80 



most profitable practice to give all such timbers a light impregnation of, say, 6 lbs. per 

 culjic foot, of creosote. 



Cut-offs, corbels and caps should, if at all possible, be placed not only above high 

 tide but above the zone of wave slop, which, as has been noted, is dangerous in respect 

 to Limnoria attack wherever water can stand without running off. (See fig. 26). 

 Whenever this is not feasible, they should at least be hea\'ily swabbed with hot creo- 

 sote. For corbels and caps a light pressure treatment of 6 lbs. of creosote per cubic foot 

 is recommended. 



If it is not desired to use creosoted timber for the floor system in a dock, care 

 should be taken to ventilate contact surfaces and to give them as thorough a treatment 

 with creosote as possilile. Hot creosote swabbed on plentifully during construction is 

 the best treatment a\'ailable under such circumstances. 



It is very desirable to place a watertight covering, such as a two-inch surface 

 coating of asphalt, over the deck of wharf structures. Such a coating makes a satis- 

 factory floor surface, gives additional fire protection and keeps surface water from 

 seeping into the wooden floor system. 



Fender Piles 



Because fender piles take the impact and friction of vessels, they are subjected to 

 severe usage and their life is limited, often to a comparatively few years. Because of 

 the flexibility required, fender piles are usually of timber, and in cases where ships 

 come in direct contact with the piles and the life of the latter is thus limited by me- 

 chanical wear, untreated timber is commonly used. If, however, the mechanical wear 

 can be reduced, treated timber can and should be used. Practices now tend toward 

 protecting fender piles with sheathing, or with blocks or stub piles bolted between the 

 piles and projecting beyond the face of the latter, to take the contact with the ships 

 and serve as wearing surfaces. Such protections are less expensive than full length 

 piles and can be renewed with comparative ease. In all cases, fender piles should t)e 

 placed so that they can be renewed readily. 



Wearing surfaces for ferry slips usually consist of diagonal sheathing, while those 

 for wharf fender piles are commonly made of untreated sawn timbers or stub piles 

 placed alternately with the fender piles and extending from about low water level to 

 the wharf floor. The hardness of Eucah-ptus, together with its supposed natural 

 resistance to borers, has led to its use where mechanical wear is involved. It has 

 proved successful for fender stubs; but when driven full length it has often been 

 broken off because of brittleness, and it has been found to be readily attacked by 

 borers. (See p. 91.) 



Fire Hazard 



Concrete provides the most effective substructure material where a definite fire 

 risk is involved. This value is often considered to justify the added expense of concrete 

 construction. The cargoes stored on wharves often have a value much greater than 

 the structures themselves and added protection is as necessary here as in land struc- 

 tures. If the superstructure is fire-proof the substructure should be likewise. Numerous 

 instances are of record of waterfront conflagrations caused by burning materials float- 

 ing on the water surface. Harbors where oil is handled extensively involve a particular 

 hazard in this respect. Wherever timber piling is used ample provision should be made 

 for quickly reaching all parts of the substructure, by means of trap doors in the wharf 

 floors. In many instances this is required by city ordinances. 



