All commercial grades of exterior plywood are now made with waterproof glues of 

 excellent quality and may safely be used for exposed decking. A slight crowning of the 

 plywood is sometimes induced by crown-trimming tlie framework to which it is fastened 

 (usually by lag-bolting) to guard against a bird-bath effect in wet weather. Some plywoods 

 have a special plastic surface that is waterproof and provides an excellent base for painting. 

 Some floating dock manufacturers provide a heat- and pressure-bonded silicone-base 

 synthetic coating with an embossed pattern that provides excellent nonskid and 

 long-wearing quality (Fig. 95). 



The laminated plank described in tlie American Society of Civil Engineers (1969) is 

 another type of timber deck that has many favorable qualities, including a pleasing 

 appearance and a high degree of stiffness. It is usually made of nominal 2- by 3-inch or 2- by 

 4-inch cedar sticks glued together side-by-side in a special endless-belt press that moves the 

 plank slowly tlirough a curing oven. As the plank emerges from the press it passes through a 

 planner that finishes the sides and edges. 



The sandwich deck has a polystyrene core glued to plywood top and bottom faces and 

 edged witii 2-inch lumber to achieve a degree of stiffness equal to or exceeding that of the 

 laminated deck. It is lighter in weight than most decking, and by increasing or decreasing the 

 thickness, the height of the deck above tlie water surface can be adjusted as desired. Cost of 

 the sandwich deck compares favorably with the laminated deck. 



Concrete slab decking provides both stiffness and durability, but unless the quality of the 

 mix is carefully controlled, it may crack or spall shortly after installation, and repair is 

 difficult. Before engaging the services of any concrete deck manufacturer, examples of 

 similar installations should be examined to judge the quality of the product. 



Metal decks of various types are available in modular units for use in a freshwater 

 environment. Modern coating techniques have been used for good weathering and wearing 

 quality. However, all parts must be factory built, and field modification is difficult if they 

 must be tailored to meet special dimensional requirements. Once bent, or pulled apart at 

 their connections, repairs may be difficult. 



All fiberglass deck panels and other synthetic decks are available with certain flotation 

 systems now on tlie market. Most of these panels have little resistance to torsional bending 

 forces and must rely on tlie framework for stiffness and prevention of damage by racking 

 action in rough water. Some panels have excellent wearing qualities, but are rather brittle 

 and may break or chip if twisted or if a lieaw object is dropped on them. Each must be 

 analyzed for compatibility with the flotation system and the physical en\ironment of the 

 site. 



k. Approach Piers and Gangways. Access to the docks and slips from the basin 

 perimeter is usually accomplished by a fixed-pier approach to a fixed-berthing s} stem and a 

 hinged gangway to a floating system. The fixed-pier approach is usually an extension of the 



153 



