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Depth is of more importance than length in attaining this resistance, partly because the water is more difficult to move the deeper you go, on account of the superincumbent weight, and partly because the motion imparted to the water by the entrance of the bows destroys much of its effect as the stern is reached, if the keel is level. Therefore, a keel or centre-board high at the fore-end and sloping quickly to a greater depth, is of more use in the way indicated, as fresh and undisturbed water is reached by each additional inch of slope until the lowest point is attained.

CHAPTER II.

THE ACTION OF THE RUDDER-THE EFFECT

OF THE WIND.

CONTINUING our consideration of the relation of the boat to the water, we come to the action of the rudder. This is the agent by which the boat's head is either turned to one side or other of the course she is pursuing, or is kept in a straight course when the opposing effect of the wind on the sail tends to turn her out of it. Everyone who has played billiards or bagatelle, and knows the result of a cannon,” knows that when one substance in a state of motion meets another at an angle both are deflected from their original course. This is precisely the case with the rudder and the water. As long as the rudder is in a line with the keel it has no effect. When it is put at any angle with the keel, the water rushing against it cannons it off, carrying the stern of the boat with it. Thus the effect of moving the rudder to one side or another is to push the stern to the opposite side, and the direction of the bows is consequently altered. It is well to remember that it is the stern which is thus slewed round, and not the bows, or when you are steering close alongside some object you may, in endeavouring to keep her bows from it, hit it with the quarters or stern.

So far does the rudder work in altering the direction of the boat, but it is also requisite in keeping the boat's head straight. One effect of the wind on well-arranged sails is to slew the boat round into the wind's eye, because the pressure is brought to bear more on the after part of a boat than the forepart. This tendency has to be counteracted by the rudder, which is turned so that the pressure of the water upon it is equal to the turning pressure of the wind

upon the sails. The diagram will illustrate this. Fig. 8 shows a vessel with the wind on the port, or left side, blowing in the direction of the straight arrow upon the sail (A). In addition to the propelling force of the wind (which will be afterwards explained), there is the tendency to turn the sail, and with it the boat, in the direction of the curved arrow (B). To counteract this and

E keep the vessel in the course she is heading, the tiller (C) is pushed over to port, and the rudder (D) of necessity goes to starboard. The impact of the water tends to push the Fig. 8. DIAGRAM ILLUSTRATING EFFECT OF

WIND AND RUDDER. rudder, and with it the stern of the boat, in the direction of the curved arrow (E) and the forces E and B equalling each other, the boat is steered straight.

A medium sized rudder acts quite as well as a large one, only it has to be put over at a greater angle. It is easier to work and has less frictional surface.

The effect of the wind on the sails and the principle of sailing close hauled, that is, in a direction against the wind, are the most difficult things to explain in a short and plain manner without going into too abstruse calculations. It is

It is easy enough to understand how a vessel can sail before the wind-she is simply blown along; but how is it she can sail in a contrary direction ? Suppose the wind to be blowing from the top to the bottom of this page, a vessel can yet sail from the bottom to the top. To do so, however, she would have to tack, and her progress would be a zigzag one, as shown in Fig. 9. Upon looking at Fig. 10 you will see that the sail (A) is trimmed at such an angle with

the keel that it will just be full of wind. The wind catches it and glances off in the direction of the dotted lines. Now, if you were to put a billiard ball at the same angle it would fly off, not

in the direction of the stroke, C

but in another at an angle with it. So in the case of the wind. The force is—to use the technical termresolved into other forces operating in the direction of the

strokes on the opposite side of B

the sail. Now the sail cannot be blown sideways towards B, because of the great lateral resistance of the keel, so that the force that way is lost-save to blow the vessel over (a result which her stability strives to prevent);

but the forward forces in the A FIG. 9. TACKING.

direction of C have a minimum of resistance offered to them, so the sail and the vessel it drags progress in that direction. The reader may get a better idea of this action of the wind if he opens and shuts the door of his room a few times and notes how the latch is forced in a certain direction by a force at right angles to that direction.

To go back to Fig. 9. A yacht will sail against the wind at about the angles shown. By a reference to the compass, hereinafter delineated, it will be seen that the vessel goes about 4 or 41 points from the wind.

In the figures from A to B she is on the port tack—that is, the wind is on the left or port side; from B to O she is on the starboard tack, the wind being on the starboard side ; and from 0 to D she is on the port tack again.

At the points B and C she has put the helm down—that is, to leeward—so that the rudder goes to windward and turns her head round, and the wind comes on the other side. This operation, called tacking, will be afterwards explained.

The flatter the sails are the more perfect will be the effect of the wind If

B they could be as

FIG. 10. DIAGRAM ILLUSTRATING EFFECT OF WIND. flat as a board the yacht would sail much faster, but that perfection of flatness cannot be achieved. In the best cut sails there is some curve or bag, and the more there is the worse the vessel sails to windward.

From what has been said upon stability, it will be seen that upon it depends the power to carry sail, and upon the power of a vessel to carry sail depends, in a great measure, her speed. We say, in a great measure, because the form of a vessel has a great deal to do with speed.

upon them.

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