the vessel from moving at all, and is usually deployed off the bow (front) of the boat so that end is presented to the oncoming waves.