But Galaxie’s near-six-foot draft has always prevented me from seeing the backside of the Keys, the stretch of water from Marathon to Biscayne Bay on the north and west side of the chain. Finally last week our delivery trip on the Gemini 105 catamaran Ding Hao opened that door.

The Keys present cruisers with several different opportunities for traveling their length. If the winds and seas are right you can come and go from Miami to Key West in the Straits of Florida, deep ocean waters that host all sorts of great sea life willing to strike a trolled plug behind a sail boat. Navigation on that route is easy: keep deep blue water under your keel and you’ll be just fine.

Hawk Channel is the route that cruisers tend to take when the ocean is a little rougher. It’s a natural channel ranging from 15 feet to 30 or more feet deep that is protected on one side by the Keys themselves and on the other by the offshore reef that is part of the Keys’ geology. The NOAA weather reports tell the story: when seas are four to six feet in the ocean, they’re usually two to three feet “inside the reef,” i.e., in Hawk Channel. Hawk Channel is generally well marked and easy to navigate, with straight course lines between sometimes far-spaced markers.

The back side of the Keys is a different story. There, the Intracoastal Waterway takes boaters from Miami to Marathon through a shallow and scenic world of mangrove hammocks and reefs lurking just beneath the surface. The ICW is marked, but sometimes those markers are a long way apart considering that very shallow water lies on each side of the route. Navigating the twists and turns of the ICW requires the person at the helm to pay close attention.

We wound up taking the backside route after 10 hours of relentless pounding bringing Ding Hao from Key West to Marathon, a distance of only about 30 miles. Seriously shallow water north of Key West prevents almost any boat of any size from traveling on the north side of Key West, so we took the Hawk Channel route, intending to make 60 or so miles to Islamorada. We had to motor into steady headwinds of about 20 knots and seas ranging from two to three feet.

For Galaxie, those conditions would be a breeze. But Ding Hao’s 27-horse diesel and the boat’s design made it a painful trek. Each wave that passed between the cat’s hulls whacked the flat bottom of the main cabin, sending a shuddering jar through the entire boat. For a while, I wished the boat had a bigger engine that could drive it harder, but then I changed my mind. Go much faster into those head seas and we might really harm the boat.

We stopped at Marathon for the night and considered our options: the next day promised much the same conditions as the one we just finished. Nobody was up for the bashing and here we were at the start of the ICW route. With its dagger boards up and rudders raised, Ding Hao sports an 18-inch draft. The choice was pretty simple.

What a remarkable change. With a southeast wind blowing the next morning we went under the Seven-Mile Bridge in Moser Channel, then turned onto the ICW route. With the main sail up and the jib set with a small reef, we breezed along nicely in nearly flat water. Depths ranged around five feet in the worst spots, plenty of room for Ding Hao’s four-foot draft with boards and rudders down.

The challenge was paying attention to the marks. A good pair of Fujinon binoculars and the boat’s Raymarine chart plotter made that relatively easy, but still the helmsman had to be alert. When we weren’t steering we admired the scenery, including the bottom skimming by just a few feet away. I saw several places that looked awfully tempting as anchorages behind mangrove hammocks. Had we not been in a hurry, I could have spent a few weeks anchoring along the way, especially if I had my little flats boat in tow to go in search of snook, redfish, bonefish and permit.