Before you throw $$ at Garmin, be sure you read their install instructions carefully.
Buried deeply in the manual (or on-line in the PDF manual) you will find that they want their current models installed at least 39" from your steering compass (or any other compass / magnetic device).
As of about two years ago, they changed the case design from a friction fit for the chip door to a powerful permanent magnet to hold it shut.
Local dealer was amazed and so was I. That sucker will hold hold our vehicle key ring tight to the exterior!
So, all the sailboats with normal mounts on the binnacle guard better pay heed. Note that interference may not show up at rest or at some direction and heal angles.
Strictly IMHO, this is not a "marine" instrument at all, no matter how many full-page ads they buy.
No one asked, but I believe that Furuno is still building chartplotters intended for use on boats, OTOH.
For the record, I have a Garmin 3005c (works ok) and the sonar option (that is physically falling apart) and a Furuno 1715 radar that is much better built.
When we get some money ahead, there is very likely a Furuno gps/radar net system in our future... when we get some money ahead.
Anyhoo, that's the raspberry from the cheap seats!
Regards,
Loren