http://books-for-sail.com/boat-design-and-theory/18-rudder-failure-why-it-happens.html

There is a nice discussion of how actual underwater forces don't match what you perceive above water in a seaway.

The trochial motion description under the 'Life on the ocean wave' section is informative. Keep in mind that the waves are usually not in-line with the Axis of the hull or the rudder(s). In fact with multiple swell and wave trains from different directions, or even the same direction, you have different underbody forces. The gets combined with the forces imposed by the wind, which often varies in a seaway, and a lot of non-observable things are happening over short periods of time.

Two other things: when the rudder(s) are hard over, and their isn't much yield room, something's that normally wouldn't break can be broken; and, don't rely on the comment that we suddenly began moving back slowly as something finite. (If flip you car in reverse while going 3 mph in forward and pop the accelerator, your comment would have been about the "bang" ....

In with you Steve, in the described conditions, the rudders and/or steering system shouldn't have failed, regardless. After all, it wasn't a monstrous situation, just pretty nasty weather in strongish winds. Hardly something legendary. ;^)))