« ForrigeFortsett »
will fall upon a centre-board. If there is a uniform, though not a great, depth of water—such as in the Norfolk rivers and broads—then the combination of shallow and deep boat, with fixed keel, such as is used on the Norfolk waters, is desirable. If there is deep water and good anchorage, such as most seaports possess, a deep, heavily-ballasted yacht is the best. So that the kind of stability to be sought for must be dependent upon the locality where the vessel is to be chiefly sailed.
Next in order to stability comes lateral resistance, or the prevention of leeway. As will be afterwards explained, there is, when sailing in FIG. 4. SECTION OF DEEP
YACHT SHEWING STABILITY. any direction except with the wind abaft the beam, a sideways pressure as well as a forward pres
The force, however, which it is necessary to utilize is the forward one; the lateral one must be resisted as much as possible, so that the vessel may move only in the direction she points, and may not drift sideways,
Fig. 5. SECTION OF CENTREable resistance. The form of a boat
BOARD BOAT SHOWING is such that the resistance to the
passage of it is but little, and the less the better, so far as the swiftness of it is concerned. The finer the bowg are the greater is the speed likely to be. The lateral resistance is obtained either by the depth of immersion and keel, or, if it is
shallow boat, by the addition of a centre-board, which is a piece of iron or wood let down through the bottom of the boat, and working in a water-tight case. Fig. 6 shows the under water section of a deep keel boat, and Fig. 7 that of a shallow centreboard boat. It will be seen that there is a greater lateral area of immersed surface in Fig. 6 than in Fig. 7, yet the actual resistance of the latter will be as great as the former, for the following reason. The resistance of a board at right angles with
FIG. 6. LONGITUDINAL SECTION OF DEEP-KEEL BOAT.
the water is far greater than one at a greater angle. In the deep keel boat the sides slope up from the keel, as shown in Fig. 2, and the angle is rapidly lessened, as in Fig. 4, under the influence of a breeze, while the centre-board is absolutely at right angles with the
FIG. 7. LONGITUDINAL SECTION OF CENTRE-BOARD BOAT.
water, and the angle is only gradually lessened, and never, to a very great degree, unless the verge of safety is too nearly approached, as we have before explained when treating of stability.
The deduction from these remarks is that, as far as lateral resistance goes, there is little to choose between the two types of yachts.
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.
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 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.
B 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 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