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Gross Tonnage
Tonnage is neither the weight of the vessel, nor a measurement of the amount of water it displaces, but rather a measurement of the vessel's volume. Gross tonnage refers to the overall volume of a vessel. You can determine your vessel’s gross tonnage precisely by hiring a
tonnage
measurer, or, estimated for many vessels up to 12 metres in length, estimate it by using the following table.
Simplified Self-Measurement of Tonnage Based on
Length
If your vessel is 12 metres or less in length overall, you may be able to use a table to find a simple measurement of tonnage. In order to do this, all of the following conditions must be met:
- The length overall (called LOA) of the vessel must be 12 metres or less;
- The maximum breadth of the vessel is not greater than 4.8 metres;
- The vessel must be of a monohull form. This means that catamarans or trimarans cannot use this method;
- There is not more than a single deckhouse/superstructure;
- The deckhouse/superstructure's length does not exceed 70 percent of the vessel's length overall (LOA); and,
- The vessel is neither a houseboat nor does it have a barge hull form. These two categories cannot use this simple method.
If after reviewing the list above, you qualify for this simplified method, then you may measure the length and calculate the tonnage yourself in two steps. You do not need a tonnage measurer.
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Step One: Measure length
► Length Overall (LOA) is the length of a ship in metres from the fore part of the uppermost end of the stem to the aft side of the aftermost permanent structure of the ship, not including guards or rubbing strakes, spars, platforms, outboard motors, Z-drives, jet drives, or transom-hung rudders, but is to include any additional enclosed hull volume that is to be added to the hull in the form of detachable or fixed volumes such as blisters, sponsons, bolted stern appendages, etc.
(See table below)
► Breadth is the maximum breadth of the ship measured in metres at any point on the length of the ship.
Step Two: Use the lookup table
Based on the ranges of length overall (LOA) in Column 1, read across to Column 2 to find the given gross tonnage.
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Length Overall
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Gross Tonnage
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Less than 8 metres
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4.6
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From 8 m to under 8.5 m
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5.0
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From 8.5 m to under 9 m
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6.0
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From 9 m to under 9.5 m
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7.0
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From 9.5 m to under 10 m
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8.0
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From 10 m to under 10.5 m
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9.5
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From 10.5 m to under 11 m
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11.0
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From 11 m to under 11.5 m
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12.5
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From 11.5 m to under 12 m
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14.5
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Equal to 12 metres
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15.0
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