From Practical sailor, the full article can be found here.
Common Causes of Anchor Drag and How to Prevent Boat Yawing at Anchor
Four common factors often cause an anchor to drag—even when the anchor is well designed and properly matched to your boat: poor seabed conditions, short scope, insufficient shock absorption, and boat yawing.
Why Boat Yawing at Anchor Is Dangerous
Boat yawing at anchor can go unnoticed until it causes a serious problem. When a boat constantly yaws, the anchor cannot set deeply in the seabed. Additionally, the tension on the rode increases significantly—often by 50 to 100 percent compared to a boat resting calmly. This elevated tension can cause the anchor to slowly drag or “walk” downwind, risking anchor failure.
How a Riding Sail Helps Reduce Boat Yawing
Using a riding sail is an effective way to control yawing and stabilize your boat at anchor. A riding sail works by pushing the boat’s transom back inline whenever it drifts to one side, and by increasing wind resistance at the stern. This steadying effect reduces fluctuating tension on the anchor rode.
Traditional one-dimensional riding sails are triangular panels set from the backstay and sheeted to a side cleat at a 15- to 20-degree angle from the boat’s centerline. This rigging encourages the boat to rest at about a 10-degree angle to the wind. On one tack, the sail stabilizes the boat, and on the opposite tack, the hull’s side provides stability. Although the boat leans slightly to one side, the wind load remains higher, maintaining control.
More advanced three-dimensional riding sails, such as Y- and V-shaped designs including the Fin-Delta and V-Delta models, align with the boat’s centerline. These provide corrective force on either side when the boat yaws, along with consistent drag to steady the boat, even when aligned directly into the wind.
Limitations of Anti-Yawing Techniques
Common anti-yawing devices deployed at the bow, such as chain kellets, often fail during strong winds when control is most critical. In contrast, riding sails improve the boat’s aerodynamic balance and work effectively in both light breezes and severe weather conditions.
While traditional riding sails reduce mild yawing, their effectiveness is limited in storm-force winds due to their 19th-century design origins. For severe conditions, consider modern alternatives or additional anchoring strategies.
https://www.vikinganchors.com/products/viking-anchor
photo from https://sailrite.wordpress.com/2013/09/12/how-to-use-an-anchor-riding-sail/
