I was visiting our local used and new boat parts store yesterday to inquire about Torqeedo motors. The owner, Kim, reported that a customer had used Torqeedo's portable solar charger during a trip to Barkley Sound this past summer. She said he was able to cruise for three hours with no net loss in battery charge while using this panel. Kim said this was the first solar charging product she has found that actually works as advertised and appears to be durable enough for a marine environment.
Here's a link to a U-Tube video of the devise in operation.