NavList:

John, you can think of a wave as a rolling iceberg. The wave rolls and rolls as it travels and, just like an iceberg, at least half of the wave is underwater. Currents have depth, too, and currents will change the wave's rolling motion. At some point something has to give - the current isn't going give up so the wave has to change it's ways. That's the simple answer.

Currents can also change the nature of swells. They're just waves of a different nature.

Anecdotal experiences? Lots. It can get quite interesting when two currents come together, such as off Cape Hatteras. Sometimes we swore we had hit a speed bump, as in an automobile parking lot. One moment things were "normal" and then you hit the goofy waves. If the weather was clear then you could see when things were going to get fun.

Temperature, color, salinity and critters are also indicators. Our condenser inlet temperatures changed by as much as 30F in five minutes when entering or leaving the Gulf Stream. When the wind's out of the north the waves got narrower (steeper), although the period didn't seem to change much. Didn't really notice a change in wave height, but height can be deceiving when you're standing 40ft above the water.

On one especially fine Navy day I saw the Amazon River 200 miles off the beach. It was a wide, light brown stream in the middle of nowhere. I can't remember which current picked up the river water. We didn't go into it.

If you're really paying attention then you can watch the critters. You'll sometimes see more birds on the edge of a current - they're feeding on the fish that are playing (and hiding), if the boundary is distinct. Not really any different behavior than in a tideway.

Sometimes you'll see weeds (plants) that don't belong there - possibly brought by a current if there hasn't been a big storm in the local area and the swell hasn't been running for very long.

Your ripple examples are interesting. I didn't pay attention that closely, I guess. The moving island analogy is very appropriate.

Joe