ANY object floating on the water will have a tendency to drift before the wind; but a boat, with its scientifically constructed hull, sails, and rudder, can be so guided as to sail with the wind on her quarter or abeam, or even close-hauled, as it is called, that is, with the wind meeting her at an angle of about forty-five degrees.
Fig. 20 represents the deck plan of a boat sailing close-hauled under two sails. The sails A and B are drawn aft with the sheets till they form an acute angle with the line of the keel. The wind, whose direction is indicated by the arrow W, strikes the sails at a very acute angle, so that they do not shake, but are just full.
The result of this pressure on the sails is that the boat is propelled forward and also sideways away from the wind, making leeway, as it is called.
If a boat has a deep keel, her lateral resistance to the water will cause the leeway to be insignificant. If the boat is of very shallow draught and so offers little lateral resistance to the water, she will not go ahead at all, and the entire force of the wind will be expended in driving her bodily to leeward. Lee-boards and centre-boards are fitted to shallow boats in order to obviate this.
The pressure of the wind on the sails, in addition to producing the above effects, heels a boat over. A sailing-boat is so constructed as to resist this tendency to capsize. Either she is made narrow and deep and is weighted with ballast as far as possible below the water-line, or she is shallow but of considerable beam. The deep and weighted boat will heel over more readily than the beamy shallow boat, but the further she heels the greater pressure of wind is necessary to make her heel still more, for the leverage of her ballast increases as she heels, and many boats with lead upon their keels are practically uncapsizable. On the other hand, the beamy shallow boat does not heel so readily, but after she has heeled to a certain angle she will capsize.
The pressure of thc wmd on the sails not only propels, drives to leeward, and heels over a boat, but, unless the sails are absolutely balanced, it tends to turn her in one direction or the other.
In Fig. 20 we have a boat with two sails. If the after sail is the more powerful, it is obvious that the wind will drive round that sail and the stern of the boat with it in the direction of the arrow c, while the head of the boat will run up into the wind. If, on the other hand, the head sail be the more powerful of the two, the bow will be driven off the wind and the boat will bear away.
The sails of a boat should be so balanced that she has a slight tendency to run up into the wind; and to counteract this weather helm, as it is called, the steersman will have to keep the rudder slightly to leeward of the line of the keel.
If a boat carrying weather helm be left to her own devices in a squall she will at once do the right thing, luff up into the wind and be in safety; whereas a boat with too much head-canvas and carrying lee-helm will run off her course and put herself in a dangerous position.
A boat should not gripe, that is, carry too much weather helm, for steering will then be very hard, and the rudder, forced far over to counteract the helm, will act as a serious drag in the water.
In balancing the sails, it must be remembered that the further out a sail is on an extremity of a boat, the greater its effect in driving that end of the boat off the wind.
Sometimes a vessel's sails are not properly balanced because the ballast has not been stowed in the right place. It is obvious, for instance, that if ballast be shifted aft the weather helm will be diminished, for the stern of the boat will draw more water and so offer more lateral resistance, whereas the stem of the boat will draw less water, and will therefore be more easily blown round. A centre-board, again, is generally placed well forward, so it is found that when this is lowered the weather helm of the boat is considerably increased.
We have explained that a boat properly constructed and rigged can sail within forty-five degrees of the wind. Now, if it be desired to sail to some point more directly to windward than this, what is called tacking becomes necessary. This consists of sailing a certain distance close hauled with the wind on one side, and then turning round and sailing close hauled with the wind on the other side. A zigzag course is thus taken, each tack being at about right angles to the last.
One diagram of Fig. 21 illustrates the process of tacklug with the wind right ahead, and in the other diagram the wind is a point or two off, so that one tack is longer than the other, there being, in sailor language, a short leg and a long leg. That the action of the rudder, when forced over till it is at an angle with the keel, is to act as a drag on that side and so deflect the boat's course, is plain enough. But it is not so obvious a fact that this action of the rudder in turning the boat is not to turn her bow round through the water, but to push the stern sideways while the bow is almost at a standstill. For the centre of rotation of a boat, that is, the imaginary pivot on which she turns, is always well forward.
In Fig. 22 >A is the centre of rotation. So when the rudder is put over to the right, the boat will revolve on the pivot A till she is in the position indicated by the dotted lines. It will be observed that the stern has moved about twice as far as the bow. The further forward the centre of rotation the greater will this disproportion be.
It is very important to remember this effect when sailing very near any object such as a buoy, for while steering so as to turn the boat's head away from the object and avoid it, the stern is made to approach the object, and the very action that seems calculated to prevent a collision may become the cause of one.
Having shown what are the relations of the sails, hull, and rudder of a boat to the wind and water, and explained how a vessel requires either ballast or beam to prevent the wind from capsizing her, and needs draught to increase her lateral resistance and prevent her from being blown to leeward, it remains to add that the longitudinal resistance to the water must be diminished as much as possible, that the the boat can slip easily through the water and travel with speed.
For this reason a sharp stem is put on a vessel, so that she can open a way for herself through the water like a wedge, and she is given what is called a fine run aft, so that her stern will not drag heavily. Again, the larger the area of the boat's greatest cross-section (Fig. 23), the more resistance that results and the slower she will travel. The area of the cross-section is diminished by making a boat of narrow beam, while the necessary displacement is obtained by increased length and depth.
Now, the difficulty arises that most of the qualities that ensure speed in a boat have a tendency to lessen her stability and even her lateral resistance. It follows that, while constructing a boat, a compromise has to be made between these three; and the problem as to how to produce the fittest craft becomes a very complicated one that has never been solved yet, and probably never will be.
Thus a long narrow shallow boat will run the fastest before the wind, but she will not turn to windward at all, and will capsize with great ease.
As it is recognized that beam is opposed to speed, it has been long the fashion in England to construct racing yachts extremely narrow and of great draught. Such craft do attain speed, but at the expense of all comfort, and when a heavy sea is running go through it instead of over it.
To come to the opposite extreme, we have the flat-bottomed very shallow and very beamy craft, with a deck plan not unlike a flat-iron — a veritable skimming-dish. Provided with a centre-board, such a boat is well adapted for shallow and sheltered waters. The centre-board can be raised while crossing a shoal, and the boat will then draw only as many inches as a deep-keel boat of her size would draw feet. She will be very fast in smooth water, but in rough water she will pound heavily into the seas, and, having no good hold of the water and little momentum, will lose her headway and soon prove dangerous.
For real comfort and seaworthiness — and some now maintain for racing purposes as well — a boat that is something between these two extremes answers the best; that is, a boat that is moderately beamy and has a moderate draught of water.
Some years ago we sailed to South America in a yacht that well represented the class of vessel we are now speaking of. Her length was forty-two feet, her beam thirteen feet, and her draught seven feet six inches. Not being one of the narrow deep class, she was an excellent sea boat; indeed, she once had the reputation of being the best sea boat of her size in the Channel. Now the advocates of the narrow boats will contend that speed must have been sacrificed to obtain this comfort in heavy weather. We scarcely agree with these gentlemen; for this boat, though furnished with exceptionally small sails, could do her nine knots an hour, and on one occasion travelled two thousand sea miles in ten days.
The author also once owned a centre-board yawl of five tons, which drew between two and three feet without her centre-board. She thus combined the advantages of the shallow boat with the seaworthiness of a boat that is sufficiently immersed to have a good hold of the water.
This compromise between the deep-keel and the centreboard types of boat has long been popular in America, and probably the recent victories of the American yachts constructed on these principles, over our own crack deep-keelers will gradually modify the English views on this subject.
Most of our yachting men maintain that a long hole through the bottom of a boat must weaken her; that the great strain of the centre-board, concentrated as it is on one small portion of the keel, must render a large craft thus fitted ill-adapted to buffet witll a really heavy sea.
On the other hand, the American builders emphatically deny that a centre-board is a cause of weakness, and point to their noble pilot vessels and trading schooners, which are all provided with centre-boards, and which are exposed to every sort of weather.
It is unnecessary to dwell longer on this controversy; for though there is much divergence of opinion as regards large craft, there can be no question as to the advantages of fitting centre-boards into many kinds of small craft, especially in those that are intended for river sailing.