b. Ice. In regions where temperature drops are not excessive and natural freezing does 

 not cause a thick ice sheet, ice formation can be prevented near piles and floating slips by 

 forced convection currents. A few typical systems that have had some success are illustrated 

 in Figure 155. These systems work on the principle that water reaches its greatest density at 

 about 39° F. and tends to stratify in layers, with the heaviest on the bottom. Forced 

 convection of this warmer but denser water from the bottom to the surface when the 

 surface temperature approaches 32°F. will prevent or at least postpone freezing. 

 Unfortunately, the internal circulation of water in a berthing basin may prevent the layer 

 stratification that makes a bubbler system work. Although success is achieved in some areas, 

 the system is ineffective in others, and a careful study of thermal interchange in a basin 

 should be made by an expert before installing such a system. 



If a bubbler system is not used, sheet ice damage can be reduced or prevented by proper 

 design. Piles can be driven deeply enough in some materials to develop sufficient withdrawal 

 resistance to prevent hfting by ice, especially if the piles are cladded with metal sheaths in 

 the ice-formation zone so that the ice slides on the smooth surface as it rises. The flotation 

 components of floating systems can be designed with rounded or tapered bottoms so that 

 the pinching effect of the ice merely squeezes them upward (Fig. 9). 



Damage to perimeter walls and revetments due to ice thrust can be prevented or greatly 

 reduced by selection of a perimeter treatment that is less susceptible to such damage and by 

 correct construction methods. A smooth concrete pavement on a perimeter slope will fare 

 much better than a riprapped slope. Thorough compaction of the backfill behind a vertical 

 wall will help to resist ice thrust. Careful design and construction will eliminate many 

 crevices, a major source of frost-expansion damage. On rivers and lakes where ice floes 

 occur, protective breakwaters may provide sufficient ice-impact protection. If not, 

 deflecting booms made of logs or heavy timbers can often be used and sited to protect the 

 berthing area from drifting ice. Chaney (1961) presents details for constructing two types of 

 ice breakers that may be used in rivers to help break floes into smaller pieces and offers 

 other suggestions for combating ice problems. 



c. Hurricanes. In regions with a history of hurricane winds, some additional design 

 considerations are suggested beyond the increased windload criteria used in structural 

 design. Guide piles and cable or chain-anchorage systems for floating docks should be 

 capable of accommodating the design fluctuations of the water level and resisting the lateral 

 forces of the wind. Special attention should be given to safety provisions for the fuel dock 

 to prevent fuel and oil spiUs. As the electric power supply is subject to failure during the 

 storm, the installation of standby power -generating equipment should be considered for 

 facilities or floodlights that might be needed at that time. All major and minor 

 improvements of the harbor such as decking, roofs, and outside trash containers, must be 

 anchored down or fastened together to prevent movement and possible collision wdth 

 berthed craft or harbor structures. Low profile, streamUned designs for structures should be 

 adopted, hurricane-type shutters should be installed, and structural projections that increase 

 wind stress should be avoided. 



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