[TorpX]

The main point I'm trying to make is that you really have no good way of knowing why they are slowing down. How do you measure their speed? This must be done over time and gives you only a mean value, not an instantanious value. The physics model seems to give a large speed drop when you turn (that's what I've seen anyway), probably too high. You said that they go into a short leg, zig pattern. This means they are making frequent turns. It therefore stands to reason, they are slowing because of the rudder drag effects. A zig pattern with longer legs would allow greater speed and might be more realistic.

If you are talking about DD's, they must slow to use their sound equiptment. If you are talking about merchant convoys, one must consider that some of the ships might be going at, or near, their maximum speed to begin with. There is also the matter of collision avoidance. I don't think it makes sense to just assume that enemy ships use a "speed switch" to slow down.