Page 323 equipment and instruments 4211 



When handlead and machine soundmg methods are used extensively, a reversible 

 propeller is desirable to eliminate much of the wear and tear on the clutch and reverse 

 gear from the frequent stops required for vertical casts. The fact that the engine oper- 

 ates at a constant speed whether going forward, astern, or at a stop, reduces carbon 

 fouling to a minimum and hence makes the motor more dependable. This feature is not 

 essential if the launch is equipped with a portable depth recorder, in which case the 

 conventional propeller, which is more efficient, should be installed. 



A survey launch should be seaworthy, strongly constructed, and should have as 

 much clear space in the cockpit as practicable. Most survey launches are hoisted and 

 carried on board the large survey ships, but sometimes, through necessity, they are towed 

 from place to place, especially where they are to be operated in conjunction with one of 

 the auxiliary vessels, which cannot hoist them. 



There are two principal types of survey launches used by the Coast and Geodetic 

 Survey. One is the United States Navy motor sailer with an open cockpit covered 

 with a canvas canopy. The other has a similar hull but is partly decked, with two 

 canopy-covered cockpits separated by a small deck at gunwale height for navigation 

 and hydrographic survey operations. The standard length of both types is 30 feet, 

 with a 3-foot draft. They are equipped with either gasoline or Diesel engines. Diesel 

 engines are being installed exclusively in all new launches to eliminate the hazard of 

 explosion and fire that is ever present when gasoline is used. The launches are con- 

 structed with hoisting pads and rings and where they are a part of the ship's equipment, 

 they are stowed in chocks on the ship between periods of use. The launches have a 

 lifeboat capacity of 24 to 30 men and a fuel capacity of 50 to 100 gallons. 



The open cockpit type of launch is preferable for transporting signal-building 

 parties, camp supplies, lumber, and bulky supplies. The partly decked or enclosed 

 launch with. the engine in a separate cockpit is more suitable for hydrographic survey- 

 ing since the various operations can be more efficiently conducted where they are sepa- 

 rated from the engine compartment and motor noises. 



Shallow draft launches are used for hydrographic surveying in extensive shallow 

 water areas. These afford adequate room for the personnel and necessary equipment 

 of a hydrographic survey unit. The launches are 26 to 28 feet m length and their 

 draft is not more than 10 or 15 inches when loaded. 



4211. Launch of Ship ** Explorer** 



One of the new launches of the Explorer is illustrated in figure 73. 



It has a length of 30 feet, width of 8^-2 feet, draft of 3 feet, is of sturdy wooden construction, 

 and is designed especially for inshore hydrography along exposed coasts. A 35-hp Navy-type Diesel 

 engine propels the launch at about 7)4 knots at 1,400 r.p.m. 



The launch is decked over except for the two cockpits. Aft of a forward deck 6 feet long is the 

 forward cockpit, which is 9)4 feet long. There is a 3J4-foot deck amidships, aft of which is the after 

 cockpit 6% feet in length, extending to the afterdeck which is 4}^ feet long. A narrow 8-inch deck 

 extends around the sides of the cockpits, which are surrounded by a coaming or washboard extending 

 6 inches above the deck. Both cockpits are fitted with canvas canopies, covered- wagon type. The 

 afterdeck has a tubular rail around its edge. At the forward end of the midship deck section there 

 is a bulkhead surmounted by a Lucite flexible glass windshield. There is a centerline opening through 

 the bulkhead for entry to the forward cockpit. The steering wheel and engine controls are located 

 on the port side of the bulkhead between the midship deck and the forward cockpit, and the coxswain 

 conns the launch from this point. 



