I would concider the DeLorme Eartmate PN-20 or the PN-40, the PN-40 is new so not much about that one yet.. But for as far as the PN-20 goes you can load in depth maps to help you out.. There is alot you can do with them.. Here is some reviews if you wish to check them out..

www.delorme.com//about/reviews/PN20_GPSReview.htm

Also some accessories that allows you to use the cigarette lighter if you want to purchase the kit. As well as a map libray that allows you to add in all the NOAA nautical maps you want..Good luck on what you or your friend decides on..

www.shop.delorme.com/OA_HTML/DELibeCCtpSctDspRte.jsp?section=10095