Let me try to get back to the general subject of keeping a lookout, or watch, while also trying to address some apparent misconceptions or lack of knowledge about sea conditions in the real world. People who have not boated in these conditions, be it from lack of experience, or experience limited to a limited area, or being a protected-waters boater may learn something new. For the sake of both objectives, I'll try to keep it to following seas in particular, and flat transom recreational power boats in general.
An essential part of keeping a proper watch is observing sea conditions, and their affect on the boat, both for the situation at hand as well as adding to the knowledge base about how one's craft behaves in reaction to the sea. Over time, these basic facts will become very apparent to the experienced yachtsman:
1) Waves often do not have
exactly the same period between them, even in a given set, virtually never among a group of sets. That is one reason why the forecasts refer to a "dominant period". Why this is I'll discuss shortly in tandem with some other factors and a rough illustration. The only way one can
precisely anticipate a certain wave is to be looking backwards, not forwards. Much easier, theoretically, for our sailing brethren, with their helms at the back of the boat, than for those of us in pilothouses and on flying bridges.
2) Waves are not the same height or shape, again even in a set. (Let's remember we are in a moving boat). Height, shape and speed have varying affects on the boat, and often subtle changes can have quite a different and dramatic affect. Contributing factors include changes in the sea bottom depth and configuration, fetch, subtle variances in wind direction and gusting, and the changing influence of current. Crossing the Gulfstream is the classic example of current affects which arise and vary as you approach, then cross and exit it; inlets are another, as current velocity changes, the width and depth of the inlet changes, and exposure to the wind changes.
3) Waves often don't even come from the same direction, be it from a combination of the factors discussed above, leading to "confused" seas, or from base swells coming from different directions, a not infrequent condition on the Pacific on the West Coast.
4) And of course, our boat's course is not always perfectly aligned with the seas, so the boat is attacked from a variety of angles and a variety of time a particular wave is influencing various sections of the boat.
So as you can see, close observation of sea conditions around the boat, rather than making many assumptions about them, is critical to a happy cruise.
In this thread a lot of discussion has been on the subject of rudder control. In following seas, I assert that throttle control is even more important. Broaching is most often the result of improper speed and thus positioning relative to the waves. This is where an autopilot can come in in very handy, allowing the helmsperson to properly adjust the throttles and more closely observe sea conditions. And in return, the AP becomes even more effective as it reacts to less violent and changing conditions on the stern.
Here are just some random pics that illustrates some of my points. These seas are relatively mild, no more than three footers, but the kind of short and somewhat steep and confused variety that can really move around the kind of boat under discussion.
