I made some sketches of my vision of the mechanical design.
In this sketch I was thinking of having a lock as on/off switch with a key attached with a magnet to the front. I've since re-thought that, but I'll cover that in a later post.
To keep the device as protected as possible from rain I would rather not have any electronic components, or switches exposed on the front. My current switch-idea revolves around having a brass lever on the front with a magnet, and a reed switch under the wood sensing the switch position.
I plan to have an on/off switch, a backlight on/off switch (without the backlight I approximately halve the energy use, and the display switches to the sunlight-readable grayscale mode), and a thumbwheel like control to zoom in and out. To keep it minimal - no pan controls, the display will always scroll with the boat.
I'm thinking to put the thumbwheel in the upper right corner in landscape mode, so that it ends up in the lower right corner. It should be recessed for protection:
The display will be mounted under some plexiglass for protection:
Here's a photo of the kind of look (mahogny/brass) I'm aiming for: