In this guide
The working formula
Required depth = Loaded draft + Safety margin + Tidal drop Loaded draft ≈ spec-sheet draft + fuel, water, gear Safety margin = 12 in (calm areas) to 24 in (exposed or sandy) Tidal drop = mean tide − mean low tide at the property
The formula is deliberately simple because the numbers are what matter. Everything below is about where each number actually comes from, and where owners get in trouble by using the wrong version of one.
Loaded draft, not spec-sheet draft
The draft printed in a manufacturer brochure is measured with the boat empty. Fuel is heavy. Water is heavy. Tender, tools, and provisions add up. A 44-foot express cruiser with a spec-sheet draft of 3 feet 6 inches can easily sit at 3 feet 10 inches once you add full fuel, full water, gear, and two crew.
Ask your manufacturer or dealer for the loaded draft, or take an honest measurement with the boat you own. Use the loaded number in the formula.
Safety margin: 12 to 24 inches
A safety margin protects the running gear from bottom contact when the boat is trimmed, when a wake pushes it down, or when the bottom is uneven. On the Gulf Coast we generally use:
- 12 inches — protected canal, sheltered basin, soft mud bottom, careful low-speed operation
- 18 inches — most Gulf Coast dock situations, mixed traffic, occasional wake exposure
- 24 inches — open or exposed dockage, sandy bottom that can shift, or a boat with props and running gear that sit low
Tidal swing on the Gulf Coast
Gulf Coast tides are modest compared with the Atlantic. Most of the Florida Gulf Coast sees a mean tidal range under two feet, but it is not zero, and wind tides can push water higher or lower than the astronomical prediction.
Two numbers matter for a specific property:
- Mean low water (MLW) at the nearest tide station — the depth you should assume for planning.
- Local knowledge about wind tides — a hard north wind in winter can pull water out of a bay for a day or more.
Controlling depth is the real number
Controlling depth is the shallowest documented point on the route the boat has to travel — from the dock, through the canal or basin, to open water. A property with 8 feet at the dock but 3 feet 6 inches at the mouth of the canal is limited by the mouth of the canal, not by the dock.
Before we help a buyer take a home seriously, we look for:
- Documented depth at the dock at MLW.
- Documented depth through the canal or basin to open water at MLW.
- Bridge and fixed-structure clearances along that route at high tide.
A worked example
A buyer is looking at a 48-foot flybridge motor yacht for a canal home in Cape Coral.
Loaded draft = 4 ft 6 in
Safety margin = 18 in
Tidal drop = 12 in (approximate MLW below mean tide)
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Required depth at MLW = 4 ft 6 in + 1 ft 6 in + 1 ft 0 in
= 7 ft 0 inThis buyer needs seven feet of documented depth at MLW everywhere between the dock and open water. A property that shows six feet at the dock at high tide has not answered the question.
Final takeaway
Depth is the one specification a waterfront home cannot fake for long. The buyers who verify loaded draft, safety margin, MLW, and controlling depth before signing avoid the majority of after-closing surprises. When a number cannot be documented, treat it as Unknown and get specialist confirmation before you commit.
Frequently asked questions
Can I just dredge to add more depth?
Sometimes, and sometimes not. Dredging on the Gulf Coast requires state and often federal permits, is not guaranteed, and adds cost and time. Never buy assuming dredging as a remedy.
Are Gulf Coast tides really that small?
The astronomical tidal range is small — often under two feet — but wind can push water in or out of a bay in ways that matter for a shallow route.
Should the safety margin be measured with the boat trimmed up or down?
Use the deepest running configuration for planning, then confirm real-world clearance with a marine surveyor.