Floating Dock Design Calculator

Calculate buoyancy, draft, freeboard, reserve buoyancy, and metacentric height (GM) for rectangular floating docks, pontoons, and barges.

Inputs

Pontoon length (m)

Pontoon beam / width (m)

Pontoon depth (m)

Dead weight (kg)

Live load (kg)

KG — center of gravity above keel (m)

Water density (kg/m³)

Tab to move between fields

Results

Draft (m)

0.57

Freeboard (m)

1.43

Metacentric height GM (m)

4.56

Displaced volume (m³)68.29

Reserve buoyancy (%)71.5

Displacement (tonnes)70

Tonnes per cm immersion1.23

Is OverloadedNo

How to Use This Calculator

Enter pontoon dimensions: length (m), beam (m), and depth (m).
Enter dead weight (kg) and live load (kg) for the pontoon.
Read draft (m), freeboard (m), and displacement (tonnes).
Check GM (metacentric height, m) for stability — positive GM indicates stable upright equilibrium.
Verify reserve buoyancy (%) and load capacity to ensure safe operational margins.

How the result changes with Pontoon length (m)

Pontoon length (m)	Draft (m)	Freeboard (m)	Metacentric height GM (m)
31	0.37	1.63	7.35
106	0.11	1.89	26.99
195	0.06	1.94	50.43
270	0.04	1.96	70.19

What each input means

Pontoon length (m): Overall length of the pontoon or floating dock.
Pontoon beam / width (m): Overall beam (width) of the pontoon.
Pontoon depth (m): Total depth (height) of the pontoon hull from keel to deck.
Dead weight (kg): Self-weight of the pontoon structure (hull, frames, deck).
Live load (kg): Maximum variable load (vehicles, people, equipment).
KG — center of gravity above keel (m): Vertical distance from the keel to the combined center of gravity.
Water density (kg/m³): Density of the water. Seawater ~1025, fresh ~1000 kg/m³.

What each result means

Draft (m): Depth of submergence below the waterline at equilibrium.
Freeboard (m): Height of the deck above the waterline. Must remain positive.
Displaced volume (m³): Volume of water displaced at equilibrium.
Reserve buoyancy (%): Percentage of total hull volume not submerged — margin before swamping.
Metacentric height GM (m): Transverse stability indicator. GM > 0 is stable; typically > 1.0 m for docks.
Displacement (tonnes): Total displacement mass.
Tonnes per cm immersion: Additional mass required to increase draft by 1 cm.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Pontoon length (m) = 20, Pontoon beam / width (m) = 6, Pontoon depth (m) = 2, Dead weight (kg) = 50000 = 7 input(s) provided
Calculate Draft
Draft = displacedVolume / waterplaneArea
0.569 = 0.569
Calculate Freeboard
Freeboard = depth - effectiveDraft
1.431 = 1.431
Calculate Metacentric height GM
Metacentric height GM = KB + BM - KG
4.556 = 4.556
Calculate Displaced volume
Displaced volume = totalMass / rhoWater
68.29 = 68.29
Calculate Reserve buoyancy
Reserve buoyancy = ((maxDisplacement - totalMass) / maxDisplacement) * 100
71.5 = 71.5

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