[Rich]

Bizer makes a chip that works on the Garmin devices.

I have a Garmin 441S that works with the Bizer chip. This unit also can have depth and fish finding if you add a transducer. They have larger screens also, they are just more money.

I used it for one year, before getting a larger boat that has a built in Raymarine unit. So now the Garmin is a spare device or may get sold. I currently have it setup with a cigarette lighter plug so I can use it as a spare or lend it to anyone.

I'd say to look at a device like this. It's perfect, can be seen in direct sunlight, and is designed for a boat, with all the weather, and water as expected. You won't drop it overboard or have the battery go dead when you need it most.