You are welcome for the data - I was sooo frustrated when I started things out not being able to find solid answers, I made a vow to collect real info and share it.
Now, I think the one thing that surprised me the most was how close our actuals tracked with the predicted. I went about predictions the hard way, and then found this tool:
PVWatts Calculator
It is designed for land installs, but with some simple tricks can be used to product very accurate results for a marine/boat install as well. For fun, I used this tool just now - and looked at the differences between Friday Harbor up in the PNW, and Key Largo, down in the Sunshine State. Here is what I got for our 480W/12v system:
Kind of interesting to see that during the peak 'cruising' months predict more out of our Solar Panels up North then in Florida! Because the modeler uses actual data as its input (you pick a reference point to use), it can make adjustments not only for latitude, but also typical cloud cover.
I have some more details about this tool, and how to make adjustments for 'marine' use here:
mv.VikingStar: Solar Panels on the Boat - Modeling and Performance
And before folks start abandoning Florida for the sunnier PNW, better remind folks about all the floating debris/logs waiting to hole your hull - Mosquitoes with first and last names, and what every I can come up with