represents the curve of stability of such a vessel as the American yacht Mohawk, which was blown over during a squall off Staten Island last summer. The vessel was at anchor, and, no doubt, from this cause felt the force of the squall more severely. Her maximum stability would be reached say at 30°, and then the squall that put her over so far would take her to the vanishing point in less time than it takes to write it. But it is quite possible that the Mohawk would not have gone clean over on her beam ends if her ballast and heavy cabin furniture had not shifted, inasmuch as when she got to 60° the wind must have had decreased effect on the sails; and, as the squall passed over very quickly the Mohawk might have righted but for the reason stated. However, beyond the accident of the ballast and heavy furniture shifting, the Mohawk was subject to another condition, which rendered her righting quite impossible: she had a very large "well" or cockpit aft, into which the main cabin opened, and soon after the deck became immersed the water rushed into the cabin, and then, of course, her chance of righting was gone. Now, from the manner of stowing the ballast in a deep yacht, there would be little chance of its shifting until the vessel got beyond her beam ends, when it might certainly come tumbling through the skylights. However, deep yachts, such as the Vanessa, Kriemhilda, Seabelle, or other similar yachts, are in no danger, even if hove down on their beam ends, providing water is not allowed to get inside their hulls. The case, however, is very different with shallow vessels and with some steamers, which have their centres of gravity high; and it is necessary for their safety that they should never be sailed very near the angle of heel where their maximum stability is reached. In practice, in small shallow boats, this is well understood, and the helmsman throws his little craft in the wind directly she is struck by a squall, or lets go sheet or halyards, whichever comes readiest to hand.

The stability or stiffness of a yacht under canvas will principally interest English yachtsmen as a matter affecting speed; and every novice knows that the more canvas a boat will carry at any given angle of heel, the faster she will be, all other things being equal. To demonstrate that power to carry canvas affects speed, it will be convenient to take two vessels of very opposite types, such as the American

it strikes the sea; and, as a yacht of that character retains a substantial 'righting' power even at the angle of 90°, she ought to recover herself even if thrown on her beam ends, provided she escapes the danger of taking in water to a dangerous extent by skylights and hatches. "What would become of the crew on deck I presume not to determine.

"It seems quite clear that a vessel of the broad, shallow style, so much in favour in America, would be exposed to a far more serious danger, although up to the angle of 30° her stability might be superior to that of the English vessel."

centre-board schooner Columbia and the English schooner Seabelle. The linear dimensions of the Columbia are 98ft. on the load line, and 25.7ft. beam; her displacement is 150 tons, and her area of lower sail 8770 square feet. The Seabelle is 90-5ft. on load line, beam 19ft., displacement 155 tons, and area of lower sails 5780 square feet.

The displacement of these two vessels is practically the same, but the sail area of Seabelle is less than two-thirds that of Columbia, or, in other words, the sail area of Columbia is 50 per cent. the greater. We have been witness that the Columbia has made 12.5 miles per hour in a lower-sail breeze blowing a little abaft the beam, the wind pressure being equal to 2lb. per square foot. Seabelle under similar conditions has made 11.4 knots per hour. At a speed of 12 knots the resistance met with by Columbia would probably be increasing as the fourth power of the speed, and if her sail area were reduced to an equality with Seabelle's, her speed would be reduced in the ratio of or about 1-15; or to about equality with Seabelle's speed.

1

If these two yachts set out to sail a course of 50 miles with a strong leading wind, the Columbia would accomplish the distance in four hours, and the Seabelle in four hours twenty-three minutes. Here are two vessels of exactly the same displacement; but one, by adding 35 per cent. to her beam, and only 8 per cent. to her length, is enabled to carry nearly 50 per cent. more canvas; and it is quite fair to assume that the advantage gained by the Columbia is mainly due to her greater area of canvas, and not to any superiority of model. That is to say, if two designers of yachts are given a displacement of 150 tons to work upon, and one produces a vessel that will carry 50 per cent. more canvas than the other, it is quite evident that the vessel with the larger area of canvas should be very much the faster, as it is unlikely that her designer would allow her to suffer from defective modelling of entrance and run. [As a matter of curiosity, we might here state that the measurement for competitive sailing under the rules of the New York Yacht Club was until two years ago one of displacement,* and if Seabelle and Columbia set out to compete under these rules, they would have been rated upon equal terms, or rather Seabelle would have given a few seconds time. We need not stop to inquire whether this would be an equitable arrangement, but it can be assumed that English yachtsmen consider the advantages which are due to length and beam are fairly taxable, as both these quantities are terms in the Y.R.A. measurement formula. By this

* The measurement is now altered to cubical volume, which is a measurement like our custom house rule, only the measurements are taken externally instead of internally; or the rule can be regarded as the same as displacement, with the part of the vessel above water added,

formula Columbia would be rated as of 264 tons, and Seabelle 140, and the time allowance would be 16 minutes for a course of 50 miles.]

The Seabelle and Columbia are representatives of extreme types, but among vessels so little varying in form as those belonging to this country, very varying stability characteristics are to be found. These varying characteristics can best be illustrated by curves of stability, which exhibit the righting power at successive angles of inclination, and a suitable contrast will be found in the curves for Jullanar and Florinda for the purpose of illustration.

The Jullanar affords an example of the kind of curve of stability a vessel has with a low centre of buoyancy and low metacentric height (see Fig. 6, page 9), brought about by a heavy displacement obtained by depth of body ballasted with lead. Her metacentre falls below the load water-line; yet, owing to her great depth of body, and the great weight of lead stowed in that depth, her centre of gravity is low, and is, in fact, an inch or two below her centre of buoyancy. Still the metacentric height is limited, and at small angles of heel the righting lever ( G, Fig. 6) is short; but that lever continues to increase up to the time that Jullanar would be on her beam ends, when it is more than double what it would be at an inclination of 30°-a condition which renders Jullanar absolutely uncapsizable. She thus has the finest seagoing elements possible-low metacentric height for ease, and illimitable range of stability for safety. Jullanar's success in extremely strong winds, as compared with her performances in light winds, is directly attributable to the peculiarities of her stability curve. Florinda is an example of a yacht with less depth of body than Jullanar, and a higher centre of gravity. Under lower sail, with a wind force of 1.71b. per square foot of canvas, Florinda would heel 15°, whilst Jullanar would heel 17°; but if the force were increased to 3lb. per square foot, Florinda would heel to 35°, whilst Jullanar would only fall over 30°. It will be seen by referring to the annexed stability curves, that at 24° (about the deck edge) the stability of Jullanar and Florinda are equal; at any further inclination the stability of Jullanar makes a very rapid gain on Florinda. At 20° inclination Florinda's deck begins to be immersed, whilst none of Jullanar's deck is put under until she reaches an inclination of 26°. This fact, coupled with her depth of body and her extraordinary low centre of gravity, can be regarded as the cause of her long range of stability, and the cause why in strong winds Jullanar is able to beat

Florinda.

The Seabelle is a vessel somewhat similar to Jullanar so far as the vertical position of her centre of buoyancy is concerned, and her curve of stability resembles that of Jullanar. The Rose of Devon, on the other

hand, like Florinda, represents a shallower type of vessel, and the curves of stability of these two are of similar character. Rose of Devon, however, has a high centre of gravity as she is ballasted wholly with iron; her curve, with 20 tons of lead on her keel, is shown by the dotted line. The character of the curve remains the same, but owing to the greater length of righting lever due to the lower centre of gravity the "righting power in foot tons" is largely increased for any angle of heel.

It has been sufficiently shown that sail-carrying power is a very large factor in the elements which make up a vessel's success in competitive sailing; and generally, as that power cannot be increased by adding to

beam and length without such additions being adequately taxed for competitive sailing, the designer exercises his ingenuity in depth and ballasting. Thus, if we find two vessels of equal length and breadth, and one exhibits an advantage over the other, that advantage will be nearly always traceable to greater sail-carrying power. The conditions upon which this power is dependent have already been explained, and the importance of well considering them has been sufficiently exemplified by the reference to the relative stability of such distinctive types as Seabelle and Columbia, Jullanar and Florinda.

CHAPTER VI.

RESISTANCE AND SPEED, AND THE INFLUENCE OF THAMES MEASUREMENT.

IT has been assumed, in the last chapter, that the qualities of the two yachts as to form, upon which their resistance to motion depended, were equal, although one by reason of inferior stability might have much greater propulsive force than the other. Of course this equality of speed as dependent on form, need not necessarily exist, and in fact, at very high speeds, the resistance, due to form and other qualities, might vary very considerably; and consequently the speed might vary independently of relative sail-carrying efficiency. According to recent investigations there are only two principal sources of resistance, and they are consequent upon surface friction and wave-making. "Surface-friction" is due to the adhesion of the water to the. immersed surface of the hull; and from the experiments made by Mr. Froude for the Admiralty, we learn that up to the period of wave-making the whole appreciable resistance is caused by surface friction alone; thus at low velocities any form, not having an absolutely flat or blunt end, would only have surface friction to contend with. A fairly modelled yacht of, say 50ft. in length, moved at a velocity of five knots an hour, need make scarcely any waves, and the resistance she would encounter would be almost entirely due to the friction of the water on the surface of her copper. From the foregoing it can be gathered that, so far as the resistance due to surface friction is concerned, it will be advantageous for a yacht to have a comparatively small area of surface immersed, and for that surface to be of the most uniformly perfect smoothness. The frictional resistance of perfectly clean copper (with no nail heads or other uneven protrusions), upon a vessel 50ft. long, is equal to 0.2461b. per square foot at a speed of six knots per hour; and the resistance increases uniformly as the 1.83 power of the speed.* But

* Practically the resistance is lb. per square foot at six knots, and 1lb. per square foot at twelve knots. Thus a well formed yacht with 1000 square feet of surface moved at the rate of six knots an hour would only require a tow rope strain or nett propelling force of 250lb.