. Wet Tows Capt. PJ Donaldson, Noble Denton
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OGP Marine Risks Workshop Proceedings . Wet Tows Capt. PJ Donaldson, Noble Denton Wet tows Management of Risk by Design and Planning Capt. P J Donaldson Senior Principal Surveyor Noble Denton Europe Ltd OGP Categories of Wet Tows Offshore barges Good, effective guidelines Well established procedure Ships in distress or going for demolition Vessels rarely in new condition and usually require a work to make them seaworthy FPSOs, large tankers or bulk carriers Current practice is a combination of good practice from the above two categories. Risk is unique © OGP International Association of Oil & Gas Producers Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Inclement Weather OGP Tanker being converted to an FSO in the shipyard © OGP OGP Marine Risks Workshop Proceedings Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP OGP Factors for Design & Planning Size and Bollard Pull of tugs Towing arrangement Emergency Anchor Riding crew Bunkering arrangements Weather Unique requirements Warranty Surveyor © OGP International Association of Oil & Gas Producers Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Size and Bollard Pull of Tugs The warranty surveyor will require the tugs to have sufficient power to maintain the tow at zero forward speed using the following criteria. 20 ms-1 wind 5m wave 0.5 ms-1 Use of greater tug power will provide higher towing speeds which can assist with weather avoidance and reduction of exposure to risk Bollard Pull is derived by calculation or through the carrying out of model tests. OGP Typical anchoranchor-handling tug © OGP OGP Marine Risks Workshop Proceedings Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Ocean Going Salvage Tug OGP Towing Arrangements Careful and early approach to design of tow connections and fairleads. Design for the bollard pull of the vessel Ensure Panama type fairleads are well spaced and suitably sized (OCIMF Guidelines provide a useful code) Smit Type brackets are still standard but under deck strengthening is intrinsic to the strength of the connection. © OGP International Association of Oil & Gas Producers Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Emergency anchor Current practice is for barges to fit an emergency anchor. Some consider this practice should be extended to large FPSOs However, Large vessel size requires large anchor Chain stowage to be provided Deployment system to be provided (unless FPSO converted probably not fitted with hawse pipe or chain locker) For much of voyage anchor cannot be used because of water depth Access to deploy in heavy weather difficult Anchor could probably only be used once On balance we consider an additional tug would reduce risk, provide a more flexible response and be more reliable than an emergency anchor OGP Riding Crew Manned (advantages) Easier to re-connect tow Heli-deck may be commissioned (pilot/emergency access possible) Pumps can be kept on permanent stand-by Fire watch maintained Watertight integrity monitored Towing chains maintained Manned (disadvantages) Fire and lifesaving equipment must be commissioned Difficult to control numbers Evacuation of larger numbers in an emergency Unmanned (advantages) No risk to personnel SOLAS requirements do not apply Less risk of fire or man made mishap occurring onboard © OGP OGP Marine Risks Workshop Proceedings Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Bunkering Arrangements Sufficient consumables including fuel should be carried to perform each leg of the voyage with a five day reserve. The tow should be controlled by tugs with adequate power whilst the main tug is bunkering. Most bunkering ports are in restricted areas Possibility of using the FPSO as a fuel reserve OGP Weather Forecasting and if appropriate, routeing services from a recognised forecasting agency should be engaged. At times of critical decision making more than one forecast may be needed Season of departure; typhoons, monsoons, gales Capacity of the equipment to withstand the transportation forces along the route should be assessed. © OGP International Association of Oil & Gas Producers Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Climatic Effects by month Particular considerations for large FPSOs Pumping capability Access to vessel Depth too high for temporary pumping system Time to activate system makes quick response difficult High sides pilot ladder not practicable Fixed access stairway required Access in greater than BF4-5 and swell difficult and dangerous Helipad may not be commissioned or FPSO out of helicopter range © OGP OGP Marine Risks Workshop Proceedings Wet Tows - Capt. PJ Donaldson, Noble Denton () OGP Other considerations during tow Piracy in restricted channels. What could pirates do? Set accommodation alight, release towline. Ports of refuge or areas of shelter Route; shortest distance may not be best (consider current, weather etc.) Daily voyage reporting (with positive reporting system) Seafastenings and securing onboard Canal and river passages; squat and bank interaction Under keel clearance. NDE recommend 1m minimum (after allowing for squat, sag, protrusions, environmental conditions etc.) OGP Role of the Warranty Surveyor Protects the interest of the Underwriter Reviews all aspects of the wet tow Is able to bring experienced assistance to the marine venture. If brought in early at the design stage can make an effective contribution to the success of the voyage. © OGP International Association of Oil & Gas Producers © OGP
