Fender Design
Criteria:
Introduction:
The principal function of the fender system
is to prevent the vessel or the dock from being
damaged during the mooring process or during the
berthing periods. Forces during the vessel
berthing or anchoring may be in the form of
impact, abrasive action from vessels, or direct
pressure. These forces may extensive damage to
the ship and structure if suitable means are not
employed to counteract them. The amount of
energy absorbed and the maximum impact force
imparted are the primary criteria applied in
accepted fender design practices.
Selection of
fender system type:
A variety of factors affect the proper
selection of a fender system. These include, but
not limited to, local marine environment,
exposure of harbor basins, class and
configuration of ships, speed and direction of
approach of ships when berthing, available
docking assistance, type of berthing structure,
and even the skills of pilots or ship captains.
It is considered impractical to standardize
fender designs since port conditions are rarely
identical. Previous local experience in the
application of satisfactory fender systems
should be considered, particularly as it applies
to costeffectiveness characteristics. Here is a
good guide for selecting a fender system fit for
your needs. We follow the PIANC 2002
and other
Standards set forth by other manufacturers with
a long history in the marine fender industry.
General Design
Procedure:
The design of a fender system is based on
the law of conservation of energy. The
amount of energy being introduced into the
system must be determined, and then a means
devised to absorb the energy within the force
and stress limitations of the ship's hull, the
fender, and the pier. General design procedures
are as follows:
1. Determine the
energy that will be delivered to the pier upon
initial impact. It is recommended to consider
the heaviest/largest vessel capable or allowed
to use your dock.
2. Determine the
energy that can be absorbed by the pier or wharf
(distribution of loading must be considered).
For structures that are linearly elastic, the
energy is onehalf the maximum static load level
times the amount of deflection. Allowance should
also be made in cases where other vessels may be
moored at the pier. If the structure is
exceptionally rigid, it can be assumed to absorb
no energy.
3. Subtract the
energy that the pier will absorb from the
effective impact energy of the ship to determine
the amount of energy that must be absorbed by
the fender.
4. Select a fender
design capable of absorbing the amount of energy
determined above without exceeding the maximum
allowable force in the pier. Please contact us
for our product catalogue. You can get specific
performance information of our products.
I.
Terminology:
Gross
Tonnage(GT):
Total Volume of
vessel and cargo. This is derived by dividing
the total interior capacity of a vessel by 100
cubic feet.
Net Tonnage(NT):
Total Volume of cargo that is carried by the
vessel.
Displacement
Tonnage(DPT):
Total weight of
the vessel and cargo when the ship is loaded to
draft line.
Dead Weight
Tonnage(DWT):
Weight of cargo,
fuel, passenger, crew and food on the vessel.
Light
Weight(LOW):
Weight of Vessel.
Ballast
Weight(BW):
Weight of ship and
the water added to the ballast compartment to
improve its stability after it has discharged
its cargo.
II.
Calculation of the Normal Berthing Energy
or Effective Berthing Energy:
Side Berthing:
Side Berthing is the most typical case for
docks. The Berthing Energy is calculated by the
following kinetic equation:
Where
E_{B}
: Berthing energy (KJ, N*m, or Lb_{F}*ft)
W_{D}
: Water displacement of the berthing ship (Tons,
Kg, Lbs). 
This is the Total Displacement Tonnage(DPT) of
the vessel.
If you do not have this information you may use
our tables to view standard vessel's information
by type and sizes. Please
click here to view our tables.
V_{B} : Berthing
velocity of the Ship at the movement
of impact against the fender (m/sec, ft/sec) 
Berthing velocity
is an important parameter in fender system
design. It depends on the size of the vessel,
loading condition, port structure, and the ease
of difficulty of the approach. Therefore the
berthing velocity is preferred to be obtained
from actual measurements or relevant existing
statistical information. When the actual
measured velocity is not available, the most
widely used guide to estimate the berthing
velovity is the Brolsma table, adopted by BSI,
PIANC and other standards. To facilitate the
calculations, designers can use tables, graphs
or equations shown below.
V_{a}:
Easy Berthing, sheltered.
V_{b}:
Difficult Berthing, sheltered.
V_{c}:
Easy Berthing, exposed.
V_{d}:
Difficult Berthing, exposed.
C_{M}
: Virtual mass factor 
As a vessel makes
contact with the berth and its movement is
suddenly stopped by the fenders, the mass of
water moving with the vessel adds to the energy
possessed by the vessel. This is called "Mass
Factor" or "Added Mass Coefficient" and the weight of the water is
generally called "Additional Weight".
The added mass coefficient makes up for the body
of water carried along with the ship as it moves
sideways through the water. As the vessel is
berthing a body of water is carried along with
the ship as it moves sideways through the water.
As the ship is stopped by the fenders, the
momentum of the entrained water continues to
push against the ship and this effectively
increases its overall mass. CM is normally
calculated with the following formula:
where,
D: Full Load Draft(m, ft)
B: Molded Breadth(m, ft)
Another
calculation method for the virtual mass factor
is:
where,
D: Full Load Draft
L: Ship Length
ρ: Sea Water Density(1.025
t/m^{3})
C_{E}
: Eccentricity factor 
In the case when a
vessel contacts a berth at a point near its bow
or stern, the reaction force with give a
rotational movement, which will dissipate a part
of the vessel's energy.
To determine the Eccentricity Coefficient, you
must firstly calculate the radius of gyration(K),
the distance from the vessels center of mass to
point of impact(R), the velocity vector angle()
and berthing angle()
using the following formulas:
Where
K: Radius of rotation of the
vessel (usually 1/4 of the vessel's length)
R:
Distance of the line paralleled to wharf
measured from the vessel's center of gravity to
the point of contact. Usually 1/4 1/5 of
vessel's length.
C_{B}:
Block Coefficient, which is related to the hull
shape and is is calculated as follows:
Where, W_{D}:
Water displacement of the berthing ship(Tons,
Kg, Lbs)
: Sea Water
density(1.025 Tons/m^{3})
L_{BP}: Length between
perpendiculars. Please see sketch below for
better explanation:
x: Distance from bow to point of
impact
B: Beam(m, ft)
If the
Length, beam and draft are not known, this table
can be used to estimate the block coefficient:
Typical Block Coefficients(C_{B}) 
Type of Vessel 
C_{B}
BS 6349 
C_{B}
PIANC 2002 
Tankers 
0.72~0.85 
0.85 
Bullk Carriers 
0.72~0.85 
0.72~0.85 
Container Ships 
0.65~0.75 
0.60~0.80 
General Cargo 
0.60~0.75 
0.72~0.85 
RoRo Vessels 
0.65~0.70 
0.70~0.80 
Ferries 
0.50~0.65 
0.55~0.65 
You may also use the following formula to
calculate the eccentricity coefficient:
Some designers prefer to calculate the
eccentricity coefficient using the simplified
formula above. Care should be used as this method can lead to an underestimation of
Berthing Energy when the berthing angle()
is greater than 10 degrees and/or the point of impact is aft of quarterpoint(x > L_{BP}/4).
To verify your calculations, the eccentricity
coefficient values generally fall within the following limits:
C_{C}
: Berth configuration factor 
This is the
portion of berthing energy which is absorbed by
the cushion effect of water between the
approaching vessel and the quay wall. The
smaller the draft(D) of the vessel
is, or the larger the under keel clearance(K_{C}),
the more trapped water can escape under the
vessel, and would give a higher
C_{C}
value. Also, if the berthing angle of the
vessel is greater than 5°, we can consider
C_{C}
= 1.
Case
1: Closed Dock
A Closed Dock would be a wharf, where you have a
concrete wall going directly to the sea ground. In this case
the quay wall will push back all the water that
is being moved by the vessel. This creates a
resistance factor that can be calculated as
follows:
If K_{C}
≤ D / 2,
C_{C }
≈ 0.8
If K_{C}
> D / 2,
C_{C }
≈ 0.9
Case 2: Open
or SemiClosed
Dock
A SemiClosed Dock is a Dock that water can
flow underneath the dock, but the depth changes
below the dock. Open Dock is usually a dock with
piles underneath and the water can flow freely
underneath the dock. In such case we can assume
the following value of 1.
C_{C }
≈ 1
C_{S}
: Softness factor 
This is the portion of berthing energy which is
absorbed by the deformation of the vessel's hull
and fender. When a soft fender is used,
C_{S }
can
be ignored. Otherwise, we can assume a value for
C_{S}
≈
0.9
II. Fender
Selection:
After the effective berthing Energy(E_{B})
of the ship is calculated as explained above,
the selection of the fender system should be
conducted in accordance with the fenders
performance(Reaction Force, Energy absorption,
and deflection curve). The fender system
selection has the following requirements:
1.
Energy absorption of the selected fender system
exceeds effective impacting energy of ships(E_{B}).
2. Reaction force of the selected fender system
is less than the ship's allowable reaction
force.
3. Surface pressure of the selected fender
system is less than the allowable hull surface
pressure. You can meet the requirements by
changing the dimensions of the frontal panel.
4. When the ship is berthing in a slanting
direction, the fenders will bear a angular
compression which will decrease the energy
absorption at point of impact. Therefore the
fender performance should be adjusted in
accordance with the berthing angles when
selecting the fender system.
5. The selected fender system should satisfy
special requirements of extreme
environments(high/cold temperature, strong
winds, waves, high/low tides, etc.)
6. The selected fender system should be chosen
wisely for the investment(performance/price).
The price of maintenance and installation
should be considered in your investment. Fenders
that have an easy installation and maintenance
are a better option for your investment.
Fender
Spacing:
This calculations are critical, due to the
possibility of a vessel hitting the dock
structure while berthing at an angle. As per
British Standards, for continuous quay, the
installation pitch is recommended to be less
than 15% of the vessel. Minimum installation
pitch of fender can be calculated with the
following equation:
Where
S:
Maximum spacing between fenders
R_{B}: Bow radius of
board side of vessel(m, ft)
P_{U}: Uncompressed
Height of fender including panel(m, ft)
C: Fender height in rated
compression.
:
Fender deflection(m, ft)
If the bent
radius(R_{B}) is not known, we can
estimate by the vessel's overall length(L_{OA})
and width(B) as follows:
For vertical
orientation arrangement, the types and sizes of
all ships berthing shall be considered. All
possible tides vary scope. To assure safe
berthing we must consider the height and draft
of the smallest and largest vessels to determine
the point of contact on the structure. Do not
design your arrangements considering only the
largest vessels berthing in your dock, since
your design might not work for smaller vessels
berthing in your dock.
Fender Panel
Design:
Hull Pressures:
Permissible hull pressures vary greatly with the
class and size ship. The best guide to hull
pressure is the designer's experience in similar
cases. If this information is unavailable, then
the following table may be used as an
approximate guide for design:
Allowed Hull Pressures 
Type of Vessel 
Hull Pressure KN/m^{2} 
Tankers 
150~250 
ULCC & VLCC(Coastal Tankers) 
250~350 
Product & Chemical Tankers 
300~400 
Bullk Carriers 
150~250 
PostPanamax Container Ships 
200~300 
Panamax Container Ships 
300~400 
SubPanamax Container Ships 
400~500 
General Cargo 
300~600 
Gas Carriers 
100~200 
Hull pressures are
calculated using the frontal panel
area(excluding leadin chamfers) as follows:
Where
P:
Hull
Pressure(N/m^{2}, psi)
ΣR: Combined Reaction Forces of
all rubber fenders
A_{1}: Valid Panel Width
excluding leadin chamfers(m)
B_{1}: Valid Panel Height
excluding leadin chamfers(m)
P_{P}: Permissible hull
pressure(N/m^{2}, psi)
Approximate
Hull Pressure for other fender types:
The above formula
and table apply to berths fitted with frontal
panel systems. However, many berths use
Cylindrical and Arch fenders safely
and without damaging the ship's hull, despite
the fact that these fenders exert higher hull
pressures. The Arch Fenders have hull pressures
of 760~1300kN/m^{2}. Cylindrical Fenders
have 460~780kN/m^{2}.
Also bear in mind that when cylindrical fenders
are used with large chains or bar fixings
through the central bore, the hull pressure will
be higher to approximately double the above
figures. Again there is no evidence to show that
this causes hull damage.
Selection
and Calculation of Chain:
There are three
types of chains in fender systems:
1. Tension Chain: The main
function of the tension chain is to protect the
fender from damage while it is under
compression.
2. Weight Chain: The weight
chained is used to support the weight of the
frontal and face panel.
3. Shear Chain: This chain
protects the fender from damage while in shear
deflection.
The following
should be noted in the chain design:
Chain dimensions should be as exact as
possible. Not too loose, not too tight.
The chain can not be twisted as this reduces
the load capacity.
Open Link is preferred.
The initial(static) angle of the chain is
important. Normally weight chains are set at a
static angle of 15  25° to the vertical and
shear chains are set to 20  30° to the
horizontal.
All chains must be designed or selected with a
safety factor of 2 to 3 times of the work load.
The dimensions of the shackle is usually the
same as the chain, but if the shackle is
required to bear the same load with the chain,
then a thicker shackle is preferred.
Where,
Ф_{1}:
Static Angle of Chain(°)
h_{1}:
Static offset between brackets(m, ft)
Ф_{2}: Dynamic Angle of Chain(°)
h_{2}: Dynamic offset between
brackets at F(m, ft)
D: Fender compression(m, ft)
R:
Reaction
Force of rubber units behind the frontal panel(N, Lbs)
W: Weight of the panel face(N,
Lbs)
F_{L}: Safe working Load
of chain(N, Lbs)
L: Bearing length of chain(m, ft)
n: number of chains acting
together
μ: Friction coefficient of face
pad. Usually equals 0.15 for UHMWPE facings.
F_{M}: Minimum
Breaking Load(N,
Lbs)
F_{S}: Safety Factor(2~3
times)
III. Other
Berthing Scenarios:
Dolphin
Berthing:
Passing Lock
Entrance:
Ship
to Ship Berthing:
_{
}
End
Berthing:
Please note
that this information is only for reference.
Please allow us to confirm your fender
selection. Provide us with all the information
needed to assure your selection. Please contact
us. We will provide you
with support for your fender system. We are
committed to our clients from the design to the
installation and even for future maintenance
inspections and consulting. Please fill up our
design condition form and send it to us. To
download or access our design inquiry form, please
click here.
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RESERVED @ DEMACO CORP. &
YANTAI TAIHONG RUBBER CO.,
LTD 2007
