level conditions. A launching ramp may 

 be surrounded by additional structures, 

 such as pilings or piers, and may be 

 protected by a breakwater. 



Structure Functions 



A launching ramp provides a means 

 to set afloat and retrieve boats which 

 are usually mounted on rubber-tired 

 trailers. However, airplanes also use 

 ramps. Launching ramps will usually 

 be accompanied by parking lots for 

 automobiles and trailers and will be con- 

 structed in conjunction with a landing 

 pier or other shoreline structures, such 

 as pilings or breakwaters. 



A ramp has many of the same phy- 

 sical characteristics as a revetment; 

 however, its function is different. Re- 

 vetments are usually installed in high 

 energy environments, whereas ramps 

 are installed in relatively quiescent 

 areas. 



Site Characteristics and Environmental 

 Conditions 



Ramps extend into the water, per- 

 pendicular to the shorelines and slope 

 at an angle of 122 to 15% from the ter- 

 restrial zone to below the low intertidal 

 zone. They are usually constructed in 

 areas where there is fairly deep water 

 close to shore and where there is a rea- 

 sonable amount of protection from winds 

 and waves. Ramps are often associated 

 with marinas and would, therefore, be 

 placed in similar environmental condi- 

 tions. 



Placement Constraints 



Engineering. The design of a 



launching ramp may wary depending on 

 expected usage and site characteristics. 

 Figures 37 and 38 show examples of two 

 different ramp designs. Ramps ranoe 

 in width from 1C ft to over 50 ft (3 to 

 15 m). Length may vary to over 60 ft 

 (18 m). The slope of a ramp should be 

 between 12% and 15%. If the ramp slope 

 is flatter than 12%, trailer wheel hubs 

 have to be submerged while launching. 

 Slopes steeper than 15% can be danger- 

 ous unless the driver is very skilled 

 (Dunham and Finn 1974). 



Dunham and Finn(1974) recommend 

 that the ramp be paved to about 5 ft 

 (1.5 m) below extreme low water level. 

 There should be a level shelf of loose 

 gravel at the end of the ramp to prevent 

 a vehicle from sliding into the water if 

 there is a loss of traction or brakes. 



The most common construction tech- 

 nique uses a gravel foundation covered 

 by a layer of concrete. The thickness of 

 these layers ranges from 3 to 6 in (8 to 

 15 cm). Deep, square-shouldered grooves, 

 perpendicular to the slope, should be 

 pressed into the concrete during con- 

 struction (Dunham and Finn 1974). This 

 not only provides greater traction, but 

 the ramp will last longer than one with 

 a course finish without deep grooves. 



Submerged ramps, constructed of 

 precast slabs, have provided the most 

 satisfactory results. One construction 

 method uses precast 6- by 12-in slabs 

 placed 3 in (7.5 cm) apart. The gaps are 

 filled with coarse gravel (Dunham and 

 Finn 1974). Other methods have not prov- 

 en as successful. Large concrete bricks 

 and building blocks often dislodge if 

 the subgrade is soft. Asphalt paving 

 will not hold up well if used on the 

 submerged part of the ramp, while unpav- 

 ed ramps will deteriorate (Dunham and 

 Finn 1974). 



Sufficient pier space should be 

 provided for boarding and for holding 

 the boat while launching. Piers are 

 usually located on both sides of the 

 ramp. Dunham and Finn (1974) recommend 

 that a single-lane ramp be at least 15 

 ft (4.6 m) wide. They suggest that on a 

 multiple-lane ramp, raised divider strips 

 or marked lanes are not necessary and 

 may reduce optimum usage during peak 

 hours. 



Proper drainage should be provided 

 for washdown facilities which are often 

 used in saltwater areas. Oil, grease, 

 and other pollutants may be washed off 

 when cleaning the boat and trailer. For 

 this reason, drains should be connected 

 to a sewer system rather than returned 

 into the water. 



Ramps should be placed in reason- 

 ably quiet waters to minimize the number 



74 



