Kevin McTaggart, Defence Research and Development CanadaSietske Hendriks, Royal Netherlands Navy

Ian Nimmo-Smith, United Kingdom Ministry of DefenceArild Øydegard, Norwegian NavyJohn Pattison, BAI Incorporated

Norbert Stuntz, Bundeswehr Technical Center, Ministry of Defence, Germany

Considerations in Development of Naval ShipDesign Criteria for Launch and Recovery

ABSTRACT

The NATO Seaway Mobility Specialist Teamis developing new ship design criteria to ensurethat ships are capable of supporting launch andrecovery operations over their life spans. Thispaper describes factors that must be consideredin the development of these new design crite-ria, with an emphasis on frigates and destroyerswith associated displacements of 3000 to 10000tonnes.

INTRODUCTION

The evolution of naval priorities combined withrapid technical advances make this a very ex-citing time in the field of launch and recov-ery. Among naval missions, search and res-cue (SAR) of migrants along with humanitarianaid and disaster relief (HADR) have become in-creasingly important in the current geopoliticallandscape. These missions dictate a require-ment for safe transfer of both military person-nel and civilians from smaller boats to ships.Counter-piracy and drug interdiction missionsrequire rapid deployment of boarding parties,which can have 12 or even more personnel. He-licopter operations continue to be an integralpart of naval ship missions. Unmanned vehi-

cles, both autonomous and remotely piloted,are being increasingly used for air, surface, andunderwater operations.

The increasing importance of launch and recov-ery within navies has stimulated much relatedactivity. The LAURA Joint Industry Project,which has been in progress for several years, isdeveloping various designs for launch and re-covery of waterborne vehicles from ships us-ing cranes [1]. Navies have been collabora-tively sponsoring additional work by industryon launch and recovery of waterborne vehicles.The European Defency Agency has performedwork on unmanned maritime systems, includ-ing launch and recovery.

Among ship operators worldwide, the UnitedStates Coast Guard appears to have the mostexperience with launch and recovery of wa-terborne vehicles. Fortunately, the US CoastGuard has been very willing to share its experi-ence and knowledge in the open literature, withseveral references cited later in this paper. Itshould be noted that there is significant over-lap between missions of the US Coast Guardand international navies, thus making lessonslearned highly valuable.

Due to rapidly evolving missions and technolo-gies associated with launch and recovery, itcan be challenging to design ships that will

c©Her Majesty the Queen in Right of Canada, as represented by the Minister of National Defence, 2016

DRDC-RDDC-2016-N044

be suitable for launch and recovery operationsthroughout their long lives. To address thisproblem, the NATO Seaway Mobility SpecialistTeam is developing new ship design guidelineswith the goal of supporting launch and recoveryoperations through ship life. The new guide-lines are assimilating lessons learned to dateand are also aiming to anticipate future devel-opments that will impact on design for launchand recovery operations. This paper intendsto share the foundations for new ship designguidelines and also to encourage feedback thatwill enhance these guidelines.

SIDE LAUNCH ANDRECOVERY USINGLIFTING APPLIANCES

Launch and recovery of waterborne objectsfrom the sides of ships is commonly done us-ing lifting appliances, which can include davits,boom cranes, and articulated cranes. A reviewof side launch and recovery has been performedto provide information for development of asso-ciated ship design guidelines.

Review of Side Launch and Recovery

Figure 1 shows a wave buoy being launchedfrom the side of a Royal Canadian Naval Mar-itime Coastal Defence Vessel using a boomcrane. The launch and recovery of the wavebuoy is a relatively simple operation for the fol-lowing reasons:

• The ship and buoy are both moving withminimal speed;

• No personnel are being lifted as part of thelaunch and recovery operation;

• The shape and size of the buoy make iteasy to handle for personnel on deck.

There are several factors that contribute to thesuccess of launch and recovery operations withthis combination of ship and crane:

• The deck at the crane location is a suitabledistance above the water, in close prox-imity yet sufficiently high to prevent deckwetness;

• Personnel on the bridge (not shown) haveexcellent views of the crane;

• The crane is relatively simple;

• There is adequate space in the vicinity ofthe crane for movement and storage of ob-jects;

• Although the crane is located at the sternof the ship, the vertical motions of thecrane relative to the water surface aregenerally acceptable due to the moderatelength of the ship (49.0 m length betweenperpendiculars).

Figure 1: Launching of Wave Buoy from Side ofShip Using a Boom Crane

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Further insight can be gained by consideringthe launch and recovery of boats, such as thatshown in Figure 2. A crane is connected to theboat at a conventional single lift point on theboat. The interface between the crane and theboat significantly influences engineering aspectsof both the ship and boat, and also greatly in-fluences launch and recovery operations. Con-figurations with a single lift point, such as thatshown in Figure 2, are widely used because oftheir simplicity, versatility, and proven reliabil-ity. In such configurations, a painter line usu-ally runs from the bow of the boat to a pointforward on the ship deck. Personnel on the shipdeck often use tag lines connected to the bowand stern of the boat to maintain desired yaworientation of the boat during launch and recov-ery. When performing launch and recovery ofa boat using a single lift point, it is imperativethat the lift point be located sufficiently highon the boat to ensure roll and pitch stability.

More sophisticated lifting appliances can limityaw motions of the small craft, with the ben-efit of reducing the need for tag line hanlders.Figure 3 shows a lifting appliance that includesrestraint of the the boat in yaw using a rigidlift connection. Such connections are usuallydesigned to allow some initial yaw of the boatduring the connection process. Another com-mon approach for restraining yaw is to use adual point lift system, such as that shown inFigure 4. The lifting appliance has two cablesconnected to fore and aft points on the boat.

The selection of connection type between thelifting appliance and boat is often the subjectof much deliberation. A conventional singlelift point on the boat enables usage of a rel-atively simple lifting appliance, such as a boomcrane or articulated crane. A rigid lift connec-tion requires a more sophisticated lifting appli-ance and a tailored connection on the boat. Adual lift point system also requires a sophisti-cated lifting appliance. Operational experience

Figure 2: Boat Attached to Crane with Single LiftHook (courtesy of Welin Lambie)

Figure 3: Boat Attached to Davit with Rigid LiftConnection (courtesty of Vestdavit)

Figure 4: Boat Attached to Davit with Dual LiftPoints (courtesty of Vestdavit)

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with dual lift point systems has highlighteddangers associated with unintentional release ofone connection point while the other connectionpoint is still attached to the lifting appliance;thus, care must be given to ensure that bothconnection points are released simultaneously,and only when expected. A single point con-nection has proven to be adequate for launchand recovery at lower speeds (e.g., 6 knots andless). Experience of the United States CoastGuard [2] has led to modification of the Na-tional Security Cutter to use dual point davitsfor side launch and recovery, enabling opera-tions at higher ship speeds.

The painter line plays an important role inside launch and recovery at forward ship speed.When the boat is attached to the lifting ap-pliance and has contact with the water, thepainter line should normally be connected. Op-erational experience has led to increasing usageof a lateral boom such that the fore end of thepainter line is attached to a point extended lat-erally from the side of the ship. The usage of aboom helps to maintain a suitable gap betweenthe boat and the side of the ship during launchand recovery. Good directional stability of theboat is important for maintaining this gap andoverall safety during launch and recovery.

Figure 5 shows a boat launch and recovery sys-tem situated within an alcove on a ship. Shipstealth and protection of crew from harsh en-vironments are among the reasons for situatinga launch and recovery system within an alcove.The limited space available within an alcove canintroduce challenges for design and operation.

Launch and recovery systems continue to evolverapidly. To reduce risk to personnel, automatedmechanisms are being increasingly used for con-nections between lifting appliances and objectsbeing launched and recovered. This rapid evo-lution of systems highlights the importance ofships having the ability to be refitted with newsystems during their lives.

Figure 5: Boat Launch and Recovery System In-side Alcove on Ship (courtesty of Vestdavit)

Preliminary Ship Design Guidelinesfor Side Launch and Recovery

Table 1 gives main areas for ship design guide-lines to facilitate side launch and recovery.Each area is discussed in greater detail below.

Ship motions will be dependent on the shipitself and also on the location onboard shipselected for launch and recovery. Table 2shows RMS ship motion limits developed bythe United States Coast Guard [3]. Note thatthe originally published values were given assignificant single amplitudes, which have beendivided by 2.0 to give RMS values, which arecommonly used by NATO. Fortunately, shipmotions at launch and recovery locations canbe reliably evaluated using available numericaltools.

Deck wetness events can pose significant haz-ards to personnel during launch and recov-ery operations. Consequently, it is proposedthat a very low incidence of deck wetness in-

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Table 1: Main Areas for Ship Design Guidelinesfor Side Launch and Recovery

Ship motions

Deck wetness

Proximity to water

Visibility for launch and recovery systemoperators

Communication with bridge

Space for launch and recovery appliances andpersonnel

Ability to move objects away from launchand recovery area

Table 2: United States Coast Guard RMS ShipMotion Limits for Side Launch and Recovery

Roll angle 4.0 deg

Pitch angle 1.25 deg

Vertical acceleration 0.1 g

Lateral acceleration 0.1 g

cidence be specified (e.g., 0.1 deck wetnessevents per hour). The evaluation of deck wet-ness incidence is challenging due to the influ-ence of steady scattered waves arising from shipforward speed, radiated waves, and diffractedwaves. To account for modelling errors, a possi-ble approach is to specify that the deck wetnessincidence criterion be satisified for a location ata specified distance below the actual deck level(e.g., 1.0 m below deck level).

Launch and recovery operations become morechallenging if the distance between the shipdeck and water is large. As this distance in-creases, launch and recovery times increase. Inaddition, there will be greater variations in theclearance distance between the boat and theside of the ship. To mitigate such problems,a maximum distance could be specified for theheight of the deck above the water (e.g., 15 m).

Good visibility for launch and recovery sys-tem operators is essential for safe operations.Achievement of this requirement could be chal-lenging on ships with launch and recovery sys-tems confined to alcoves.

Communication between the bridge and launchand recovery area is required for a variety ofreasons, including ensuring that the ship trav-els at appropriate speed and heading for op-erations. Visual line of site, electronic videotransmission, and audio transmission can allcontribute to successful communications. Ship-borne aircraft operations have provided valu-able lessons in this area.

Area on deck for a launch and recovery systemmust include clearances for all operational andmaintenance envelopes. In addition to the mainlaunch and recovery area, additional space for-ward can be required for booms or other equip-ment used to handle painter lines. When de-signing a new vessel, consideration should begiven to future equipment that might requiremore space than original installations.

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It is recommended that a ship have the abilityto move objects away from launch and recoveryareas as required. For example, if a boat be-comes unexpectably inoperable, then the shipshould ideally be able to move the inoperableboat away from the launch and recovery sys-tem and move an operable boat to the launchand recovery system. A crane with 3 transla-tional degrees of freedom (DOF) (e.g., boomcrane or articulated crane) can be well suitedto this task. If the main launch and recoveryappliance has limited degrees of freedom (e.g.,rigid attachment system of Figure 3 or dualpoint system of Figure 4), then addition of aseparate crane with 3 DOF should be consid-ered.

STERN LAUNCH ANDRECOVERY USING WELLDOCKS AND STERNRAMPS

A well dock or stern ramp is often used forlaunch and recovery from the stern of a ship.Sheinberg, Minnich, Beukema, Kauczynski, Sil-ver and Cleary [4] give an overview of sternlaunch and recovery systems.

Figures 6 and 7 show well docks with craft in-side them. Most well docks are designed to op-erate with landing craft. A well dock can typ-ically accommodate a wide variety of organicvehicles, including subsurface vehicles. A ma-jor disadvantage of a well dock is that it has adrastic influence on the size and design of themother ship. Furthermore, launch and recov-ery operations from a well dock are usually timeconsuming and require many trained personnel.

Figure 8 shows a stern ramp with a RHIB.Stern ramps are commonly used to provide fastlaunch and recovery of organic vehicles, mostcommonly RHIBs. A stern ramp is usually

Figure 6: Landing Dock During Operations withLanding Craft and Rigid-Hulled Inflatable Boat

Figure 7: Landing Dock in Dry Condition withLanding Craft

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Figure 8: Stern Ramp with Rigid-Hulled InflatableBoat

designed for a specific vehicle, but can oftenhandle other vehicles of similar or smaller size.Much progress has been made recently in devel-opment of automatic systems for launch and re-covery from stern ramps. Note that automatedcapture mechanisms are often only operationalwith very specific vehicle geometries. To facili-tate operation in colder climates, the sill of thestern ramp can be placed above the waterlineto prevent ice entry. Operations using such de-signs can utilize a hinging stern door or cradleto ensure safe recovery. A stern ramp will be amajor driver in the design of the mother shipdue to demands for space, weight, and specificplacement.

Operational Guidelines for SternRamps

For launch and recovery using a stern ramp,the recovery operation is generally the limitingfactor. Horizontal motions and relative verticalmotions of the stern ramp strongly influenceoperations. These motions are dependent uponvarious aspects of the mother ship, includingsize, speed, heading, and motion control sys-tems. Operational limits are typically Sea State5 or lower.

Stern launch and recovery usually occurs inhead seas at speeds between 3 and 6 knots. Forlaunch and recovery of RHIBs with waterjets,the operational speed may be higher due to di-rectional stability concerns with the RHIB.

Preliminary Ship Design Guidelinesfor Stern Ramps

Many of the factors relevant to side launch andrecovery (Table 1) are also relevant to sternramps. Stern ramps introduce additional chal-lenges that must also be considered. Referencesby Sheinberg, Minnich, Beukema, Kauczynski,Silver and Cleary [4] and Sheinberg, Cleary, De-Bord, Thomas, Bachman, St. John and Min-nich [5] provide useful guidance regarding de-sign of stern ramps.

The ramp sill depth (the submerged depth atthe aft end of the ramp) will determine theramp availability time in a seaway. A minimumavailability time (the time the water level at thesill is high enough for the vehicle to enter theramp) is needed for a safe recovery. A greatersill depth gives higher ramp availability timeand therefore greater operability in waves; how-ever, the transom immersion associated with agreater sill depth can adversely affect ship re-sistance.

The shape of the ramp opening should be de-signed to prevent damage to the organic vehicleduring entry and exit, and must consider fac-tors such as the limited durability of the inflat-able portion of a RHIB.

The slope of the ramp must be sufficiently steepfor the organic vessel to overcome its own staticfriction for launching, but flat enough to ensurethat the organic vehicle is able to power itselfup far enough during recovery. The ramp sur-face plays a role in overcoming the static fric-tion of the organic vehicle, with low friction ma-terial being benefical. Low friction material will

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also reduce forces during recovery when the or-ganic vehicle is driven into the ramp.

The clearances around the organic vehicle playan important role in the safety of the crew onboard. Sufficient overhead clearance is critical,and must account for wave induced motion ofboth the mother ship and organic vehicle. Theside clearance must be large enough to havesome tolerance on both sides, but should re-strict excessive lateral motions. When the sternramp is designed for a variety of organic vehi-cles, adjustable side fendering should be con-sidered.

The stern doors or gates must be designed suchthat they do not impede safe operations. Forexample, overhead clearance is important forupward hinging gates. For downward hinginggates, the ability to withstand wave loads iscritical.

A water management system can contributegreatly to safe operation of a stern ramp, es-pecially in higher sea states. The water man-agement system should mitigate hazards, suchas waves rolling up the ramp and flushing outthe organic vehicle. Wave damping and waterdissipation are proven solutions.

The capture of the organic vehicle can be doneautomatic or manually. When a vehicle is op-erated from a stern ramp that was not de-signed for that vehicle, the automatic systemwill probably not work; thus, a capability formanual capture should always be available.

Roll, pitch, vertical acceleration and lateralacceleration of the mother ship will influencestern ramp launch and recovery. These mo-tions must be considered when evaluating rampavailability time.

AIR VEHICLE LAUNCHAND RECOVERY

Modern frigates and destroyers include thecapability to launch and recover helicopters.Many ships include sophisticated mechanicalsystems that include a cable with automatedtension between the helicopter and flight deck,increasing the operational envelope for launchand recovery operations [6].

Typically, the flight deck on a frigate or a de-stroyer is at the stern, behind the deckhouseand all of its mounted equipment, as shown inFigure 9. As the helicopter approaches to land,it encounters a complex air wake behind thesuperstructure. The air wake contains time-varying combinations of turbulence, vortices,shear flow and downwash, for which the pilotmust compensate to keep the helicopter undercontrol. The ship is also rolling and pitching inresponse to the seas it is encountering.

Figure 9: Helicopter on Approach to Land on De-stroyer

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Flight test launches and recoveries are done forevery combination of helicopter and ship in or-der to assure that these operations will be safe.The ship is driven at various speeds and head-ings relative to the wind and sea in order tofind relative wind limits beyond which the testpilots determine it would be unsafe to take offor land. The pilots are given a workload rat-ing scale to rate each launch and recovery asto its difficulty. The results are used to gener-ate ship-helicopter operating limits (SHOL), interms of relative wind speed and direction, thatthe ship operators and helicopter pilots can use.A typical envelope is shown in Figure 10. Dur-ing the test flights, the deck crew take readingsfrom the ships inclinometers of pitch and rollamplitudes. At the limits of relative wind, themaximum pitch and roll amplitudes are citedas guidance for the ship operators.

Figure 10: Typical Ship-Helicopter OperatingLimits (SHOL)

Over the years, as shipboard helicopter oper-ations expanded, it became apparent that theship designer needed sets of relative wind and

motion limits to assure that new ships wouldbe safe for these operations. Subject matterexperts from seven NATO nations assembledto produce an updated seakeeping standard [7]including more detailed treatment of air oper-ations. The document contains limiting shipmotion criteria for a variety of missions. Thedocument also references ship motion predic-tion programs that can be used to determinewhich sea states will cause limiting motions tobe exceeded. For a ship that is required to carryout a specific set of missions, the designer canuse sets of the criteria to refine the ship designfor best performance in the ocean wave condi-tions that the ship might encounter in selectedoperating areas of the world.

For fixed and rotary-wing aircraft launch, re-covery and handling, the NATO seakeepingstandard contains generic limiting motion cri-teria and generic relative wind envelopes. Forspecific aircraft and ship combinations, eachwith its unique limiting motion and relativewind characteristics, the ship designer has torely upon the results of dynamic interface seatrials on existing aircraft and ship combina-tions, and hope that he or she can find com-binations that are close enough to those of thenew ship being designed.

In the discussion which follows, fixed-wing he-licopter operations will be used to show whereimprovements can be made to the guidancegiven in the existing NATO seakeeping stan-dard. Limits for vertical and short take off andvertical landing (VTOL and STOVL) opera-tions are based on an air capable ship compar-ison by Comstock, Bales and Gentile in 1982[8] in terms of generic criteria, which could beused as default values for any design study.Specific criteria were not publically availablefor many combinations of aircraft and ships.Thus, generic criteria were presented in termsof limits for roll, pitch, vertical velocity andrelative wind (see Table 3). These limits are

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defined to permit launch and recovery of air-craft within established operational envelopes.Observations during sea trials suggested that,on an approach to landing, vertical accelera-tion of the flight deck is of more concern thanroll or pitch. Indeed, vertical acceleration is amanifestation of heave, roll and pitch and thedistance from the center of gravity of the ship.

Table 3: Generic Helicopter Launch and RecoveryCriteria Limits

Operation Performance limitations

Launch Roll 2.5o RMS

Pitch 1.5o RMS

Relative wind (Figure 10)

Recovery Roll 2.5o RMS

Pitch 1.5o RMS

Vertical velocity 1.0 m/sRMS at flight deck

Relative wind (Figure 10)

The generic envelope shown in Figure 11 rep-resents the limits of relative wind speed, withrespect to relative heading, into which the air-craft may be launched or recovered. Launch orrecovery outside of the safe envelope results inunacceptable crosswind or turbulence for safeand efficient operation. By mapping this enve-lope into the plane of possible ship speeds andheadings for the ambient winds associated witheach sea condition, wind envelopes satisfyingthe relative wind requirements can be defined.Figure 12 shows an example of this mappingfor mid Sea State 5 with a mean ambient windspeed of 22 knots. The operating envelope isthe non-shaded region.

Figure 11: Generic Helicopter Relative Wind En-velope

Figure 12: Generic Helicopter Wind OperatingEnvelope for Sea State 5 with Mean AmbientWind of 22 knots

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During the time since writing of the NATO sea-keeping standard [7], computational methodshave been developed to determine the effects ofvarious ship topside design features upon theship’s air wake, and in particular various fea-tures of the air flow over the flight deck as anincoming aircraft would encounter it. This in-cludes combinations of turbulence, downwashand shear flow for different ship speeds andheadings relative to the ambient wind. Aircraftaerodynamics have been coupled to the ship’sair wake in such a way that control marginsand variances, and thus pilot workload, can bepredicted. Model tests have been used to checkthe results and to help refine the computationalmethods. Though more work needs to be doneto validate the methods, the results have beenused successfully in flight simulators to predictthe relative wind envelopes for a few new com-binations of aircraft and ships, even in earlydesign stages before physical models were builtand tested.

Since 2002, three successive research taskgroups from the NATO Applied Vehicle Tech-nology (AVT) Panel have assessed various as-pects of the evolving science and technology ofaircraft launch and recovery in a ship air wakeenvironment. The third of these, NATO RTGAVT-217, completed its program of work in De-cember 2015, and submitted a technical reporton Modeling and Simulation of the Effects ofShip Design on Helicopter Launch and Recov-ery [9] to the NATO Collaboration Support Of-fice for final editing before publication. The fo-cus of this work was on critical technical areaswhere details of ship design would affect theperformance of helicopter launch and recoveryfrom a flight deck at the stern of the ship. Crit-ical technical areas included:

• Air wake – an evaluation of the methodsavailable to compute features of the airflow behind the ship superstructure and itsinteraction with the aerodynamics of the

helicopter, including shear flow, downwashand turbulence. As to the design of thesuperstructure, for the methods used, it ispossible to model the shape of the deck-house and all appendages including anten-nas, stacks, and weapon systems. It is alsopossible to evaluate flow control devicessuch as turning vanes and fences.

• Anemometer placement – an assessment ofthe methods employed to locate anemome-ters on the ship superstructure in order toreliably determine relative wind speed anddirection for helicopter operations.

• Ship exhaust – an evaluation of the effectsof stack gas, including increases in temper-ature, on power margins in the helicopterand ways to mitigate the effect by betterplacement and design of stacks and possi-ble redirection of the gas plume.

• Ship motion – an assessment of the abilityto predict the motions of the flight deckand their effects on launch and recoveryof different combinations helicopters andships.

The NATO RTG AVT-217 technical report alsoincluded an assessment of the capability to in-corporate the findings of each of the criticaltechnical areas into integrated modeling andsimulation of the effects of ship design on thelaunch and recovery of helicopters. Once thefinal draft of the technical report is approvedfor release to NATO nations, it will be usedto prepare an Allied Naval Engineering Pub-lication (ANEP) on ship design guidance forsafe launch and recovery of helicopters. TheANEP will supplement guidance presented inthe NATO seakeeping standard [7] in order torefine the flight deck wind and motion limits fora variety of new aircraft and ship combinations.

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APPLICATION OFMODELLING ANDSIMULATION

Modelling and simulation (M&S) can be veryuseful when designing ships that will performlaunch and recovery operations. The maturityof available tools depends largely on the com-plexity of phenomena being investigated.

M&S for Ship Motions

Ship motion predictions are routinely per-formed to support ship design and operation.When applying ship motion predictions to shipsperforming launch and recovery, the complex-ities of ship motions are somewhat simplifiedbecause operational conditions normally dic-tate relatively small forward speed Froude num-bers (e.g., U/

√g L < 0.2, where U is ship

forward speed, g is gravitational acceleration,and L is ship length between perpendiculars)and moderate wave conditions (e.g., significantwave height rarely exceeds 7 m).

Frequency domain strip theory [10] is widelyused and gives good results for slender ships(e.g., length-to-beam ratio L/B > 6) in typi-cal launch and recovery conditions. For non-slender ships, three-dimensional methods forpredicting hull forces [11] will give noticeablybetter motion predictions than strip theory.Due to challenges predicting viscous roll damp-ing, vertical plane motions are easier to predictthan lateral plane motions [12].

M&S for Relative Vertical Motionsbetween Ship and Ocean Surface

Relative motions between the ship and theocean surface have a profound influence onlaunch and recovery of waterborne objects. Forside launch and recovery, relative motions are

a major driver for locating launch and recoverysystems near midships. For stern launch andrecovery, experience has shown that operationswith longer vessels can be challenging due tohigh relative motions at the stern.

When evaluating relative motions at a locationon a ship, it is common practice to considerthe rigid-body ship motions and incident waves,but to ignore the radiated and diffracted wavescaused by the motions and presence of the ship.Beck and Loken [13] provide insight into theinfluence of radiation and diffraction on rela-tive motions. The current high level of inter-est in launch and recovery will likely stimulatenew work examining relative motions in greaterdetail. Note that many ship motion predic-tion methods use simplifying assumptions whenmodelling the influence of ship forward speedon the free surface. Although these simplifyingassumptions are quite acceptable for predictingship rigid-body motions at moderate forwardspeed, their adverse influence on relative mo-tion predictions are likely more pronounced.

Multi-body Simulation

Capabilities continue to progress for simulatingmulti-body complex systems, such as launchand recovery of an object from a ship. Complexphysical phenomena can be modelled, includinghydrodynamic interactions and collisions be-tween entities. Henry, McTaggart, de Kraker,and Duncan [14] describe a simulation of alaunch and recovery system for a NATO subma-rine rescue vehicle which is deployed from thestern of a ship using an A-frame. Söding andReppenhagen [15], McTaggart, Roy, Steinke,Nicoll, and Perrault [16], and Carette [17] de-scribe simulations of launch and recovery fromthe side of ships.

Multi-body simulation presents various chal-lenges, including the interoperability of vari-ous simulation entities. Validation of multi-

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body simulations is challenging, with the tran-sient nature of launch and recovery being acontributing factor. Fortunately, progress con-tinues to be made due to the high priority oflaunch and recovery work among navies. Fig-ure 13 shows a recent simulation of a RHIB be-ing launched from a frigate. Multi-body simula-tions can provide insight into various phenom-ena, including crane loads and RHIB motions.

Figure 13: Simulation of RHIB Being Launchfrom a Frigate

M&S for Air Vehicle Launch andRecovery

The NATO AVT-217 Technical Report [9] dis-cusses the state-of-the-art in modeling and sim-ulation of manned and unmanned helicopterlaunch and recovery, and how it is being used tooffer ship design guidance. M&S provides thedesigner with the potential capability to eval-uate a new ship design in terms of its impacton the aircraft and pilot workload, includingthe effects of air wake, ship exhaust and shipmotion.

Many different types of ship-aircraft simula-tions exist, including computational, experi-mental and flight simulation methods. Thesemethods are at varying stages of developmentand verification and require different levels ofresources (computational, temporal, and finan-cial) to execute them.

M&S can be used as a risk reduction tool forship design by identifying potential problemsfor aircraft operations prior to ship build. Cur-rently, the available tools can inform the designprocess when used as part of an iterative designcycle. For example, comparative analysis of anew platform compared to an existing platformcan be used to estimate whether an improve-ment to the air wake has been achieved with acertain design change.

Post ship build, simulation can be used to iden-tify limiting wind conditions to potentially re-duce the time required for Ship-Helicopter Op-erating Limits (SHOL) testing. Although thisprocess has yet to be fully validated, it couldbe used in the near-term to inform the SHOLprocess and assist in test planning.

CONCLUDING REMARKS

The NATO Seaway Mobility Specialist Teamcontinues its efforts to develop a new standardto ensure that ships are able to support launchand recovery operations throughout their lives.These efforts will be supported by experiencesshared by others and also by new work, in-cluding application of modelling and simula-tion. Ongoing dialogue with the naval launchand recovery community will be essential dur-ing development of the new standard.

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[2] M. Haycock. Overview of launch andrecovery onboard U.S. Coast Guardcutters: Requirements, state-of-the-artand future developments. In Launch andRecovery Symposium 2014, Linthicum,Maryland, 2014.

[3] C. Cleary. In-service launch and recoverypanel discussion. In Launch and RecoverySymposium 2014, Linthicum, Maryland,2014.

[4] R. Sheinberg, P. Minnich, T. Beukema,W. Kauczynski, A. Silver, and C. Cleary.Stern boat deployment systems andoperability. Transactions, Society ofNaval Architects and Marine Engineers,111:1–32, 2003.

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[6] R. Langlois and P. Keary. Methodologyfor ensuring safety of an embarkedhelicopter securing system probeinstallation. In Congress of theInternational Congress of AeronauticalSciences, Toronto, Canada, 2002.

[7] North Atlantic Treaty Organization.Common Procedures for Seakeeping in theShip Design Process, 2000.Standardization Agreement No. 4154,Edition 3.

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[13] R.F. Beck and A.E. Loken.Three-dimensional effects in shiprelative-motion problems. Journal of ShipResearch, 33(4):261–268, December 1989.

[14] G. Henry, K. McTaggart, K. J.de Kraker, and J. Duncan. NATO virtualships standards. In SimTecT 2008,Melbourne, Australia, 2008.

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[16] K. McTaggart, A. Roy, D. Steinke,R. Nicoll, and D. Perrault. Simulation ofsmall boat launch and recovery from aship with a crane. In Launch andRecovery Symposium 2012, Linthicum,Maryland, 2012.

[17] N. Carette. Model tests and time domainsimulations for launch and recoverysystems with manned and unmannedvehicle. In Launch and RecoverySymposium 2014, Linthicum, Maryland,2014.

AUTHOR BIOGRAPHIES

Kevin McTaggart is a Defence Scientist atDefence Research and Development Canada.He has a Ph.D. in civil engineering from theUniversity of British Columbia. His research in-terests include ship motions in waves, ship ma-neuvering, and distributed simulation of shipsystems. He chairs the NATO Seaway MobilitySpecialist Team, which is producing standardsfor ship maneuvering, seakeeping, and ship de-sign for launch and recovery.

Sietske Hendriks is a hydromechanical engi-neer at the Dutch Defense Materiel Organisa-tion. She graduated with a master of science inmaritime technology from the Technical Uni-versity of Delft. Her work includes researchon ship motions in waves, including fast smallplaning craft and launch and recovery. She isthe national delegate to the NATO Seaway Mo-bility Specialist Team and is a member of JIPLAURA.

Ian Nimmo-Smith Ian Nimmo-Smith is anaval architect with the United Kingdom Min-istry of Defence. He works in the Naval Au-thority Group providing technical assurance forconstruction, stability and hydrodynamics tothe Royal Navy and wider defence community.He has masters degrees in civil engineering andnaval architecture and is the UK delegate tothe NATO Seaway Mobility Specialist Team.

Arild Øydegard is the head of the Naval Ar-chitecture Section in Norwegian Defence Ma-terial Agency. He has a bachelor’s degree inmilitary technology from the Royal NorwegianNaval Academy and master’s degree in marinehydrodynamics from the Norwegian Universityof Science and Technology. He is the Norwe-gian delegate to the NATO Seaway MobilitySpecialist Team.

John Pattison is a senior scientist and en-gineer part time with BAI Incorporated inAlexandria, Virginia, USA. In 2003, he retiredfrom the Naval Sea Systems Command wherehe was the director of ship hydrodynamics tech-nology. Since then, he has consulted with theOffice of Naval Research in their work withthe NATO Applied Vehicle Technology Panelin evaluations of the science and technology forshipboard aircraft operations.

Norbert Stuntz is head of the hydrodynamicbranch at the Bundeswehr Technical Center ofthe German Ministry of Defence. He is respon-sible for the hydrodynamic aspects of the Ger-man Navy ships from initial design to end oflife.

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