{"id":51735,"date":"2026-04-17T23:44:04","date_gmt":"2026-04-17T22:44:04","guid":{"rendered":"https:\/\/maritimehub.co.uk\/?p=51735"},"modified":"2026-04-17T23:44:04","modified_gmt":"2026-04-17T22:44:04","slug":"ahts-winch-operation","status":"publish","type":"post","link":"https:\/\/maritimehub.co.uk\/ahts-winch-operation\/","title":{"rendered":"AHTS Winch Operation"},"content":{"rendered":"
\n

ON DECK -> Offshore Deck Operations<\/p>\n

Position on Deck<\/strong><\/p>\n

Operation Group:<\/strong> Offshore \/ Anchor Handling<\/p>\n

Primary Role:<\/strong> Controlled deployment, tensioning, and recovery of anchor-handling wire and associated tow gear via the main winch system.<\/p>\n

Interfaces:<\/strong> Bridge team, winch operator (deck), OIM\/barge supervisor, DP system, tow-pin\/shark-jaw, stern roller, tension monitoring and data recording systems, vessel stability management.<\/p>\n

Operational Criticality:<\/strong> Absolute \u2014 the main winch is the single system through which all anchor-handling forces are transmitted. Its failure, or the failure of those who operate it, places the vessel and every person on the aft deck in immediate danger.<\/p>\n

Failure Consequence:<\/strong> Uncontrolled wire release or parting under tension. Snap-back across the aft deck. Loss of anchor or tow. Potential capsize from unmanaged stern loading. Fatalities.<\/p>\n<\/div>\n

A winch does not fail in silence. It gives warnings \u2014 in the spooling, in the wire, in the gauges. The failures come when those warnings are heard and not acted upon.<\/em><\/p>\n

Introduction<\/h2>\n

The main winch is not a component of an AHTS vessel. It is the reason the vessel exists. Everything else \u2014 the stern roller, the shark jaw, the tow pins, the DP system, the hull form itself \u2014 is built around the requirement to deploy and recover wire under enormous and variable loads. Strip away the winch, and the vessel is an oddly-shaped platform supply vessel with a work deck it cannot properly use.<\/p>\n

Yet the winch is also the single piece of equipment most routinely misunderstood in terms of its operational limits. Its controls look simple. Its operation, at a glance, appears mechanical and repetitive. This simplicity breeds a dangerous familiarity. The operator who has run a thousand metres of wire without incident is precisely the operator who may fail to notice the subtle cues \u2014 a slight change in spooling rhythm, a momentary flicker on the tension display \u2014 that precede catastrophic failure.<\/p>\n

This article addresses the main winch as what it is: the defining system on the vessel, and the one whose operation most demands an unbroken chain of awareness between the person at the controls, the officer on the bridge, and the condition of the wire itself.<\/p>\n

Contents<\/h2>\n
    \n
  • 1. Construction: What the Winch Actually Is<\/li>\n
  • 2. Control Philosophy: Local, Bridge, and Emergency<\/li>\n
  • 3. The Wire’s Life On and Off the Drum<\/li>\n
  • 4. Pay-Out, Haul-In, and the Question of Rate<\/li>\n
  • 5. Heave Compensation and Its Limits<\/li>\n
  • 6. Tension Monitoring, Alarms, and Recording<\/li>\n
  • 7. Shared Situational Awareness: Winch Operator and Bridge<\/li>\n
  • 8. Failure Points: Fairlead, Stern Roller, Termination<\/li>\n
  • 9. Common Failures That Should Never Be Common<\/li>\n
  • Closing Reality<\/li>\n<\/ul>\n

    1. Construction: What the Winch Actually Is<\/h2>\n

    The main winch on an AHTS is a hydraulically driven storage and tensioning system. At its core is a split or single drum, sized to carry the vessel’s full working length of wire at the required SWL. The drum’s diameter is not arbitrary; it is set by the minimum bending radius demanded by the wire’s construction. An undersized drum will destroy a wire from the inside out, cycle by cycle, regardless of what the tension gauge reads.<\/p>\n

    Around the drum sit the systems that make controlled operation possible: the spooling gear, the brake, the clutch, and the render\/recover logic.<\/p>\n

    Spooling gear<\/strong> ensures the wire lays evenly across the drum face. When it works correctly, it is invisible. When it does not, wire stacks, crosses, and crushes. Spooling faults are the most commonly ignored precursor to wire failure on an AHTS.<\/p>\n

    The brake system<\/strong> \u2014 typically a band brake on the drum, hydraulically applied and spring-set \u2014 is the last line of defence when hydraulic power or control is lost. Its holding capacity is a fixed, measurable value. That value degrades with wear. There is no alarm for it. It requires physical inspection and measurement at defined intervals. A brake that was adequate six months ago may not be adequate today.<\/p>\n

    The clutch<\/strong> allows the drum to be decoupled from the drive motor. In some operations \u2014 controlled wire rendering, for example \u2014 this is deliberate. In others, an inadvertent clutch disengage under load is an emergency. The clutch interlock logic must be understood completely by the operator. Not generally. Completely.<\/p>\n

    Render\/recover logic<\/strong> is the automated or semi-automated system that allows the winch to pay out wire when a preset tension threshold is exceeded and haul it back in when tension drops below a lower threshold. This is not heave compensation. It is load protection. Its settings are operation-specific, and altering them without full understanding of the current catenary and sea state is a route to losing control of the wire.<\/p>\n

    2. Control Philosophy: Local, Bridge, and Emergency<\/h2>\n

    Main winch control can typically be exercised from three positions: the local control station on the aft deck, the bridge console, and the emergency release.<\/p>\n

    Local control is the primary operating position for anchor-handling operations. The operator at the deck station has direct visual contact with the wire on the drum, the spooling, the stern roller, and the working area. This visual information is irreplaceable. No camera feed, no matter how well positioned, provides the same resolution as trained eyes ten metres from the drum.<\/p>\n

    Bridge control provides the master or DP operator with the ability to operate the winch directly. This is essential during phases when the aft deck is cleared of personnel \u2014 during final tensioning, during heavy-weather recovery, or when snap-back risk makes the deck a no-go zone. Bridge control demands that the officer has full access to tension readouts, wire-out indicators, and the render\/recover status. Operating the winch from the bridge without these displays is operating blind.<\/p>\n

    Emergency release \u2014 typically a single-action brake dump or wire-cutter activation \u2014 exists for the situation where controlled recovery is no longer possible and the vessel is being pulled into a dangerous attitude. The emergency release is not a routine tool. Its activation means that every other option has been exhausted or has failed.<\/p>\n

    An emergency release that has never been tested is a button, not a safeguard.<\/em><\/p>\n

    The handover of control between local and bridge must follow an explicit protocol. The operator on deck must confirm transfer. The bridge must confirm acceptance. At no point should both positions believe the other has control. The dead zone in between \u2014 where neither is actively managing the winch \u2014 is where people die.<\/p>\n

    3. The Wire’s Life On and Off the Drum<\/h2>\n

    Wire rope on an AHTS main winch lives a brutal life. It is bent repeatedly over the stern roller. It is crushed under its own layers on the drum. It is subjected to cyclic tension that varies with every swell. And between jobs, it may sit for days or weeks on the drum, often wet, under the residual tension of the outermost wraps.<\/p>\n

    Torque build-up<\/strong> is an inherent feature of wire that is bent and tensioned repeatedly in the same rotational direction. On a conventional-lay wire, this manifests as a tendency to twist. If the wire is not free to rotate \u2014 and on many AHTS rigs, it is not \u2014 this torque accumulates until the wire’s internal structure begins to yield. The result is birdcaging: a sudden, visible distortion where the outer strands splay outward from the core.<\/p>\n

    A birdcaged section is finished. It cannot be repaired. It cannot be straightened and reused. The wire must be cut back beyond the damaged section, or \u2014 more often \u2014 the entire wire must be replaced. Birdcaging that occurs on the drum, under wraps, may not be visible until the wire is paid out. By then, it may have already been run over the stern roller under load.<\/p>\n

    Crushing<\/strong> occurs when wire on the lower layers of the drum is subjected to the compressive load of multiple outer layers wound on under tension. The inner wraps flatten, the core is distorted, and the wire’s breaking strength at that point drops significantly below its nominal MBL. This is not theoretical. It is measurable, and it is the reason that wire breaking strength certificates issued for the rope as delivered do not represent the actual strength of wire that has been in service on a drum under cyclic loading.<\/p>\n

    Core damage<\/strong> \u2014 failure of the fibre or IWRC core \u2014 is invisible from outside. The wire looks normal. It measures normal on a calliper. But its internal support structure is gone, and its resistance to crushing and bending fatigue is fundamentally compromised. Core damage is detected by discard criteria during inspection: a reduction in diameter beyond published thresholds, an increase in wire flexibility at a localised point, or \u2014 in the case of total core failure \u2014 a visible flattening under moderate tension.<\/p>\n

    A wire that looks right and measures right can still be dying. The core does not advertise its failure.<\/em><\/p>\n

    4. Pay-Out, Haul-In, and the Question of Rate<\/h2>\n

    The rate at which wire is paid out or hauled in is not a matter of preference. It is governed by the operational phase, the sea state, the catenary in the wire, and the vessel’s heading and speed relative to the rig or anchor.<\/p>\n

    Excessive pay-out rate creates slack wire. Slack wire, when tension is suddenly reapplied by vessel motion or rig movement, results in shock loading. Shock loads can exceed the wire’s MBL even when the steady-state tension is well within limits. There is no alarm for a shock load that occurs faster than the sampling rate of the tension monitoring system. The first indication may be the wire parting.<\/p>\n

    Excessive haul-in rate against a catenary that is not being managed risks overloading the winch or, worse, dragging the vessel’s stern down and aft. On an AHTS, stern loading is the single greatest stability threat. The bollard pull of a modern AHTS can approach or exceed the displacement forces that keep the stern above water. Winch tension, unchecked, can capsize the vessel.<\/p>\n

    Rate control is therefore a continuous judgment, informed by tension readings, visual observation of the catenary, vessel motion, and communication with the rig. It is not set-and-forget. It is hands-on, eyes-up, every second the wire is under load.<\/p>\n

    5. Heave Compensation and Its Limits<\/h2>\n

    Some AHTS winch systems incorporate active heave compensation \u2014 a system that adjusts wire pay-out and recovery in real time to counteract the vessel’s vertical motion at the stern roller. The intent is to maintain a relatively constant wire tension as the vessel pitches and heaves, reducing cyclic fatigue on the wire and minimising shock loads transferred to the anchor or rig.<\/p>\n

    Heave compensation works within a defined stroke and response time. Outside those parameters, it does not compensate. It lags, and the lag introduces exactly the tension spikes it is designed to prevent.<\/p>\n

    In heavy seas, where the vessel’s heave amplitude exceeds the compensator’s stroke, the system saturates. The wire alternately goes slack and snaps taut. The operator who relies on heave compensation in conditions beyond its design envelope is relying on a system that has already stopped working.<\/p>\n

    Heave compensation reduces fatigue. It does not eliminate risk. In the conditions where it is needed most, it is most likely to be overwhelmed.<\/em><\/p>\n

    Operators must know the compensator’s rated stroke and response frequency. They must know at what sea state and heading those limits will be exceeded. And they must have a plan \u2014 already discussed, already agreed with the bridge \u2014 for what happens when compensation is no longer effective. That plan is usually: stop the operation.<\/p>\n

    6. Tension Monitoring, Alarms, and Recording<\/h2>\n

    The tension monitoring system on the main winch is not advisory. It is the primary instrument through which the vessel’s safety is managed during anchor-handling and towing operations.<\/p>\n

    Tension is typically measured by load pins in the fairlead or guide sheaves, or by hydraulic pressure transducers in the winch drive circuit calibrated to give a wire tension readout. Both methods have limitations. Load pins can drift. Hydraulic readings include friction losses that vary with temperature and system condition. Calibration must be current. An uncalibrated tension display is a number, not a measurement.<\/p>\n

    Alarms are set at defined percentages of the wire’s SWL and, separately, of the vessel’s bollard pull limit and stability thresholds. These alarms must be audible and visible at both the deck control station and the bridge. They must be set before the operation begins, as part of the toolbox talk, and they must not be altered during the operation without explicit agreement between the winch operator and the bridge officer.<\/p>\n

    The most dangerous alarm is the one that is acknowledged and not acted upon.<\/p>\n

    This happens. It happens because the alarm fires during a phase of the operation where stopping feels inconvenient. It happens because the operator assumes the spike is transient. It happens because the alarm has fired before and nothing went wrong. Until something does.<\/p>\n

    Tension recording \u2014 the continuous logging of wire tension against time \u2014 is a regulatory requirement on most AHTS operations and a contractual one on virtually all. The recording exists not just for post-incident investigation but as a live operational tool. Reviewing the tension trace at shift handover, or after a heavy-weather hold, reveals patterns that real-time displays do not: gradual upward trends in peak tension, increasing frequency of alarm activations, asymmetric loading that suggests a spooling fault or catenary problem.<\/p>\n

    The data recorder knows what happened. The question is whether anyone looks at it before the wire parts.<\/em><\/p>\n

    7. Shared Situational Awareness: Winch Operator and Bridge<\/h2>\n

    The winch operator sees the drum, the wire, the spooling, the aft deck. The bridge officer sees the vessel’s position, heading, speed, DP status, the rig’s position, the weather, the tension readout, and the bigger tactical picture of the operation.<\/p>\n

    Neither picture is complete without the other.<\/p>\n

    The winch operator who feels a change in wire vibration, or sees an irregularity in the spooling, holds information the bridge does not have. The bridge officer who sees a DP excursion developing, or a heading change from the rig, holds information the deck does not have. If these two streams of awareness are not continuously shared \u2014 not by periodic check-ins, but by a running, open communication channel \u2014 then the operation is being managed on partial information.<\/p>\n

    Partial information is the precondition for every anchor-handling incident that begins with the phrase ‘the wire parted without warning’.<\/p>\n

    There is no such thing as a wire parting without warning. There is only a warning that was not transmitted, not received, or not understood.<\/p>\n

    Communication protocols between the winch operator and the bridge must be established before the first metre of wire leaves the drum. They must define who reports what, when, and in what language. They must define the abort criteria and who has the authority to call a stop. On a well-run AHTS, anyone can stop the job. On a poorly-run one, stopping the job feels like a career risk.<\/p>\n

    The vessel where stopping the job is harder than continuing it is the vessel where someone will eventually not come home.<\/em><\/p>\n

    8. Failure Points: Fairlead, Stern Roller, and Termination<\/h2>\n

    Wire failure does not occur at random points along its length. It occurs at stress concentrations. On an AHTS, the three primary stress concentrations are the fairlead, the stern roller, and the termination on the drum.<\/p>\n

    At the fairlead,<\/strong> the wire changes direction under load. If the fleet angle is excessive \u2014 because of poor spooling, because the vessel is not aligned with the tow, because the fairlead geometry does not match the operation \u2014 the wire bears against the edge of the fairlead guide under enormous side-load. The outer strands wear, flatten, and eventually break. This damage is localised and progressive. It is detectable on inspection. It is often not inspected until the wire has parted.<\/p>\n

    At the stern roller,<\/strong> the wire undergoes its most severe bending cycle. Every metre of wire that passes over the roller is bent from straight to the roller’s radius and back again, under full working tension. The roller diameter is designed to minimise this fatigue, but it cannot eliminate it. Wire that has passed over the stern roller thousands of times has a fatigue life that is measurably shorter than wire of the same age that has sat on the drum. Sections of wire that habitually sit at the roller contact point during long static holds accumulate disproportionate damage.<\/p>\n

    At the termination on the drum,<\/strong> the wire’s end is secured \u2014 typically by wedge-and-socket or by wraps around the barrel with a clamp. This termination is never at full MBL. It cannot be. The termination efficiency is a percentage of the wire’s nominal strength, and that percentage degrades if the termination is corroded, if the wedge has shifted, or if the securing wraps have loosened. The final few wraps on the drum are the last line before total loss of the wire. They must remain on the drum at all times. Any operation that pays out wire to the point where the termination wraps are bearing load has already gone wrong.<\/p>\n

    9. Common Failures That Should Never Be Common<\/h2>\n

    Three failures recur across AHTS winch incident reports with a frequency that should be unacceptable. They persist because they are normalised.<\/p>\n

    Spooling faults ignored.<\/strong> The wire begins to stack or cross-lay. The operator notices. The operation continues because stopping to re-spool means delay, and delay costs the client money. The crossed wire bites into the layer beneath it. The next time that section is paid out under tension, it catches, lurches, and shock-loads the system. Or it simply crushes the underlying wire, creating a hidden weak point that fails on a later deployment.<\/p>\n

    Spooling faults are not cosmetic. They are structural damage in progress.<\/p>\n

    Torque alarms acknowledged without action.<\/strong> The tension alarm fires. The operator presses the acknowledge button. The bridge notes the alarm. Neither party reduces tension, slows the operation, or investigates the cause. The alarm becomes background noise. When the alarm fires for the last time \u2014 the time the wire actually parts \u2014 the recording will show a string of prior activations, each acknowledged, none acted upon. The investigation will call this ‘alarm fatigue.’ It is not fatigue. It is choice.<\/p>\n

    Brake holding capacity degraded through wear.<\/strong> The band brake is the winch’s last passive safeguard. It holds the drum when hydraulic pressure is lost. Its capacity is a function of the friction material’s condition, the band’s tension, and the drum’s surface. All three degrade with use. Brake testing \u2014 static pull-testing against a known load \u2014 is straightforward. It is also frequently deferred, recorded as done when it was not, or performed against a load that does not represent the actual worst-case scenario. A brake that cannot hold the maximum anticipated wire tension is not a brake. It is a mechanism that will allow uncontrolled wire release at the worst possible moment.<\/p>\n

    Every one of these failures is preventable. Every one of them is preceded by a choice to continue rather than stop.<\/em><\/p>\n

    Closing Reality<\/h2>\n

    The main winch on an AHTS is not complicated. It is a drum, a drive, a brake, and a wire. Its controls can be learned in a day. Operating it safely cannot.<\/p>\n

    Safe winch operation is not a matter of knowing which lever to pull. It is a matter of understanding what the wire is doing at every point along its length \u2014 on the drum, through the fairlead, over the stern roller, and out into the catenary. It is a matter of reading the tension display not as a number but as a story: what the load is doing now, what it has been doing for the last hour, and what it is likely to do in the next thirty seconds.<\/p>\n

    It is, above all, a matter of acting on what the winch is telling you. Not acknowledging. Acting.<\/p>\n

    The winch gives warnings. The wire gives warnings. The tension trace gives warnings. The spooling gives warnings. The warnings are there for those willing to see them and \u2014 more critically \u2014 willing to stop the job when they do.<\/p>\n

    A stopped operation is an inconvenience. A parted wire across the aft deck is a body bag.<\/p>\n","protected":false},"excerpt":{"rendered":"

    The main winch defines the AHTS. Its operation demands more than lever-pulling \u2014 it demands constant awareness of wire condition, tension, and the gap between alarm and action.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"fifu_image_url":"","fifu_image_alt":"","c2c-post-author-ip":"2a02:c7c:2ef8:2400:931:afb1:9971:4a62","footnotes":""},"categories":[1,14],"tags":[1416,9291,9180,9397,9389,9396,9395,9249],"class_list":["post-51735","post","type-post","status-publish","format-standard","hentry","category-latest","category-on-deck","tag-ahts","tag-anchor-handling","tag-deck-safety","tag-heave-compensation","tag-offshore-deck-operations","tag-tension-monitoring","tag-winch-operation","tag-wire-rope"],"acf":[],"_links":{"self":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51735","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fcomments&post=51735"}],"version-history":[{"count":1,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51735\/revisions"}],"predecessor-version":[{"id":51738,"href":"https:\/\/maritimehub.co.uk\/?rest_route=\/wp\/v2\/posts\/51735\/revisions\/51738"}],"wp:attachment":[{"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fmedia&parent=51735"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Fcategories&post=51735"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/maritimehub.co.uk\/?rest_route=%2Fwp%2Fv2%2Ftags&post=51735"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}