Trivia on Tonnage Measurement

(Tonnage Measurement, 1762)

There are three ways of measuring ships now in use:—

Mr Baker's Old Rule — The old way, which was established in Queen Elizabeth's time, and never questioned all King James time, is this: The length of the keel, leaving out the false post, if there be any. Multiply by the greatest breatdh within the plank, and that product by the depth taken from the breadth to the upper edge of the keel produceth a solid number which divided by 100 gives the contents in tons, into which add one third part for tonnage, so have you the tons and tonnage.

The Adventure of Ipswich

	ft.
Length	63.6	1802	7737
Breadth	26.2	1417	8037	Within ye plank.
Depth	11	1041	3927	To ye upper edge of the keel.
Divisor	100	70	—
Tons	182,80	1261	9701
One third for tonnage	60,93
	243,73	tons and tonnage.

It is credibly averred by Sir H. Mervyn and Sir H. Palmer that the old way of measuring was to take the breadth without ye plank and the depth from the breadth to the lower edge of the keel. And this was Bakeräs way of measuring.

Second Way — The second way is assumed by the shipwright of the river to be the old way, but it is not, which makes the ship to be 28 in the hundred greater than the former, and is this: The length of the keel taken as before, or ought to be. The breadth from outside the plank to outside. The depth or draught of water from the breadth to the bottom of the keel all multiplied together and divided by 94 (say they) give the content in tons, into which add one third for tonnage.

	ft.
Length	63.6	1802	7737
Breadth	26.8	1426	230	Without ye timber and plank.
Depth	12.3	1088	1361	To ye lower edge of keel.
Divisor	94	8026	8721
Tons	220,71	—	—
One third for tonnage	73,57
	294,28	tons and tonnage.

If you divide this by 100 (which is said to be here done by 94) it is y^e true old way, called Baker's way.

Third Way — The third way was proposed by Mr Gunter, Mr Pett, Mr Stevens, Mr Lyddiard, and myself, who were required by warrant from my lord Duke of Buckingham and the commissioners for the navy (then being) to measure the Adventure of Ipswich, the greatest bilged ship in the river, and from her dimensions to frame a rule that in out best judgements might be indifferently applicable to all kinds of frames. This we performed and yielded our reasons for it, which, to avoid the abuse of furred sides and deep keels and standing strakes, which increaseth the burden but not the hold, was thus: the length by the keel as the first; the depth in hold from the breadth to the seeling; the mean breadth within that seeling at half that depth multiplied together, and the prpduct divided by 65, gives the tons, into which add one third part for tonnage.

	ft.
Length	63.6	1802	7737
Breadth	22	1342	4227	Within the seeling.
Depth	9.8	985	4265	To the seeling.
Divisor	65	8187	866
Tons	207,83	2317	7095
One third for tonnage	69,27
	277,10	This increaseth 12 per 100 above the old rule.

There is a fourth way, devised by the shipwrights and Trinity masters, but exploded for the great excess which makes the ship 30 in the hundred greater than the first, and it is thus: length of the keel as at first, middle breadth beneath the greatest, viz. the breadth at the wrunghead, depth to the outside of the plank, all multiplied together and divided by 70.

	ft.
Length	63.6	1372	5438
Breadth	23.7	1051	1525	Without timber and plank.
Depth	11.3	1802	7737
Divisor	70	8154	9019
Tons	240,68	1381	3719
One third for tonnage	80,22
	320,90