APPENDIX C - BREAKWATERS
FLOATING BREAKWATERS
Floating breakwaters can be constructed of virtually any buoyant material, such as rubber tires,
logs, timbers, and hollow concrete modules. Floating breakwaters are particularly advantageous where
offshore slopes are steep and fixed breakwaters would be too expensive because of water depths, where
the tide range is large and fixed breakwaters would be subject to widely varying degrees of submergence,
and where temporary protection of vegetation is required.
One disadvantage of floating breakwaters is that they are effective only against small, short-period
waves (less than five seconds). Fortunately, these are all that strike the great majority of sheltered
shorelines. They also may be regarded as eyesores in some areas and they tend to collect floating debris
and require more maintenance than fixed breakwaters.
Rubber Tires
Two possible arrangements are shown in Figure C-1. The upper configuration, known as a wave-
Maze, is patented and cannot be used unless royalties are paid to the patent holder (see OTHER HELP
Section). The bottom configuration was developed by the Goodyear Tire and Rubber Company for
promotional purposes and may be used without royalties. The use of other configurations is limited only
by the imagination of the designer.
The length parallel to shore should be sufficient to provide protection according to the structure's
distance from shore. The width will depend on the wavelength at the site. To determine this, time 11
successive wave crests as they pass a stationary point. Divide this time by 10 to obtain the wave period,
T. The breakwater width should be 2.5 x T2 (e.g., if the wave period is 5 seconds, the width should be 2.5
x 5 x 5 = 62.5 feet).
The depth of penetration in the water (draft) will determine the structure's effectiveness. A
breakwater riding only on the surface does little to break up waves. The draft should be greater than one-
half the wave height. Two-layer structures or the use of truck or tractor tires help to achieve greater
draft.
The air trapped within the top of vertical tires provides sufficient flotation in most cases. In still
water, the air is eventually dissolved by the surrounding water, but wave action replenishes the air
supply. Of course, care must be taken not to use tires with puncture holes. More permanent flotation is
possible with Styrofoam blocks or foam injected into the crowns of the tires. In salt water, marine growth
will eventually sink the structure unless it is periodically scraped off. Sand can also collect in the tires
and sink them, but this can be prevented by drilling holes in the bottoms of the tires. In that case,
flotation aids, such as styrofoam blocks, should be used.
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