headwalk deck and supporting floats will conform more or less to the wave [profile, as the 

 ordinary stringer system will not support even the dead load in bending witli supporting 

 points 80 feet apart. The tloats in the crest area may be depressed a few inches below, and 

 those in the trough area raised a few inches above their free-floating position, but the 

 resultant deflection will still be about 1.5 feet in 45 feet. Either the stringers must flex this 

 amount or their splice -joints must loosen and allow a hinging action that will permit this 

 deflection. Once this type of hinging begins, the structural integrit}' of the system starts to 

 deteriorate, and major repairs may be necessary if the loose joints are not tightened 

 immediately. 



With proper splice -jointing, timber stringers will flex enough between joints and float 

 attachments to accommodate all reasonable wave action in a berthing basin for an indefinite 

 period. No evidence of pure fatigue failure in a timber stringer system has yet been reported. 

 Most damage from interior wave action has resulted either from loose bolts in the stringer 

 splices or from loose connections between the floating elements and the stringers. Mucli of 

 this damage could have been prevented by the use of larger bolts, larger washers, and better 

 positioning of splice points. 



In many. floating berth marinas the fingers are hinged to the headwalks because of the 

 above-mentioned differential movements caused by wave action. Where necessary, the 

 hinges should be of rugged construction with fairly large pins. Special cast-steel hinges used 

 for this purpose in the Shilshole Bay Marina, State of Washington, have performed 

 effectively, even with the heavy concrete floating system used and the proximity of the 

 basin to occasional high waves coming from Puget Sound to the area just outside the two 

 entrances. In most cases, however, hinging of finger connections is unnecessary if strong, 

 rigid junctions are used. 



In some proprietary steel-frame systems the floating components are interconnected 

 entirely by bolting. They are intended only for freshwater lakes and rivers, as the galvanizing 

 or other coatings will not provide adequate protection in a saltwater environment. The 

 quieter waters of most freshwater locations will not overstress these systems, but where 

 higher waves from a large lake may penetrate into the berthing area, these systems should be 

 checked for structural adequacy under wave action of the type previously discussed. 



j. Deck Materials and Surfacing. Many wood-plank decks without a coating have given 

 many years of satisfactory life without maintenance. In most larger installations, however, 

 some coating is provided for improved appearance and to minimize splintering. These 

 coatings usually have a roughened surface texture to give a nonskid quality. Because of the 

 shrinkage and expansion of wood planking and the tendency to curl as the planking loosens 

 and gains moisture, tlie planks should not be more than about 10 inches wide and spaced 

 about a quarter of an inch apart. Diagonal planking is sometimes used for floating docks to 

 provide cross-bracing strength (Fig. 94). 



151 



