Floating vs Fixed Docks: Tide Range Decides

By Ed Brannigan, Marine contractor. Reviewed by Amanda McCallister, editor.

Dock & Pier Repair | Boat Lift Installation I've driven piles in every kind of bottom from Beaufort to Biloxi. But the job that taught me the most about docks was a little one in Mobile Bay, where the tide doesn't even move a foot. That one was fixed, concrete pilings, pressure-treated deck, $18,000 all in. Client was happy as a clam. Meanwhile I'd just come off a job in Charleston where a fixed dock had the deck ten feet above the water at low tide, and the owner was having second thoughts.

The Tide Range Test

Here's the honest truth: tide range decides. I don't care if you're building a million-dollar marina or a 16-foot personal dock next to your boathouse. If the water goes up and down more than about three feet, you'd be a fool to go fixed. Call it three feet. That's the line I use. On the Gulf, where the tide swings one to two feet, a fixed dock is simple, cheap, and rock-solid. On the Atlantic — Charleston runs six feet, give or take — a floating dock is the only thing that makes sense. And if you're up in the Bay of Fundy, forget it. You'd need a ten-story-tall fixed dock and a staircase to heaven.

Floating Docks: The Good and the Bad

A floating dock keeps your deck level with the boat. Period. No ladders, no steep ramps, no reaching for the cleat when the tide drops. I've built them with aluminum frames and concrete floats from brands like Bellingham Marine, and they work like a dream. But they've got their own headaches. You need protected water — if you've got a big fetch and a hard chop, a floating dock will pound and twist and tear free. You also need to anchor it somehow. Concrete floats can handle a lot, but you'll still rely on piles or anchors to keep it from drifting off to Cuba during a nor'easter. And the cost: for a typical 40-foot dock, you're looking at $20,000 to $30,000, maybe more, depending on the plant. That's twice what a fixed dock might run you.

Fixed Docks: When They Make Sense

Fixed docks are the backbone of the industry. They've been around forever and they're dead simple: piles, stringers, decking. On protected waters with a modest tide, they last decades with minimal fuss. I've built them with 12-inch treated pine and creosote piles — a crew of three can set one in a day. But they punish you when the tide swings big. At low tide, you're looking down at a boat that's five feet below. That's how you get hurt — owners trying to hop down with a cooler. And at high tide, the docks can be under water if you didn't set the deck high enough. You can build high, but then you're climbing up. Fixed is best when the water level is steady, period.

Pilings and Bottom Conditions

Let me digress for a minute, because the bottom decides more than the tide does. I've driven piles in coral sand in Florida and soft mud in Louisiana. In mud, you could send a pile down 30 feet and still not hit resistance. In sand, you might get away with 10 feet. And if you've got a ledge, you're blasting or banging in steel piles. That'll run your price up fast. For floating docks, you can use lighter piles or even anchors, but the bottom still matters. A 10-foot tide range with a floating dock needs strong vertical guides — often two piles per corner — to keep the dock from swaying. If your bottom is soft, you need to drive deep. I've seen guys cheat the depth and end up with a dock that tilts like a drunk sailor. Don't do that.

My Rule of Thumb

So here's what I tell every homeowner who calls me up: check NOAA's tide charts for your local gauge. If the difference between mean high and mean low is less than three feet, fixed is your friend. If it's more, go floating. It ain't rocket science. And don't forget waves and wind. A floating dock in an exposed spot is a maintenance nightmare. If you've got a two-foot tide but open water, you might still want a fixed dock with a cleat system that lets the boat rise and fall. Or you compromise — a fixed ramp down to a short float. I've done that plenty. That's the beauty of this work: no one size fits all. You just have to read the water.

Frequently Asked Questions

What tide range is the cutoff for floating vs fixed docks? I use three feet as my rule of thumb. Less than that, a fixed dock is simpler and cheaper. More than that, a floating dock keeps you level with the boat and safer. Can you convert a fixed dock to a floating dock? Sometimes, but it's usually not worth it. You'd need to pull the old deck, drive new piles for guides, and buy floats. Often it's cheaper to start over — but it depends on the existing structure. Which is cheaper to build, floating or fixed? For a modest tide, fixed is usually 20-30% cheaper. Floating runs higher because of the floats and anchoring. But if you factor in the long term, floating can save you in repairs to your boat. Do floating docks work in cold climates with ice? Ice is a killer. Floating docks can get crushed by ice pans, and the guide piles can snap. If you get solid ice every winter, you need a fixed dock on heavy pilings, or a removable float system. I've done both, but it's not for the faint of heart.