The majority of machine control articles in the press and associated advertising literature focus on land based civil construction applications. This isn’t a surprise as that is where the bulk of the work is and has kept machine control suppliers happily in business for many years. However as well as providing solutions for dozers, excavators, graders, drilling and piling rigs etc machine control also has its uses in the smaller niche market areas, one of these being offshore and dredging. Now dredging itself is big business, but in machine control terms it has a more limited adoption when compared to land based applications. This doesn’t mean to say that machine control suppliers haven’t risen to the challenge and ignored the potential of this market area and there are many indications to suggest that it will continue to grow. So how is machine control applied in the offshore world ?

Well lets first have a look at the work and machines that can have machine control applied :

Dredging the seabed – does what it says ! The work is usually required to clear a harbour, silted channels in rivers, clear / renew shipping lanes etc.  Some applications are for remedial and decontamination work where over many years toxins have accumulated on the floor within a harbour and a known seabed layer needs to be removed. Machine types to perform these tasks vary from the pontoon based excavator type dredgers to the much larger cutter suction dredgers and grab dredgers.

Marine construction – whist not dredging (the removal of material) it falls into the category of offshore work and can be found in areas such as foundation work (offshore construction such windfarms etc) and harbour breakwater and marina construction. This type of work requires the placement of material, usually large rocks and / or accropodes etc. Machine types can be pontoon based excavators or cranes.

The basics behind the use of these machines and applications were covered in a previous article by Randy Noland. Refer here  What I will focus on are the particular challenges that need to be met with the hardware and software.

Operation / software - Dredging
Before a client will commit to a machine control purchase, he will want to be able to justify to himself the cost benefits before signing that cheque. The benefits for land based applications are well documented and will also more or less apply to the marine application, although the working practices may be applied in a slightly different way. Because the dredging operation is below water then the operator is working blind and needs to rely on some method to give depth indication.

Prior to machine control (using an excavator as an example) the simple way of knowing the excavator equipment depth was to mark the arm at known intervals and use this as a basic depth guide by noting where the mark on the arm lay relative to the water level.  As time progressed this was advanced to basic 2D systems that as well as monitoring the excavator equipment would also use a tide gauge to reference the machine on the water (sometime with the inclusion of draught gauges) and give a much more accurate representation of the excavator position in relation to the target surface. However what is really required is not only knowing where the excavator is, but also where it has been  and hence the now more accepted method of using GNSS to measure the excavator position on the water.  3D allows the system to be able to track its progress as the job proceeds, but more importantly gives the option of showing the target depth (the level we want to cut) and the existing surface. The surface is created using a bathymetric scanning and is the reference surface against which the design relates. Being able to see these two layers on a screen in real time operation gives the following advantages :

*Knowing where the surface is means you are not taking by surprise as the tool point starts to cut / excavate – quite an advantage if the ground is hard !.
*The system can show the progress of the dig to design by showing the progress through the existing surface layer depth to target and can show if they have under / over excavated or are at the design level.
*The system can show progress as to the area covered by the dredger, avoid repeat dredging in areas already correctly worked.
*Knowing the difference between the actual surface and design and monitoring the area excavated means that extracted volumes can be calculated
*The surface design topography can be updated in real time as the job progresses
*The work is automatically documented.
*Reduction in the quantity of bathymetric surveys to confirm work done and accuracy
*If the removed material is placed elsewhere on the surface design then this can be shown as an increase of the surface material at that point.
*The excavator may be fixed or free to move on the barge. Its position relative to the barge can be shown and more importantly offer warning if the barge has the potential of being damaged by the excavator equipment – I can recall at least three occasions where I have been informed of an excavator puncturing the barge during dredging !

A machine control system on a cutter suction dredger can offer all of the above benefits except for the last as it is not possible to damage the barge with the cutter head (or so I am led to believe, but am willing to be put right if wrong).

As the machine will be operating offshore what are you going to do about collecting the data, updating terrain models, updating software ? This is where having a decent command and control function in the machine control software can benefit. See my previous articles Refer Here

Operation / software – Marine Construction
With regards to marine construction, it is all about the placement of material. As with dredging, the operator is working blind and needs some method of knowing where the material is being placed. Traditionally this has been done through the employment of divers to guide and check the placement of material, however there are a couple of drawbacks – cost and safety, no need to say anymore, but divers aren’t cheap and being in the water while someone is placing big heavy rocks is not the safest of environments. 3D machine control overcomes these obstacles and will allow the operator to see the existing surface and relate this to the design surface. It is a “fill” operation so we are building up material to a known profile and volume. As each rock / accropode is placed then it can be marked on the screen and also record any associated parameters if required – material type, weight etc so that a complete documentation of the design build can be created.  The design may give the exact position for the placement of certain objects, by having all this information in the cab without receiving any external guidance makes the process much quicker  - my past experience has seen work completed many weeks / months ahead of schedule due to the deployment of 3D machine control.

Hardware considerations
In a nutshell - It’s a marine application so you want it waterproof, you don’t want it to corrode and you don’t want it damaged by underwater obstacles. Sounds obvious, but the solution isn’t always that easy, take waterproof for example. There are many different IP ratings giving reference to ingress protection from water and dust. The only rating we care about here is IP68 which is continued immersion at depths beyond 1m or immersion under pressure. It is up to the manufacturer to specify at what depth his product is rated to, just stating IP68 only tells part of the story. (Note : IP67 is only good for depths of up to 1m and is therefore not suitable for dredging applications).  Protection against corrosion can be achieved a variety of ways from the material selection (e.g. stainless steel) to a protective coating. The main issue that causes problems is that of damage. Because the system is working blind it is very easy to hit rocks and obstacles, get the cables and / or hoses caught and very easily damage a system. Downtime of a dredger is very expensive and you don’t want a machine control system to be the cause of it so you have to ensure that when it is installed certain measures are put into place such as :

*Cable routing and protection – make sure that the cable is not able to be caught by any external object, protect it by running it through a thick braided hose that is firmly fixed to the machine.
*Cover sensor with additional armour protection – weld cover plates over any known trouble spots (bucket sensors are always a favourite for damage).
*Custom hardware – offshore work does not always use standard configuration machinery and requires some flexibility in the approach of the machine control supplier in terms of both hardware and software. Excavators are pretty standard, but something such as a lattice boom crane may require various methods of monitoring the cable payout for the grab depth and open / close status. This is why this particular market area is quite niche as it doesn’t appeal to the mass 3D machine control supplier, flexibility and customisation are the key. It is also sometime of benefit to fit a hydraulic flow sensor to monitor a piece of equipment as a standard sensor may be exposed and prone to damage – again flexibility and customisation is required. All machines and applications need to be carefully assessed prior to proposing a solution.

The GPS / GNSS solution needs to be considered as well, most offshore work referred to here is still well within site of the mainland so any RTK baseline issues will not come into affect however it should not be taken for granted when assessing the application.

I have hopefully provided some useful information about the differences between offshore and land based 3D machine control applications and the implications in applying the technology. The marine market for 3D machine control is strong and thanks to mother nature there will always be a need for dredging , marine construction and coastline protection and I am certain that over time we will see an increase in solution providers. However it is not an area for the faint hearted and requires good hardware and software, the ability to customise and most importantly of all the capability to support the product 24 / 7.