In short
- A dock tide clearance calculator checks two things: water under the keel at low tide, and space above the boat under a bridge or lift canopy at high tide.
- It uses NOAA levels for Fort Myers: the everyday tide moves only about 1.3 ft between the average lowest and highest daily levels.
- You measure depth and headroom once, say which tide level you measured at, and the tool carries them to low and high water.
- Many boaters keep at least 1 ft under the keel and above the boat; that is a rule of thumb, not a code rule.
On this page
This dock tide clearance calculator is for Cape Coral canal-front owners who want to know whether their boat has enough water and headroom at any tide before ordering a new dock or boat lift. It uses your own measurements and NOAA tide levels, with no prices. It supports our Cape Coral dock and boat lift permit checklist and the guide to sea level and tides in Cape Coral.
En español: calculadora de marea y calado para muelle en Cape Coral
| Tide level | Under keel | Over boat |
|---|
What it means
Example: 5 ft of water and 9 ft of headroom measured at mid-tide (MSL), 2.5 ft draft, 7 ft boat above the waterline, 1 ft margin, 0.5 ft extra for wind.
How the check is worked out
- Set the reference.
NOAA measures tides from MLLW (zero). At the Fort Myers gauge, middle of the tide (MSL) is 0.63 ft above that zero and the highest daily tide (MHHW) is 1.32 ft.
- Carry the water to each level.
Depth at a level = your measured depth + (that level minus the level when you measured). With 5 ft at mid-tide, at MLLW it is 5 + (0 - 0.63) = 4.37 ft.
- Subtract the draft.
4.37 - 2.5 = 1.87 ft under the keel. With 0.5 ft extra for wind: 1.37 ft.
- Run the headroom the other way.
Space above the water shrinks as the tide rises: at MHHW it is 9 - (1.32 - 0.63) = 8.31 ft. Subtract the boat height (7): 1.31 ft to spare.
- Compare with your margin.
If the smallest gap is below the margin you chose, the tool flags it.
NOAA tide levels at Fort Myers
| Level | Ft above MLLW | Ft NAVD88 |
|---|---|---|
| MHHW, highest daily | 1.32 | 0.28 |
| MHW, average high | 1.10 | 0.06 |
| MSL, middle of tide | 0.63 | -0.41 |
| MLW, average low | 0.15 | -0.89 |
| MLLW, lowest daily | 0.00 | -1.04 |
NOAA station 8725520, data epoch 1983-2001. The mean range of tide is 0.94 ft. These are averages: wind and storms can push the water much higher or lower. NOAA's datums page lists a record low of about 2.9 ft below MLLW, in September 1965.
Your canal may differ. The gauge is on the river, a few miles from Cape Coral. Some canals follow the tide and some are held at a set level. Measure the water in your own canal, and see the NOAA gauge page for the full numbers.
Dock and lift heights come from the permit drawings. If you are planning a lift, also use the boat lift capacity calculator, and for dock length the dock projection vs canal width calculator.
Questions to ask your dock or lift builder
- What tide level and reference do the plan heights use? Ask for it in writing, in MLLW or NAVD88.
- What is the depth at my slip at low tide? Ask them to measure it, not guess.
- How much headroom is left with the boat raised on the lift?
- Who pulls the permit and handles state and federal approvals?
Next step: get a written quote
This tool checks measurements, not the price or the job. We are a referral service, not a dock builder; we connect visitors with independent local providers. Use the form below to ask independent local contractors for a written quote, and read how to choose a seawall contractor first.
Sources
- NOAA CO-OPS: datums, station 8725520 (Fort Myers, FL): MLLW, MSL, MHHW, mean range and record low.
- NOAA CO-OPS: station datums data (API): values in feet above station datum; NAVD88 = 5.40 ft.
Frequently asked questions
Does the tide in Cape Coral change enough to matter for a boat lift or dock?
Not by much on a normal day. NOAA's Fort Myers gauge (station 8725520), the nearest long-running one, lists a mean range of tide of 0.94 ft and a great diurnal range of 1.32 ft. Wind, storms and canal structures change that, so a shallow slip or a tight canopy still deserves a check.
What is MLLW and why does the calculator use it?
MLLW is mean lower-low water, the average of the lower of the two daily low tides. It is the low reference NOAA uses for charts and depths. At the Fort Myers gauge it sits 1.04 ft below NAVD88, the height reference most surveys use.
How much clearance should I leave under the keel?
Many boaters keep at least a foot of water under the keel, and more where waves or boat wakes move the boat. That is a rule of thumb, not a code rule. Pick the margin you are comfortable with in the calculator.
Does this tell me how high to build my dock or lift?
No. Dock and lift heights come from the permit drawings and the designer. The calculator only checks whether a boat you already know fits the water and the headroom you measured.
Is the Fort Myers gauge the same as my canal?
Not exactly. It is on the Caloosahatchee River at Fort Myers, a few miles away. Some Cape Coral canals are tidal and some are held at a set level by weirs, so measure your own water depth and check with a marine contractor.