After some thought I decided not to have a fixed tablet in the cockpit because I found it much more convenient to be able to use it while sitting or lying on the benches rather than having to be at the helm to look at it.
Basically on passages the helmsman needs only to keep course (and at close quarters keep looking around), so there I installed an older GPS unit which contains a very basic chart and has the waypoints programmed. Typically it provides the "highway" view, but can be switched to other pages for additional information.