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SECTION 3105F — MOORING AND BERTHING ANALYSIS AND DESIGN

3105F.1 General.


3105F.1.1 Purpose.


This Section establishes minimum standards for safe mooring and berthing of  vessels at MOTs.


3105F.1.2 Applicability.


This Section applies to onshore MOTs; Figure 31F-5-1 shows typical pier and wharf  configurations.


FIGURE 31F-5-1— TYPICAL PIER AND WHARF CONFIGURATIONS





3105F.1.3 Mooring/Berthing Risk Classification.


Each MOT shall be assigned a mooring/berthing risk classification of  high, medium or low, as determined from Table 31F-5-1, based on the following site-specific parameters:


1.   Wind


2.   Current


3.   Hydrodynamic effects of  passing vessels


4.   Change in vessel draft


Exceedance of  any of  the defined condition thresholds in Table 31F-5-1 places the MOT in the appropriate mooring/berthing risk classification.


The maximum wind, Vw, (corrected for duration, height and over water) and maximum current, Vc, shall be obtained (see Section 3103F.5).


In order to determine if  there are significant potential passing vessel effects on moored vessels at an MOT, see Section 3105F.3.2.


The range of  vessel draft shall be based on the local tidal variation and the operational limits of  the vessels berthing at the MOT.


Multiple berth MOTs shall use the same conditions for each berth unless it can be demonstrated that there are significant differences.


MOTs with high mooring/berthing risk classifications (Table 31F-5-1) shall have the following equipment in operation: an anemometer (N/E), a current meter (N/E) (may be omitted if  safety factor according to Section 3103F.5.3.1 is applied to current) and remote reading tension load devices (N).


3105F.1.4 New MOTs.


Quick release hooks are required at all new MOTs, except for spring line fittings. Quick release hooks shall be sized, within normal allowable stresses, for the safe working load of  the largest size mooring line and configuration. To avoid accidental release, the freeing mechanism shall be activated by a two-step process. Quick release hooks shall be insulated electrically from the mooring structure, and should be supported so as not to contact the deck.


3105F.1.5 Analysis and Design of  Mooring Components.


The existing condition of  the MOT shall be used in the mooring analysis (see Section 3102F). Structural characteristics of  the MOT, including type and configuration of  mooring fittings such as bollards, bitts, hooks and capstans and material properties and condition, shall be determined in accordance with Sections 3107F.4 and 3103F.10.


The analysis and design of  mooring components shall be based on the loading combinations and safety factors defined in Sections 3103F.8 through 3103F.10
, and in accordance with ACI318 [5.1], AISC-LRFD [5.2] and ANSI/AF & PANDS-1997 [5.3], as applicable.

3105F.2 Mooring Analyses.


A mooring analysis shall be performed for each berthing system, to justify the safe berthing of  the various deadweight capacities of  vessels expected at the MOT. The forces acting on a moored vessel shall be determined in accordance with Section 3103F.5. Mooring line and breasting load combinations shall be in accordance with Section 3103F.8.


Two procedures, manual and numerical are available for performing mooring analyses. These procedures shall conform to either the OCIMF documents, "Mooring Equipment Guidelines" [5.4] and "Prediction of  Wind and Current Loads on VLCCs" [5.5] or the Department of  Defense "Mooring Design" document [5.6]. The manual procedure (subsection 3105F.2.1) may be used for barges.


A new mooring assessment shall be performed when conditions change, such as any modification in the mooring configuration, vessel size or new information indicating greater wind, current or other environmental loads.


In general, vessels shall remain in contact with the breasting or fendering system. Vessel motion (sway) of  up to 2 feet off  the breasting structure may be allowed under the most severe environmental loads, unless greater movement can be justified by an appropriate mooring analysis that accounts for potential dynamic effects. The allowable movement shall be consistent with mooring analysis results, indicating that forces in the mooring lines and their supports are within the allowable safety factors. Also, a check shall be made as to whether the movement is within the limitations of  the cargo transfer equipment.


The most severe combination of  the environmental loads has to be identified for each mooring component. At a minimum, the following conditions shall be considered:


1.   Two current directions (maximum ebb and flood; See Section 3103F.5.3)


2.   Two tide levels (highest high and lowest low)


3.   Two vessel loading conditions (ballast and maximum draft at the terminal)


4.   Eight wind directions (45 degree increments)


3105F.2.1 Manual Procedure.


For MOTs classified as Low risk (Table 31F-5-1), simplified calculations may be used to determine the mooring forces, except if  any of  the following conditions exist (Figures 31F-5-2 and 31F-5-3, below).


TABLE 31F-5-1 MOORING/BERTHING RISK CLASSIFICATION


RISK CLASSIFICATION
WIND, (Vw) (knots)
CURRENT,
(Vc (knots)
PASSING VESSEL EFFECTS
CHANGE IN DRAFT (ft)
High
>50
>1.5
Yes
>8
Medium
30 to 50
1.0 to 1.5
No
6 to 8
Low
<30
<1.0
No
<6


1.   Mooring layout is significantly asymmetrical


2.   Horizontal mooring line angles (a) on bow and stern exceed 45 degrees


3.   Horizontal breast mooring line angles exceed 15 normal to the hull


4.   Horizontal spring mooring line angles exceed 10 degrees from a line parallel to the hull


5.   Vertical mooring line angles
(q) exceed 25 degrees

6.   Mooring lines for lateral loads not grouped at bow and stern


FIGURE 31F-5-2—HORIZONTAL LINE ANGLES [5.4]





FIGURE 31F-5-3—VERTICAL LINE ANGLES [5.4]





When the forces have been determined and the distance between the bow and stern mooring points is known, the yaw moment can be resolved into lateral loads at the bow and stern. The total environmental loads on a moored vessel are comprised of  the lateral load at the vessel bow, the lateral load at the vessel stern and the longitudinal load. Line pretension loads must be added.


Four load cases shall be considered:


1.   Entire load is taken by mooring lines


2.   Entire load is taken by breasting structures


3.   Load is taken by combination of  mooring lines and breasting structures


4.   Longitudinal load is taken only by spring lines


3105F.2.2 Numerical Procedure.


A numerical procedure is required to obtain mooring forces for MOTs classified as Medium or High (See Table 31F-5-1) and for those that do not satisfy the requirements for using simplified calculations. Computer program(s) shall be based on mooring analysis procedures that consider the characteristics of  the mooring system, calculate the environmental loads and provide resulting mooring line forces and vessel motions (surge and sway).


3105F.3 Wave, Passing Vessel, Seiche and Tsunami.


3105F.3.1 Wind Waves.


MOTs are generally located in sheltered waters such that typical wind waves can be assumed not to affect the moored vessel if  the significant wave period, Ts, is less than 4 seconds. However, if  the period is equal to or greater than 4 seconds, then a simplified dynamic analysis (See Section 3103F.5.4) is required. The wave period shall be established based on a 1-year significant wave height, Hs
. For MOTs within a harbor basin, the wave period shall be based on the locally generated waves with relatively short fetch.

3105F.3.2 Passing Vessels.


These forces generated by passing vessels are due to pressure gradients associated with the flow pattern. These pressure gradients cause the moored vessel to sway, surge, and yaw, thus imposing forces on the mooring lines.


Passing vessel analysis shall be conducted when all of  the following conditions exist (See Figure 31F-5-4):


1.   Passing vessel size is greater than 25,000 dwt.


2.   Distance L is 500 feet or less


3.   Vessel speed V is greater than Vcrit


WHERE:


Vcrit
= 1.5 + L - 2B 4.5 (knots)    ( 5-1)
500 - 2B

EXCEPTION:
If  L £ 2B, passing vessel loads shall he considered.

L and B are shown in Figure 31F-5-4, in units of  feet. V is defined as the speed of  vessel over land minus the current velocity, when traveling with the current, or the speed of  vessel over land plus the current velocity, when traveling against the current.


FIGURE 31F-5-4—PASSING VESSEL





When such conditions (1, 2 and 3 above) exist, the surge and sway forces and the yaw moment acting on the moored vessel shall, as a minimum, be established in accordance with Section 3103F.5.5. If  the demands from such evaluation are greater than 75 percent of  the mooring system capacity (breaking strength of  mooring lines), then a more sophisticated dynamic analysis is required.


For MOTs located in ports, the passing distance, L, may be established based on channel width and vessel traffic patterns. The guidelines established in the Navy's "Harbors Design Manual," Figure 27 [5.7] for interior channels may be used. The "vertical bank" in Figure 27 of  [5.7] shall be replaced by the side of  the moored vessel when establishing the distance, "L ".


For MOTs, not located within a port, the distance, "L ", must be determined from observed traffic patterns.


The following passing vessel positions shall be investigated:


1.   Passing vessel is centered on the moored ship. This position produces maximum sway force.


2.   The midship of  the passing vessel is fore or aft of  the center-line of  the moored ship by a distance of  0.40 times the length of  the moored ship. This position is assumed to produce maximum surge force and yaw moment at the same time.


The mooring loads due to a passing vessel shall be added to the mooring loads due to wind and current.


3105F.3.3 Seiche.


A seiche analysis is required for existing MOTs located within a harbor basin and which have historically experienced seiche. A seiche analysis is required for new MOTs inside a harbor basin prone to penetration of  ocean waves.


The standing wave system or seiche is characterized by a series of  "nodes" and "antinodes ". Seiche typically has wave periods ranging from 20 seconds up to several hours, with wave heights in the range of  0.1 to 0.4 ft [5.7].


The following procedure may be used, as a minimum, in evaluating the effects of  seiche within a harbor basin. In more complex cases where the assumptions below are not applicable, dynamic methods are required.


1.   Calculate the natural period of  oscillation of  the basin. The basin may be idealized as rectangular, closed or open at the seaward end. Use the formula provided (Eqn. 2-1, page 26.1-40) in the Navy's "Harbor Design Manual" [5.7] to calculate the wave period and length for different modes. The first three modes shall be considered in the analysis.


2.   Determine the location of  the moored ship with respect to the antinode and node of  the first three modes to determine the possibility of  resonance.


3.   Determine the natural period of  the vessel and mooring system. The calculation shall be based on the total mass of  the system and the stiffness of  the mooring lines in surge. The surge motion of  the moored vessel is estimated by analyzing the vessel motion as a harmonically forced linear single degree of  freedom spring mass system. Methods outlined in a paper by F.A. Kilner [5.8] can be used to calculate the vessel motion.


4.   Vessels are generally berthed parallel to the channel; therefore, only longitudinal (surge) motions shall be considered, with the associated mooring loads in the spring lines. The loads on the mooring lines (spring lines) are then determined from the computed vessel motion and the stiffness of  those mooring lines.


3105F.3.4 Tsunami.


Run-up and current velocity shall be considered in the tsunami assessment. Table 31F-3-8 provides run-up values for the San Francisco Bay area, Los Angeles/Long Beach Harbors and Port Hueneme.


3105F.4 Berthing Analysis and Design.


In general and for new MOTs, the fender system alone shall be designed to absorb the berthing energy. For existing MOTs, the berthing analysis may include the fender and structure.


The analysis and design of  berthing components shall be based on the loading combinations and safety factors defined in Sections 3103F.8 and 3103F.9 and in accordance with ACI 318 [5.1], AISC-LRFD [5.2], and ANSI/AF&PA NDS-1 997 [5.3], as applicable.


3105F.4.1 Berthing Energy Demand.


The kinetic berthing energy demand shall be determined in accordance with Section 3103F.6.


3105F.4.2 Berthing Energy Capacity.


For existing MOTs, the berthing energy capacity shall be calculated as the area under the force-deflection curve for the combined structure and fender system as indicated in Figure 31F-5-5. Fender piles may be included in the lateral analysis to establish the total force-deflection curve for the berthing system. Load-deflection curves for other fender types shall be obtained from manufacturer's data. The condition of  fenders shall be taken into account when performing the analysis.


When batter piles are present, the fender system typically absorbs most of  the berthing energy. This can be established by comparing the force-deflection curves for the fender system and batter piles. In this case only the fender system energy absorption shall be considered.


FIGURE 31F-5-5—BERTHING ENERGY CAPACITY





3105F.4.3 Tanker Contact Length.


3105F.4.3.1 Continuous Fender System.


A continuous fender system consists of  fender piles, chocks, wales, and rubber or spring fender units.


The contact length of  a ship during berthing depends on the spacing of  the fender piles and fender units, and the connection details of  the chocks and wales to the fender piles.


The contact length, Lc can be approximated by the chord formed by the curvature of  the bow and the berthing angle as shown in Equation 5-2 below.


L
c = 2r sin a    ( 5-2)

WHERE:


Lc
    = contact length

r   = Bow radius


a
   = Berthing Angle

In lieu of  detailed analysis to determine the contact length, Table 31F-5-2 may be used. The contact length for a vessel within the range listed in the table can be obtained by interpolation.


TABLE 31F-5-2 CONTACT LENGTH


VESSEL SIZE (dwt)
CONTACT LENGTH
330
25 ft
1,000 to 2,500
35 ft
5,000 to 26,000
40 ft
35,000 to 50,000
50 ft
65,000
60 ft
100,000 to 125,000
70 ft


3105F.4.3.2 Discrete Fender System.


For discrete fender systems (i.e., not continuous), one fender unit or breasting dolphin shall be able to absorb the entire berthing energy.


3105F.4.4 Longitudinal and Vertical Berthing Forces.


The longitudinal and vertical components of  the horizontal berthing force shall be calculated using appropriate coefficients of  friction between the vessel and the fender. In lieu of  as-built data, the values in Table 31F-5-3 may be used for typical fender/vessel materials:


TABLE 31F-5-3 COEFFICIENT OF FRICTION


CONTACT MATERIALS
FRICTION COEFFICIENT
Timber to Steel
0.4 to 0.6
Urethane to Steel
0.4 to 0.6
Steel to Steel
0.25
Rubber to Steel
0.6 to 0.7
UHMW* to Steel
0.1 to 0.2


*Ultra-high molecular weight plastic rubbing strips.


Longitudinal and vertical forces shall be determined by:


F =
mN    ( 5-3)


WHERE:


F = longitudinal or vertical component of  horizontal berthing force


m
= coefficient of  friction of  contact materials


N = maximum horizontal berthing force (normal to fender)


3105F.4.5 Design and Selection of  New Fender Systems.


For guidelines on new fender designs, refer to the Navy's "Piers and Wharves" handbook [5.9] and the PIANC Guidelines for the Design of  Fenders Systems: 2002 [5.10].


3105F.5 Layout of  New MOTs.


The number and spacing of  independent mooring dolphins and breasting dolphins depends on the DWT and length overall (LOA) of  vessels to be accommodated.


Breasting dolphins shall be positioned adjacent to the parallel body of  the vessel when berthed. A minimum of  two breasting dolphins shall be provided. The spacing of  breasting dolphins shall be adequate for all sizes of  vessels that may berth at the MOT.


Mooring dolphins shall be set back from the berthing line (fender line) for a distance between 115 ft and 165 ft, so that longer bow, stern and breast lines can be deployed.


For a preliminary layout, the guidelines in the British Standards, Part 4, Section 2 [5.11], may be used in conjunction with the guidelines below.


1.   If  four breasting dolphins are provided, the spacing between exterior breasting dolphins shall be between 0.3 and 0.4 LOA of  the maximum sized vessel expected to call at the MOT. The spacing between interior breasting dolphins shall be approximately 0.3 to 0.4 LOA of  the minimum sized vessel expected to call at the MOT.


2.   If  only two breasting dolphins are provided, the spacing between the dolphins shall be the smaller (0.3 LOA) of  the guidelines specified above.


3.   If  bow and stern lines are used for mooring, the spacing between exterior mooring dolphins shall be 1.35 times the LOA of  the maximum sized vessel expected to call at the MOT.


4.   The spacing between interior mooring dolphins shall be 0.8 times the LOA of  the maximum sized vessel expected to call at the MOT.


The final layout of  the mooring and breasting dolphins shall be determined based on the results of  the mooring analysis that provides optimal mooring line and breasting forces for the range of  vessels to be accommodated. The breasting force under the mooring condition shall not exceed the maximum fender reaction of  the fender unit when it is being compressed at the manufacturers rated deflection.


3105F.6 Symbols.


a
   = Berthing Angle. It also indicates the angle of  horizontal mooring lines, see Fig 5-2.

D
   = Deflection

q
   = Vertical mooring line angles

B    = Beam of  vessel


F    = Longitudinal or vertical component of  horizontal normal berthing force


L    = Distance between passing and moored vessels


Lc
   = Contact length

N    = Maximum horizontal berthing force


r    = Bow radius


m
   = Coefficient of  friction of  contact materials

V    = Ground speed (knots)


Vc
   = Maximum current (knots).

Vcrit
   = Ground speed (knots) above which passing loads must be considered

Vw    = Maximum wind speed (knots)


3105F.7 References.


[5.1]   American Concrete Institute, ACI318-02, 2002, "Building Code Requirements for Structural Concrete (318-02) and Commentary (318R-02)," Farmington Hills, Michigan.


[5.2]   American Institute of  Steel Construction (AISC), 2001, "Manual of  Steel Construction, Load and Resistance Factor Design (LRFD)," 3rd Ed., Chicago, IL.


[5.3]   American Forest & Paper Association, 1999, "ASD Manual - National Design Specification for Wood Construction," ANSI/AF & PA NDS-1997, Washington, D.C.


[5.4]   Oil Companies International Marine Forum (OCIMF), 1997, "Mooring Equipment Guidelines", 2nd Ed., London, England.


[5.5]   Oil Companies International Marine Forum (OCIMF), 1977, "Prediction of  Wind and Current Loads on VLCCs," London, England.


[5.6]   Department of  Defense, 1 July 1999, "Mooring Design," Handbook, MIL-HDBK-1026/4A, Alexandria, VA, USA.


[5.7]   Department of  the Navy, Dec. 1984, "Harbors Design Manual, "NAVFAC DM-26.1, Alexandria, VA, USA.


[5.8]   Kilner F.A., 1961, "Model Tests on the Motion of  Moored Ships Placed on Long Waves." Proceedings of  7th Conference on Coastal Engineering, August 1960, The Hague, Netherlands, published by the Council on Wave Research - The Engineering Foundation.


[5.9]   Department of  the Navy, 30 October 1987, "Piers and Wharves," Military Handbook, MIL-HDBK-1025/1, Alexandria, VA, USA.


[5.10]   Permanent International Association of  Navigation Congresses (PIANC), 2002, "Guidelines for the Design of  Fender Systems: 2002, " Brussels.


[5.11]   British Standards Institution, 1994, "British Standard Code of  Practice for Maritime Structures - Part 4. Code of  Practice for Design of  Fendering and Mooring Systems", BS6349, London, England.


Authority: Sections 8755 and 8757, Public Resources Code.


Reference: Sections 8750, 8751, 8755 and 8757, Public Resources Code.


Division 6