Section 3105F — MOORING AND BERTHING ANALYSIS AND DESIGN

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

MOTs shall have the following equipment in operation: 1. An anemometer (N/E). 2. A current meter in high velocity current (>1.5 knots) areas (N/E). 3. Remote reading tension load devices in high velocity current (>1.5 knots) areas and/or with passing vessel effects for new MOTs.

4. Mooring hardware in accordance with Section 3105F.8 (N/E).

Berthing systems shall be in accordance with Section 3105F.4 (N/E).

Monitoring systems and instrumentation shall be implemented considering the parameters in Section 3102F.3.6.1, and shall be installed, maintained and calibrated in accordance with Section 3111F.9.3.

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 in accordance with Section 3105F.8 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 shall be supported so as not to contact the deck.

Section 3105F.5 and the OCIMF guidelines [5.4] shall be used in designing the mooring layout.

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.7 and 3105F.8.

The analysis and design of mooring components shall be based on the loading combinations and safety factors defined in Sections 3103F.8, 3105F.7 and 3105F.8, and in accordance with ACI 318 [5.1], AISC 325 [5.2] and ANSI/AWC NDS [5.3], as applicable.

A mooring analysis shall be performed for each berthing system, to justify the safe mooring of the various vessels at the MOT. Review of vessels calling at the MOT shall be performed to identify representative vessel size ranges and mooring configurations. Vessels analyzed shall be representative of the upper bound of each vessel size range defined by DWT capacity (see Section 3101F.6). The Terminal Operating Limits (TOLs) shall be generated based on the mooring analyses (see Section 3102F.3.6.1 and Figure 31F-2-1).

The forces acting on a moored vessel shall be determined in accordance with Section 3103F.5. Mooring line and breasting load combi- nations 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 (MEG 3) [5.4] or UFC 4-159-03 [5.5]. The manual procedure (Section 3105F.2.1) may be used for barges. In order to simplify the analysis for barges (or other small vessels), they may be considered to be solid free-standing walls (Chapter 29 of ASCE/SEI 7 [5.6]). This will eliminate the need to perform a computer assisted mooring analysis.

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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.

The most severe combination of the environmental loads and limiting conditions shall be justified based on site-specific evaluation, and considered in the mooring analyses. At a minimum, the following shall be considered and documented:

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)

5. Vessel motion limits (as applicable)

6. Fender properties

7. Mooring hardware capacities

8. Minimum mooring line properties (such as MBL of the weakest line permitted for vessel size range)

9. Passing vessel forces

In general, vessels shall remain in contact with the breasting or fendering system. Vessel motion (sway) of up to 2 feet off the breast- ing 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 mooring analyses outputs define the wind load and other limitations.

Upon completion of the mooring analyses, the following shall be checked, as applicable:

1. The fender system compression/deflection performance.

2. Anchorage capacity of each mooring hardware component.

3. Capacity of supporting structure(s) exceed each mooring line demand.

4. Maximum allowable capacities for mooring lines.

5. Vessel motion does not exceed the maximum allowable extension limits of the loading arms and/or hoses.

3105F.2.1 Manual procedure. Simplified calculations may be used to determine the mooring forces for barges with Favorable Site Conditions (see Table 31F-3-8) and no passing vessel effects (see Section 3105F.3.2), except if any of the following conditions exist (Figures 31F-5-2 and 31F-5-3).

1. Mooring layout is significantly asymmetrical

2. Horizontal mooring line angles ( α ) 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 ( θ ) exceed 25 degrees

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

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

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

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

3105F.2.2 Numerical procedure. A numerical procedure is required to obtain mooring forces for MOTs that cannot use manual procedure. 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.3.1 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, T s , 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, H s . 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 V crit

where:

Equation 5-1

V crit = 1.5 + -------------------500L –– 2B2B - 4.5(knots)

Exception: If L ≤ 2B, passing vessel loads shall be 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.

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 or by dynamic analysis.

For MOTs located in ports, the passing distance, L, may be established based on channel width and vessel traffic patterns. The guidelines established in Figure 5-17 of UFC 4-150-06 [5.7] for interior channels may be used. The “vertical bank” in Figure 5-17 of UFC 4-150-06 [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 centerline 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.

FIGURE 31F-5-4 — PASSING VESSEL

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3105F.3.3 Seiche. A seiche analysis is required for existing MOTs located within a harbor basin and which have historically experi- enced 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 Chapter 2 of UFC 4-150-06 [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. Section 3103F.5.7 and Table 31F-3-6 provides run-up values for the San Francisco Bay area, Los Angeles/Long Beach Harbors and Port Hueneme.

The analysis and design of berthing components shall be based on the loading combinations and safety factors defined in Sections 3103F.8 and 3105F.7, and in accordance with ACI 318 [5.1], AISC 325 [5.2] and ANSI/AWC NDS [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, L c , can be calculated using rational analysis considering curvature of the bow and berthing angle.

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In lieu of detailed analysis to determine the contact length, Table 31F-5-1 may be used. The contact length for a vessel within the range listed in the table can be obtained by interpolation.

TABLE 31F-5-1—CONTACT LENGTH

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-5-2 may be used for typical fender/vessel materials:

TABLE 31F-5-2—COEFFICIENT OF FRICTION

Longitudinal and vertical forces shall be determined by:

Equation 5-3 F = µN

where:

F = longitudinal or vertical component of horizontal berthing force

µ = 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 UFC 4-152-01 [5.9] and PIANC

[5.10]. Velocity and temperature factors, contact angle effects and manufacturing tolerances shall be considered (see Appendices A and B of PIANC [5.10]). Also, see Section 3103F.6.

Guidelines for layout of new MOTs are provided in OCIMF MEG3 [5.4]. 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.

Offshore MOT moorings shall be designed and analyzed considering the site water depth, metocean envi- ronment and class of vessels calling per OCIMF MEG3 [5.4] or UFC 4-159-03 [5.5].

3105F.6.1 Mooring analyses. Analysis procedures shall conform to the OCIMF MEG3 [5.4] or UFC 4-159-03 [5.5], and the following: 1. A mooring analysis shall be performed for the range of tanker classes and barges calling at each offshore berth. 2. Forces acting on moored vessels shall be determined according to Section 3103F.5 and analysis shall consider all possible vessel movements, contribution of buoys, sinkers, catenaries affecting mooring line stiffness and anchorages. 3. Correlation of winds, waves and currents shall be considered. The correlation may be estimated by probabilistic analysis of metocean data.

4. The actual expected displacement of the vessels shall be used in the analysis. 5. Underwater inspections and bathymetry shall be considered. 6. Both fully laden and ballast conditions shall be considered. 7. Dynamic analysis shall be used to evaluate moorings performance.

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3105F.6.2 Design of mooring components. Design of mooring components shall be based on loading combinations and safety factors defined in Sections 3103F.8, 3105F.7 and 3105F.8 and follow the guidelines provided in either the OCIMF MEG3 [5.4] or UFC 4- 159-03 [5.5].

Safety factors for different material types of mooring lines are given in Table 31F-5-3. The safety factors should be applied to the minimum number of lines specified by the mooring analysis, using the highest loads calculated for the envi- ronmental conditions. The minimum breaking load (MBL) of new ropes is obtained from the certificate issued by the manufacturer. If polyamide tails are used in combination with wire mooring lines, the safety factor shall be based on the weaker of the two ropes.

TABLE 31F-5-3—SAFETY FACTORS FOR ROPES [5.4]

Mooring hardware shall include, but not be limited to, bollards, quick release hooks, other mooring fittings and base bolts. All mooring hardware shall be clearly marked with their safe working loads (or allowable working loads) [5.4]. The certificate issued by the manufacturer normally defines the safe working loads of this hardware.

3105F.8.1 Quick release hooks. For new MOTs or berthing systems, a minimum of three quick release hooks are required for each breasting line location for tankers greater than or equal to 50,000 DWT. At least two hooks at each location shall be provided for breasting lines for tankers less than 50,000 DWT. Remote release may be considered for emergency situations.

All hooks and supporting structures shall withstand the minimum breaking load (MBL) of the strongest line with a safety factor of 1.2 or greater. Only one mooring line shall be placed on each quick release hook (N/E).

For multiple quick release hooks, the minimum horizontal load for the design of the tie-down shall be:

Equation 5-4 F d = 1.2 × MBL × [1 + 0.75 (n-1)]

where:

F d = Minimum factored demand for assembly tie-down.

n = Number of hooks on the assembly.

The capacity of the supporting structures must be larger than F d (See Section 3107F.6).

3105F.8.2 Other fittings. Other fittings include cleats, bitts and bollards.

If the allowable working loads for existing fittings are not available, the values listed in Table 31F-5-4 may be used for typical sizes, bolt patterns and layout. The allowable working loads are defined for mooring line angles up to 60 degrees from the horizontal. The combination of vertical and horizontal loads shall be considered.

TABLE 31F-5-4—ALLOWABLE WORKING LOADS

3105F.8.3 Base bolts. Base bolts are subjected to both shear and uplift. Forces on bolts shall be determined using the following factors:

1. Height of load application on bitts or bollards.

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2. Actual vertical angles of mooring lines for the highest and lowest tide and vessel draft conditions, for all sizes of vessels at each particular berth. 3. Actual horizontal angles from the mooring line configurations, for all vessel sizes and positions at each particular berth.

4. Simultaneous loads from more than one vessel.

For existing MOTs, the deteriorated condition of the base bolts and supporting members shall be considered in determining the capacity of the fitting.

α = Horizontal mooring line angles

Δ = Deflection

θ = Vertical mooring line angles

B = Beam of vessel

DWT = Dead Weight Tonnage

F = Longitudinal or vertical component of horizontal normal berthing force

F d = Minimum factored demand for assembly tie-down

L = Distance between passing and moored vessels

MBL = Minimum breaking load

n = Number of hooks on the assembly

N = Maximum horizontal berthing force

μ = Coefficient of friction of contact materials

V = Ground speed (knots)

V c = Maximum current (knots). V crit = Ground speed (knots) above which passing loads must be considered

[5.1] American Concrete Institute (ACI), 2014, ACI 318-14 (ACI 318), “Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14),” Farmington Hills, MI.

[5.2] American Institute of Steel Construction, Inc. (AISC), 2017, AISC 325-17 (AISC 325), “Steel Construction Manual,” 15th ed., Chicago, IL.

[5.3] American Wood Council (AWC), 2017, ANSI/AWC NDS-2018 (ANSI/AWC NDS), “National Design Specification (NDS) for Wood Construction,” Washington, D.C.

[5.4] Oil Companies International Marine Forum (OCIMF), 2008, “Mooring Equipment Guidelines (MEG3),” 3rd Ed., London, England.

[5.5] Department of Defense, 3 October 2005 (Change 2, 23 June 2016), Unified Facilities Criteria (UFC) 4-159-03, “Design: Moorings,” Washington D.C.

[5.6] American Society of Civil Engineers (ASCE), 2016, ASCE/SEI 7-16 (ASCE/SEI 7), “Minimum Design Loads and Associated Criteria for Buildings and Other Structures,” Reston, VA.

[5.7] Department of Defense, 12 December 2001 (Change 1, 19 October 2010), Unified Facilities Criteria (UFC) 4-150-06, “Military Harbors and Coastal Facilities,” Washington D.C

[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 Defense, 24 January 2017, Unified Facilities Criteria (UFC) 4-152-01, “Design: Piers and Wharves,” Washington D.C.

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

Authority: Sections 8750 through 8760, Public Resources Code.

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

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Division 6