5 As the masts and yards taper towards their extremi ties, it is not only necessary to know their greatest diameters, but also the ratio in which those diameters are diminished, to give them the form which experi ence sanctions as best adapted to resist strains to which they arc exposed. The interval between the greatest and least diameters being divided into four parts, the diameter at each of the divisions should be as follows: The lower masts are found to be well pro portioned when their diameter at the place of the trestle trees is one-eighth less than at the deck. So that the diameter at the deck being 128, at the first division it will be 127, at the second 12.1, at the third 119, and at the fourth 112. The thickness within the 5 trestle trees should be and above at the head, — 5 of the diameter at the deck. The top masts should have — less diameter under the cross trees than at 5 the cap of the lower masts. So that the diameter at the cap being 80, at the first division it will be 79, at the second 76, at the third 71, and at the fourth, be low the cross trees 64. The thickness within the cross trees and above at the head will be 5 of the diameter 9 at the cap.
If the greater diameter of the lower and top sail yards be 27, at the first division it trill be 26; at the second 23, at the third 18, and at the end 11. If also the greater diameter of the top gallant yards be 32, at the first division it will be 31, at the second 28, at the third 23, and at the yard arm 16. The bowsprit has usually at its extreme end a diameter only half that at the gammoning. If the diameter at the latter part be for example 60, at the first division it will be 59, at the second 55, at the third 46, and at the fourth SO. Brigs and snows have their fore masts and its appendages, as well as the bowsprit, of the same proportions as frigates. But the height of the main mast of brigs ought to be such, that its top may be on a level with the cap of the fore mast, the head of the main mast being equal to the head of the fore mast. The main top mast should be of the same
length with the fore top mast, and the main yard and main top mast yard the same as the fore yard and fore top mast yard. In snows, the main mast is a mean between the masts of a frigate and brig, and so also the top masts; but the main yard and main top sail yard are of the same dimensions as those of frigates.
East India ships should have the length of the main mast = 2.43 x their breadth; the length of the main top mast = 0.586 x the length of the main mast; the length of the main yard = 0.54 x the length of the ship; the top sail yard 0.8 X main yard; the main top gallant yard 0.7 x top sail yard, and the mizen 3 top mast 4 — of the fore top mast. The cap of the fore mast is 2 of the length of the head of the main 5 mast lower than the cap of the main mast, and the cap of the mizen mast is on a level with the main top.
The masts and yards are first proportioned, after which a draught of them is made, including the rig ging and sails. Their moment is the finally com pared with the moment of stability, which will deter mine the masts and yards suitable to the moment of the sails.
Such are the observations of Chapman on the pro portions of masts and yards for merchant vessels— proportions deduced of course from Swedish vessels, but which nevertheless merit much of the attention of the English shipbuilder. And in quoting for the last time the name of this learned and indefatigable man, we would impress most earnestly on the atten tion of our readers his important investigations, founded as they are on a large and extended experi ence. To the young naval architect we would hold him up as a model worthy of the closest imitation.*