Vessel Hoisting in Heavy Seas – Hoisting Directly to a Vessel
Factors for Hoisting Directly to a Vessel in Heavy Seas: Motion and Environment
Large ships with high freeboards often require a hoist directly to the deck. The vessel’s motion—largely influenced by speed, heading relative to the waves, size (length, beam, height, tonnage), and weight distribution—must be evaluated before conducting a hoist. Prior to arrival on scene, coordinate with the vessel’s captain to adjust speed and heading for the smoothest possible ride, while maintaining a helicopter heading that supports an effective and safe hoist. As with any hoist, the optimal hoisting area and aircraft heading represent a balance among multiple factors: obstacles, visual references, wind conditions (including potential orographic turbulence), vessel motion, the ability to observe approaching waves, available power margin for hover, rotor wash effects, and maintaining a clear escape path in the event of an emergency.
Large Vessel Motion Dynamics in Heavy Seas: Choosing the Hoist Area
When hoisting to a large vessel in heavy seas, different parts of the vessel can move much farther and more rapid than other parts of the vessel. When a vessel pitches in heavy seas, the bow and stern experience more pronounced movement than the middle of the ship, and the rails move more than the centerline during rolls. Consequently, hoisting towards the middle of a deep-draft vessel, if feasible, can be advantageous due to reduced vertical and lateral motion.
Cable Management and Flight Mechanic (FM) Techniques
Cable management is crucial to prevent both excessive slack and potentially damaging shock loads caused by vessel movement. A crew member who announces incoming waves is essential for coordinating the timing of deliveries and recoveries to coincide with the rise of the boat on a wave or during lulls between wave sets. A shock load to the swimmer will occur if the boat drops out below them and the cable goes taught. A skilled FM will anticipate vessel movements, “conn” the aircraft and manage cable accordingly, particularly with larger vessels that have large, but muted, responses to big waves.
Crew Decision to Optimize Hoist Effectiveness by Maintaining a Stable Hoist Platform while the Hoist Target Moves Under the Helicopter
There is a lot of hoist camera footage of Coast Guard crews hoisting to large vessels in heavy seas that shows minimal relative movement between the helicopter and the vessel, but significant cable swing as the Rescue Swimmer (RS) is being deployed to the vessel. The ensuing cable swing is problematic for both the Flight Mechanic (FM) and RS and is a direct consequence of the helicopter chasing the boat, a tendency the pilot should avoid in most heavy seas boat hoists. Years of training precision helicopter positioning in calm seas, where the pilot attempts to keep the helicopter directly over the hoist target, can impede effectiveness when hoisting to a large vessel pitching and rolling in heavy seas as the lateral movement necessary to maintain the helicopter’s precise position over the vessel creates a big swing in the hoist cable and a more challenging situation for both the FM and RS. When hoisting to a vessel in seas, the crew should make a conscious, collective decision to either keep the helicopter directly over the hoist target or keep the helicopter steady, let the hoist target move underneath the helicopter, and allow the FM to time the deployments and recoveries.
Pilot Flying (PF) Techniques: Maintaining Helicopter Stability in Heavy Seas Boat Hoisting
For the PF, the key to maintaining stability during a hoist to a large boat in heavy seas is to *avoid chasing* the boat’s pitch and roll. Because fixating on a close-in reference that is constantly moving, such as a swinging mast or moving superstructure, will cause the helicopter to mirror that object’s motion, instead, the PF should use the horizon (if one is present) as a primary visual reference for stability and use a vessel hoist reference that is as far away as possible (e.g., the bow if you are hoisting to the middle of the ship) to achieve overall aircraft stability. Combining this visual scan with establishing a trim baseline for the average speed and direction of the vessel through the water and noting this reference on the hover bars (or available EGI derived hover vector) will help facilitate a steady hover. Furthermore, if the only visual references the right seat pilot has are close in visual references (e.g. a moving crane, mast, superstructure, etc.), it may be more advantageous for the left seat pilot to fly during the hoist if they have a view of the whole vessel and can extend their scan down a large boat. The goal is to keep a stable platform above the vessel, allowing the FM to time the delivery and pick up as the boat moves under the steady helicopter.
Trail Lines and Weight Bags
If individuals on deck are physically capable of tending a trail line and understand its intended use, the trail line can be an excellent tool to simplify Rescue Swimmer (RS) deployments. Once on deck, the RS will often employ the trail line for subsequent hoists to improve efficiency. Effective use of the trail line enables the Flight Mechanic (FM) to enhance precision, control device spin and swing, and reduce pilot workload. Because heavy offshore seas are typically accompanied by strong winds, trail lines may “sail” significantly—being blown backward by the wind. In these conditions, using a heavy-weather (long) trail line, double trail lines, or heavier/double weight bags can help counter the challenges of deep-draft vessel hoisting in heavy seas.
The Importance of a Dry Run and Slow, Dynamic Approaches
Finally, a dry run or overhead check (as detailed in the Hoist Dry Run or Overhead Check post) is invaluable for assessing clearance, hover references, power requirements, and hover stability relative to the vessel’s movement. That said, for the most effective hoist evolution, it will likely be beneficial for the pilots to move away from the hoist target after the overhead check and then initiate a second approach to conduct the hoist. A slow, dynamic hoist, in which the helicopter steadily approaches the hoisting area, often makes it easier for the pilot to keep the helicopter stable. Conversely, executing the hoist directly from the location of the overhead check can be more difficult because it extends the amount of time the helicopter is directly over the target hoist location, making it much harder for the pilot to maintain a steady hover due to the pilot induced hover oscillations that can occur from the large movements of the boat under the helicopter.
A slow, controlled helicopter approach with careful cable management that limits the Rescue Swimmer’s (RS) exposure to rotor wash provides the most stable deployment conditions. The area where rotor wash converges beneath the helicopter forms a turbulent flight zone (TFZ), typically most pronounced about one rotor diameter below the fuselage. Hoist operators should move the RS through the TFZ smoothly and without delay, as pausing within this zone can induce swinging. A gradual, continuous approach helps shift the TFZ rearward, reducing cable swing and spin. Maintaining slight forward flight allows the RS to transit the zone with forward momentum, enhancing overall stability—particularly in calm wind conditions.
By providing a stable hoist platform and a RS on a relatively steady cable beneath the helicopter, a slow, dynamic hoist enables the flight mechanic to time the delivery of the RS to a pitching and rolling deck of a vessel in heavy seas. A stable hover also allows for effective subsequent recoveries of survivors and the RS.
Video Review
Below is a link to some Coast Guard helicopter hoists documented by The Discovery Channel in a show titled “Deadliest Catch’s Most Amazing Rescues.”
MEDEVAC Example: Swimmer Deployment to a Vessel in Heavy Seas
About 11 minutes and 30 seconds into the video, there are a few minutes of hoist footage in which we can briefly compare a night time hoist attempt, presumably without a horizon, to a daytime hoist with a horizon in similar seas. Although swing is evident in both hoists, the swing from trying to fly precisely over the boat at night is particularly impressive. The footage highlights the necessity for pilots to avoid fixation on close in references and the importance for the aircrew to choose to be a stable hoist platform, rather than trying to chase the hoist target, empowering the flight mechanic to time the swimmer deployment.