GPS antenna HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

OK guys, especially the ellectronics gurus here...I really need your help with a question, please.

I have a Garmmin 185C GPS on my boat, that has it's dedicated antenna, that was embedded in the deck for low profile.

Now, as most know I have a radar I am installing, and that has GPS feature.

My question is, do I need a dedicated antenna for the raymarine or I can "tap" off the Garmin's antenna??

If I can what wire and connectors should I use.

I hate having to drill holes on my boat for a second GPS antenna..that's why I ask.

Thank you for your responses

Alex