Boaters, what GPS handheld unit do you recommend? Need help fast - DH bday Sat!

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We are new boat owners as of last summer. DH's birthday is on Saturday, and I just thought of picking him up a handheld GPS unit for him. I would like to keep it under $400. Can anybody help me...please? What should I look for, what to avoid, and suggested models? Thanks!!

I know, I know...nothing like waiting until the last minute!