Methods of Measuring Ships for Tonnage

Measuring Ships for Tonnage. The methods at present in use (1833) are as follow:


By the 13 Geo. III. cap. 74, it is directed that,

The length shall be taken in a straight line along the rabbet of the keel of the ship, from the back of the main stern-post to a perpendicular line from the fore-part of the main stem under the bowsprit.

The breadth shall be taken from the outside of the outside plank, in the broadest part of the ship, either above or below the mainwales, exclusive of all manner of doubling planks that may be wrought upon the sides of the ship.

In cases where it may be necessary to ascertain the tonnage of vessels afloat, by 26 Geo. III. cap. 60, the length is to be taken as follows. Drop a plumb-line over the stern of the ship, and measure the distance between such line and the after-part of the stern-post at the load water-mark : then measure from the top of the said plumb-line, in a parallel direction with the water, to a perpendicular point immediately over the load water-mark at the forepart of the main stem, subtracting from such admeasurement the above distance; the remainder will be the ship's extreme length, from which is to Be deducted the three inches of every foot of the load draft of water for the rake abaft.

From the length, taken in either of the ways above-mentioned, subtract three-fifths of the breadth taken as above, the remainder is esteemed the just length of the keel to find the tonnage: then multiply this length by the breadth, and that product by half the breadth, and, dividing by 94, the quotient is deemed the true contents in tons.


The three measures of length, breadth, and depth are multiplied together, and divided by 94 for the tonnage.

In Single-decked Vessels.

The length is taken from the after-part of the stem on deck to the stern-post; the extreme breadth is taken, being measured inside from ceiling to ceiling, and the depth from the ceiling to the under surface of the deck.

In Vessels of two Decks.

At Bourdeaux, the length of the upper deck, and that of the.........

With various adjustments for the remaining main European maritime nations.

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