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Wind Affects Power and Speed = Wind Resistance Estimated for Three Vessels—A 10-Knot Freighter— A 20-Knot Passenger Liner—And a 20-Knot Cross Channel Steamer HIS paper is an investigation | of the effect of wind pressure on the horsepower and speed of different types of ships. The paper deals with effect of the wind pres- sure in increasing the resistance to mo- tion, and also considers the extra re- sistance of the rudder when a large degree of helm angle has to be car- ried to counteract a wind on the bow or quarter. No attempt is made to consider the effect on resistance of rough water resulting from wind. The procedure adopted has been to assume in each case the. wind act- ing directly ahead and to assume that the resulting pressure on the vessel can be expressed in the form K A V’ where K is a constant, A is an area, and V is the speed of the vessel rela- tively to the wind. The value of the constant K adopted throughout has been 0.0048, and the areas have been measured in square feet, velocities in knots, and the resulting pressure in pounds. As a first approximation to the pressure on the superstructure it is usual to measure the transverse -thwartship area of the vessel above the water line and use this for A in the formula above, it being. assumed that the frictional air resistance is negligible. The constant K_ covers not only the pressure on the forward side of the surface but also covers the effect of the rear suction on the surface exposed to the wind. The as- sumption that the whole of _ the thwartship area above the water line is exposed to a head pressure, similar to that on a plane advancing at right angles to the wind, is obviously not Paper read at the spring meeting of the six- ty-eighth session of the Institution of Naval Architects, at London, April 8, 1927. The author is an associate member. BY HUGH J. R. BILES, Esq., B. Sc. correct, for the portion of the vessel between the waterline and the weath- er deck is of easy form, and it is ob- vious that the resistance of this por- tion of the above-water structure is usually almost entirely frictional, and is very small in comparison with the head resistance of a plane whose area is the same as the midship area of the vessel between the waterline and the weather deck. On the other hand, when there is discontinuity in the su- perstructures, and a fair distance be- tween these discontinuous portions, the wind will exert its full force not only on the foremost superstructure but on the ones abaft it which seem to be masked by the leading super- structure. Moreover, if the wind be a few degrees on the bow, then it will exert some effect on discontinuous superstructures however close togeth- er they may be. The resistance due to air pressure has been estimated for three vessels: one a 10-knot 400-foot cargo vessel of about 8000 tons deadweight, of the poop, long bridge and forecastle type; the second a 20-knot passenger liner of about 650-foot length; and the third a 20-knot cross-Channel steamer of about 320-feet length. Before giving the results of these estimates of wind pressure it will be as well to outline how the calculation has been made. (1) Cargo Steamer—The forecastle has been taken as having a rear suc- tion effect only and no pressure effect. This is accounted for by taking half the area of the after end of the fore- castle instead of the whole area. The bridge space has been taken as hav- ing the full pressure and_ suction effect. In the case of the poop, the area of the fore-end of the poop has TABLE I Air Resistance Due to Wind of Velocity V Relatively to Ship (1) Cargo Vessel Resistance, Lb. 207 829 1,870 8,315 5,180 7,450 10,150 13,260 20,700 29,900 18 Air Resistance Per cent naked re- sistance at 10 knots MARINE REVIEW—May, 1927 been multiplied by three-fourths to represent full pressure on the front of the poop, and a suction effect on the after and of the poop equal to half houses on the bridge deck in any way that of a flat surface. None of the mask each other, and they have been taken in a straightforward way. The funnel effect has been taken as equal to half that of a rectangular-shaped funnel. Frictional resistance was also estimated and found to be about 3 per cent of the head resistance, and an addition of 2 per cent was also allowed for fittings, viz. deck ma- chinery, ventilators, rigging, rails, boats, skylights, etc., and 2 per cent allowed for air eddies round the counter of the vessel. (2) Passenger Line—A similar pro- cedure has been adopted in this case, the only difference in the results being that as most of the superstructures and houses were continous, or with very small gaps, between them, the forward superstructures were in gen- eral the only ones that were reckoned as acted upon by the full force of the wind. The funnels were treated in exactly the same way as the cargo vessel, except that there was a suffi- cient interval between the funnels to allow the full pressure acting on all of them. In this case the frictional air resistance was found to be about 4 per cent of the remainder. Eddies round the stern were estimated at 2% per cent and deck fittings at 2% per cent. (3) Cross-Channel Steamer—The method of estimating was similar to the two previous cases. The fric- tional resistance in this case was es- timated to be 3% per cent of the total, but owing to a very square stern the estimate for the _ stern eddies resulted in an addition of 6% per cent to the total. Two and a half per cent was again added for the resistance of fittings, etc. In Tables I, II, and III are given for the three vessels the estimated resistance in pounds due to wind pressure corresponding to various relative speeds of wind and_ vessel. In addition, a column is given which shows the percentage that this air resistance bears to the naked re sistance at load draft of the ship, at 10 knots in the ease of the cargo vessel and at 20 knots in the cases