A propososal for a Royal Navy FLO FLO heavy lift transport ship

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Float on FLoat Off (FLO-FLO) heavy lift ships are incredibly versatile, the Royal Navy, or perhaps more accurately, the Royal Fleet Auxilliary (RFA), should evolve their future plans to include one, two would be better.

The US Expeditionary Transfer Dock and Expeditionary Mobile Base

The US Expeditionary Transfer Dock vessel is an interesting example of a FLO-FLO ship, useful to inform wider discussion

The US sea basing concept envisaged a far offshore collection of logistics and combat vessels that could deliver forces and all their sustainment needs directly to the objective without needing to build up stores at a beach location or operate in vulnerable areas close to shore. The sea base would eliminate the need to organise, redistribute and repack supplies onshore, and palletise what was needed, to order, all whilst afloat. Technical challenges included asset visibility in the deployed logistics management system, ship to ship transfer of stores and vehicles in high sea states and very high fuel usage rates for the high speed connectors (LCAC, CH-53K and V-22). The planning requirement for a fourteen thousand strong Marine Expeditionary Brigade (MEB) is just under a thousand tonnes per day and even with the excess of airlift available to the US forces it was not deemed practical at distances greater than 60 nautical miles offshore.

It is important to recognise that this was not for the assault phase but in order to provide the throughput required to sustain the ashore force at the stand-off distances envisaged, the only sensible option was a high speed surface connector, the LCAC hovercraft. Neither is it used with amphibious assault shipping, instead, the landing platform is used with logistics vessels, the Large Medium Speed Roll On Roll Off (LMSR) for example. If it were to be contextualised in UK terms, it would be one of the Point ‘class’ strategic RORO vessels.

One of the initial concepts was called an Interface Landing Platform which would be carried ‘side loaded’ in a similar fashion to a Mexeflote on a Bay Class vessel, unloaded in-situ and then recovered when not needed. This was a simple, cheap and quick to deploy concept but somewhat size limited.

A mobile landing platform concept was advanced that examined a number of vessel configurations.

The concept of using a semi-submersible vessel to allow the LCAC to ‘drive on’ was proven with the M/V Mighty Servant 3, a commercial heavy lift Float On Float Off (FLO-FLO) vessel, as shown in the image below.

There has been much change since these early iterations of the sea-base concept but one of the survivors is the landing platform, now called the Expeditionary Transfer Dock. Instead of a commercial heavy lift FLFO vessel with superstructure forward, the final design is a NASSCO modified Alaska Class Tanker

Video 1

Video 2

Video 3

The large deck area affords the crew the ability to turn and queue vehicles to maximise flexibility and throughput, certainly an advantage over the smaller ILP.

It does add cost though, the vessels were not cheap and it is hard to avoid view that the US is often guilty of recreating what it already has but at great expense. The existing method of offloading RORO ships is for vehicles and containers to be driven down the ships ramp onto a floating platform called a Roll On Roll Off Discharge Facility or RRDF.


They are then transferred from the platform to lighters and landing craft.


When weather and sea conditions preclude safe operation of the RRDF vehicles and equipment will be loaded onto lighters over the side rather than driven off the RORO ramp.


Unsurprisingly, there is a Navy and Army version.

RRDF comparison

RRDF has also been used with LCAC’s

Because of doctrinal and scale differences, the lack of high speed connectors and cost, it would be difficult to envisage the UK adopting a similar, highly specialised, vessel.

More likely would be to develop further the Strategic RORO/Mexeflote combination.

Three of the five contracted ‘MLP’ vessels have been delivered in a different configuration, the Afloat Forward Staging Base, or Expeditionary Mobile Base as it is now known. For this second role (ESB), the large open deck is fitted with a prefabricated module that has space for small craft, unmanned systems and helicopters.

Includes a two-spot flight deck, hangar facility, helicopter fueling capability, ordnance storage, operation planning and work spaces, and berthing for 101 permanent military crew and 149 personnel of an embarked military detachment.Has a mission deck below the flight deck with a crane for storing and deploying the various mine-hunting and clearing equipment used with the MH-53E helicopters; explosive ordnance demolition boats and equipment may also be stored and handled on the mission deck.

Although many seem to focus on the more glamorous aspects of the ESB, the MCM role seems to be well suited to a future that includes and increasing reliance on off-board stand-off systems.

To support Airborne Mine Countermeasure operations including hosting a squadron of four legacy MH-53E helicopters. Provide storage and deploying capabilities of the various mine-detecting and clearing equipment, which are used with the helicopters. To support explosive ordnance demolition boats

The media below show some of the key features.

Lewis Puller ESB (2)

Lewis Puller ESB (7)

Lewis Puller ESB (9)


There is a very good write up of the the type here

Would something similar be useful for the UK?

Perhaps yes, but it is difficult to see the significant advantages over using a Bay class vessel and Mexeflote given the cost and the simple fact that the UK has long since moved away from amphibious operations at scale. Given the UK has no defined requirement for amphibious ‘sea basing’ logistics and no spare cash either, this post would naturally end here. That said, where it is arguably worth taking the discussion forward is in the context of a broader future requirement and see where it takes us.

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A Heavy Lift Vessel for the Royal Navy

Several years ago BMT looked at the options for replacing RFA Diligence under the Operational Maintenance and Repair (OMAR) study. It concluded that the optimum solution was an unpowered barge carried to the area of operations on Float On Float Off (FLOFLO) heavy lift vessel. The barge was 120m x 30m and displaced approximately 3,500 tonnes.

OMAR BargeThe study suggested using a FLOFLO vessel of opportunity or one on a long term charter. With the withdrawal of RFA Diligence and pending withdrawal of RFA Argus,  it is perhaps worth another look at the general concept.

Putting aside heavy lift barge/tug combinations, there are three basic configurations for a heavy lift ship;

Lift On Lift Off; the ship has a large open deck area onto which outsize and extremely heavy cargos are lifted on and off using dockside or integral cranes.

Roll On Roll Off; the payload is moved on-board using multi wheeled heavy lift platforms called Self Propelled Modular Transporters (SPMT). Ballasting allows a straight path to be established between the ships deck and quayside

Float On Float Off; the deck area flooded after ballasting down to an appropriate depth and the cargo manoeuvred in, usually with tugs, although when transporting smaller vessels, they can self-load. The ship is ‘re-floated’ and secured for the journey.

Different ships can use one or more of these methods, the most flexible being able to use all of them.

Movable Deck

The more one looks at the above the more they start to look like one of these…

A robust, cheap and adaptable vehicle which is used for shifting stuff, or with the addition of ‘modules’ a more integrated device for more complex roles.

Operators include Jumbo MaritimeBigroll, Dockwise, RollDock and Combilift. For transporting leisure craft, Yacht Transport provide a specialised service, the FLO-FLO vessels generally have higher capacity accommodation for the yacht crew.




Yacht Transport

The Combi Dock is longer than the Roll Dock ST class, 170m and 151m respectively, but in other regards, they are very similar.

Rolldick 1

Moveable deck panels are used to create a deck at one of six levels and a temporary bulkhead can also be installed to allow the vessel to be submerged without flooding the cargo hold. The cranes can be used together for a tandem lift of approximately 700 tonnes.The hold has enough space for 1,383 TEU .








RollDock 1

Rolldock 3

Overhead view

RollDock 4


RollDock 5

With a little shaved off the width, the BMT OMAR barge would fit perfectly on the cargo deck.

The M/V Combi Dock cost €100m to build, these are not expensive.

Interestingly, the later vessels in the Combi Dock series have been purchased and converted for use in the offshore industry

The OIG Giant II, formerly Blue Giant, formerly Combi Dock IV, is just such a conversion. The work included modifications to the cranes (anti heave and lift extension) and adding a helideck, moon pool, accommodation module, additional generators and a Dynamic Positioning system using azipods and thrusters. The 500 tonnes 13mx18m accommodation module is built across seven decks and includes facilities for 86 personnel, including leisure, sleeping, work spaces and water/waste treatment.

A new build contract at the same ‘offshore’ specification for two was reportedly €200m for the pair.

Giant 1


Vessel Conversion Video

If the UK is going to make use of such a design the mantra must be ‘minimum modification’ but would the heavy lift cranes really be needed, probably not.

If there were no FLOFLO or RORO capacity, there might be an argument for retention, but otherwise, there is no real need for them. The only thing they would be used for is lifting the hatch covers in and out of the cargo hold. Using a fixed crane, 3 in the case of the Combi Dock, allows the entire length of the cargo deck to be covered, but it does mean they have to be hefty enough for the weight at a specific outreach.

An alternative to the very expensive heavy lift cranes might be smaller travelling rail cranes such as those used in the offshore anchor handling industry. The large ones can lift 10-15 tonnes so when acting in tandem, a pair could easily lift the hatch covers.

Rail Crane

A different view is that the cranes could be used for lifting small craft, or even larger patrol craft as part of a ‘mothership’ type approach. They would also be problematical if any of the larger modules used an aviation capability, obviously they would be a hazard. Leaving the centre crane in place but removing the other two would allow it to be stowed in a forward position for aviation operations but this would limit the amount of cargo deck it could cover, there would be gaps to the front and rear.

This assumes the jib length is the same.

By accepting a lower lift weight than 350 tonnes, a longer jib length would allow a single crane, at the cargo deck mid-point to cover the entire deck. A 60m jib length crane, with heave compensation, is available from MacGergor, Liebherr and others. Passive heave compensation could also be used for traversing the splash zone.

A few different crane options to consider, but that would be about it for the changes save for specific communications or other such systems.

Roles and Modules

The question remains though, what would they be used for?

There are two role categories, straightforward transportation and more complex missions that will likely include some form of ‘module’.


Over 1,300 TEU’s is a lot, but easily carried by the Combi Lift design described above.

They can be lifted on and off using harbour or the ships own crane. Containers could also be off loaded whilst at sea, the heave compensated crane allows much safer operation without pendulation. The containers could be loaded onto Mexeflotes, landing craft or other lighters. With a single crane, this would not be a particularly fast option though.

Containers could be simple dry types, tank containers or other specialist shelters.

A 20ft Tank Container, for example, could hold 24,000 Litres of water, fuel or other liquids.

At 4m width, there is 528 Lane Metres, with vehicles using a shore based loading ramp or lifted in and out. This would be across two decks using the standard hatch covers only, each deck being just over 4m high. There would also be space on the hatch covers if it were permissible to carry vehicles exposed to the elements.

The USMC used the MV Combi Dock III for just such a deployment

As with containers, the vehicles could be easily lifted onto lighters whilst at sea, in reasonable sea states.

Because the vessels are semi-submersible, they can be used ot transport small craft and patrol boats, and even submarines.Smaller craft such as patrol boats or MCM unmanned boats could simply be lifted from the deck into the sea. Using the two deck approach, the vessel could comfortably transport 110 Pacific 24 RHIB’s, more than we have in service.

Where this gets interesting though is with larger vessels.

A crane lift would be preferred because the lengthy docking down process would not be required.

Lift On Boats

With one crane, a 350 tonne limit allows a range of fast patrol craft, work boats and hovercraft to be transported to theatre. To be fair, we don’t actually have many of these, but with a credible deployment capability, we would be able to exploit the type of patrol craft we don’t have precisely because we have a need for global deployability but no means of doing it at short notice within our control. Anything up to 20m should be a simple lift, weather and sea conditions dependant.

To provide some sense of scale, a handful of examples.

Landing Craft Vehicle Personnel (LCVP) Mk5; these smaller craft are generally used for personnel only although they can carry small vehicles and light stores up to a weight of 6 tonnes.

One FLOFLFO could carry 21 LCVP Mk5 on a single deck, more than we have.

Army Work Boat; in addition to a number of Combat Support Boats, 51 (Port) Squadron RLC have four Army Work Boats made by Warbreck Engineering in Liverpool, subcontracted to VT Halmatic (now BAE).

One FLOFLO could carry 21 Army Work Boats, also more than we have.

Offshore Raiding Craft; Designed and built by Holyhead Marine, the Offshore Raiding Craft is in service with the Royal Marines used in insertion, patrol and security operations.

One could carry 44 ORC’s, more than we have.

Hovercraft; The £1 million Griffon Hoverwork 2400 TD LCAC(L)(R) was a direct replacement for the 4 existing LCAC’s and feature armoured panels and bulletproof glass in addition to greater performance.

One could carry 16 2400 TD’s, more than, well, I think you get the picture!

Island Class; the CAMARC designed and Holyhead Marine manufactured Island Class Patrol Boats are used by the Royal Marines to protect high value Royal Navy shipping on the Clyde, Gare Loch and Long Loch.

If we wanted, a FLO-FLO ship could carry them all

Landing Craft Utility (LCU) Mk10; Part of the programme for the Albion and Bulwark LPD’s were new Landing Craft Utility, Mk 10, replacing the Mk9’s carried aboard HMS Fearless and Intrepid.

LCU-01-Image-Plain-MilitaryOne FLOFFLO could carry 8 LCU Mk10, the full number in service.

When used in the simple transport role a single Combilift type vessel could carry a significant quantity of vehicles, containers and other dry cargo. By utilising the semi-submersible capability this opens up a whole host of opportunities for using them as a means of transporting smaller craft and patrol vessels.

As the Royal Navy moves to offboard MCM, it is easy to envisage a collection of such systems being deployed from the UK in response to an emergent crisis.


If we consider the huge open hold to be a space into which we put ‘modules’, the potential adaptability of a CombiDock type FLO-FLFO vessel can start to be envisaged.

Mention the word module and people tend to think of the Royal Danish Navy Stanflex or the US Navy’s LCS, and jump straight in with why it is a bad idea. The reason for this is twofold, it may well be a bad idea, but mostly, because the wrong reasons for modular payloads are highlighted. The idea that a seaframe can be an ASW frigate one minute and a MCM vessel the next, purely by virtue of swapping a few modules is clearly suspect. For these highly complex and difficult tasks, ship system crew must be focussed and integrated. But if the idea of changing roles and modules every other week is put to one side, modularity starts to make a lot more sense.

Common physical attributes, electrical, data and other interfaces, compliance with a set of known standards and even common lifting points allow the module to be developed in isolation from whatever is carrying it and fitted to a vessel without each vessel being redesigned to suit. As systems and ships evolve at different speeds the benefits of this become obvious. Add ease of maintenance, damage repair, familiarity and training, and the arguments for modular payloads become compelling.

But we need to be pragmatic, we need to be realistic about what can usefully be modularised and we need to be certain where the limits lie.

The offshore industry is a long standing user of modular systems and approaches. Beyond various stores containers, there are accommodation, power generation, compressors, medical, laboratory, ROV launch and recovery, workshops and even blast resistant refuge modules for use on production platforms. All of these are based on the familiar ISO container format. For use in the offshore industry, these modules have to comply with a significant amount of safety related regulation including maintenance of a positive pressure environment and high levels of fire resistance.

Accommodation and welfare modules, with different densities and build standards, shown below.

Sleeper Module 2

Sleeper Module 3

Using these would be similar the the offshore industry variant shown above, maybe just for the crews of vessels or vehicles being transported.

For more complex roles, more complex modular fit outs are available.

Workshop Module

Data Centre Module

It is easy to envisage a variety of ISO container sized modules being used to support different roles and requirements. Add in a demountable deck shelter and one or two other systems and this could be expanded to encompass the MCM ‘mothership’ role or as an afloat base for a collection of small vessels and hovercraft in the littoral security role.

Of course, it would not be a warship, so the temptation to think of it as one must be avoided but the flexibility to experiment with different configurations using a cheap but flexible base hull is the embodiment of ‘payloads not platforms’

The options above focus on transportation and the ability to utilise 20ft ISO container modules to expand accommodation or enable more complex roles but if we look at the unique design of the ships and systems used in the offshore industry, another option presents itself; the Maxi Module.

The Combi Dock is designed to accommodate very large constructions, weighing hundreds or even thousands of tonnes. FLO-FLO loading can accommodate a maximum load of 7,000 tonnes and RORO, 4,000 tonnes.

Instead of the twenty tonne module we should lift our horizons and look at the thousand tonne module.

Module 3

The Primary Casualty Receiving role, in reality, is used infrequently, major combat operations or unusual deployments like Operation GRITROCK, the ebola response. And yet despite this low usage rate, the demands of the role require a complex fit out, which means a dedicated vessel and not a collection of ISO modules lashed to a deck. This is the dilemma for some of these roles that are only valued in combat operations, they are infrequently used, and so a vicious circle appears. We might be able to allocate secondary roles to improve utilisation but the odds are always stacked against them in budget discussions.

RFA Argus Hospital 3

Facilities required include resuscitation, operating theatre, intensive care wards, advanced diagnostics (X ray, MRI etc), recovery wards, sterilisation, pharmacy, hyperbaric facilities, blood/blood component storage, medical waste disposal, command and control, laboratory, dental, isolation, medical gas handling, power generation, uninterruptible power supplies, storage space, catering, mortuary, laundry, extensive communications for telemedicine and a computing environment that supports the secure generation, storage and processing of large volumes of data.

Building the PCRS capability into a large module allows it be stored onshore and used as a training facility but when needed for a planned deployment, wheeled on to the FLOFLO ship and deployed to the operational area.

Module 6

An MCM command module could include UUV/USV storage, aviation, command and workshop spaces all within a single structure.

Module 2

For repair, maintenance and salvage, the Maxi Modules would be arranged to include heavy, electrical and composite workshops, electronic workshops, stores, personnel accommodation, helicopter landing facilities, stores lifts, power generations, compressors, extensive diver support

Module 5

By maintaining a realistic view of what can be achieved it is certainly possible to envisage a range of configurations and designs for such ‘go large’ modules. Storage and moving onto the empty vessel is entirely normal in the heavy lift industry, it really is a common occurrence.


If all the vessel is used for is a transfer dock for a non-existent amphibious capability then of course, the justification for such a vessel is zero, but if we utilise a commercial design with superstructure forward there are many alternatives and a great deal of potential.

Above all, it provides the basis for experimentation and developing capabilities as we go.

Starting with a simple transport vessel the inherent flexibility to move cargo, vehicles and small craft/hovercraft is valuable. Add in some modest accommodation modules and the value increases but where it gets interesting is the ability to create demountable modules at ‘large scale’ for expanding the role menu list.

A few ideas…

Humanitarian Assistance Disaster Response; Transport of stores, personnel and the ability to deploy multiple landing craft, helicopters and pontoons.

Training and Defence Engagement; a lot of space means a lot of training opportunities and the aviation facilities would also allow that be included in the training matrix.

Maritime and Littoral Security; with a combination of multiple helicopters, UAV’s, RHIBS and larger patrol craft, and even hovercraft, it would be a very good ‘mothership’

Medical Support; Using a large module, a Role 3 medical facility could even be combined with another like an engineering and repair module. A single vessel could then deliver against multiple requirements.

Salvage, Repair and Fire Fighting; by retaining the large crane, using a modular workshop facility (similar to those used in the land environment) and modular diver support system, it would provide excellent salvage/repair and submarine tender facilities.

Experimentation and Systems Development; I think it would be taken for granted, that the large open deck, crane, services connectivity and additional accommodation would provide a very good platform for experimentation and systems development, especially emerging unmanned surface vessels and aerial vehicles.

MCM and Survey; It would be able to carry many off-board platforms, host emerging unmanned aerial vehicles in the MCM role, and carry out the MCM command function for larger and/or enduring deployments. Its excess space and excellent handling facilities, coupled with accommodation for many personnel, would make an interesting system, if unmanned systems mature as expected.

Ship to Shore Logistics Support; in addition to carrying supplies, vehicles, personnel and engineering plant for port repair, another suitable task would be that of providing a ship to shore fuel transfer capability. It would also be able to carry a great deal of supplies in their own right

Special Forces and Intelligence Support; whether carrying raiding craft, small landing craft, vehicles, personnel or even a swimmer delivery vehicle, the carrying capacity and flexibility afforded by the main deck space would provide obvious utility for special forces. Containerised signals equipment could also be used to provide an additional and innocuous capability for gathering intelligence. Unmanned systems would also be potential carries and the aviation capacity would provide another valuable enhancement.

Am sure there are many others.

Is any of this possible or wothwhile, am not a naval architect or requirement manager so I genuinely don’t know, but as ever, this is just a converstion opener.

Maybe when we next look at the strategic RORO contract we could include one these and take it from there?

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 01/01/2018 Initial issue
 22/07/2021 Format refresh 
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