Interesting Features of Cup-defender Construction

Category: 1920 : CHALLENGE N°13

Details of Resolute, Vanitie and Defiance

© 1914 SCIENTIFIC AMERICAN, INC : MAY 16, 1914 - COMPLEMENTING our article and drawings of May 2nd, giving the principal features of the three cup-defending yachts, we present in this issue excellent illustrations of the "Resolute" on her first trial spin, and also some interesting details of the hull and spar construction of the yachts.

It will be noticed that each boat is framed on the system which was first originated, for yacht construction, by Herreshoff in the "Constitution" of the year 1901.

As far as we know, previous to that date, reliance upon keeping the hull to shape was placed upon a large number of closely spaced, light, and shallow frames. Now the strength of any member to resist bending in the plane of its depth, others things being equal, is generally proportional to the square of its depth. It was in recognition of this law that Herreshoff, in building the "Constitution," determined to introduce a number of deep, web frames, thereby greatly increasing the stiffness of his hull without making any corresponding increase in the weight of the material used.

When "Constitution" made her appearance it was mistakenly reported that Herreshoff had abandoned transverse framing in favor of a system of longitudinal framing. As a matter of fact, he had increased the stiffness of the transverse framing, and the so-called longitudinal framing consisted of T-irons and bulb angles, introduced, respectively, along the seams of the plating and intermediately between the seams, in order to form the butt joints and to assist in holding the very light hull plating to true form. It is a distinct tribute to the constructive skill of Herreshoff that his two competitors in this season's racing have adopted the principle of construction which distinguished the "Constitution" of twelve years ago.


There are sixty-two frame stations in the hull of the "Resolute," and on seventeen of these there are web frames, varying in depth from 8 to 12 inches. These frames run entirely around the hull and across the deck. Intermediate between each pair of web frames are three smaller sub-frames, which are carried up well into the bilges, but not above the water line. The six strakes of plating are laid on with flush seams, the edges of the plating being riveted to nickel-steel, 4½- by 4½-inch T-irons, running along the seams, with 3-inch by 2-inch bulb angles running longitudinally midway between the seams. The covering board of the deck is of galvanized steel 7/32 of an inch thick by 18 inches wide. The balance of the deck is covered with aluminum plate 7/32 of an inch thick and 18 inches wide, the deck plates being lapped toward the covering boards. The whole deck is covered with canvas and sanded. The manganese hull plating is 5/32 of an inch in thickness, except the top strake and the garboard strake, which are 7/32 of an inch in thickness. There are six strakes of hull plating, the bottom strake overlapping the lead, to which it is very securely fastened.

Evidently, Herreshoff expects to do some experimenting with his sail plan, for he has provided two mast steps, one 33 inches abaft of the other. Judging from the photograph of the trial spin of "Resolute," it would look as though the footing of the mast was at present on the after step.

The mast, 20 inches in diameter at the foot, is built of nickel steel, stiffened longitudinally with ten 1 by 1½-inch nickel bulb angles. The foot of the topmast houses within the mainmast, footing upon a hollow steel cone riveted to the shell of the mast, as shown in our drawing. About every 10 feet of the length of the mast there is a steel diaphragm, cut away at its outer periphery to allow the bulb angles to pass through, and lightened by having holes drilled out.


An interesting drawing among those showing the construction of "Vanitie" is that of the junction of the framing with the lead. A bronze casting, to the flanges of which the frames are riveted, is attached to the lead by heavy lag-screws, an oak plank being interposed between lead and casting. Two other interesting details are those of the gammon-iron and rudder-post, each of which in a bronze casting. The gammon-iron makes a very neat finish at the stem head; it will be noted that it is recessed to receive the top strake of the plating. The rudder-post sleeve casting is also a neat piece of design. The Gardner boat has the largest centerboard of the three yachts; also, the center of gravity of the lead is lower than that of the other boats, and this, coupled with the harder bilges, would tend to give the "Vanitie" greater sail-carrying power than her competitors. The "Vanitie" has an extremely fine bow, with a very decided hollow, a feature which has marked the latest of Gardner's fast yachts. This designer has always built a very beautiful boat, and "Vanitie" will probably be the most shapely of them all.


The half midship section of "Defiance" shows very clearly the nature of the webbed frame construction, to which reference has been made above. Owen, her designer, more than either of the others, has cut away every ounce of superfluous material, not only in the web framing, but in every part of the construction from which it could be removed without impairing the structural strength.

The loss of longitudinal bending strength, due to the adoption of a wooden skin in the place of bronze plating, is compensated in the Owen boat by making the seams of the inner and outer skins of wooden sheathing break joints, as shown in one of our drawings. We noted in our previous article that the inner skin of fir is fastened to the framing by bronze bolts, one of which is shown herewith in a separate sketch. Attention also is drawn to the bronze screws which pass through the inner skin from the inside and take hold of the 1¼-inch outside mahogany skin. The hull will be painted with white enamel paint below the waterline and above the waterline the mahogany will be highly varnished. An interesting detail is the turning up between the transverse frames of the edges of the diagonal strapping of the hull, in order to gain additional stiffness.

The mast construction is generally similar to that of the "Resolute," with the difference that there are six bulb angles of deeper section running the length of the mast in place of the ten shallower bulbs used in the mast of the "Resolute."