Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

The final piece of the jigsaw in regards of CONCEPT 2 is wave attenuation.

No you could reasonably argue that the crew and shore personnel managed to conduct an offload and load operation in high sea and wind states onto a RORO platform but it was very quick, a handful of vehicles only. This is not acceptable and the ships crew would be very familiar with the particular port

The video below shows the effects of wave motion induce crane pendulation

The load in question is a heavy cargo drum but still a minnow compared to an armoured vehicle or loaded container.

In order to allow safe and efficient offloading at the Pier Head the relative motion between the free floating ship and fixed Pier Head must be minimised.

Conventional breakwaters are usually massive reinforced earthworks, sometimes with protective sheet piling. Protection against erosion caused by waves is provided by combinations of geotextiles, aggregates and in many cases, large concrete blocks lifted into position such as those made by Xbloc

11242064364 c955e6ccf5 z Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

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Obviously, within the time and logistics constraints of CONCEPT 2, bringing ones own concrete is not the best of ideas. Neither is using large concrete caissons and old ships like on D Day, imagine the environmental impact statement!

Some form of floating breakwater is therefore required.

Floating Breakwaters

Background

The first recorded use of a floating breakwater was at Plymouth in 1811 and since then the floating breakwater has evolved in a number of specialist areas such as marina and aquaculture.

Going back to D Day, the problem of wave attenuation was a big one, the location and time the invasion was planned for meant waves would be significant and much thought was given to the issue.

After many different ideas were tried the actual means of wave attenuation coalesced on three methods.

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The image above clearly shows the effectiveness of the wave attenuation capabilities of the combinations of these methods.

First were a row of 60 blockships, old and obsolete ships that were stripped, towed into position and sunk. Preparations including destroying their water tight bulkheads to ensure they sank quickly when amatol charges punched holes into their hulls. Once in place, they were overlapped and sunk. The overlapping was needed to prevent scouring at the bow and stern. The lack of such overlapping on UTAH meant the US blockships suffered from this effect and several of the ships had their backs broken by voids opening up underneath them.

Their main advantage was they could get to the beaches under their own steam, not requiring precious tugs but due to their comparatively low height there were unable to be used across the entire area and thus, deeper concrete caissons were needed.

Second, were large concrete caissons called PHOENIX, 150 of these were built in six depth variations to accommodate different water depths, the largest (Type A1) displacing 6,044 tons and the smallest (Type D), 1,672 tons. Each was a standard 60m in length with a boat hull to facilitate towing operations. Some of the PHOENIX caissons had anti-aircraft guns and barrage balloons, with the necessary crew quarters built into the structure. The caissons were pre-fabricated in the UK and when towed into position their scuttling valves were opened, flooded and sunk.

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Finally, an anchored wave attenuation device called BOMBARDON was used. These were 200 foot long cruciform cross section floating steel constructions that were anchored to the sea bed and each other in long ‘strings’. 24 Bombardons, each with a 50 foot gap between them, created a breakwater 1 mile long. Water was then let into the three lower fins as ballast. Each was designed for a Force 6 storm, unfortunately.

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Of these three methods, only one could be considered as a floating breakwater, the Bombardon, and only one that could be considered for CONCEPT 2.

Types of Floating Breakwater

Floating breakwaters are often selected for deeper water, where soil conditions preclude the construction of soil and rock structures and where water quality needs to be maintained, aquaculture being particularly sensitive to this.

Short choppy waves can be affectively attenuated with floating breakwaters but longer period waves encountered offshore can be difficult to deal with because the transmitted wave (that behind the breakwater) depends on the ratio between the incoming wave and width of the breakwater.

In the years since the Bombardon there has been a great deal of research into floating breakwaters and many designs and configurations tested. The increasing size of container vessels and the need for smaller feeder ports has also resulted in a modest increase in research in floating breakwaters.

Floating tyre or log mats can be used although they are not easy to deploy and less effective than other types, they are cheap though.

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A more common types is the floating box, concrete or steel in construction, often foam filled, linked together with flexible pins and moored to the sea bed.

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The image above shows a floating pontoon breakwater installed in Holy Loch, Scotland. The 240m long structure comprises twelve 20m long pontoons, each weighing 42 tonnes and the image below, a similar concrete box construction floating breakwater in Italy from Ingemar

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The image above shows clearly their utility in exposed water and the unit is designed for a maximum wave height of 1.5m before being over topped, with a maximum wave length of 18m and period of 5 seconds. This would correspond to a sea state of between 3 and 4. To improve efficiency they can be post tensioned in order to increase stiffness although this creates significant forces.

Floating or bottom tethered pontoons or tubes have also seen widespread use with individual designs being influenced by specific conditions encountered at the intended location.

Inflatable types

A significant advantage of inflatable breakwaters is their ability to absorb wave energy by structural deformation, unlike fixed pontoon or box structures. This can also result in lower stress on the mooring system. They can also be inflated and deflated in situ, an obvious space advantage  for a deployable solution but can obviously be deflated by puncturing.

Newer designs, generally aimed at the marina and leisure market used moulded plastics to form long flexible strings of breakwaters, examples include Waveeater and Whisprwave

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Traditional inflatable semi submersible types are also available

Mooring

The most likely failure point in any floating breakwater is the mooring because it has to maintain the floating structure across a vertical range, alternating between slack and taut. Many studies have shown that the influence of the mooring system on the overall effectiveness of the floating breakwater is significant.

Mooring systems that can accommodate depth variations are most effective, those of Superflex being good examples

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Rapidly Installed Breakwater System (RIBS)

In the mid nineties the USACE Military Engineering RDT&E Program of the Coastal and Hydraulics Laboratory (CHL) carried out what was probably the most comprehensive study into deployable breakwaters since the Bombardon.

As described above, floating breakwaters are most effective when their width is a quarter wavelength, in open water where long wavelength waves are more common than ‘choppy’ short wavelength waves closer to shore the problem becomes extremely difficult due to simple dimensions required.

RIBS was required to reduce wave height by 50% in Sea State 3 to 2, be survivable at Sea State 5 and be able to be deployed and redeployed quickly using in service shipping.

It was not specifically aimed at creating a stable platform for ship offloading to a fixed pier but for offloading large ships to lighters. The same principle still apply to CONCEPT 2 though.

11257771243 1eed12fe54 z Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

After testing many designs the CHL came up with the ‘Double Delta’ shape, as below

11257729046 8acd54431a Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

The cells were filled with expanding foam and a rigid curtain extended between them at a sufficient depth to stop wave energy penetrating beneath the breakwater.

It would be deployed in a V shape with the tip of the V facing into the waves, the floating structure deflecting waves rather than reflecting them as traditional breakwaters might, this was a big departure from those described above.

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At the point of the V was a nose buoy that was moored to the surface and allowed the angle to be varied between 0 and 60 degrees. Scale testing indicated up to 85% wave attenuation.

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The first tests used a rigid structure but these were rapidly changed to inflatable beam structures, called the Hydro RIB

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The final test was at full scale using a design called XM-2001 that unspooled from a large bobbin before pressurisation

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The larger scale testing demonstrated reduction from upper sea state 3 to 1 in the lee of the breakwater.

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Pretty damned impressive and more so because the deflection mechanism allowed moorings to be relatively low strength and simple.

Then funding was stopped as the OMFTS and STOM crowd started hoovering up funding for sea basing and high speed over the horizon amphibious operations.

RIBS was as cheap as chips and self evidently, extremely effective. Deployment was simple and the whole assembly was very compact pre installation.

Putting a single CONCEPT 2 pier head in the lee of the V shape would need a much longer leg length than envisaged but there is no reason to suppose that combining some of the newer plastic moulded systems with the pressurised beam technology of RIBS a similarly deployable yet effective system could not be created.

Sources and Further Reading

Floating Breakwater Response to Waves Action Using a Boussinesq Model Coupled with a 2DV Elliptic Solver

Fishing harbour planning, construction and management – Chapter 7 Breakwaters

FM 5-480 Port Construction and Repair

Floating Breakwater – Theoretical study of a dynamic wave attenuating system

Breakwater stability under tsunami attack

A PERFORATED MOBILE BREAKWATER FOR FIXED AND FLOATING APPLICATION

Potential uses for the Rapidly Installed Breakwater System

Other Posts in the Series

Ship to Shore Logistics – 01 (Introduction)

Ship to Shore Logistics – 02 (History – 1944 Europe)

Ship to Shore Logistics – 03 (History – 1982 the Falkland Islands)

Ship to Shore Logistics – 04 (History – 2003 Iraq)

Ship to Shore Logistics – 05 (History – 2010 Haiti)

Ship to Shore Logistics – 06 (Case Study Observations)

Ship to Shore Logistics – 07 (Doctrine and Concepts)

Ship to Shore Logistics – 08 (Requirements and Drivers)

Ship to Shore Logistics – 09 (Current Capabilities and Future Plans)

Ship to Shore Logistics – 10 (Allies – the USA)

Ship to Shore Logistics – 11 (Mid Point Review)

Ship to Shore Logistics – 12 (Ports, Beaches or Both)

Ship to Shore Logistics – 13 (Expeditionary Port Access Concepts)

Ship to Shore Logistics – 14 (Expeditionary Port Access – Concept 1 – Survey and Munitions Clearance)

Ship to Shore Logistics – 15 (Expeditionary Port Access – Concept 1 – Repair and Debris Removal)

Ship to Shore Logistics – 16 (Expeditionary Port Access – Concept 1 – Dredging, Aids to Navigation and Mooring)

Ship to Shore Logistics – 17 (Expeditionary Port Access – Concept 1 – RORO Link Span and Cargo Handling)

Ship to Shore Logistics – 18 (Expeditionary Port Access – Concept 1 – Summary)

Ship to Shore Logistics – 19 (Expeditionary Port Access – Concept 2 – Introduction)

Ship to Shore Logistics – 20 (Expeditionary Port Access – Concept 2 - Why Not Just Buy JLOTS)

Ship to Shore Logistics – 21 (Expeditionary Port Access – Concept 2 – Requirements and Components)

Ship to Shore Logistics – 22 (Expeditionary Port Access – Concept 2 – Pier Head and Material Handling)

Ship to Shore Logistics – 23 (Expeditionary Port Access – Concept 2 – Access Pier)

Ship to Shore Logistics – 24 (Expeditionary Port Access – Concept 2 – Fuel)

Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

Ship to Shore Logistics – 26 (Wrapping Up)

 

 

About Think Defence

Think Defence hopes to start sensible conversations about UK defence issues, no agenda or no campaign but there might be one or two posts on containers, bridges and mexeflotes!

9 thoughts on “Ship to Shore Logistics – 25 (Expeditionary Port Access – Concept 2 – Wave Attenuation)

  1. KRT

    The best solution to withstand high sea states was the Bombardon, the more recent solutions were for less rough sea. Inflating such a structure can be integrating with filling it with a foam to provide stiffness and resilence of structural integrity in case of penetration.

    You discussed using one breakwater to reduce the sea state within. What if two breakwaters are used, a less efficient solution handling high sea states and within one of the listed more efficient solutions with limits on exposure to rough seas.

    Phoenix and the floating boxes could be cross posted as possible solutions for the pierhead and pier construction.
    Having the facilities to produce cheap transportable harbour components in required quantity out of concrete and foam offers a solution for a number of amphibious forces (multi-national sharing of the capabilities), use and installation during catastrophies (most likely in the Indo-Pacific) and has a constant peacetime demand due to customers creating non-military ports. It would be a standardized transportable small harbour that is produced on a constant basis for various customers and for this reason allows pooling resources of different nations into this project with pay offs for each, while not requiring each to maintain the product as floating rarely used capability.

  2. Simon

    Can’t for the life of me find a vid but there is a wave-power system that sucks so much of the surface wave power out that the sea “behind” it is as flat as a millpond.

    So you could not only protect shipping, but also provide free power.

  3. Simon

    Ant,

    I checked wiki before I commented. It didn’t seem to be there.

    It was a line of “floats” that were all shaped a little like a ducks body. In fact I think they were yellow on the prototype.

  4. Ant

    Then what wf said on the December Open Thread: Salter’s Ducks I guess.
    IIRC they had trouble withstanding extreme waves and tended to break.

    To be honest I’m not sure getting a wave energy farm at your beachhead is worth it, but the Pelamis concept, made of the same stuff as that Hydro RIB/XM-2001, and in an array moored out to seaward may help by:
    a) attenuating wave energy arriving at the breakwater proper
    b) withstand exceptionally high sea states
    c) therefore make the breakwater proper more survivable, and with less anchor drag.

    Not that I know anything.

  5. Simon

    Ant, wf,

    Looks like it could be the Salter.

    I vaguely remember it being Scotish.

    Shame if it doesn’t work :-(

  6. wf

    @Simon: I think it worked, just failed too often so it fell out of use. Doesn’t mean we can’t use it for this, since it’s lifetime is liable to be measured in weeks and if they fail to generate power, who cares, it’s a side effect only :-)

  7. Ant

    But you still have to get them there, and they’re quite hefty for a working set..
    By contrast the Hydro RIB/XM-2001 thingy really is a Hesco of the sea.

  8. A Different Gareth

    Could dracones (or perhaps the smaller, tougher boat barriers units) be used in the same way as RIBS? Two units submerged by filling with water with a third filled with air on top.

    I like KRT’s idea of a production line for modular harbours. It would most often be meeting a steady need for new ports and renovating old ones but in an emergency aid money could be used to obtain recently made units either waiting to be shipped or already on route to their intended owner (who would either be compensated for the delay they suffer while replacement units were made or will have paid a low price for it on the understanding that the supply of it could be interrupted).

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