Why not just get a "”conventional” hand-held
GPS, which can be used in the dingy, or for walking, since they have their own small display, buttons, etc?
They will at least display your lat/lon location, and may include many other features - depending on the
software contained inside. Examples include the lower cost
Garmin models like GPS12, GPS12XL and Etrex, or the 310 or 315 from
Magellan. Many of these have a
NMEA interface and an optional interface cable.