increasing versatility. Stiff -leg derricks of various types and sizes can be purchased complete, 

 or designed and built with readily available structural members and mechanical components 

 to fit any given situation. 



Any type of lifting equipment requires a spreader bar to avoid crushing a hull or 

 springing the structural framework of the craft. Heavy-duty straps of woven nylon or other 

 strong synthetic fabrics are available for any size boat normally handled by such equipment. 

 Straps must be examined periodically and replaced if signs of severe wear or dangerous cuts 

 indicate incipient failure. Some sailboats and small motorboats have lifting eyes that are 

 integral with the structural framework of the hull and can be lifted with hooks rather than 

 straps. Many yacht clubs and a few marinas require that aU craft have lifting eyes to 

 standardize and speed up the launching operation. 



Three types of lift slips used in some marinas do not transfer boats to dry land. One is 

 the elevating work slip that merely raises the boat out of the water so that the hull may be 

 washed or minor damages to huUs, rudders, or screws repaired (Fig. 132). The boat remains 

 on a cradle or in a sling in raised position above the water only until the operation is 

 completed. In the second type of lift slip, a pair of hoists that remain as part of the berthing 

 facility hold the craft above the water while not in use (Fig. 133). The third type is used in 

 some berthing sites along the shores of large lakes or bays that cannot be protected at 

 reasonable cost against the moderate wave climate of the area. This is merely a 

 fixed-framework hoist that will allow the waves to pass through the supporting legs without 

 overturning. The berthed craft is hoisted high enough to clear the worst "sea" condition 

 anticipated (Fig. 134). Another reason for using the second and third types of lift slips is to 

 prevent hull damage due to barnacle incrustations, corrosion, or ice formation. 



e. Launching Ramps. Hoist -launching operations involve the use of mechanical 

 equipment and usually trained operators. Many small-boat owners resent paying high fees 

 for such service; therefore, some marinas provide only a launching ramp to get any boat that 

 can be transported by trailer into or out of the water. Some boating facilities consist only of 

 a launching ramp and a car -trailer parking lot, with no provision for berthing small craft in 

 the water, except temporarily for boarding purposes. Regardless of the purpose for which 

 they were installed, all fixed launching ramps have essentially the same design criteria. 



The slope of the ramp ranges between 12 and 15 percent. Few trailered boats can be 

 launched with a ramp slope flatter than 12 percent without submerging wheel hubs of the 

 pulling vehicle. Slopes steeper than 15 percent are dangerous for all but the most skilled 

 drivers. Many trailered sailboats cannot be launched without hub submergence, even on a 

 15 percent slope. The best alternatives are to use a trailer-tongue extension or to launch the 

 craft with a hoist. 



The surface of the ramp should be paved down to an elevation of about 5 feet below 

 extreme low water level; the top should be rounded over on a 20-foot vertical curve until it 

 becomes nearly level at about 2 feet above extreme high water. The bottom of the ramp 

 should end in a level shelf of loose gravel so that a vehicle losing brakes or traction would be 

 stopped before sliding deeper into the water. 



189 



