Three cases of environmental loading on the vessels were analyzed as follows:

a) 25-year return period wind
b) 4% exceedance long-period waves (waves with periods greater than 25 seconds)
c) 6.3% exceedance short-period waves (waves with periods less than 25 seconds)

These environmental loadings were selected based on initial model simulations of wind and wave forcing which did not cause mooring line tensions to exceed criteria specified in the Marine Oil Terminal Engineering and Maintenance Standards (MOTEMS) recently adopted by the State Lands Commission as the standard for design of marine oil terminals. The occurrence of these resultant wave heights at the berth was determined based on historical data from San Pedro Wave Buoy with these deep water waves transformed to the berth location as discussed in the waves section of the coastal engineering studies. A schematic showing a mooring configuration with 14 lines for a VLCC is illustrated in the figure below.

Ship motion due to wind, with extreme wind conditions occurring once every 25 years, is not significant for ship motion for any class of ship when compared to the motion and mooring line forces for the wave induced forcing.

Ship motion due to long-period waves with periods greater than 25 seconds, referred to by some as “wave surge” are not significant for PANAMAX and AFRAMAX class ships, with maximum lateral motion below 2.0 feet. Ship motion due to long-period waves for the VLCC class can reach 5.3 feet in peak to peak surge when loaded. This motion is within the acceptable limits of the berth capabilities.

Short-period waves, with periods greater than 10 seconds and less than or equal to 25 seconds are commonly referred to as "ocean swell." The short waves do not impact the VLCC class ship since it does not “feel” them. However, short-period waves have substantially greater impact on the PANAMAX and AFRAMAX ships. Although the federal breakwater reduces the higher incident short period wave energy dramatically at the proposed project site, there will be noticeable vessel motion during major storm events.

Model simulations included a 2-year wind blowing the vessels off the fenders and a worst case wave direction at the ship. The mooring line pretensions range between 7 to 12 percent of the minimum line breaking strength. The maximum surge and sway motion and maximum line tension for the three classes of vessels under these wave and wind conditions that will not cause line loads in excess of the MOTEMS criteria are shown below.

In addition to the environmental loading on the moored vessels, there is a potential for significant forces on the moored vessel caused by another vessel passing adjacent to berth. Passing ships traveling at high speed and/or proximate to moored vessels can impose large forces and moments on the moored vessel. These forces can be sufficient to part mooring lines or produce large vessel motions. Typical results are shown in the figure below which illustrates a relatively large, but transient load is experienced by the moored vessel. The forces on the moored vessel are dependent on the distance to the passing vessel, the speed of the passing vessel, the underkeel clearance of both vessels, and the displacement of the two ships.

At Pier 400, the closest line of approach to the moored tanker is when vessels are passing parallel to the berth. More oblique angles will result in a vessel track further from the moored tanker. The side-to-side passing analysis, therefore, represents a conservative scenario for assessing the terminal vulnerability to passing effects.

The analysis showed that a passing post-PANAMAX containership with a speed of 5 knots or greater may result in loads that are higher than the safe working load of the vessel mooring lines for berthed VLCC tankers. Adding additional mooring lines reduces the loads, but the safe working load is still exceeded. However, if container ship speed is reduced to 4 knots or less and passing distance is maintained at 300 feet or greater, mooring line loads are kept within acceptable limits and manifold excursions are reduced to less than 1 meter.

Smaller tanker classes were less susceptible to passing ship effects; therefore the VLCC represents the limiting condition. The analysis shows that the deeper the vessel draft, the larger the hull displacement, the smaller the underkeel clearance, the higher the resulting passing vessel forces. The limiting case of 4 knots and 300-foot separation was also analyzed coincident with a 30-knot gusting wind. While the wind resulted in higher mooring forces, the mooring line loads remained within the safe working limits.

The loads and vessel motions imposed by passing vessels at the terminal can be managed to acceptable levels so long as a minimum mooring line pre-tension is maintained at all times and passing vessels be limited to a speed of 4 knots and a hull-to-hull passing distance of 300 feet or greater.