208
R.H. Charlier and Chr. P. De Meyer
Pontoons and floating breakwaters produce an effect resembling that of a rigid
thin barrier plunging to some depth. Some were used on the Normandy coasts
during WWII.
The Queens University pontoon relies on reflection along its bottom to reduce
wave transmission. A vertical plate supports two cylindrical floats, necessarily 2
wave lengths apart, parallel to the wave crests. Silvester (op. cit.) has suggested
making a raft of welded together oil drums. Partly and wholly flexible rags have
been tested, as have floating water-filled bags, log-jams, U-shaped sideperformed wooden booms, fascine mattresses, rectangular and triangular boxtype floats, series of submerged horizontal tubes and others.
Somewhat expensive are such transportable breakwaters as caissons, bubble
breakwaters and floating mattresses (P.S. Butson, 1967, Transportable
breakwaters :Dock and Harbor Authority, J. 48, 41-46).
Besides the traditional construction, submerged breakwaters with openings for
oufflowing surge water, steel pilings, and other configurations exist. Permeable
breakwaters offer some advantages but effectiveness may be impaired where they
are too porous. Floating breakwaters may not be suitable in areas of high wave
energy ; they have the advantage to be able of adjusting their direction with
changing winds or currents. Discarded car and truck tires can form an
inexpensive floating breakwater when tied together. Scrap tires are commonly
used for floating breakwaters construction material. Easily installed, readily
adaptable, they have a high energy absorption power.
Units used on the Atlantic coast of the United States frequently consist of twenty
tires ; they reach breaking strengths of up to 6237 kg (13750 lbs). A 152.5 by 6.4
m (500x21fl) breakwater, for instance, requires 4260 tires (213 units) (fig. 10).
On Narragansett Bay (Rhode Island) such breakwaters successfully withstood the
strain of 1.22 m (4 t) waves, currents reaching 1.3 knots (2.41 km/h ; 1.5 mi/h)
and temperatures ranging from 2.2 to 18.9 ° C (36 ° to 66 ° F).
Tying materials can be made of steel, rubber or plastic material and be wires,
ropes, chains or belts. They are subject to a large variety of wear and tear factors :
besides fatigue, abrasion, corrosion, ultraviolet- and biodegradation will take
their toil. The environmentally inert system consisting of rubber conveyor belt
edging with nylon fastening is probably the most desirable from all points of
view. Still another type of floating breakwater has been tried at the Scripps
Institution of Oceanography (La Jolla CA) : rows of spherical balls are anchored
to the sea floor but float close to the surface. By moving in the direction opposite
to that of the waves, they absorb an estimated 50% of the waves' energy.
R.H. Charlier and Chr. P. De Meyer
Pontoons and floating breakwaters produce an effect resembling that of a rigid
thin barrier plunging to some depth. Some were used on the Normandy coasts
during WWII.
The Queens University pontoon relies on reflection along its bottom to reduce
wave transmission. A vertical plate supports two cylindrical floats, necessarily 2
wave lengths apart, parallel to the wave crests. Silvester (op. cit.) has suggested
making a raft of welded together oil drums. Partly and wholly flexible rags have
been tested, as have floating water-filled bags, log-jams, U-shaped sideperformed wooden booms, fascine mattresses, rectangular and triangular boxtype floats, series of submerged horizontal tubes and others.
Somewhat expensive are such transportable breakwaters as caissons, bubble
breakwaters and floating mattresses (P.S. Butson, 1967, Transportable
breakwaters :Dock and Harbor Authority, J. 48, 41-46).
Besides the traditional construction, submerged breakwaters with openings for
oufflowing surge water, steel pilings, and other configurations exist. Permeable
breakwaters offer some advantages but effectiveness may be impaired where they
are too porous. Floating breakwaters may not be suitable in areas of high wave
energy ; they have the advantage to be able of adjusting their direction with
changing winds or currents. Discarded car and truck tires can form an
inexpensive floating breakwater when tied together. Scrap tires are commonly
used for floating breakwaters construction material. Easily installed, readily
adaptable, they have a high energy absorption power.
Units used on the Atlantic coast of the United States frequently consist of twenty
tires ; they reach breaking strengths of up to 6237 kg (13750 lbs). A 152.5 by 6.4
m (500x21fl) breakwater, for instance, requires 4260 tires (213 units) (fig. 10).
On Narragansett Bay (Rhode Island) such breakwaters successfully withstood the
strain of 1.22 m (4 t) waves, currents reaching 1.3 knots (2.41 km/h ; 1.5 mi/h)
and temperatures ranging from 2.2 to 18.9 ° C (36 ° to 66 ° F).
Tying materials can be made of steel, rubber or plastic material and be wires,
ropes, chains or belts. They are subject to a large variety of wear and tear factors :
besides fatigue, abrasion, corrosion, ultraviolet- and biodegradation will take
their toil. The environmentally inert system consisting of rubber conveyor belt
edging with nylon fastening is probably the most desirable from all points of
view. Still another type of floating breakwater has been tried at the Scripps
Institution of Oceanography (La Jolla CA) : rows of spherical balls are anchored
to the sea floor but float close to the surface. By moving in the direction opposite
to that of the waves, they absorb an estimated 50% of the waves' energy.