Hi Jim
I found your last post interesting and followed your link. They did recommend a controller, admittedly the panel they were discussing was 10 watt but apart from controlling the current, it is also needed to prevent reverse charging of the panel.
I had always assumed my panels incorporated a diode to prevent this happening but when I was installing the 20 watt panel I needed to extend the cable and as the existing junction box, a black plastic moulding, bonded to the panel, was looking a bit loose I decided to remove it and connect the new cable directly at this point. I had always assumed the diode was also housed in this moulding but I was surprised that there was no diode and the original wires were soldered directly to the foil strips incorporated in the panel!
Without going to the boat I can't remember the make of the panels but they are well known German ones and I was intending to connect to a controller in any case. I have seen panels advertised as incorporating a diode so guess this is a feature worth checking when deciding to fit solar panels without using a controller.
Peter (Zephyr)