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Fishery and Sea Resourcesbeen reached at a fictitious aft warp attachmentposition (i.e. moving further 55mmbackward to the existing last one). Finally,we can extract some conclusions ofthe doors’ impact on the seabed studyingthe reaction force. The reaction force was,in general, smaller at sea than in the flumetanktests, probably due to the small towingspeed used in flume-tank tests. In theflume-tank test the reaction has been measuredand we observed, for a given attackangle, it is smaller in Clarck-Y door thanAR door. For sea trials data, a predictionof reaction force has been calculated consideringan equivalent hydrodynamic of theflume-tank experiment. In sea trials theestimation of reaction force was stronglydependent on towing speed, in particularthe doors’ impact decreases when towingspeed increases. In particular, Clarck-Ypresents positive values of reaction forcewhen towing speed is around 3.8 kn, whichmeans a poor warp and backstrop rigging.Although, computational modelling is avaluable complementary tool to assess behaviourof an otterboard [3], and it can estimatedoor performances and loads, designdefects are clearly visible in flume tankand do not require more questioning, whileviewing the results of the simulation canbe sometimes more complex. For this reason,scaled prototypes in flume-tank experimentshave been extensively used to predictthe behaviour of the fishing gear [4].However, it is difficult to achieve a dynamicsimilarity between the prototype andthe full-scale gear. Comparing flume-tanktest data and sea trials data from otterboardwe also noticed important differences. Thisdifference is important in AR door (a factorof 2) and using only flume-tank test resultsit is not possible to predict the real spreadof the door at sea. Moreover, it is noticeablethat comparing flume tank data andsea trials, AR door has similar trends versusattack angle of drag, lift and efficiencywhile for the Clarck-Y door there is noevidence of coherent tendencies. In addition,the optimum attack angle (maximumlift and maximum efficiency) for Clarck-Ydoor is very different in sea trials and flumetank. Meanwhile for AR door the optimumbehaviour is reached at an attack angle of32.8º (warp towing point HF=3) which isonly 1.3 degrees smaller than in the flumetank. The current paper shows that datafrom the flume-tank do not always seemto reflect the real performance of doors atsea, where there is a valuable impact onthe seabed. It is well known that at seaother variables like towing speed, heel orpitch, soft seabed may also affect the hydrodynamicsand behaviour of the otterboards[1]. Notwithstanding the foregoing,there was generally a better agreement betweenthe result from the flume tank testsand the full-scale trials with the traditionalAR door: the full-scale door and the modelreacted in similar ways. But the behaviourof the Clarck-Y door at sea correspondedpoorly with that obtained in the flume-tank.However, we foresee future works with thisdoor because the promising door performancewas in general not verified.5 AcknowledgementsThis study was conducted with financialsupport from the Commission of the EuropeanCommunities, Project “DEGREE:Development of fishing Gears with ReducedEffects on the Environment”, contractno. SSP8-CT-2004-022576) and withsupport from DGICYT (Spain) under thegrant DPI2008-01408. These supports aregratefully acknowledged. We are indebtedto Dominic Rihan and Tan Huan (BIM, Ire-1886