RULES BY MR. PARKYNS, LATE OF HIS MAJESTY'S YARD, CHATHAM.

RULE I. For sharp Ships, particularly those of the Royal Navy.

1. Take the length of the gun-deck, from the rabbet of the stem to the rabbet of the stern-post, or between the perpendiculars. Then take 23/24 of this length, and call it the keel for tonnage.

2. To the extreme breadth add the length of the gun-deck, or length between the perpendiculars; then take 1/23 of this sum, and call it the depth for tonnage.

3. Set up this depth from the limber strake; and, at that height, take a breadth also from out to outside of the plank at dead-flat, and another breadth between that and the limber strake; add together the extreme breadth and these two breadths; taken one-third of the sum, and call it the breadth for tonnage.

4. Multiply the length for tonnage by the depth for tonnage, and the product by the breadth for tonnage, and divide by 49. The quotient will be the burthen in tons nearly.

The following trials have been made to prove the accuracy of this rule:

	Tonnage by the King's or common rule.	Tonnage by Mr. Parkyn's rule.	Tonnage actually received on board.
Victory, of 100 guns	2162	1839	1840
London 90	1845	1575	1677
Arrogant 74	1614	1308	1314
Diadem 64	1369	1141	965
Adamant 50	1044	870	886
Dolphin 44	879	737	758
Amphion 32	667	554	549
Daphne 20	429	329	374

RULE II. For Ships of Burthen, or Commercial Ships, in general.

1. Take the length of the lower deck, from the rabbet of the stem to the rabbet of the stern-post; them take 31/32 of this length, and call it the keel for tonnage.

2. To the extreme breadth add the length of the lower deck; then take 3/55 of the sum, and call it the depth for tonnage.

3. Set up this depth from the limber strake; and, at that height, take a breadth also from, outside of the plank at dead-flat. Take another at two-thirds of this height, and another at one-third of the height. Add the extreme breadth and these three breadths together, and take one-fourth of the sum for the breadth for tonnage.

4. Multiply the length for tonnage by the depth for tonnage, and the product by the breadth for tonnage, and divide by 36.6666 or 36 2/3, and the quotient will be the burthen in tons.

The following trials among many others, shew that this rule does not deviate far from truth.

	Tonnage by the King's or common rule.	Tonnage by Mr. Parkyn's rule.	Tonnage actually received on board.
Granby, East-India ship	786	1179	1179
Northington, East-India ship	676	1053	1064
Union, a collier	193	266	289
Friends' Goodwill, a collier	182	254	277

Steel: The Shipwright's Vade-Mecum.
David Steel, London, 1805. pp 251-252.

Transcribed by Lars Bruzelius

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