How Do Ships Protect Against Typhoons? Anchorage, Typhoon Avoidance Routes, and the Dangerous Semicircle Rule

The core of typhoon protection for ships is early departure, avoiding the dangerous semicircle, and selecting proper anchorage. This article analyzes avoidance decisions for merchant and fishing vessels, responses to dragging anchor, and lessons from historical maritime disasters.

No Shelter at Sea: "Early Action" is Paramount

While land-based typhoon defense involves reinforcing structures and holding ground, the core of maritime typhoon defense is always early maneuvering to avoid. Modern typhoon track forecasts have an error margin of about 200–300 km over a 3-day period, providing ships with a valuable decision window—but this requires a willingness to alter courses and accept schedule delays.

The First Rule of Typhoon Avoidance: Stay Clear of the Dangerous Semicircle

In the Northern Hemisphere, the right side relative to the typhoon's direction of movement is the dangerous semicircle: here, the cyclonic wind speed adds to the storm's forward motion, resulting in stronger winds and higher waves, while the wind direction tends to push vessels into the typhoon's path. The left side is the navigable semicircle, where winds are relatively weaker and tend to push vessels away from the typhoon.

Classic avoidance maneuvers:

• If located ahead and to the right of the typhoon's path → Head into the wind with the starboard bow and proceed at full speed away from the path.
• If located ahead to the left or behind → Keep the wind on the starboard quarter and move away to the left.
• Regardless of position, maintain a safe distance of at least 200 nautical miles from the typhoon center.

Anchorage for Typhoon Shelter: Dropping Anchor Does Not Guarantee Safety

Selecting an anchorage requires considerations of "shelter from wind, waves, and swell, plus good holding ground":

• Prioritize anchorages surrounded by hills with openings facing away from the wind direction.
• Sandy or muddy seabeds are ideal; rocky bottoms offer poor holding power and make dragging anchor highly likely.
• Use two anchors or extend the anchor chain (5–8 times the water depth), ensuring sufficient swinging room from neighboring vessels.
• Keep engines on standby: If the anchor drags, immediately use engine power to head into the wind. Historically, many maritime disasters resulted from engines not being ready.

Lessons Learned from Tragedy

• 1996 Zhanjiang Typhoon 9615: A large number of vessels in Zhanjiang Port dragged anchor, collided, and sank, causing severe losses within the harbor.
• 2014 Typhoon Rammasun: Multiple fishing boats in the Qiongzhou Strait capsized due to insufficient time to seek shelter.
• Lessons from the Ever Given Era: Ultra-large vessels have massive windage areas. The risk of dragging anchor while sheltering is actually higher than for medium-sized ships; sometimes, staying in deep water far from shore is safer than entering port.

Key Points for Fishing Vessels

• Upon receiving typhoon warnings, return to port immediately without taking chances—fishing vessels have much lower wind resistance than merchant ships.
• After returning to port, all personnel must disembark and go ashore. Historically, most casualties in fishing ports occurred among crew members who stayed onboard to keep watch.
• Small fishing boats can be lifted ashore or towed into the deeper parts of sheltered basins. When mooring multiple vessels together, ensure sufficient fenders are used.