Hedderwick: Marine Architecture (1830)



The just proportioning of the masts and sails is an object of the very utmost importance, insomuch that, however beautiful may be the shape of the hull for fast sailing, yet if the masts and sails are not duly proportioned, the sailing and other movements of the vessel will fall short of what might otherwise be expected. Lest any doubt on this point should arise from a knowledge of the great diversity in the dimensions of the masts, rigging, and shape of the sails of vessels of different nations, let it be remembered, that each is adapted to the construction of the vessel to which they are applied.

There is a particular proportion for the masts, and shape for the sails, of each distinct class of shipping, found to answer best. Although vessels of the same rigg may be foud to differ a little in their general dimensions, and each to answer their sailing movements, yet, if these dimensions differ materially, and their construction become dissimilar, the same form and dimensions of sails, masts, and yards, will not answer both, so as to be equally convenient and effective. Hence the necessity of employing two or three masts, and of giving the sails a particular form, agreeable to the magnitude and construction of the vessel.

If a ship were always exposed to the action of some unvarying force, or the action of uniform winds and waves, and always loaded to the best advantage, we might be able to deduce, by mathematical investigation, the best form and dimensions of the sails for every description of vessels; but as these requisite conditions do not exist, it is only actual trial, experience, and observations on the behaviour of ships at sea, that can supply the desideratum. However, from a mathematical method of digesting these observations, we are enabled to draw the most reasonable conclusions, for finding the proportions of the masts and sails for the different classes of shipping.

The first thing to be known previous to proportioning the masts and sails of any vessel is her ultimate stability; and as it is only experience and a comparision of the stability of other vessels of a similar construction that can discover this to the requisite degree of exactness, the rules which we lay down must ne founded on a knowledge of the dimensions of the masts and spars of such vessels as are well proportioned and rigged, and have been found to answer their steering and sailing movements.

It has been shewn that the stability or side-stiffness of all common constructed vessels is — 1st, As the squares of the breadth; 2d, Singly as the length; 3 d, Singly as the depth. The side-pressure of the sails, or their power to heel or cant the vessel over, according to their height and dimensions and particular form, is simply as the breadth, and as the squares of the height of the sail. From this mathematical view of the principles by which the masts and sails should be made proportional to the ship, it appears that the height of the sails should be proportioned by the breadth of the ship, and the breadth of the sails by the length of the ship. However, there are certain circumstances which preclude acting entirely on this principle.

The method of finding the length of the masts by the breadth of the ship alone, which is the general practice, would be found sufficiently correct, were the length, breadth, and depth of all vessels in the same proportion; but we find that this is not the case, and know that the sails cannot, in many instances, be made in proportion to the length of the ship. In long, narrow vessels, if the length of the masts (which regulates the height of the sails) are in proportion to their breadth alone, before a sufficient quantity of canvas can be spread, the sails become too broad to stand well by the wind; also the stay-sails lie with too flat an angle, by which their propelling power is considerably diminished, and these sails in particular require to be set to a certain height to produce their greatest effort.

Two vessels may be of the same breadth, and yet the one 6 to 8 feet longer than the other; the stability of the long one will be 1-6th or 1-8th greater than the other, the capacity being that much more. Now we find, that by proportioning their masts by their breadth alone, there would be no difference in their lengths, and also that the breadth of the sails cannot be made proportional to the additional stability of the long ship over the other. That they may stand well by the wind (by increasing the surface of the sails, without adding to their height, the yards become long and unhandy), it becomes necessary that a sufficient quantity of canvas be spread, by giving the sails more hoist than would be indicated by proportioning the length of the masts by the breadth of the ship only. There is therefore a necessity of thaking in a certain portion of the length of the ship, as well as the breadth, to find the length of the masts. The principle on which the following rules for the length of masts are founded, is the taking a proportion of the length of the ship, and disposing it in such a manner that the masts will vary in their lengths, agreeable to a mean proportional of ships of the same breadth, but differing in length to the extent observed in the general construction of merchant ships; and it is hoped that these rules will be found worthy of attention, as they will produce a medium dimension strictly consistent with well tried experience.

Peter Hedderwick: A Treatise on Marine Architecture, containing the theory and practice of shipbuilding, with rules for the proportions of masts, rigging, weight of anchors, &c including Practical Geometry and the Principles of Mechanics; observations on the Strength of Materials, Hydrostatics, &c. with many valuable tables calculated for the use of shipwrights and seamen; also the proportions, scantlings, construction, and propelling power of steam-ships. Illustrated with twenty large plates, containing plans and draughts of merchant-vessels from fifty to five hundred tons, with mast and rigging plans; plans and sections of a steam-boat of eighty-horse power; and eight quarto plates of diagrams, &c., by Peter Hedderwick.
Printed for the Author, Edinburgh, 1830. pp 351-352.

Transcribed by Lars Bruzelius

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