type of bumper stripping for the edge of a finger or dock is a synthetic extrusion that runs 

 along the top edge of the outside stringer with a Up extending over the top. The usual 

 accident that destroys the continuity of such a fender strip is a sharp-edged bow or stem 

 impact that bites into the synthetic material and tears it out at naiUng points (Fig. 120). For 

 heavy-duty use, an extrusion with a slight recess for metal fastening strips should be 

 obtained to resist this tearing action (Fig. 121). Materials that have good weathering 

 qualities and resilience retention are neoprene and butyl rubber. Other commercially 

 available materials may also prove satisfactory, but many turn brittle or chalk off with age 

 in an exposed environment. 



Outside-corner tendering requires special consideration, because this is where most 

 collisions occur; also, extrusions cannot bend around a sharp corner. Molded corner 

 bumpers of the same material as the extrusion can often be obtained and will provide 

 adequate protection for smaller craft. Large cruisers and sailboats can best be 

 accommodated with corner wheels (Fig. 122), especially where the finger extends all the 

 way out to an interpier fairway. Entry into the slip can then be made by easing the craft 

 against the wheel before it is fuUy turned and then completing the turn Uke a large vessel 

 uses a turning dolphin. Corner wheels are used primarily on floating systems, where they are 

 always at the proper level with respect to the hull of the boat; seldom wiU they work 

 properly on a fixed system at all water levels. Some floating fingers are manufactured with 

 rounded ends, thus avoiding the sharp corner problem (Fig. 123). 



Because of water level changes, the fendering of fixed piers usually runs vertically rather 

 than horizontally. Projections beyond the hull of a boat such as a rub strake or overhanging 

 gunwale coping may catch on any horizontal member of a fixed-fender system during a 

 rising tide. The most commonly used fenders for fixed systems are vertical timbers spaced at 

 8- to 10-foot intervals along each side of a finger pier (Fig. 124). The size of the timber 

 ranges from 3 by 4 inches to 8 by 8 inches depending on the size of the berthed craft. 

 Lengths are determined by a need to extend upward above the highest part of a gunwale at 

 extreme high water and to extend below the lowest rub strake at extreme low water. Pier 

 attachments must be adequate to resist any moment that might be applied by cantilever 

 bending loads up to the design moment of the fender section. Bolt heads or nut and bolt 

 ends must be countersunk into the fender pieces to avoid scoring of boat hulls. This 

 countersinking reduces the strength of the fenders and must be accounted for in the 

 calculations. 



A softer vertical fender is the plastic tube stretched between points of support or 

 suspended from a top fastening with a heavy pendulum weight hanging below the lowest 

 possible point of hull contact (Fig. 125). The tube works on the same principle as the 

 vertical timber fender except that it cannot take cantilever loading. Its milder impact on 

 huUs and long lasting quahty makes the plastic tube worth the extra cost in many marinas. 

 Special instructions for installation are supplied by the manufacturer. 



178 



