The Ventilated Trouser

The Ventilated Trouser VIV Suppressor (the VT).

The VT suppressor comprises a loose fitting sleeve with a net substructure and integral bobbins. The bobbins are arranged in a particular configuration and are designed in such a way that coherent vortex shedding is suppressed.

To ensure optimum suppression performance, the bobbin dimensions and spacing of each VT are matched to the diameter of the riser or cylinder of interest.

The VT sleeve is supplied in discrete lengths to suit the deployment method and application. In each case the whole system is engineered to suit the application for safety, efficiency, speed, and practicality.

The VT has no bearings or moving parts – once installed it mere translates downstream to assume its optimum operating attitude. The VT can be utilised in sheared current regimes, even opposing currents or any combination thereof.

Unlike other methods of VIV Suppression the VT can be used to contain and control umbilical bundles as shown in the video on this subject. Also unlike other systems, the VT has a negative lift coefficient throughout its operational range. This means it will always try and self-correct (or damp out) any oscillations; minor excursions are quickly corrected, as can be seen in the videos. This is a unique feature not present in other systems.

The suppression ratios (amplitudes suppression ratio or ASR) relative to the amplitude of bare cylinders have been consistently over 92% and as high as 97% in some cases.

The VT is simple to deploy and retrieve, the VT sleeve only requires to be suspended and attached by means of karabiner type clips, as do the seams. There is no requirement for permanent riser fixing points and there is no additional added weight in the operating mode as the VT is neutrally buoyant.

The VT eliminates all high frequency vibrations above the fundamental, a major factor in fatigue issues.

The VT does not impose any additional drag on the structure under consideration over that of a bare pipe at equal Reynolds Numbers.

It brings stability to the riser system and increases the operating window in areas where solitons or LOOP events take place and where drillers would otherwise have to suspend drilling.

The VT can pay for itself in less than two days for a typical drilling spread in the GOM.



  1. Initial proof on concept and geometry tests in Solent Towing Tank – UK
  2. Extended and confirmatory tests on geometry at various diameters and current velocities. Findings and results consistent with proof of concept tests. IFREMER flume Boulogne , France.
  3. Series of research tests demonstrating negative lift coefficient and cylinders in tandem. IFREMER flume , Boulogne , France.
  4. Demonstration at full scale on 21inch slick (bare) riser. MARINTEK , tow tank , Trondheim , Norway. Results show consistency at over 95% ASR ( Amplitude Suppression Ratio).
  5. Demonstration of VT on a complex arrangement of different diameter cylinders, Full scale stiffened wireline lubricator for use by Shell International on a sensitive investigation project. Solent Towing tank – UK
  6. Demonstration of an application for catenary risers and mooring lines. IFREMER, Boulogne, France
  7. Direct comparison of amplitudes of catenary risers and mooring lines with and without VT fitted. Results consistently recorded 95% ASR. IFREMER flume, Boulogne, France.
  8. Test programme to demonstrate capability of VT to contain and completely suppress FIV of a group of loose umbilical and control hoses in a strong current. Solent Towing Tank, Southampton UK.All the above have been recorded, logged and videoed and can be found in the video section of the site.
  9. Full scale ‘dry’ demonstration of VT deployment and recovery from a 7 inch completion riser, and a 16m tall scaffolding tower. Fleetwood UK.
  10. Full-scale deployment and recovery of VTs from a 7inch completion riser and from a group of umbilical and control hoses using techniques perfected in 9 above. Warren Joe Douglas Jack-up rig, Trinidad.

All the above have been recorded, logged and videoed and can be found in the video section of the site.


a) Shell International – investigative application for a sensitive stiffened wireline lubricator.

b) 7 inch Completion riser, Trinidad and Tobago BHP Billiton.

c) Umbilical bundle encapsulation and control, Trinidad & Tobago, BHP Billiton.

In addition Fugro have taken delivery of a VT suitable for a 7 inch riser. Currently awaiting installation.


Trinidad Underwater both VTs_2
Underwater & site shots of Lubricator