surcharge loading of this operation. Also, a specially contoured curb must be located on the 

 exact line that will positively prevent any further forward motion of the vehicle and yet will 

 allow the fork ladder to clear the top of the wall when lowered into the basin. Such details 

 must be obtained from the manufacturer. 



Overhead-rail launchers, either monorail or duorail, function the same as a straddle 

 vehicle except that they are not mobile (Fig. 128). For daily trailer-boat launching where 

 versatility is not required, this system provides a rapid operation at less cost per cycle than 

 can be obtained with mobile equipment. The overhead rail is pushbutton-operated, hence 

 requires less operational skill, and is easier to maintain. However, an electric power source is 

 required, and because of the extensive structural framework, the installation cost may equal 

 or exceed that of a straddle-vehicle system. Unless the framework is high, the overhead rail 

 cannot be used for masted or high-superstructured craft. Some proprietary rail-hoist systems 

 include the structural framework, and others have only mobile and hoisting components, so 

 that the design of the supporting framework can be tailored to the requirements of the site. 



Because only one rail hoist can normally be afforded at any given marina or launching 

 site, and the cost increases rapidly with design lifting capacity, the selection of size is 

 critical. A forecast of probable use will indicate the largest craft to be handled in sufficient 

 numbers to make a rail-hoist operation feasible. A rail hoist of this capacity should then be 

 installed; larger craft must go elsewhere or be handled by a stiff -leg derrick or other 

 large-capacity equipment that may also be installed at the same marina for such oversize use. 

 A graph for selecting the proper capacity hoist for various lengths of power boats and 

 sailboats is shown in Figure 129. 



The counterpart of the rail hoist for sailboat launching is the jib-boom crane (Fig. 130). 

 The crane is generally less costly than a rail hoist of the same capacity and can handle power 

 boats and sailboats. Two main drawbacks of the crane are the relatively short reach of the 

 boom and the slower operation because of the need to rotate the craft as the boom swings. 

 The rotation is done by hand to avoid any contact by mast or rigging with the boom and to 

 lower or raise the craft without scraping the hull on the bulkhead wall. These hazards are 

 not in a rail-hoist system. The excessive cantilever bending moment at the base of the crane, 

 caused by the eccentric load, requires a rugged foundation that must be close to or made a 

 part of the bulkhead wall without endangering stability. Unless the foundation is designed 

 initially, the later addition of a jib crane could require costly modification of the bulkhead 

 at the crane site. 



The stiff-leg derrick is usually less costly tiian other launching equipment with equal 

 lifting capacity (Fig. 131). The derrick has the rotational problem of the jib crane and also 

 requires greater skill by the operator and usually a tag-line crew to control the craft while in 

 the air. Derricks are usually installed in larger capacities for handling larger craft that cannot 

 be handled by the faster operating but lighter equipment. In very large €apacities, cost is less 

 than the other types, and with a long boom can operate over a fairly large area, thus 



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