Chapter 25, -NEW DEVELOPMENTS IN NAVAL ENGINEERING 



AIR INTAKE AND STRUT 

 TRUNK HOUSING 



FORWARD FOIL 



PROPELLER FOR FOILBORNE 

 OPERATION 



PROPELLER FOR 

 HULLBORNE OPERATION 



NACELLE 



3.88 



Figure 25-1. -Hydrofoil (USS High Point , PCH 1) 



In the plenum- chamber type , air is forced 

 down from the top of one chamber and allowed to 

 escape around the edges at the bottom. 



In the air-curtain type , the interior is divided 

 into sections, with open air ducts between the 

 sections. Air is forced down through the ducts to 

 form a high pressure air cushion for the craft to 

 ride upon. Air jets, pointing downward and in- 

 ward, are installed around the periphery of the 

 craft; the air from these jets holds the air bubble 

 in place. In some air-curtain designs, the air 

 jets are used only at the front and the rear. Side 

 walls (called skegs ) are used to enclose the air 

 bubble at the sides. 



In the water- curtain type , a scoop and a water 

 pump are used to form water jets (instead of air 

 jets) around the peripheryof the craft. The water 

 jets are even more efficient than the air jets in 

 keeping the air cushion under the craft. Ob- 

 viously, the water- curtain design is suitable only 

 for craft operating over water. 



The air cushion gets the hydroskimmer into 

 the air, but it does not provide it with any means 

 of horizontal propulsion. Both airscrews and 

 water screws have been tried; each type has some 

 advantages, with the choice depending upon the 

 nature of the vehicle and the service conditions. 



The hydroskimmer, although still experi- 

 mental at this stage, gives promise of being a 

 very fast and effective craft for a variety of uses. 

 Speeds of 80 to 120 knots are considered feasible. 

 The hydroskimmer is being considered for such 

 uses as ASW craft, patrol craft, high speed trans- 

 port, amphibious assault, mine countermeasures 

 craft, and rescue craft. The Navy's 25-ton re- 

 search hydroskimmer, SKMR-1, is shown in 

 figure 25-3. This vessel was built with the speci- 

 fic aim of providing more knowledge on the pre- 

 ferred shapes, propulsion machinery, and pro- 

 pulsive devices for this type of craft. The air 

 cushion system for SKMR-1 is shown in figure 

 25-4. 



PROPULSION AND STEERING 



For more than a hundred years, the under- 

 water screw propeller has been the conventional 

 device for ship propulsion. Although the screw 

 propeller is in nodangerof being replaced within 

 the foreseeable future, the increasing emphasis 

 on high speed ships has led to an increasing con- 

 cern with other types of propulsion devices. Some 

 of the propulsion devices presently under de- 

 velopment or consideration are mentioned here. 



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