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stream in being guided directly rear- wards, imparts additional useful thrust in the direction of motion of the vessel. Fig. 8 shows the method of developing a Contrarudder blade. It should be noted that for every sec- tion of the propeller blade there is a corresponding Contrarudder section so designed as to properly accommo- date the flow at this point. Proof of the foregoing statements is found in model basin tests made to determine the relative merits of the Contrarudder, and the symmetri- cal streamline rudder as compared to the conventional design of sternpost and plate rudders. The results of two such tests are found in Tables I and II. Service data obtained from vessels that are Contrapropeller or Contra- rudder equipped has corroborated the results found in the model basin. For example, tank tests made with the model of the S. S. PENNSYLVANIAN of the American Hawaiian line indicated that a saving in power of 14 per cent at 11.75 knots might be expect- ed when this vessel was equipped with a Contrapropeller of the type shown in Fig. 3. An examination of this vessel’s performance over a three year period after the fitting of the Contrapropeller shows a sav- ing in power of 14.12 per cent which closely approximates the _ results found in the tank. Good Results in Actual Service The American Hawaiian line fol- lowed up the Contrapropeller instal- lation on their S. S. PENNSYLVANIAN with a Contrarudder installation on their S. S. GoLpEN SuN, a vessel of 11,000 tons capacity engaged in the transpacific trade. An examination of her logs over a period covering a year’s service before and after the Contrarudder installation gave the following results: S.S. Golden Sun—Results Westbound Voyages Plate Contra Differ- Rudder Rudder ence Mal Ors ee. 216.77 192.60 —24.17 Speedin: vt. es 8.94 10.12 +1.18 SDE rere. 18.0 8.60 —9.40 Displacement... 14,787 12,697 — 2,090 Revolutions.... 69.10 69.97 +0.87 Eastbound Voyages Plate Contra Differ- Rudder Rudder ence Buel Ones 215.40 185.58 —29.82 Speed.. 9.94 10.58 +0.64 GHD ees wees 9.36 L270 —7.66 Displacement... 10,495 9,687 —808 Revolutions.... 69.10 67.35 —1.75 Note: Fuel oil, in barrels per day; Speed, in knots; Slip, in per cent; Displacement, in tons Revolutions, per minute. It will be noted from the above that the Contrarudder has effected a material gain in the form of in- creased speed and reduced fuel con- sumption, even after an average al- lowance of about 15 barrels per day is made for the smaller displace- ment on the trips with the Contra- rudder. Fig. 9, showing the trial data of two sisterships identical in all re- spects except for the rudder arrange- ments, gives a comparison of un- usual interest. This figure gives the results obtained over the measured mile under similar conditions and also indicates the types of rudder arrangements used. It will be noted that although the rudders are iden- tical, the M. S. NorviInn has a rounde@ sternpost while the M. S. NorroLp has a Contrapropeller which serves as a sternpost. Due to the influence of the Contrapropeller, the NorroLp was able to maintain the same speed as her sister ship with 14 to 17 per cent less horsepower. Fig. 7 shows the most improved de- sign of Contrarudder fitted to ves- STREAMLINE RUDDER Ee tale DEVELOPED f PINTLES — SECTIONS Sane ane 29 err eee ms Ls Sey THRUST REGAINED Fig. 8—Showing principle of Contrapropeller action 32 MARINE REvVIEw—February, 1932 sels already in service. The note- worthy features are: (a) A portable hub cap, cast in halves and faired into the center- piece boss, permits removal of pro- peller without disturbing any por- tion of the Contrapropeller. (b) A sturdily built streamline rud- der retains the old rudder plate. (ec) Portable plates allow for lift- ing of rudder and permit easy access to pintles. The Contrarudder can readily be incorporated in the design of a new vessel. Such a design includes a Contrapropeller made as an integral part of the stern frame, that is, the Contrapropeller is substituted for the obsolete rectangular sternpost. In- stallations of this type include five 21,500 ton vessels of the S. S. Pa- CIFIC SUN class, built by the Sun Ship- building & Drydock Co. for the Motor Tankship Corp., and the S. S. Ex- CALIBUR and §S. S. EXocHorRDA built by the New York Shipbuilding Co. for The Export Steamship Corp. This arrangement, which is also adaptable to a vessel having a dam- aged stern frame, was used in the case of the S. S. WILLIAM N. PAGE of the Mystic Steamship Co., which lost her rudder and broke her stern frame by grounding off New Eng- land. Such a replacement, which is illustrated in Fig. 5, can be made for practically the same cost as would be required to renew the convention- al stern frame and plate rudder. Application on Hog Island Ships A class of single screw vessels de- serving of notice is the Hog Island ““A’”’ type ships, in which a semi- balanced rudder replaces the conven- tional stern frame and rudder. This class of vessels has proven very pop- ular, and several companies operating them are undertaking to increase their speed from 10.5 to 13 knots to fulfill mail contract requirements. One such company is the Missis- sippi Shipping Co., operating between New Orleans and the East coast of South America, who have converted two Hog Island ships into modern passenger vessels. Besides adding passenger accommodations and over- hauling the machinery and power plant, a Contrarudder and Contra- propeller guide vanes were fitted to the first ship, the Drt Norrer, as il- lustrated in Fig. 6. From this pho- tograph it will be noted that the ex- isting rudder balance was replaced by a section employing the Contra- propeller principle, together with guide vanes installed forward of the propeller which also have the Con- trapropeller curvature. The Det Norte averaged 13.76 knots oved a 90-mile course between Mobile Sea Buoy and South Pass, and to date has averaged over 13 knots loaded on the two voyages made from New Orleans to Rio de Janeiro against the adverse current encountered on this run. In addi-