A Ship that is Not a Frigate – Part 3 (Design Discussion)

Rolls Royce patrol vessel

One of the trends seems to favour compact vessels and then shoehorn as much equipment as possible and in a nod to those secondary roles, squeeze in a couple of containers spots and call that job done, again, a distortion of priorities.

Although the well-worn phrase about cheap steel and free air only has some validity in the round, it is worth noting that ‘going large’ does not necessarily increase costs proportionally and space affords a great deal of flexibility.

A custom-designed ship can draw together a set of requirements and balance length and beam to create the optimal mix of space, seakeeping, stability and economy.

However, that all sounds expensive so SIMSS is based on an in-service, tried and tested commercial platform design.

The Offshore Supply Vessel is designed for low cost, durability, flexibility, capacity and excellent sea keeping so it is this on which SIMSS is based.

These vessels have pioneered a number of complementary technologies such as unmanned systems, moon pools, small boat launch ramps, heave compensated cranes, modular accommodation and in an interesting development, dual diesel/LNG power generation and propulsion.

There is much to learn from the civilian offshore sector and some of the work done in the USA on the HSV and Sea Fighter programmes.

A common baseline ship can be reconfigured to cover the roles described in the previous post and systems evolved over time on different development paths.

The start point for SIMSS is an already established design, the offshore platform supply vessel. Modifications would of course be required but the maturity of the basic design strips the project of a great deal of risk and contributes to the depressed cost of SIMSS. A bespoke design might be the ‘better’ solution but SIMSS is not about perfection but god enough.

There are a number of variations on the basic offshore support vessel theme; the main ones are Platform Supply (PSV), Anchor Handling Tug Supply (AHTS) and a number of specialist construction or Multi-Purpose Support Vessels (MPSV)

The PSV is the simplest, just basic cargo carrying. The AHTS adds high capacity winches, cable handling cranes and deck fittings and the final, more complex category usually adds large cranes, moon pools, ROV handling and storage systems.

Each successive type has increasing costs but even new build PSV’s are being delivered for less than £25million. The base design is actually very cheap, competitive forces running rampant!

The offshore platform has been chosen for the following reasons;

  • Maturity
  • Competition
  • Innovation
  • Toughness
  • Cost


The basic design has remained relatively unchanged over many decades of demanding operation in extreme environments such as the North Sea. But what has changed over this period are the details, refined in response to a number of demanding customer requirements the designers have responding over many iterations to the point where mature designs are available almost off the shelf. The supply chain and support ecosystem is equally mature and this brings its own benefits.


A vibrant and healthy global market invariably has competition and this competition has created a fertile atmosphere for innovation. Because there are many experienced designers, shipyards and suppliers worldwide we can tap into this extremely competitive market and drive out benefits. This is in sharp contrast to naval shipbuilding which is generally sclerotic, relying on government subsidies and often failing to innovate at the same rate.


Although the fundamentals have remained fairly constant, subsystems have evolved at a rapid pace, benefitting from competition, steady demand and an overwhelming need to reduce operating costs by increasing utilisation. Wave piercing designs such as the Ulstein X Bow are genuine innovations that we can take advantage of, the innovation being essentially paid for by the oil and gas industry.


So-called commercial shipbuilding rules are often criticised for not being tough enough but operating in the North Sea is no place for flimsy construction and designs and construction reflects this workmanlike industrial toughness. Design life is generally shorter for the offshore industry than naval forces but by taking a modular approach to payloads we will be in a position to do the same. Instead of designing ships to last 40 years, we can design them for 15 or 20, the ships operating on a different


By a combination of innovation, design maturity and competition the cost of basic offshore vessels is extremely low, an ideal starting point. Construction in overseas yards and fit-out in other nations is an accepted practice and the UK should not be hamstrung by industrial issues, preventing the use of this technique.

Other nations have recognised the utility of the basic offshore support vessel form factor and created coastguard and EEZ protection vessels.

No stranger to innovation, the Norwegian armed forces (Coastguard in this case) have taken a Rolls Royce UT512 design for their Harstad vessel. Iceland followed suit with the ICGV Þór and India is also taking delivery of Rolls Royce UT517 design coastguard vessels. Ulstein is also offering an X Bow type design, the SX116.

The Start Point – Viking Poseidon

SIMSS will be larger than the UT designs above so there has to be a start point. Assuming that SIMSS is based on an existing design there are many to choose from.

For the purpose of this article and in the interest of actually getting down to detailed discussion the chosen donor design is the offshore construction vessel Ulstein designed SX121 Viking Poseidon currently owned by Eidesvik

This is a large vessel, 120m overall length, a beam of 25m and a deck area of 1,500m2. Top speed is just under 15knots and standard accommodation is for 106 persons.

A variation on the basic SX121 design is the M/V Sarah and M/V Island Constructor/Intervention, datasheets here and here

The variations include a slightly longer hull, mezzanine decks and differences in deck machinery but the basic design forms the basis of SIMSS, without the forward helicopter landing pad, large crane, ROV hangar and moon pool

The innovative X Bow is said to provide a number of advantages…

  • Higher transit speed in calm water due to low angles of entry and increased waterline length
  • No bow flare, eliminating bow impact and slamming in foreship
  • Lower pitch and heave accelerations due to foreship volume distribution and slender hull water line
  • Reduced noise and vibration levels in foreship due to soft entry into waves
  • Less spray
  • Negligible occurrences of green water on the bridge deck
  • Working deck and deck equipment better protected due to hull extended to full beam in the accommodation area
  • Higher transit speed in head and a following sea, giving reduced power consumption and/or higher fuel efficiency in waves and still water

Although I have chosen Ulstein as the starting point we need not be prescriptive, there are other equally suitable designs from any number of designers and manufacturers including Havyard, Rolls Royce, STX and Damenfor example.

Viking Poseidon – Ship Bucket style (illustrator – Why Me)

As you can see from above I have used the Ship Bucket format for illustrating the design. At this point I want to thank those members of the Ship Bucket Forum that have provided drawings and information, I can’t possibly hope to match their very high standards.

Basic Design Features

Whenever ships that are supposed to carry out secondary roles discussion tends to move to just exactly how small they can be made. Modern corvettes take this to the extreme but there are penalties and for the roles that will be carried out by SIMSS, the inverse is true.

Large size provides stability in high sea states, robustness and space to fill with stores, fuel and role-specific equipment.

It should be as large as possible; instead of thinking small, we need to think BIG, hence the base design.

Weights and Measures

Basic dimensions will be approximately 130m long and 25m wide, as per the Viking Poseidon.

This puts SIMSS in the same bracket as the Echo class, slightly larger and wider, the US LCS-1 or MEKO CSL. Where it differs is in the percentage of the volume devoted to high-speed propulsion, the LCS for example, sacrifices a great deal of volume for high speed and reflecting the slightly different mission sets this results in a completely different approach. The draught is also greater, a typical offshore supply vessel has a draught in excess of 7m but HMS Echo is only 5.5m, LCS1 only 4m and the MEKO CSL 4m.

Is this significant leap in size ridiculous, I don’t think so and will explain in more detail later!

Propulsion and Machinery

LNG is an increasingly popular choice for offshore vessels because it is cheaper than diesel but availability in operating areas might be an issue so conventional diesel engines are the obvious choice. Some of the latest designs are also dueled fuel but this would add extra cost for marginal benefit.

This of course results in the obvious choice of medium speed maritime diesel engines as the means of power generation. Rolls Royce supply end to end systems, from the fuel bunker to the tip of the propeller and their Bergen range of engines are ultra-reliable with extremely low cost of operation. The worldwide supply and support network will also reduce through-life costs as the main equipment like propulsion and electrical distributions are widely used.

The latest PX105designs from Ulstein feature a seawater injection system for exhaust gasses and instead of routing the exhaust pipes up through the ship, leaving behind the bridge as per most designs, it is exited at sea level. This is done to provide an improved field of vision from the bridge but there are obvious tactical advantages as well.

When handling ROV’s, anchor cables or cargo precise positioning relative to a fixed point is vital, offshore designs feature GPS assisted positioning systems that incorporate multiple computer-controlled thrusters. SIMSS will also need precise positioning so there is no reason to remove this standard feature from the base design.

Various designs are available for the thrusters and propulsion units, mainstream manufacturers include Rolls Royce and Brunvoll

A couple of innovative systems from Rolls Royce and Brunvoll include podded propulsorsand electromagnetic rim drive thrusters, they might be worth a look if efficiency improvements can be achieved.

Speed, whilst providing many advantages, is very expensive in any design so SIMSS takes a view that for its roles, speed can be traded for endurance, space and low cost. The base design starts at around 12-15 knots and this would be sufficient if the compromise is accepted. Greater speed could be achieved but it would result in greater cost, increased fuel consumption and reduced space.


Conventional offshore vessels need a high level of visibility from the bridge to assist with deck operations and manoeuvring in close proximity to offshore installations. This results in a high set design with plenty of glass but the huge glass area could be a problem in tactical situations so the SIMSS bridge design would be similar configuration but perhaps use a smaller glass surface area and that glass would be toughened or have ballistic protection.

Conventional warships have an operations room, usually deep down in the hull but for the roles covered by SIMSS a single large bridge area would double up.

Construction Standards

The difference between civilian and naval design and construction is much more than the colour of the paint and it is a tremendously complex subject, far outside the scope of this proposal. However, design and construction to so called civilian norms does not mean SIMSS will fall apart at the first bump and the base design is incredibly robust. Continuous operation in the North Sea places a great deal of demand of structural integrity and safe operation but naval rules might dictate greater compartmentalisation, CBRN wash down systems, resistance to underwater shock, blast fragmentation resistance, fire detection, signature reduction and all manner of other protection systems.

Can we utilise the established civilian norms to drive down cost but create a vessel that can operate in a security (rather than combat) environment?

Most commercial vessels are constructed under the rules of the Classification Society, DnV or Lloyds for example and these have seen convergence with naval norms in many areas.

Designing for ice conditions is also an area definitely worth consideration given likely operating environments and recent news about the RN being unpreparedin this respect. SIMSS is not an ice breaker and the International Association of Classification Societies (IACS) Polar Rules describe various classes (Class 1 to 7), it would be prudent to seek a compromise on ice strengthening and additional cost.

There are a couple of excellent documents on the issue here and here

The key thing to remember is that SIMSS is very much a compromise design, it’s not a frigate and does not need to be designed like one.

Taking the Viking Poseidon as the start point, removing the landing pad, moving the exhaust to the hull sides at just above water level, creating a water level fall off on the rear deck area, removing the boat and ROV hangars and removing all open deck machinery results in something like the diagram below, not forgetting a new coat of paint as well.

SIMSS – Start Point

Deck and Storage Configuration

One of the design issues is how to package the various mission modules because this influences the design of the mission deck and other areas.

Should they be is a bespoke form factor or in standard ISO sizes. Although we might gain some advantage by creating a bespoke series of modules we cut ourselves off from the numerous design, manufacturing and support organisations that like everyone else, use standard ISO sizes.

The standard 20 foot ISO container should be the basic building block with the 10ft (bicon), tricon and quadcon in specific roles. The smaller containers are supportable using standard RAS and VERTREP, some may be air-transportable for rapid role changing.

So the answer would seem to be not to concentrate on one type or another, employing the best for each application.

Main Deck Enclosed Area

The key to the flexible, role configuration capability of SIMSS is its ability to plug modules into what might be called a ‘service keel’.

The deck layout will be divided into a grid configuration and sited along the full length of the side walls will be utility connection panels that will enable a containerised or free form module to be ‘mated’ with the ship. This really does have to be plug and play, utilising industry-standard connector systems wherever possible to include;

  • Grey water
  • Potable water
  • Sewage
  • Compressed air
  • High voltage power
  • Low voltage power
  • Dual fibre optic network

Concealed in the deck area, beneath protective panels, might also be a subset of these service connections

Once loaded and installed, securing modules, vehicles or containers will need to be fully secured against movement in high seas. Vehicles can be lashed using strops and chains so lashing points must be distributed throughout the deck area.

If chains and strops are used the tie-down containers from the top, the angle of the chain or strop is such that space is needed between containers to form the correct angle. This is not acceptable in a space-constrained deck area as it wastes valuable space. Something better is needed so pop up locking risers should be fitted on the gridded layout that container twist locks can be attached to. This will allow a more compact arrangement of containers to be secured and allows shock absorbing twistlocks to be used for sensitive containers and modules.

Air handling, lighting, fire detection and suppression systems would also be fitted.

The area would be secured against the elements by an access door to the main deck open area. Given the width, it might not be feasible to install a single piece roller shutter arrangement because of transverse flexing but splitting the aperture in two would reduce flexibility too much so other systems should be investigated, such as roller shutters made of flexible materials.

The covered and open area deck would of course be at the same level.

Main Deck Open Area

The open area is merely an uncovered extension of the covered area or garage. Because it is open to the elements there are fewer height restrictions and access to the stern for launch and recovery of unmanned systems easier.

The length of the open deck area is predicated on the length of a 40ft ISO container and the launch and recovery system for the NATO submersible rescue system.

Platform supply vessels tend to have an enclosed stern whilst the anchor handling type has a fully open area, the radiused form is to support safe handling of anchor and tow cables.

The video below shows this type of open deck area in heavy weather.

Some types combine the best of both with a hydraulic assembly that raises and lowers a rear door and this might provide SIMSS with a good trade-off.

Air Operations Deck

Aviation is an important component of most role sets but aviation facilities are complex, far from simple and inexpensive. Deck handling equipment, tie-downs, night vision device compatible lighting/markings, landing aids and a number of other systems add to the cost. Modelling deck movement is also a complex task.

The large size of SIMSS should in theory make a more stable platform for aviation operations

As an example of complexity, look at the Claverham Deck Lock System, here, or the Prism Defence systems, here

An aviation deck is not just a flat piece of material.

Sizing the aviation deck and hangar also involves a number of trade-offs.

The larger the hangar and deck area the smaller the open deck area on the main level, for a given length so the relative importance of aviation facilities must be balanced against the value of an open deck area.

Being able to fully maintain and operate helicopters means a hangar of suitable size, folded Merlin for example will require about 18 to 20m length and 10m width. Landing requires in excess of 25m and a Chinook even more.

Folding or temporary structures can also mitigate some of these size issues and the folding or collapsible option might be worth exploring even though they add cost and maintenance. The Canadian manufacturer Indal Technologies has been manufacturing telescoping hangars for some time and the German company Aljo, have also supplied many systems.

The role would dictate the type of helicopter carried, Wildcat for example is relatively lightweight and compact with excellent deck handling characteristics, click here to see why it is such a great maritime helicopter. It would be suitable for the maritime security role but less suited if SIMSS were supporting a land focussed operation in support of special forces, where a transport type such as Merlin would be more relevant.

It would be easy to dismiss the role of aviation and dispense with a hangar, opting instead for a simple landing pad, but this is far from ideal and does not recognise the fundamental role aviation plays in support of many of SIMSS roles.

The design must therefore accommodate a Merlin sized helicopter in a fully enclosed hangar or pair of Wildcats.

It is this requirement that pushes the overall length of the vessel out to 120m.

Supporting the weight of a fully-loaded Chinook will also dictate structural robustness that might create weight and balance issues. Without carrying out detailed calculations it is impossible to say whether this goal can be achieved but making the assumption it can, this will be a significant capability that delivers great utility.

Lower or Tween Deck

Look at any cutaway diagram of a typical offshore support vessel and the lower deck comprises nothing but storage tanks. In this environment, they are used for drilling mud, cement, recovered oil and other dry and liquid bulk cargoes.

Although SIMSS has a secondary pollution mitigation role these tanks and handling equipment/pipes would be largely redundant, given it is desirable to keep significant structural changes to a minimum we must find something to fill the void.

The Viking Poseidon base is not designed for storing drilling mud or oil recovery but has significant lower deck volume devoted to the moon pool and associated equipment, I have chosen to delete the moon pool and utilise the space for other things.

It is important that SIMSS remains as self-sustaining as possible, able to carry out long deployments without significant RFA support. This means that fuel, consumables, spares and food must be carried in large quantities; it is these items that will be stored in lieu of drilling mud, cement and moon pool spaces.

Viking Poseidon has 4@2850KW and 2@1530KW generators = 15,450KW total

With a total fuel capacity of 3280m3, the endurance at full load is very roughly 40 days. This needs to be increased to at least double that, if not more.

The lower deck would therefore comprise largely of fuel, potable water, waste and refrigerated/dry stores to provide maximum unsupported duration. A small armoury and ammunition store would also be located below the main deck.

Deployments might not always use this extended duration capacity but having it available provides planning flexibility.

Cranes and Lifts

To achieve maximum flexibility the ability to move modules, vehicles, pallets and containers on and off-board is an essential capability.

There are three main ‘spaces’

  • Main Deck Enclosed Area
  • Air Operations Deck
  • Main Deck Open Space

There is also a need to move equipment on and off the ship, to other ships, small craft and ashore.

Main Deck Garage

Inside the main deck garage, a simple overhead gantry hoist with a lifting capacity of up to 50 tonnes will enable the vast majority of modules and equipment to be moved and containers double stacked as needed. The main deck garage has enough headroom (6m) for a single hi-cube ISO container or double-stacked standard.

Typical suppliers are Noreq, Street, Stahl and Demag.

Because the garage area is enclosed, separated from the open deck area by roller shutter doors, transferring containers and other payloads between the two areas becomes a challenge.

In the configuration proposed there are two on-deck storage areas, one open to the elements and one fully enclosed, so the corrosion potential issue identified would not necessarily arise if only dry modules were stored in the main deck garage. The need to shift large container modules in and out, transferring between the garage and open deck area, becomes less of an issue as it would only generally need to be carried out during role changes. This could be done by an articulated loader or simple container dollies until it could be accessed by the overhead gantry hoist.

Container dollies can be powered or unpowered and allow the container to be lifted from its lock down points and moved into position either by ‘many hands’ or a small electric tug/forklift.

Container castors from Tandemloc can also be fitted to containers and secured when the move has been completed, as the video below shows, moving containers need not utilise overhead hoists. High sea states would obviously make this very dangerous so again, it would normally only be carried out during role changes carried out in port.

ISO container lifting gantries and similar post/dolly/castor solutions are also available from Toutenkamion, HetekandCDK Mobile Systems

The US Army has been quietly moving forward with its HSV programme and tackling similar problems. One solution that came out was the air skid from Air Float, basically a series of hover pads that allow the container to be moved on an air cushion. All the system needs is a source of compressed air.

Air Operations Deck

Although the air operations deck will generally be used for just that, there may be occasions where it is used for equipment storage and VERTREP may also require equipment and stores from the aviation deck to the lower decks, either the enclosed or open sections. Clearly, a hangar type deck lift would add a great deal of cost for the marginal benefit and would of course require significant floor space in the enclosed area to be left free.

Some form of crane or jib is therefore needed that can reach onto the aviation deck and lift equipment and stores onto the open deck for storage there, or transfer to the enclosed area. The ability to move equipment, vehicles and stores from the enclosed and open deck onto the aviation deck is also an obvious requirement.

If this crane is located on the aviation deck its configuration and size may cause problems with the helicopter launch and recovery envelope, ideally, the deck would be a single open and uncluttered space. Positioning the crane on the open deck area will impinge on the space available but this provides the greatest flexibility.

A compact crane on the aviation deck would still be very useful though, moving UAV’s for example, so a travelling rail, folding hydraulic jib could be fitted. The cranes would be fitted on both the port and starboard sides of the aviation deck and free to move along sliding rails, fore and aft. For air operations, these would be stowed in the forward position, well out of the way but the pair would be able to cover the entire aviation deck area and move small loads onto the shore, alongside vessels and onto the open deck area. In order to keep these travelling rail cranes small their reach and lifting capacity would be limited.

Travelling rail deck cranes are usually used in Anchor Handling vessels where the ability to move forward and back is essential, moving anchors and cables in safety without personnel being on the deck.

These are generally called cargo rail cranes, a good animation of how they work can be found on the Triplex website, click here

Cargo Rail Crane

They are also available from a number of manufacturers including Odim, McGregor Cargotec and Rolls Royce

Although the cargo rail would reduce the width of the aviation deck by perhaps a metre on each side this is a reasonable trade.

Main Deck Open Area

Maritime cranes may seem a rather dull subject but there are some interesting innovations about, especially in heave compensation. Heave compensation is used primarily in offshore support vessels and other facilities to safely compensate for ship movement when handling cargo and especially Remotely Operated Vehicles (ROV’s) through a moon pool. This allows precise and safe control of, for example, a tethered ROV working at depth on undersea oil production facilities, in higher sea states that a non-compensated type.

There is a lot of science behind what might seem relatively simple, get a couple of headache tablets ready and click here for a read or have a look at the video below showing Active Heave Compensation from TTS.

Passive heave compensation can provide an interim level of heave compensation, examples from Cranemaster, click here

The US Navy have also been putting a great deal of effort into heave compensated cranes for ship to ship transfer of containers and vehicles at sea, as part of the Sea Basing programme of activity. The Office of Naval Research has a series of papers on the subject here. Oceaneering, the system integrator, also have some good information here and a couple of great videos here and here.

This is an important technology to watch, perhaps not for SIMSS but certainly for larger RFA and amphibious vessels.

Back to SIMSS

A large crane on the open deck area will add cost and reduce space available for stores or equipment. If it is too large it will also influence the aviation launch and recovery envelope, perhaps so adversely it will make the safe operation of helicopters impossible. If a crane is to be fitted it must be sufficiently clear or low enough to not impede aviation operations on the upper deck, a challenge.

The first question to resolve is what for?

If modules and vehicles can be driven aboard whilst the ship is in port then the crane would generally be used whilst at sea. Depending on the role being carried out these at-sea operations might include small craft, unmanned systems and ship to ship transfer of stores. This latter activity might be used if SIMSS was acting as a logistic enabler or mothership to a larger number of small ships.

Because it will not be involved in offshore construction projects where loads in excess of 300 tonnes are common a smaller design can be selected. These larger designs from Huisman, Cargotec and Lagendjik tend to start at around 120 tonnes lifting capacity which is too much, given their size.

If we need to lift the unmanned vehicle, container, vehicle or small boat then something in the order of 15 to 20 tonnes is more appropriate. Combined knuckle boom and telescopic type offer the advantages of reach and capacity but in a compact and foldable form. The process would involve trading lift weight, reach and space, each design type has different features

A pedestal mounted crane at the stern would provide flexibility and capability and if one of the telescopic or folding types were used then space and restriction on aviation would be reduced.

An alternative to a pedestal mounted crane would be a telescopic A-frame, this would provide a greater lift capacity but less flexibility for side access.

Cargo Access Ramps

At the head of the main deck covered area and on both port and starboard sides will be a single, folding access door and extending RORO ramp. Although access to this area is also available to vehicles from the main deck open area having additional means of loading and unloading for vehicles and modules provides extra flexibility when the rear deck area is loaded.

Loading and unloading via these side doors might be problematic for very long loads and could restrict access in some circumstances but this is an acceptable restriction.

The ramp would be rated for heavy vehicles, if you look at pictures of the HMDS Absalon class of vessels rear loading area this is a similar concept although on SIMSS it might be slightly smaller.

A typical manufacturer of side access ramps is the Italian Navalimpianti Group that provided side access ramps and doors for the Cavour.

A pallet lift between the main deck and lower deck would be fitted to allow ammunition and stores pallets to be stored below the deck.


Small Craft and Unmanned Systems Launching

Although the deck cranes may be used to launch small craft and unmanned systems a more sophisticated system would be advantageous.

SIMSS derives much of its functionality from its small craft and for the survey and MCM roles, a range of unmanned systems.

Stern ramps have started to appear on offshore support vessels and some of the newer coastguard and naval vessels where the ability to safely launch and recover small boats such as RIB’s or rescue boats is needed. (background papers here and here)

As can be seen from the video below recovery is a very quick operation that can be carried out whilst the vessel is underway. BMT has carried out a great deal of research in this application and demonstrated the launch and recovery of small boats up to Sea State 5. In the offshore market, this is especially important for Fast Rescue Craft (FRC) and where the distance between the ship and sea is small the relative difference at the peak and trough of a wave is reduced.

The problem with a stern ramp system on SIMSS is the space on the open rear deck it would take up, reducing flexibility. It would also require some redesign to compensate for a change of buoyancy from normal and the opening and closing doors common on most configurations might require a significant uplift in maintenance effort.

So, this method of launch and recovery is discounted.

If we look at typical small craft that will need to be carried it breaks down into two types, up to 8m RIB’s and up to 20m work boats, patrol craft or landing craft. A single, large bay, measuring 30m will be fitted on both port and starboard.

Small craft launch davits are available from a number of manufacturers such as Caley, Noreq, Macgregor Aukra, and Vestdavit

The Caley Davit is proven up to Sea State 6, click here for a flash animation and the video below shows the same system

If we look at the product range from Vestdavit for example, the single-bay telescoping davit would seem to offer an ideal solution. They can be triaxially motion-compensated, cope with small craft up to 5 metres wide and up to 28 tonnes in weight.

It would be preferable if the small boat bays had a telescoping or folding door but given the substantial 30m length this might not be possible in a single piece. A single door allows combinations of vessel lengths, a single 20m and 10m for example, or 3x 10m. If this is not possible then a 20m and 10m door assembly should be fitted (the drawing below shows a twin door approach.

An alternative small boat accommodation area might be the covered main deck area, the BMT Venator design takes this approach but in order to retain as much as the working area as possible in this area and to allow an x y gantry crane to be fitted the dedicated small boat hangar is preferred.

More discussion on boats and small craft later

Vessels working on deep offshore oil and gas facilities generally use tethered unmanned systems or Remotely Operated Vehicles, sometimes at extreme depths in excess of 2,000m. The mode of operation is different with survey and mines countermeasures unmanned systems so evidently, launch and recovery systems will also be different.

Most of the MCM unmanned systems are relatively compact in comparison to the large, heavy duty, ‘work class’ ROV’s commonly used in the offshore industry and tend to be autonomous or untethered.

Moon pools are designed to provide offshore vessel operators with maximum operating time in deep water and extreme sea states, time being very definitely money. Mines countermeasure norms might be inshore, shallower water and less extreme weather so the advantages of a moon pool might not be as evident and given that they take up considerable volume and add complexity and cost, inclusion on the SIMSS design is not automatic.

Operating deep ocean survey equipment is another mission for SIMSS and this might offer a better justification for a moon pool but on balance, and in the absence of a detailed design study I have excluded it, even though it is included in the base design.

Therefore, unmanned systems, whether for mines countermeasures or survey, or autonomous or tethered/guided, will be launched and recovered over the stern, from the open deck area.

As above, the open deck is fitted with a folding knuckle boom type crane and this might be sufficient but there are many alternative options.

Containerised Launch and Recovery Systems (LARS) are now a mature technology, self contained apart from power and network connectivity, they can be quickly and easily loaded.

There are a number of suppliers of mines countermeasures equipment (more later) including Saab, Atlas Elektronik, Kockums and Kongsberg (recently purchased Hydroid) with Atlas recently demonstrated an advanced system for the Royal Navy.

What is characterising these newer systems is the move to modularity and away from specialised ships, putting distance between the ship and the mine(s) reduces the need for specialist signature reduction techniques and allows a greater range of vessels to contribute to the operation.

To take a single example, the Kongsberg/Hydroid REMUS 600, it has a self contained ISO compatible launch and recovery system.

A tipping A frame seems to be the most common configuration for larger unmanned systems and a number of compact systems are available from SEPRO, Lidan, Macgregor, Oceaneering, Intervention Technology, Ulmatec, Cetix,Techsafe and Ocean Engineering.

Balancing the factors, the preferred mode of operation for SIMSS based unmanned systems is modular handling equipment rather than integral moon pools and permanently installed lifting equipment or moon pools.

The SX121 base design has large ROV hangars immediately in front of the open deck area but for SIMSS these would be replaced by an enlarged small craft hangar and configured slightly differently.


Although the standard crew would be relatively modest the mission specialists could swell these numbers considerably. One option is to have the mission specialists bring their own accommodation as part of the role fit but this might compromise space available and be inefficient. A better solution would be to install accommodation and hotel services that can cope with most role types.

Some roles might still see accommodation modules added to the enclosed deck area but the norm would be permanently installed accommodation, even if on many occasions, it was empty. One of the operating requirements of SIMSS is long endurance so accommodation standards, at least for the bulk of the operating crew, must reflect this.

In addition to basic accommodation there would also be extended capacity for dining areas, kitchens, ablutions, food storage, exercise, medical etc.

Hotel and accommodation facilities should be able to cope with up to 100 personnel on a routine basis and double that on stretch.

The base design is configured for 102 in modern and well appointed cabins that could support extended deployments and a range of recreation and other common areas are also fitted.

Sensors and Communications

Sensors and communication systems have the potential to push the cost of SIMSS through the roof and we have to guard about over specification, remembering the title of the series but if we skimp too much then value for money is compromised.

A balance needs to be achieved and space for growth included, the dreaded fitted for but not with.

The underlying principle should be that equipment is off the shelf and this is not a frigate.

If we look at the sensor and communication fir for the River Class we would not be far off a baseline for SIMSS. The radar is a mid range model from Terma called the Scanter 4100which is a surface and air surveillance device. This is complemented with a range of communication equipment and obstacle avoidance sonar, pretty basic but functional.

Scanter 4100 has been fully integrated with the Ultra Electronic OSIRIS maritime combat and mission management system and this would seem an ideal, immediately available solution.

A more sophisticated system might be the ARTISAN (Advanced Radar Target Indication Situational Awareness and Navigation) radar from BAe that will be fitted on future RN vessels, replacing the 996 on Type 23 as well as being fitted on Ocean and the Albion class. This is very capable but likely to be too expensive and arguably too much for what is needed.

In line with the general modular nature of this proposal we might see some benefit from installing a small, integrated mast. Although these are not particularly new I think they have a great deal of potential in this type of vessel. The entire mast structure is a single, swappable module that can be lifted on and off as needed.

The mast contains much of the electronics and power conditioning equipment so when an upgrade or maintenance is needed the whole structure is simply lifted off and removed to a controlled environment that suits the activity, the thinking being that it is easier to lift off the mast, drive it to a workshop and carry out any work under cover and on dry land than it is to work on a mast that is still aboard. I am not sure how ‘quick’ this activity would be or if it would make more sense to maintain and upgrade in situ but it’s an interesting concept nonetheless.

We are not going to be swapping masts out whist deployed to get some extra capability, but for deep maintenance and parallel development it seems a logical approach.

The mast as a system can also be developed separately to the ship, tested ashore and simply swapped out as a whole unit as docking schedules permit. Developments can be carried out in a known reference environment and the system as a whole incrementally upgraded over time.

The Thales iMasthas taken this concept and realised it, various configurations and sizes area available with equipment simply slotted into to the open architecture, delivered as a single unit to shipbuilders. A single power and cooling infrastructure is designed to reduce maintenance

At the baseline spec the iMast fitted to SIMSS will generally be at a modest level of capability, we have to show some discipline here, it would be easy to say, can’t we just fit x or y, it won’t add much to the overall cost?

But we must remember that we are designing this vessel down to limited cost; that is the whole point. Could we include an i-Mast as part of SIMSS, not sure if it is a step too far in terms of cost.

See how easy it is to be seduced by shiny toys!

Given the likely benefit of even a very basic integrated mast I tend to think it’s worth prioritising and include what might be called an austere fit of basic volumetric search radar, IFF, electro optical, VHF/UHF and SATCOMS.

It might be feasible to reduce crew overhead by using some of the new automated watch systems.

Basic obstacle avoidance sonar would also be fitted.

The difficult aspect of this is understanding the cost and trading off capability in other areas to pay for improved sensor and communication equipment. Of course it would be great to have ARTISAN with all the trimmings but perhaps this would be too much so a basic non integrated mast with a Scanter 4100 might make more sense.

One for discussion I think.

Weapons and Countermeasures (Fitted)

Like sensors and communications equipment, weapons and countermeasures have the potential to add significantly to the cost but as above, we have to be realistic about operating environments and roles and question every aspect of weapons and countermeasures.

The basic fact is that SIMSS is a naval vessel so must have a baseline level of self defence capability against likely threats in the most likely operating areas whilst fulfilling the most likely roles.

These factors may change over time so the basic vessel must be fitted for an escalating level of ‘fightiness’, an extension of the fitted for but not with concept that is widely derided but eminently sensible when faced with a finite budget.

The SIMSS baseline weapon fit would be no more than manually aimed automatic weapons, sited at a number of locations distributed around the upper hull. These provide an adequate short range self defence and deterrent capability against a limited threat.

Basic structural modification to provide for a stronger systems fit will need to be designed in from the outset. SIMSS is, to refer yet again to the title, not a frigate, however, they might be operating in conjunction with other surface combatants in a higher threat environment that might include submarines, aircraft, small craft, suicide attackers and even anti surface missiles.

There has to be a limit but a more robust self defence capability option must form an integral part of the design.

With this in mind, located to the port and starboard of the bridge and on extended wings would be a weapons mounting position. This affords maximum coverage for self defence weapons and another position, behind the bridge provides extra coverage or space for countermeasures.

The wing positions would be sized to accommodate a 10ft ISO container size (Bicon) system and the bridge rear area, a full size 20ft ISO container, although the weapons themselves might not be delivered in a containerised package the overall dimensions must be bounded to support easy transportation.

Because of the height above sea level of these three positions weapon weight might be constrained and any direct fire gun based system must be able to depress sufficiently to counter close in surface targets.

More on these later…

These demountable weapons may also enable deployments in politically sensitive areas or those covered by treaties (Antarctic for example)


All operators of ships want to reduce manning to the minimum because of cost issues. Reducing personnel below a certain threshold has serious implications with regard to situational awareness, self defence, crew fatigue, maintenance, damage control and attrition so it is always a fine line.

The SIMSS baseline crew would be enough to operate the vessel safely, carry out routine maintenance and provide adequate situational awareness on a sustained 24×7 basis. What does this mean in practice; it’s difficult to answer that question without detailed analysis and would be dependent on systems and automation.

Similar donor vessels have a crew of approximately 25 but for SIMSS this would likely increase to 35 to 40.

Payloads bring their own crews so if the vessel is embarked on an MCM task then specialists for that task would embark separately.

Taking this modular approach to manning is not without risk, a ship’s crew must function as a whole and the fragmented natures of ‘drivers’ plus ‘mission specialists’ can be a little artificial given that each must contribute and have any number of secondary roles. We might consider this a risk, but one that can be mitigated with training flexibility or at least accepted if advantages accrue elsewhere.


Putting these together results in a configuration below


Comments on the Part 5 post so they are all in one place

PART 1 – Introduction

PART 2 – Roles and Requirements

PART 3 – Design Discussion

PART 4 – Modules and Payloads

PART 5 – Operational Concepts