Some say the General Method, which has been pitch'd upon by the great number of Shipwrights and others, and may be term'd Shipwrights Hall Rule, is to take the Length of Keel, measured from the Back of the Main Post, to the Fore-side of the Stem at the upper Edge of the lower Harping [or wale], by a Perpendicular made from thence to the upper or lower Edge of the Keel, only 3/5 of the main Breadth, from the Outside of the Plank one side to the Outside of the Plank of the other side, at the broadest Place of the Ship, being set backward or aftward from the Right Angle made by such a Perpendicular and Base. Observing also, that as several Ships and Vessels have no false Post, in such a case there ought to be allowed 1/3 of the main Post from the after Part of such a Stern-Post. Then to take the extream Breadth as aforesaid, and in case the Ship heels much, to use a large Square and a long streight Staff that will reach from one Side of the Ship to the other, taking the Perpendiculars and Parallels very exactly.
The half Breadth is made use of instead of the Depth in Hold, which was formerly used; but then the Ship's Depth in Hold, and half Breadth, were very equal; and now it is general to take the largest.
But not to enter upon Disputes, the Length as aforesaid is multiply'd by the Breadth, and again by half that Breadth, and the Sum being divided by 94, the Quotient is the Tunnage of the Ship, for either sharp or full Ships, Merchant-men or Men of War.
Transcribed by Lars Bruzelius
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Copyright © 1996 Lars Bruzelius.