With advances in deepwater technology the need for remote intervention as part of field installation has seen major increases in the number of deepwater remotely operated and autonomous underwater vehicles.
As the complexity of these vehicles evolves the demand for lower density, high performance composites buoyancy systems has increased. This is an area where Balmoral has made significant technological advances.
The use of conventional cast composite buoyancy packs still has many commercial benefits for large vehicles used for trenching of pipelines or submarine cables. However, for deep dive work class ROVs, operating beyond 2000msw, the performance benefits of Balmoral’s LDF series becomes significant.
This low density, pure foam composite provides the operator an opportunity to increase the uplift (buoyancy) of the vehicle thereby resulting in increased payload capacity. It also provides an opportunity to reduce the size of the buoyancy modules thereby reducing the overall weight and dimensions of the vehicle.
Balmoral LDF buoyancy is available from stock for operating at depths to 7000msw.
Balmoral also supplies ROV support equipment for use on the umbilical systems including floats and FlexLinkTM, a buoyant umbilical bend control system.
Composite foam systems
A “composite” buoyancy system refers to a syntactic foam comprising glass microspheres and macrospheres held together within an epoxy resin system to create a homogenous matrix.
Composite buoyancy systems are cast using dedicated mould tooling providing repeatable consistent production and are therefore ideally suited in applications such as work class ROV’s - particularly on a multi-build requirement.
Each component within any given Balmoral syntactic foam is individually rated for specific operating depths resulting in a strong, lightweight composite formulation.
There is an overlap in the operating depth ranges which is caused by macro efficiency changes in design operating depths. This means that more efficient, lower density composites may generate improved uplift for a given volume as the operating depth increases.
Composite buoyancy systems comprise an integrated shell to ensure maximum protection of the core material in the event of accidental impact.
Pure foam systems
Pure foams offer many advantages over macrosphere composite foam systems including robustness, ease of repair and modification in the event of damage or design changes, and extremely low water ingress rates.
It should be noted, however, that this is a premium product and is therefore typically selected for more demanding service conditions such as extreme operating depths and/or service criticality such as manned service.
The “ultra-low density range” of pure syntactic foam is normally produced in pre-cast blocks. These blocks may be supplied for client assembly or can be factory assembled into finished buoyancy modules.
The buoyancy performance of Balmoral’s ultra-low density material is understood to be unique amongst ROV buoyancy foams in that the buoyancy does not progressively reduce due to hydrostatic compression as the ROV moves into deeper water. This is because the bulk modulus - ie, the compressibility under hydrostatic pressure – of the foams is marginally less than sea water.
Pure foam ultra-low density range (LDF)
|Operating depth (ft/msw)||
Typical core density kg/m3
|3250 / 1000||
|6500 / 2000||
|9850 / 3000||
|13100 / 4000||
|16500 / 5000||
|23000 / 7000||
|32800 / 10000||
ROV/AUV external finishing
Selecting a coating for buoyancy modules of any type is a critical issue. These coatings provide impact and abrasion resistance while offering a high visibility smooth gloss finish.
The most frequently supplied ROV/AUV coating is a 3-5mm spray-applied elastomer which is applied to all upper and external surfaces to give a very effective finish, particularly for work class vehicles.
Standard finishes are provided in high gloss yellow, orange, red or white. Other colours are available to suit project parameters. An extremely high quality smooth finish is available for specialised applications.
Where a quantity of modules of the same generic shape is required, in applications such as skid module blocks or trim modules for example, Balmoral provides an alternative to PU or GRP skins by utilising rotationally moulded polyethylene shells.
Polyethylene is a material used extensively in the offshore industry and these shells can be manufactured for heavy duty applications with thicknesses ranging from 6-14mm.
Provision should be made within the design to accommodate the tolerances applicable to rotationally moulded products.
ROV buoyancy machining and milling
During 2013 Balmoral Offshore Engineering introduced an in-house ROV buoyancy block milling capability.
Taking internal control of this process allows Balmoral to create intricate ROV PFS and LDF buoyancy profiles with virtually no size limitations using its 5-axis CAD/CAM-controlled milling machine.