To Gage a Ship, and cast up how many Tuns her Burthen is.
MEasure the Length of her Keel, the Breadth at the Mid-ship-Beam, and the Depth of the Hold; Multiply these three one by the o∣ther, and divide the Product thereof by 100, and so you shall find how many Tuns her Bur∣den [ 40] is; For Example.
Suppose a Ship having the Length of her Keel 50 Foot, and the Breadth at the Mid-ship Beam 20, and the Depth in the Hold 10 Foot; how many Tuns will the Ship carry?
Multiply 50 by 20, which makes 1000; and that Multiplyed by 10, makes 10000, which di∣vided by 100, cutting off the two last Figures, shews the Ships Burden to be 100 Tuns.
But this reckoning is only for the Kings Ships; As for Merchants Ships, who give no allowance for Ordinance, M••sts, Sails, Cables, and Anchors, which are all a Burden▪ but no Tunnage, you must divide your Product by 95; so the foresaid Ship will be found to be 105 Tuns, 25/95 Parts.
But this way of reckoning the Tunnage of Ships, though it may come near in some Ships, yet it may miss much in others; for all Ships are not built of the same Fashion; therefore it is the best and surest way to cast up the Content of the Ship more exactly according to the Rules of Art, with respect had to the Mold, and shape of the Ship, and so to find out how many Cubick Feet the Ship doth contain; and every Cubick Foot of Water according to some, weighs 55 li. Averdupoiz; but a Cubick Foot of Water according to some Artists, weigheth 62 li. 588 parts. Now every Tun being 20 hundred Weight, and every Hundred 112 li. which makes 2240 li. divide this by 62 li. 588 parts, it makes 35 Foot, 79 parts; so that about 36 Cubick Feet makes a Tun weight.
But observe that if you measure thus a Ship within, you shall find the Content or Burden the Ship will hold, or take in. If you mea∣sure the Ship on the out-side to her Light-mark, as she swims being unladen, you shall have the Weight or Content of the empty Ship; and if you measure from the Light-mark to her full Draught of Water, being laden, that will be the true Burden or Tunnage of the Ship.
Knowing the Measures of a Ship of one Burden, to make another Ship of the same Mold, which shall be double, or treble, or in any Proportion, more or less, to the said Ship.
Multiply the Measurs of the Length, Breadth, and Depth of the Ship Cubically, and then double, or treble the Cube, and extract the Cube-Root thereof.