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EQUIPMENT AND INSTRUMENTS 



4248 



4248. Catamaran 



A catamaran is a two-hulled craft, the hulls being joined by cross beams. Two 

 boats of the same type and dimensions are generally used, either dinghies, skiffs, or 

 dory-skiffs. An outboard motor is usually attached to the stern of one of the boats, 

 but may be attached alongside, or to the deck between the two boats. Sometimes a 

 whaleboat is used alongside a smaller boat to which the outboard motor is attached. 



The main advantage of a catamaran is as a substitute for a shallow-draft launch 

 for hydrographic surveying in protected waters when such a launch is not available. 

 The two boats, when properly secured together, give the craft a stability which permits 

 the freedom of movement required by the personnel of a hydrographic party. 



The shallow draft enables the craft to go close inshore and to operate freely over 

 extensive shallow areas. Survey parties operating from auxiliary vessels have con- 

 structed catamarans and used them successfully when no other means were available to 

 accommodate a launch hydrographic party. 



FiGiRE 74.— Handlead sounding from a catamaran. 



4249. Sea Sled 



A sea sled, occasionally useful in surveying, is a light craft of about the same 

 length as a dinghy but with considerably more beam. Its particular characteristics 

 are its shallow draft and concave-shaped bottom, which is tunneled fore and aft along 

 the centerline. The craft attains high speed when propelled by an outboard motor, 

 as the tunnel produces a sort of air pocket and a planing effect, which reduces water 

 friction and enables the sea sled to skim along the surface of the water. 



