Drogue vs. a riding sail
After reading Geoffrey Van Gorkum's response to Scott Rhoads's question regarding boats sheering from side to side when on a sea anchor ("Relaxed riding on a sea anchor," Jan/Feb 2000, Issue No. 103) I began to wonder if there isn't an alternative to a riding sail. The riding sail works well on a mooring or at anchor, but the wind is usually moderate. When a sea anchor is out, the winds are higher, and having any sail up can be a concern. If the sea anchor is holding, a fair amount of wave pressure should be passing under the boat from bow to stern. Would a small drogue (bucket, warps) provide the same drag as the riding sail? This keeps the windage down, and provides an option to boats that do not have a riding sail in their inventory (like most racing boats I've been on).
Sheering of a boat while at anchor is common in both ground and sea anchoring. The theory of why a boat sheers at anchor has been amply discussed but corrective means are not very well defined except by various individuals' experiences. The riding sail has long been used (on both sail and power boats) with varying degrees of success with the latest improvement being a wedge sail (see "Wedge-shaped riding sail prevents 'flogging,'" March/April 2000, Issue No. 104). Both the flat and wedge sail add to the inventory of the sailboat (except in the case of a ketch) and are single use devices. There is, however, another way of damping sheering motion that originated as a ground-anchoring technique, and that is to deploy a small drag device in the water off the bow of the boat. As it is dragged alternately to port and starboard by the bow of the boat, its drag tends to impede the crosswind movement of the bow much as does a secondary ground anchor in the hammerlock moor.
In its simplest form this drag device can be a strong canvas bucket as suggested by Bill Hunter, suitably weighted and hanging in the water at the bow where it can slow the athwartship sheering motion. Such a bucket should already be on every vessel for deck sluicing work. If not, it can be hand made as a satisfying exercise in seamanship or purchased. Creative Marine markets an 11-inch diameter bucket which has a maximum drag of 65 lb. at six knotspossibly suitable for a small size light displacement racer/cruiser. Its lifetime in this application may not be long, but it will be better than a plastic bucket which probably will not last more than one cycle.
A more durable device is a trolling sea anchor as marketed by Cal-June (they come in 18-, 24-, and 30-inch diameters). These can be used on larger boats as shown in The Complete Book of Anchoring and Mooring. While both a sea bucket and a trolling sea anchor represent additions to a boat's inventory, they can at least be used for other purposes when not in heavy weather. Boats that have reason to carry a true made-for-the-purpose heavy-weather drogue can experiment with using it for sheer control in a similar manner. A dinghy anchor or lead dive weight can serve as ballast.