Jullanar exemplifies up to a certain point what may be considered true principle in ship designing, so far as the development of speed goes. The design, taken broadly, shows in an eminent degree how three leading principles in the design of a sailing ship, although primarily antagonistic, can be so reconciled as to assist each other. We have length, the wave form, and a minimum of immersed surface which form the principle of small resistance ; an effective plane for lateral resistance, which is the principle of weatherliness ; and great stability, which is the principle upon which depends the magnitude of the propulsive force. It cannot be supposed that the apt combination of these fundamental principles was the result of mere chance, and it becomes necessary to here state how Jullanar was designed. Mr. Bentall, writing in February, 1877, said : " The object I had in building Jullanar was not to avoid any rule, but to carry out a principle to its legitimate results—that is, the longest water-line, the smallest frictional surface, and the shortest keel.' I could carry it no further and keep her centres right." The latter sentence refers to the " theoretical assistance " Mr. Bentall received from Mr. John Harvey. The original design of Jullanar in its crude state as it came from Mr. Bentall resembled, so far as the contour of the sheer plan goes, the design now published of the actual Jullanar, but in reality the general design was a very different affair. The midship section was of smaller area, and had much more hollow near the garboards ; the displacement to the designed load-line was lighter (about 143 tons, so far as we recollect) ; and the area of immersed vertical longitudinal section (sheer draught) was greater, and differently disposed. So also was the disposition longitudinally of the displacement. Mr. John Harvey altered the design, taking away here and adding there, until he got the centres of gravity of various equidistant water planes, and the fore-and-aft position of the centre of buoyancy corresponding to those water planes, into such positions as accorded with a certain theory formed by Mr. Harvey.
Jullanar was built from Mr. Harvey's modified drawing, and Mr. Bentall has acknowledged that Mr. Harvey gave him "efficient assistance." The craft was afloat in 1875, and was soon reported to be a wonder to windward, and fast along the wind ; whilst her qualities as a sea-boat were pronounced unparalleled. In 1877 Jullanar (having been bought by Mr. A. D. Macleay) made her debut as a racing craft, and her performance fully justified all Mr. Harvey had predicted concerning her.
It would be interesting and instructive to know what process Mr. Bentall employed in designing Jullanar ; but the probability is that no system was pursued farther than that sketched out by himself, as just now quoted. The fact is, one arbitrary and unusual condition led up to certain modifications of the common type, and Mr. Bentall could not very well have had his short keel without the other conditions as well.
For instance, by placing the sternpost upright and in such an unusual position, great depth under the load line was necessary at the heel of the keel, and very little depth forward under the load line. In fact, in spite of the great difference in the draught of water fore and aft, as Mr. Bentall designed it to be, Mr. Harvey found it necessary
to cut a large piece away from the fore foot, and add a little to the draught aft. By cutting away so much of the dead wood, of course the area of immersed surface was largely reduced, and thus Mr. Harvey was able to attain one of the objects Mr. Bentall had in view. With the keel so much raked upwards, it became almost impossible to have anything like hollow lines forward, and the displacement would have been seriously reduced—in fact, the Jullanar would have been in the condition familiarly known as " all ends and no middle." The con sequence is that the lines which bound horizontal planes in Jullanar's fore body are convex, and do not resemble wave lines. This was another condition favourable for reducing the immersed surface, inasmuch as a smaller displacement would have been the cause of an increase in the immersed surface. Another important condition depended upon the abstraction of dead wood from the fore body and upon the parabolic character of the horizontal lines (water lines) ; and that was, that the displacement of the fore body is so disposed as to be a pure wave form.
We are not aware if Mr. Bentall or Mr. Harvey had any particular object in making Jullanar's water lines convex, beyond that of keeping a certain amount of displacement in the fore body, and the area for surface friction small ; but Mr. Colin Archer, in 1877, when he made known his theory as to the true form of wave bow, pointed out that such a bow could exist without the presence of a single line with a contrary flexure in the vessel. This is undoubtedly true ; and, supposing that all we need have in a vessel is the wave-form bow, independent of the form of any particular horizontal curve, to obtain the best results, then the Jullanar, so far as her fore body is concerned, exactly fulfils the condition.
What we consider the weak point about Jullanar is her attenuated after body. In fact, the displacement of the after body is disposed almost similarly to that of the fore body—that is, the curve of displace ment of the after body more nearly resembles a curve of versed sines than a trochoid. Whether or not Jullanar would have been a better vessel if the displacement of the after body had been greater, so as to correspond with the trochoidal curve, is more or less a matter of con jecture ; we are inclined to think that she would. No doubt the fineness of the after body of Jullanar is to a great extent dependent upon the place where her sternpost is fixed ; and if her sternpost had been raked aft from the heel of keel to the end of her water line la Kitten,* no doubt she would have had fuller lines aft, and thus have had a heavier after body.
Jullanar has not a large area of lateral resistance, but it is a most effective one (see page 15). Here again we find the fortuitous com bination of conditions, which we have before spoken of, operating to render the surface effective for its purpose. Mr. Harvey, to get the centre of gravity of the vertical longitudinal plane sufficiently far aft, cut away more of the gripe than even Mr. Bentall had designed for, and by so doing the keel obtained the excessive upward rake.