BRITANNIA LOSS PREVENTION JULY 2024 OCCASIONALLY, THE CLUB RECEIVES CLAIMS REGARDING DAMAGES TO MEMBERS’ SHIPS CAUSED BY INTERACTIONS OR SURGES WHILE ALONGSIDE THE BERTH WITH NEARBY PORT INFRASTRUCTURES. UNDERSTANDING SURGE AND INTERACTION DAMAGE These damages typically involve the ship’s gangway placed on the wharf, incidents with mooring lines parting, or even contact damages between moored ships and berth facilities. The common conclusion often attributes the interactions or hydrodynamic surges causing ships at berth to range to excessive speed or ships passing too closely to moored vessels. On the other hand, passing ships typically defend themselves by asserting that the ships alongside were not properly moored or that the mooring configuration was unsuitable. 2 | BRITANNIA LOSS PREVENTION | GUIDANCE FIGURE 1 Initial approach between both ships on reciprocal courses, experiencing repulsive forces HYDRODYNAMIC INTERACTIONS HYDRODYNAMIC INTERACTION OCCURS WHEN A SHIP MOVES THROUGH THE WATER. AS IT MOVES, IT CREATES A HYDRODYNAMIC PRESSURE FIELD AROUND THE HULL, WHICH WILL INTERACT WITH OTHER SHIPS, OR FIXED OBJECTS SUCH AS THE QUAYSIDE STRUCTURES OR SEABED. Ships often encounter hydrodynamic interaction, with other ships or their surroundings, especially when navigating in shallow waters, narrow channels, or when passing too closely to other ships, fixed structures, obstructions, or riverbanks. Ship-to-ship (STS) interactions happen when ships are navigating through shallow waters, and the water surrounding the underwater volume of the ship (displacement) gets displaced and pushed ahead and/or to the sides of the ship. STS interactions can generate significant hydrodynamic forces that can impact the manoeuvrability of the ships. When considering the pressure distribution around each ship, they may experience a ‘repulsive’ or ‘attractive’ force, particularly noticeable when one ship overtakes or passes another on reciprocal courses at close range. FIGURE 2 When the interaction occurs, both ships feel suction forces acting on their hulls SHIP A SHIP B SHIP A SHIP B FIGURE 3 Both ships experience suction forces acting on the parallel body of the hull when passing FIGURE 4 Both ships experience repulsive forces acting near the stern areas SHIP A SHIP B SHIP A SHIP B 3 | BRITANNIA LOSS PREVENTION | GUIDANCE FIGURE 5 Ship-to-ship interaction when approaching moored ship SHIP A SHIP B • SHIP (A) MOVES IN CLOSE PROXIMITY • HYDRODYNAMIC FORCE PUSHES SHIP (B) TO SURGE AHEAD FIGURE 6 Ship-to-ship interaction when the bow passes moored ship SHIP A SHIP B FIGURE 7 Ship-to-ship interaction when alongside moored ship • INTERACTION CAUSES SHIP (B) SWAY BODILY AWAY FROM BERTH SHIP A SHIP B • INTERACTION CAUSES STERN OF SHIP (B) TO SWAY AWAY FROM BERTH 4 | BRITANNIA LOSS PREVENTION | GUIDANCE FIGURE 8 Ship-to-ship interaction when stern passes moored ship SHIP A SHIP B • INTERACTION CAUSES BOW OF SHIP (B) SWAY AWAY FROM BERTH FIGURE 9 Ship-to-ship interaction when passed moored ship SHIP B • INTERACTION BETWEEN BOTH SHIPS CAUSES SURGING FOR MOORED SHIP (B) navigators should allow for larger passing distance. When passing closely is unavoidable, the navigator should reduce the ship’s speed. It’s also recommended to ensure that the ship’s manoeuvring speed aligns with the terminal’s regulated speed limit and is suitable for the current circumstances and conditions. Another point to note is the blockage effect, the larger the displacement of the ship, th