Dashboard Fixed GPS units from Garmin, Magellan and StarNav are suitable for boats with internal or external GPS aerials displaying colour or black and white mapping.
Fixed GPS can be directly wired to a modern autopliot via NMEA input/output and can assist to steer the boat with the course you have programmed into the GPS.
Fixed GPS has a larger screen than handheld versions and is much clearer to view from a distance.
Fixed GPS is powered by the power supply on the boat/vehicle (usually 12 volts) and comes complete with the power lead, which may also have NMEA data transfer so the GPS can talk to your autopilot and radar and for DSC VHFs, which will be able to give your position to the rescue services and other shipping.
The Fixed GPS either comes complete with a built-in antenna which must see the sky (so only to be used on open-type boats) or will have an externally mounted antenna which can be mounted outside while the set is fitted inside the boat's deck. Most sets will come with a flat mounting base for fitting.