Ship Assist and Escort Winches for Dynamic Seas the ARR Winch for Crowley Maritime Tug RESPONSE

8/19/2019 Ship Assist and Escort Winches for Dynamic Seas the ARR Winch for Crowley Maritime Tug RESPONSE

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(ITS 2004 logo here) International Tug & Salvage Convent ion Organised by the ABR Company Limited

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Ship Assist and Escort Winches for Dynamic SeasThe ARR Winch for Crowley Maritime Tug RESPONSE

Barry Griffin, B.A. Griffin Associates, Inc. USA

SYNOPSIS: The concept, design engineering, and first year of operation of the AsymmetricRender Recover (ARR) electric winch system on Crowley Marine Service’s Escort Tug

RESPONSE is presented. A brief overview of the history of North American hawser winchesleading to the definition, engineering, construction, trials, and operation of an all electric winchcapable of render-recovery in excess of the maximum indirect bollard pull of escort tugs in tankerarrest maneuvers is detailed. The operational issues leading to the need for ARR performanceis demonstrated. Construction photos and videos of winch and tug-tanker operations areincluded.

INTRODUCTION

Line handling systems for North American harbor and near-shore assist tugshave evolved in three phases over the past 30 years. During this periodmerchant ships have become larger, faster, and more specialized. Assist tugs

have increased their size, power and performance to keep pace with newmaneuvering requirements. The development of tanker escorting and indirecttowing created a separate need for specialized tugs, hawsers, and deckmachinery.

Traditionally, and to a certain extent continuing today, ship assist lines areworked by hand off the tug’s bow and stern bitts. As new build tug size andhorsepower (HP) increased there became a point where a line with adequatebreaking strength became too big and heavy for a man’s hand to grip effectively.This size is generally considered to be 75mm diameter. Simultaneousadvances in rope technology led to significant increase in fiber strength andabrasion resistance, and reduction in the weight and size of standard assist lines.For comparison, consider that an 80 mm diameter Manila hawser of the 1940’swith a breaking strength of 38 tons can today be replaced with a Ultra HighMolecular Weight Polyethylene (UHMW-PE) hawser of the same diameter, lowerweight, and a breaking strength of 427 tons.

Improvements in assist lines allowed the higher HP tugs to continue workinglines over capstans and bitts. It is not uncommon to still see a pack of six or more2,000 - 4,000 HP tugs head out to help a major container ship round BergenPoint in New York harbor in a blow, working 75mm and 100mm diameter lines by


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hand on bow bitts. Another common strategy for tugs above 6000 HP is to deploytwo lines in parallel to achieve the required breaking strength.

The second phase began with the application of Voith and ASD propulsionsystems to assist tugs. The maneuverability and force levels now possiblecreated the desire to have direct and instantaneous control of the tug assist linefrom the pilothouse. Two high power agile tugs with fewer crew could nowaccomplish the work of four or more traditional tugs.

At the same time, crew cost and safety became important issues in new tugdesign. Man-handling lines was now too slow and too risky. Bow winches werefitted to handle wire and softline on all types of tugs. Traditional wire towwinches were also fitted with synthetic tow hawsers when necessary. Thisapproach continues to this day.

As a side note on hawser sizing , it should be mentioned that current hawserwinches are almost exclusively fitted with UHMW-PE softlines with initialbreaking strengths in the range of five to seven times the tug’s static bollard pull.These large safety factors are necessary to handle the substantial gravity loads(proportional to tug displacement) that occur when working ships at high leadangles, as well as loads that would be encountered when working in the indirecttowing mode, if present. Lines typically fatigue to one half their initial breakingstrength before being retired from service. The initial five to one safety factortherefore maintains at least a two and one half to one safety factor throughout aropes useful life, which is more in keeping with commercial wire rope towing

practice.

The current and third phase of winch design addresses the special needs oftanker escort tugs which developed after the Exxon Valdez incident. Current tugsin Valdez and North Puget Sound typically have twice the HP of the previousgeneration. The following paper discusses the development of a special winchfor this service.

CLASS 1 ASSIST WINCHESUntil recently, winches and ropes for tugs in US flag escort and assist servicehad changed little since 1970. Despite major changes in tug operations,

propulsion systems, and hull form, a basic winch satisfies most needs. Thestandard hawser winch derives from common towing and mooring winch designswith the following special emphasis:

Line drum for Spectra/Plasma (UHWM-PE) softlines. Winch frame of stout design to absorb high shock loads. Drum brake with high static holding power band brake(s) Escape function to provide high speed “instant” hawser payout. Line recovery speeds approaching three knots.


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It is useful to group these basic winches into a Class 1 category when discussingtheir capabilities, as shown in Figure 1. Typical winch performance provides aline pull equal to 20% to 40% of the tug’s static bollard pull, and line payout andretrieval speeds approaching 20% of the tug’s free running speed. Remotepilothouse controls allow simple and direct proportional payout and retrieval ofthe tug hawser, in addition to automatic and manual control of the massive drumfriction brake(s). Pressing the large and high visible “ESCAPE” button allowsthe brakes to instantly release, even under full load, and free the drum to payoutthe hawser at high speed.


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Most assist tugs are fitted with 600 to 1200 feet of hawser. Therefore it can beappreciated that upon escape at speed, little time remains before coming to the“end of your rope”. For this reason a separate brake override lever is providedto hopefully stop the drum before this occurs. Unfortunately any subsequentdifferential in speed between the tug and ship creates a significant shock load


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when the brake is set and the hawser comes taut. For example, I have seentension spikes over 300 tons when this occurs on a 4400 HP harbor tug at anindirect towing speed of six knots and a probable tug to ship speed of two knots.

Attenuating these and other inadvertent loads led to the development of theClass 2 winch.

CLASS 2 ASSIST WINCHES

Crowley Maritime conceived the original Class 2 winch, or “Render- Recover”operational concept for use on Crowley’s tanker escort and assist tugs. Theiridea was to develop a winch that would increase the performance, speed, andsafety of tug escort and assist operations by automating certain winch functions.The primary goal was to allow the winch to automatically payout and recover the

softline connecting the tug to the assisted vessel during extended tetheredtransits, thus reducing operator fatigue and wear and tear on the tug and towinghawser (see Photo 1). They were clear in distinguishing the future need forrendering in excess of the traditional “constant tension” winch, and thus thenotion of a “Render-Recover” winch with potentially higher retarding of payoutforces was envisioned. The Render-Recover term implies asymmetry asopposed to the symmetrical payout and haulback of constant tension machines,such as the familiar ship mooring winch.

VMS asked Markey Machinery Company to develop and retrofit their concept ontwo existing tugs with traditional Class 1 winches. The system has worked

better than expected, and has become a standard feature on over 20 US flagtugs now fitted with the Markey system.

As shown in Figure 1, the Class 2 winch provides adjustable automatic “constanttension” inhaul up to the innate power limits of the winch drive. It is important tonote that no constant tension winch can provide significantly more power indynamic braking or load attenuation than it can provide hauling in the load,unless some other means is provided to add braking power.

This limitation led to the development of the Class 3, or Asymmetric RenderRecovery winch.

CLASS 3 ARR WINCHESCrowley Maritime and Vessel Management Services, Inc. along with B.A.Griffin

Associates and Markey Machinery recently completed the development anddeployment of the first Class 3 hawser winch on Crowley Maritime’s 7200 HPVoith tug RESPONSE for assignments in North Puget Sound.

As shown in Figure 1, the ARR winch system has significant performanceimprovements over previous winch systems, including:


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Tow Hawser “ Render and Recover” during Indirect Towing. Increase in winch pull from 50% to 250% of static bollard pull.(see Photo 2)

Improved maneuvering speed. Increase in winch speed from 20% to 50% of free running speed. Improved shock load control.

Rapid and precise dissipation of 1600 HP of system energy. Improved control of hawser spooling on the winch drum.

Pilothouse control of drum spooling to 1.4 million pound side load. High overall system efficiency and redundancy.

250 HP combined total HP, using two motors and VFD-AC drives. Low cost per winch HP.

Ten times the line pull and five times the line speed with three timesthe overall cost.

RATIONALE Crowley Maritime wanted to significantly increase tanker escort tug performanceand vessel safety in the dynamic sea conditions often encountered in the NorthPuget Sound. Relatively shallow inland seas combine with a 100 Km fetch toPacific Westerlies to create steep short seas of three meters with six to eightsecond periods. Several oil terminals are roughly perpendicular to the weather,thereby compounding the assist issues when sailing a tanker broadside to theseas. Adding a Nylon surge pennant midway in the standard UHMW-PE hawserwas briefly considered as a means of reducing the extreme shock loads that

occur as the tug pitches in head seas at full bollard pull. The Nylon method hasbeen used successfully in escort modes. However, Crowley was looking for amore universal solution.

In these seas, and for the purpose of this discussion, several operationalchallenges arise:

Connecting and maintaining the hawser during hour long tethered escorts. Quickly applying steering and braking maneuvers from non-ideal positions. Putting a tanker to sea from the terminal as weather deteriorates. Simultaneous control of heading, propulsion, and winch in high energy

maneuvers. Uncertainty of hawser tension and deployed length. Re-establishing hawser control following a hawser abort event. Preventing “pull-down” and burying of the hawser on the winch drum.

Crowley asked the following question:

“Could the existing Render Recover system concept be improved to address theexpected operational requirements, including full indirect towing to 300% ofbollard pull?”


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It was my assignment as the winch and hawser system engineer to answer thisquestion, and eventually lead the project team that built, installed andcommissioned the winch and control system.

Review of existing winches revealed the following issues and led directly to thefinal design decisions.

Electric winches offer the highest overall system effic iency.The existing and proposed hydraulic winches could provide high pulland high speed but with 20% less power when asked to provide bothpower and speed. Auxiliary HP is typically limited on tugs of thistype, so efficiency is an important issue. It was decided early on tofocus on an all-electric system with redundant auxiliary electric

generators and winch motors, capable of remote and parallel controlfrom the pilothouse.

After one year of service the electric drive has proven to be muchmore powerful, significantly quieter, and more accurate to control thanour previous best hydraulic system.

In addition, the control computer associated with the electric motorsystem integrates well with the overall computer control of the winch.This overall control allows the winch motors, the three speedautomatic gear transmission, the torque measuring load cell, and the

independent dynamic brake to provide nearly ten times the power andoperational envelope than previous systems.

The electric drives dissipate regenerative braking energy into resistivegrid banks sufficient to dissipate the full winch power when renderingthe hawser at full drive performance.

Synthetic hawsers are difficu lt to spool at high load.No existing highpull softline winch appeared to address the questionof how the line would spool, lay, or bury on the winch drum at suchhigh loads, especially at the winch side flanges, with the typical 12

strand UHMW-PE hawsers in current use.

We have had some success with what is termed “open weavespooling”, in which the rope windings cross over one another in aproprietary pattern. Narrow drums without spooling gear are anotheroption, although these drums compromise capacity or full drumperformance.

It was decided to provide independent control of the drum spoolingsystem to allow the Captain to override the automatic spooling by


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moving the normal winch control lever to port or starboard to create asimilar motion of the spooling head. This system has worked verywell and provides the ability to lay the hawser on the drum withcomplete control even under full escort indirect towing forces.

Typical winch brakes are not suitable for dynamic conditions.Traditional band or caliper drum brakes lack sufficient control andthermal capacity for continuous response to the anticipated highspeed and long duration shock loads.

It was decided to rely on a low inertia and water cooled dynamicbraking system instead of the typical static band brakes. We haveused dynamic brakes before on anchor handling tugs for dissipatingthe anchor lowering loads. We also investigated their use on marine

cranes before a final decision was made.

The eventual design employs redundant fresh water cooled discbrakes, capable of continuously dissipating a combined 1600 HP (seePhoto 3). Each brake contains a series of plastic and copper frictiondisc elements. The discs are unusual in that their static frictioncoefficient is lower than their dynamic coefficient, or just the reverse ofcommon winch braking materials and drum surfaces. This differenceeliminates the stick-slip jerking behavior of typical winch brakes whenattempting to payout heavily loaded line using the brake alone.

This static/dynamic coefficient relationship and the inherent linearnature of disc brakes enables the total braking force to be directlyproportional to the air pressure used to compress the discs together.In the ARR winch the electrical command signal from the pilothouse orwinch computer directly controls an air pressure actuator mountedclose to the brake, which in turn creates the required amount ofbraking effort. Heat generated is carried away by the multiplefreshwater cooling jackets and dissipated in a sea water heatexchanger.

The “Asymmetric” function occurs when the hawser tension exceeds

the power capacity of the electric winch drive grid bank. Withinmilliseconds the dynamic brake applies a restraining load equal to theelectric drive capability, releases the electric drive, and continues toapply braking until the load lessens to a level where the electric drivecan be safely and automatically engaged.

For utmost safety, the electric and pneumatic control of the brake isderived from the tugs 24 Volt DC battery bank service and ship enginestarting air supply, in addition to being wired to the pilothouse controlwith direct copper wire connections. This provides a high level of


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certainty in the ability to release the hawser under all possibleconditions.

The feedback from the tug crew indicates that the dynamic brake isthe most significant advance over previous designs for two reasons:

1. The shock loads that occur in dynamic pitching conditions areabsorbed more smoothly because the dynamic brake can be set moreprecisely and reliably to a known level.

2. The brake allows the winch to render line when towing indirectly athigh force levels, reducing the need to escape and recover underconditions that previously created shock loads. In the event of arecovery from abort, the brake can be brought on smoothly, while

allowing the tug to slowly “catch up” to the tanker.

Existing hawser tension moni toring is inadequate.Knowledge of hawser tension is increasingly important information forescort tug operations, especially when towing in the indirect mode.Existing hawser tension monitors rely on brake pin load cells, orinterpretation of motor currents or pressures. Both systems aresusceptible to shock damage, and calibration and environmentalerrors.

The decision was made to place the winch system load cell in the gear

train between the winch drum and the drive-brake system.Consequently, the load cell continuously and directly measures drivetorque, which is used both to control the ARR functions and to displayhawser tension, as calculated from a separately determined amount ofline payed out.

Operator controls are inadequate for high power winches.

Anyone who has worked in a pilothouse at night or in other demandingconditions, knows how easy it is to pull the wrong lever. The decisionwas made to clearly separate and define the ARR control functions to

lessen these potential errors. Operator errors have specialimportance for a winch capable of pulling over three times the staticbollard pull of the tug (see Photo 4 and 5).

It was decided to separate the controls into a “Manual” or “Primary”group, all located to the operator right, and an “Electrical Drive”, or“Secondary” group to the operators left. The Manual group controlsall the failsafe, “Escape”, and dynamic brake functions, all of which arepowered by primary ships power and directly connected to theircorresponding actuators on the winch.


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The “Electrical” group controls the winch electrical drive system, theparalleling of the tugs generators, the speed and direction on thewinch, the override control of the hawser spooling system, and thelevel of Render-Recovery.

Although the overall winch system is more complex than previousdesigns, experience so far has shown that separating the controls hasprobably reduced errors.

DESIGN, CONSTRUCTION AND INSTALLATION Tug winches are long term investments, with typical life spans of 20 or moreyears. Construction quality and detail are important issues for longevity, safety,and competitiveness. In most cases, the goods at the end of the wire or tow

hawser are a customer’s valuable possessions.

For these reasons, the design and construction compromises that can be madeon utility winches, fishing equipment, and even some mooring winches do notgenerally find favor among tug owners and crews. Fabricated frames with bolt oncomponents are inadequate for these applications.

Tug winches must therefore be true machines built using heavy welded andstress relieved frames, with machined surfaces incorporating robust andconservative internal components (see Photo 1). For example, the completedweight of the ARR winch was over 60 Tons.

The ARR winch was designed to “drop” into a reinforced rectangular hole in themain deck, and therefore allow compact and unit mounting of the electric motors,transmission, and dynamic brake system below deck (see Photo 2). Theelectrical 175 Hp and 75 HP Dual Motor drive enclosures and dynamic brakecooling system were installed independently in close proximity to the winch in aforward, well ventilated compartment, thus limiting the overall outfitting cost.

CONCLUSION AND FUTURE DEVELOPMENT

The Response is in its second year of operation. The ability of the dynamic braketo ease shock loading is the safety feature most appreciated by the crew. It haslikewise been discovered that the ARR system allows the tug to steam away, orshear off, at three knots differential speed while applying full bollard pull. On theother hand, because the winch drive can overpower the tug’s static bollard pull,the tug can approach the ship at up to 0.4 knots while applying full static backingforce. Taken together these discoveries allow the tug to simultaneously work theship and seek a new position. We are exploring what advantages this featuremight offer in tight quarters and rapid response situations.


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Application of the ARR concept to wire towing winches is a promising outcome ofthis project. We have recently provided our first two Class 2 Electric TowingWinches for 700 Meters of 50 mm. wire for a pair of 4000 HP tugs. This winchRenders and Recovers to 80% of static bollard pull. The customer reports theirlong time Senior Captain was amazed that all he had to do to bring in the towwas back off on the throttles and wait for the barge to “magically” appear at thestern, paying easily in and out during swells along the way.

This project has shown that current winch technology can provide a wide rangeof performance options for dynamic conditions. UHMW-PE rope can be operatedsuccessfully at high load on a winch with provisions for proper control ofspooling. The electric drive has overtaken hydraulics as the preferred winch drivesystem for most applications. Computer controls can be successfully combinedwith primary failsafe controls.

The author would like to thank Crowley Maritime for their vision and support infunding this advance in winch and control technology. In addition credit must begiven to Mr. Ron Greene, Senior Engineer at Markey Machinery Company,without whose creative and analytical skills the winch could not have been built.

PHOTO RECORD


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PHOTO 1 ARR WINCH TETHERED TANKER ESCORT


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PHOTO 2 ARR WINCH INDIRECT MANEUVER

PHOTO3 ARR DYNAMIC BRAKE


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PHOTO 4 ARR WINCH PILOTHOUSE CONTROLS

PHOTO 5 ARR WINCH OPERATION


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PHOTO 6 ARR WINCH ASSEMBLY

PHOTO 7 ARR WINCH INSTALLATION

Ship Assist and Escort Winches for Dynamic Seas the ARR Winch for Crowley Maritime Tug RESPONSE

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