Drogue

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

A drogue

A drogue is a device external to the boat, attached to the stern used to slow a boat down in a storm and to keep the hull perpendicular to the waves. The boat will not speed excessively down the slope of a wave and crash into the next one nor will it broach. 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. A properly functioning drogue should also prevent pitchpoling.

Use

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

Weights such as chain are usually employed to keep the drogue from breaching the surface of the water and skimming across the top. In addition, experienced boaters add a floating trip buoy so that the drogue can be deflated before recovery. The trip buoy line is a floating buoy attached to the top of the parachute cone which collapses the cone when pulled. In the case of series drogue lines, they are attached to the end of the line. Trip lines are especially helpful on series drogues because of their difficult recovery.

While similar in design, the sea anchor is quite different in application from a drogue. The sea anchor is usually much larger, is intended to slow the vessel to a near complete stop, and is usually deployed off the bow (front) of the boat so that end is presented to the oncoming waves.

Parachute variety

Drogues come in several varieties. Of these the parachute variety is the most common commercially manufactured type. A parachute drogue is generally constructed of heavy flexible material in the shape of a cone. Holes or strips are usually cut in the drogue for stability, to reduce loads on the material, or both. Unless two such drogues are deployed in series, the length of the tow line must be adjusted as the distance between the waves changes. See also drogue parachute.

Series drogue

Retired aeronautical engineer Don Jordan is widely agreed to be the inventor of what are now known as series drogues;^[1] however, before his invention, numerous mariners had experimented with pulling several large drogues in series. Jordan expanded upon this idea, and affixed a large number of small parachute drogues to a nylon rope with a weight at the end. The large number of smaller drogues results in there always being a drag force on the line; it does not have to be adjusted to be in phase with the waves as the drag is spread out over many waves. Because the drogue line is prevented from becoming slack there is no jerking or snapping of high loads on the line. This prevention reduces damage to deck fittings and reduces the chance of breakage. The number of small parachutes, the length and thickness of the line, and the size of the end weight are all matched to the displacement of the boat. Another key design feature is the V-bridle. The two attachments should be made at the outer corners of the transom with the lengths of the two bridle lines being 2.5 times the width between the attachment points. With this deployment no steering of any kind is needed.

An advantage of the series drogue is that it does not have to be adjusted during a storm. As sea conditions requiring a drogue are usually hazardous to be on deck, this is a considerable advantage over other drag devices. Also, the series drogue can be deployed safely with one hand from the cockpit. Recovering a series drogue before the storm abates takes effort, but unlike parachute anchors and unitary drogues, the process is safe and straightforward. It can be winched in on sheet winches if the cones are small enough to travel around the winch drum without jamming. The series drogue is currently made by three manufacturers, one in Australia, one in the United States and one in the United Kingdom. Any sailmaker can make one and you can make one yourself, though it is a tedious job.

Jury rigged drogues

Studies undertaken by the U.S. Coast Guard have indicated that drogues made of old tires, long lengths of chain, etc. are not effective in slowing most vessels. Old tires may skim along the surface at storm speeds. Extremely long lengths of chain are required for any appreciable drag effect from chain alone. Nevertheless, these drogues continue to be used.

References

1. ^ Taylor, Roger D. (2010). Mingming & the Art of Minimal Ocean Sailing. Troubador Publishing Ltd. p. 325. ISBN 9780955803512. http://books.google.com/books?id=NxQgUYdAEgwC&pg=PA325. Retrieved 28 October 2010. 

• U.S.Coast Guard Report
• Maloney, Elbert S. (28 September 2006). Chapman Piloting & Seamanship. Sterling Publishing Company, Inc.. ISBN 9781588162328. http://books.google.com/books?id=gOLEhDB0vzgC. Retrieved 28 October 2010. 
• Roth, Hal (2008). Handling Storms at Sea : the five secrets of heavy weather sailing. International Marine, McGraw Hill. ISBN 9780071496483.