Sea Anchor - Use

Use

Sea anchors can be used by vessels of any size, from kayaks to commercial fishing vessels, and were even used by sea-landing naval Zeppelins in World War I. While the purpose of the anchor is to provide drag to slow the vessel, there are a number of ways this can be used:

• The first, and probably most well known use, of the sea anchor is to aid vessels in heavy weather. A boat that is not kept bow- or stern-on to heavy seas can easily be rolled by the action of breaking waves. By attaching the sea anchor to a bridle running from bow to stern, the boat can be held at any angle relative to the wind. This is useful in sailboats in conditions too windy to use the sails to maintain a heading, and in motor vessels that are unable to make sufficient headway to maintain steerage.
• Sea anchors also reduce the speed at which a vessel will drift with the wind. Often sold as drift anchors or drift socks, sea anchors are used in fishing vessels to hold them stationary relative to the water to allow a certain area to be fished, without having to use the motor.
• The related drogue can provide directional control of a sailboat in the case of a steering failure. By towing a drogue from a bridle off the stern, the direction of the boat can be controlled on a running course.
• The related drogue can be used to control the speed of a sailboat, in cases where delicate handling is required in high winds.
• The related drogue can be used behind a towed vessel to maintain tension on the towing line, and prevent the radical side-to-side motion exhibited by some vessels under tow.
• Sea anchors may also be used as anchors to allow warping of a vessel in deep water.

The length and type of the line, or rode, used to attach the sea anchor to the bow is also important. In addition to connecting the sea anchor to the hull, the rode also acts as a shock absorber. The stretching of the rode under load will smooth out the changes in loading caused by the changing force of the waves interacting with the hull of the vessel. Because a high degree of stretch is desirable in this application, a material with a low elastic modulus is preferred, such as nylon. If there is no concern about breaking waves and the only reason the sea anchor is being used is to reduce drift from the wind, then you can use a short rode. If short rode is used on large ocean swells, its length should be tuned to the wavelength of the waves; either under 1/3 of the wavelength, or an even multiple of the wavelength. A line significantly shorter than the wavelength means the anchor and hull will ride over the crests together, while a line equal to the wavelength will keep the hull and anchor from ending up out of phase, which can result in severe loading on the anchor. In stormy seas, and when breaking waves are a concern, it is important not to tune the rode length to the waves, so that the anchor and boat are not rolled by the same wave or by adjacent waves. The ability to absorb shock is even more important. Under these conditions, a rode as much as 10 to 15 times the length of the hull should be used to provide a high degree of shock absorption.