Yawning at anchor occurs due to a variety of dynamic forces acting on the vessel causing the vessel to fall in and out of balance with these forces. We tend to think of wind forces as homogenous in force and direction but this is never true for a boat whether on the hard, anchored, or in open sea. As psneeld points out, in open water boats will tend to turn broadside to the wind to a point where the center of effort (CE) aligns itself with the center a lateral resistance (CLR) and the boat heaves to and stays there until something upsets this balance. It should come as no surprise then when we anchor, we are in essence moving the CE so far forward the boat can no longer rotate to a naturally balanced position. The whole boat will now react to the varying loads by sailing forward, falling back, falling off and tacking continuously in a harmonic cycle. To better understand these forces, we need to consider the hull shape itself as a sail or wing which will always strive to balance high pressure and low pressure surfaces by creating lift. As wind loads increase, the boat is pushed back and one side will invariably experience higher wind pressure causing the bow to blow off to one side. Next the rode begins to apply a declaration force slowing this downwind drift until it stops and is overcome once again by a asymmetric lift forces driving the boat forward once again. If you want to stop this cycle then you have to either move the CE back to the CLR, or move the CLR forward to the CE, or some combination of the two. Think riding sails aft, or drouges on anchor rode's forward, otherwise enjoy the changing views.
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