I have done this before but not with a Grady. 29 Luhrs and 42 Egg Harbor. Three winters. Have been trailering my 268 Islander down every Winter since 2008.
Taking the ICW is a long process. When we did it it was a combination of running inside when we had to and outside when we could. You also need a boat that you can live on and stop for the night somewhere.
I have never been above Mansaquan River in New Jersey. I took my Luhrs down the ICW in NJ to Cape May once when I bought the boat. The canal from Manasquan River to Barnegate Bay can be dangerous. Strong currents and idiot boaters. The ICW is not well maintained up North and you really need to be careful especially at low tide.
Our Florida trips were leaving out of Cape May. Alway started out late October. We usually make the run to Rudee or Oregon inlet outside, across the sound and stay inside down thru Georgia. From Cape May you can run up the Delaware river and thru the CD canal to the Chesapeake. We have done this too.
The ICW below Cape May gets more use and is in better shape.
Get yourself a Waterways Guide app, Guide book and paper chart book. I find that the paper charts and easier to plan with. When you come out of a small canal into a large body of water it's important to have a heading to proceed to next. There can be numerous markers out there and you need to know which one you are headed for. A good chart plotter is important too. You can build routes and follow them but it's better to have your head out in front of the boat and know what you are doing next. Waterway guide will help you plan stops at marinas too.
The Waterway guide can help you find a place to keep your boat for the winter. Over the years Florida marinas have been moving away from live-aboard dockage for extended stays. Transient is fine though.
ChartKit® with Companion CD from Maptech® Maptech's ChartKit® books are full-color reproductions of NOAA charts bundled together in large cruising regions.
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Waterway Guide Ship Store - Mid-Atlantic - Complete Print + Digital Guidebook
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Leaving the boat in Florida will depend on the marina. What I have done is I made friends with my neighbors and a mate that worked on a boat in that marina. They would keep and eye on the boat. Some marinas have a more formal service.