MR. CHAPMAN's "Treatise on Ship-Building" is a work truly original, and the best which has been written on the subject by a Professional Man, and indeed appears to us to have thrown great light on this important branch of Maritime Science.
This celebrated Builder commences by shewing a new method of calculating (déplacement) the quantity of water displaced by the Ship's bottom, or measurement under the water-line, which, without being much longer, is infinitely more exact than that in common use. The curves of the water-line are generally considered as grounds or data: Mr. Chapman, taking them for segments of a parabola, from the nature of a conic section or trapezium, draws a foundation for a most simple calculation. Some persons may consider this minuteness frivolous, but when we revert to the object, we must allow it demands the utmost degree of attention. It is but too true, that even in these days Ship-Building is in some degree defective; this perhaps arises from a multitude of little inattentions, each of trifling value when separately considered, but united in the same scale amount to a capital defect, and produce the most unpleasing effects.
The Chapter on Stability (Stiffness) affords nothing new, as that subject has been treated by many authors. Mr. Chapman follows their steps; at the same time Mr. Chapman wishes to establish a proposition on the Mould of the Ship's Bottom (la Carene); according to which, the Ship should sink a determined quantity by a determined weight: but he makes a considerable mistake in simplifying his calculation; and thus the product being erroneous (as is shewn by M.V. du C.), the system built on such a foundation must consequently fall. However, as this Treatise is rather elementary than systematic, this error does not in the least affect what follows.
What Mr. Chapman says of the Centres of Oscillation and Percussion, in relation to Rolling and Pitching, may be found in the good Writers of our nation (French), particularly in M. Bizout's "Mechanics." From every thing that has been said on this subject we may conclude, that to lessen this motion the most considerable weight must be removed to the sides, in order to give what is termed a greater inert momentum. It is right to remark in this place, that this rule, although founded upon just principles, has been sometimes misunderstood. The Stability of more than one vessel has been lost by placing a large quantity of iron ballast in the wings, because they have exhausted the hold, by removing so great a weight to the extremes of the floor timbers. In a Ship that has but a sufficiently Stability, the weight in the wings must be regulated by the quantity on board not to exceed a determined proportion.
The Chapter which treats of the Resistance a Ship meets in her course through the Water, appears to us to contain sufficient lights (which has been noticed by other Authors from the intelligence he has afforded); and when taken up by those men of genius who interest themselves in this important question, may being to maturity this long wished-for fruit, not expected from a single individual.
The Ship being motionless, every part of her bottom is pressed by the fluid in which it is immerged: when she is moving the resistance of the water is to be considered, as well as the quantity of motion in the Ship; but towards the stern, the Ship rising from the water, there is a cessation or a kind of negative impulse on that part, the consequence of a positive impulse on the head, which should be added to the force with which it resists the motion of the head. This is the opinion of Mr. Chapman; in consequence of which, he calculates the resistance on the head and towards the stern according to a compound ratio, in a manner perfectly satisfactory. He makes a sum of the resistance, which he rectifies with great judgment, by taking into consideration the elevation of the water towards the stem, and its declining as it recedes. He gives examples of this calculation in every sense complete.
The Power of the Wind upon the Sails is a Subject Mr. Chapman treats with great ability, and he considers the Quantity of Sail proportioned to the Stability of the Ship. Without speaking of the force of the wind, which is one of the elements, he from experience draws a conclusion which, at the same time that it conveys information to the professional man, is perfectly intelligible to those who are not.
In the Sixth Chapter the Forms and Dimensions of Ships are discussed, which must be well received from a Builder, and from which great utility may result. In this also were some trifling errors, which M.V. du C. has corrected.
He has constructed a Table of the Proportions, Capacity, &c. of Merchant Ships of four classes, which must have been the result of deep investigation: Builders only can declare its true value by applying it to the finest Ships. If this Table is really as good as we have reason to think, it is a most valuable production. He has not omitted to give a practical proof.
The Author in his Seventh Chapter enters into the same discussion respecting Chacing Ships, which is applicable to Frigates, and directly serviceable to the Royal Navy. Nothing escapes him; Masts, Sails, Rigging, Men, Military Stores, Provisions, Stowage, the Weight of every particular, their Disposition in the Hold, every thing is considered. He gives general outlines, which agree to all Ships of War not of the Line, from which he forms several Tables, of which we may say the same that has been said of the preceding.
It is for the Officers employed in Building, and the Corps of Engineers, to say their value, by comparing them with those Ships of War which are allowed to excel. It is for those gentlemen also to make them square with Ships of the Line, many particulars applying to either. This may be expected from those gentlemen at a convenient time.
The Eighth Chapter is confined to treat of the Dimensions, Sails, and Rigging of Merchants Ships. Œconomy should modify this theory.
We find in the following Chapter the Practical Part of Ship-Building. He beings with Tables of the Dimensions of the Timbers. Mr. Chapman gives a method of finding the exact cube of every piece; and by means of the weight and place of each piece, to determine both the centre of gravity and weight of the whole building. He then enters upon the method of laying down the plan of a Frigate on the best construction. Young Officers, who wish to understand this art, will find here what they will in vain seek elsewhere. This Chapter finishes with the method of making the Scale of Solidity, which may, from its simple construction, be very useful.
Mr. Chapman displays his whole Theory of Resistance in the Tenth Chapter, to determine the place of the Masts, so that the vessel may keep her wind well, and not gripe too much; and considers the centre of the impulse on the Hull in conjunction with the centre of the power of the wind on the sails. He gives an example of a long calculation, which may be depended on, as Mr. Chapman shews it perfectly coincides with the principles on which those Ships which answer the most perfectly were built. He demonstrates geometrically, that a Ship with masts placed according to the old theory is no way manageable.
In the Eleventh and last Chapter he has considered the method of Measuring a Ship, and other instructions more particularly serviceable to Privateers, but which may nevertheless be of some service to the Navy in respect to Transports which Government may have occasions to freight.
In the original there is a Twelfth Chapter, which solely relates to the great work of the Author in Plates, entitled, "Naval Architecture," &c. and which is but a repetition of what accompanies the said work.
Report of the Commissioners appointed by the Royal Naval Academy to examine M.V. du Clairbois' translation of Mr. Chapman's "Treatise on Ship-Building.
A Collection of Papers on Naval Architecture. Part I, London, 1791. pp 45-48.
Transcribed by Lars Bruzelius.
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