TONNAGE OF SHIPS OF WAR.

Various methods for determining the length of the *Keel for Tonnage*, as part of the data by which to ascertain the *Tonnage* of a Ship, and different rules for calculating the *Tonnage*, have been adopted at different periods. — The following in an account of some of the said rules and methods.

1st.—Mr Willett says, "The old mode of calculating the Tonnage of Men of War "was by multiplying the length of the Keel by the extreme breadth, and the product by the depth in Hold, and then dividing by 96."*

2d.—In the year 1719, the following method of determining the length of the Keel for Tonnage, and rule for casting the Tonnage, were settled by the Lords Commissioners of the Admiralty, viz.

On a straight line with the lower part of the Rabbit of the Keel, erect a perpendicular or square line to the upper edge of the Wing Transom, at the after part of the plank, and at the Stem to the fore part of the plank at 5/6 parts of the height of the Wing transom; the length between the said perpendiculars added to 1/24 of the extreme breadth (allowing for the Stem and Stern Post without the Rabbits), from which subtract 6/25 of the height of the Wing Transom for the Rake abaft, and also 3/5 of the Main Breadth for the Rake afore, leaves the length of the Keel for Tonnage:— Which multiply by the breadth, and the product by half the breadth, and divide by 94, gives the Tonnage.

3d.—By an order of the Navy Board, in 1781, the length of the Keel for Tonnage and the Main breadth, are to be ascertained as follows:

The length to be taken on a straight line along the lower side of the Rabbit of the Keel, from a perpendicular or square from the back of the Main Post, at the height of the Wing Transom, to a perpendicular or square at the height of the Upperdeck (and Middledeck of Three-decked Ships) from the fore part of the Stem: then from the length between those perpendiculars subtract 3/5 of the breadth for the Rake forward, and 2½ inches for every foot the Wing Transom is high above the lower part of the Rabbit of the Keel, for the Rake abaft:— The remainder is the length of the Keel for Tonnage.

The Main breadth to be taken from the outside of the outside Plank or Thickstuff, in the broadest part of the Ship, either above, on, or below the Wales, deducting from the said Thickstuff or Plank all that it exceeds the thickness of the Plank of the bottom, which shall be accounted the Main breadth: so that the Moulding breadth, or breadth of the Frame, will then be less than the Main breadth, so found, the thickness of the Plank of the bottom.

Then multiply the length of the Keel for Tonnage by the Main breadth so taken, and the product by the half breadth, and divide the whole by 94; the quotient will be the Tonnage.

* See Archæologia, vol. 11, p. 154, &c.

Charles Derrick: *Memoirs of the Rise and Progress of the Royal Navy.*

London, 1806. pp 301-302.

Transcribed by Lars Bruzelius

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