TM 5-850-1
minimum indicated bearing of 5 tons by the driving
the maximum allowable force in the pier.
The
formula. For deep deposits of soft material, fender piles
comparative merits of different construction materials in
should extend at least to the penetration reached under
energy-absorption capacity at allowable working stress
the weight of the driving hammer and preferably to a
due to transient loading is shown in table 9-4.
bearing capacity of 2 to 3 tons by the driving formula.
b. Pile fenders. Spacing, corner clustering, and
Experience has indicated that the bearing capacity
embedment of pile fenders under various conditions are
increases sufficiently after completion of driving to
indicated below.
provide the necessary resistance for fender piles.
(1) Spacing.
Where consistent with the
(4) Batter and chocking. Fender piles should
requirements for strength, pile spacing should be as
follows: for light service, 12 feet maximum (10 feet
not be battered outboard more than 2 inches in 12
preferred); for cruisers and auxiliaries, 7 to 9 feet, with 8
inches. Fender piles should be dapped and tightly
feet predominating; for heavy service, 5 to 7 feet,
chocked.
c. Hung fenders.
usually at one-half the bent spacing. Pile spacing less
Where consistent with
than 5 feet is undesirable.
requirement for strength spacing should be about 2 feet
(2) Corner clusters. Outboard and exposed
less than the values indicated for pile fenders with a
corners of piers may be protected by clusters of fender
minimum of 5 feet. Hung fenders will be tightly
piles. For small vessels, including destroyers up to
chocked. Check to make certain that the cantilever
3,000 tons, groups of seven to nine piles are arranged in
bolts are strong enough to support the suspended
two nesting rows at an exposed corner; for piers
weight.
d. Resilient fenders. For springs or rubber buffers,
accommodating vessels larger than those indicated
above, decks at exposed corners should be built in a
where consistent with requirements for strength, spacing
circular arc with a 4to 12-foot radius. Space fender piles
of vertical fenders may be increased to the upper limits
closely in two staggered rows, except in cases of larger
of the spacings previously listed for the various classes
ships, for which three rows or even four rows may be
of ships. For Raykin and dashpot types, spacing should
provided if the location is severely exposed. The
conform
to
the
load
and
energy-absorption
number of piles in these groups may vary from nine to
requirements. For resilient fenders, metal or wood
thirty piles. If springs or rubber buffer blocks are used,
rubbing surfaces (or wales) are required, except for
fender piles are placed in two nesting rows and are
rubber bumpers, transversely loaded. Draped rubber
bolted to segmental wales that bear against the energy-
bumpers should be provided with drain holes at the low
absorbing units.
If tubular rubber absorbers are
point of the draped section. Eyebolts to hold the chains
provided, fender piles are arranged in two separate rows
for rubber bumpers should be recessed into the pier
connected by wire rope windings. The number of piles
structure.
e. Suspended fenders. Suspended fenders are
in a group will vary from 20 to 40. Chains or cables
should be provided to restrain longitudinal and lateral
widely spaced in multiples of the bent spacing and in
movement of the entire group. For retractable systems,
accordance with the requirements for load and energy
the corner cluster may be eliminated and a special
absorption. These fenders may be fitted with timber or
corner section of retractable rendering substituted.
metal rubbing surfaces. Furthermore, fenders must not
Corner clusters should be tightly blocked and securely
swing in reacting to waves.
Some motion is
wrapped with galvanized wire rope at one or two levels
unavoidable; therefore, guides should be installed to
above mlw, depending on the deck height.
prevent chattering. Consider any buoyancy acting on
(3) Embedment. Establish the embedment of
the suspended weight. Where possible, the weight will
fender piles in accordance with bottom firmness and the
be concentrated above mean high water. Fenders must
possibility of future deeper dredging. For firm bottoms
either resist longitudinal forces or be detailed to roll
below the final dredged depth, a penetration of 10 feet is
away from the longitudinal rubbing motion of ships.
sufficient. An appropriate increase may be made if
When possible, the weight of the fender should be
deeper dredging is likely in the future. If a shallow layer
formed from removable ballast. A full retraction fender
of soft material less than 10 feet in thickness overlies a
rise may not cause the supports to project beyond the
firm bottom, fender piles should penetrate the firm strata
fender face. Full fender retraction force should not
at least 8 feet and have a
exceed the strength of either the pier or the ship's hull.
9-8
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