Untitled - CNR

Marine research at CNRCL=Eff). For the sea trials, the resultsare presented for two cases: zeroing theheel term, ST(H0), and without any constraintof the heel, ST(H). In each casethe corresponding warp towing point (HF)have been also calculated. For AR door,in general the differences of the estimatedattack angle values between sea trials at0° heel and flume tank tests is around 7degrees (Table 4). The warp attachmentposition to the otterboard with maximumlift at sea was found at HF=3, with a correspondingattack angle of 34.2º. At thesame HF, this otterboard works in optimumcondition (CL=Eff) and attack angleof 32.8° (Table 4). Meanwhile the maximumefficiency was reached at sea with theHF=2 and a correspondent α=25.6°. ForClarck-Y door, in some cases it was notpossible to find these values (see Figure4). The optimum behaviour of this door atsea was reached at HF=6 (α=47.4°), whichdoes not exist. Therefore, the statisticalmodel applied estimated a fictitious backwardwarp attachment position to get optimumcondition of Clarck-Y door. As aresult of the model we have also foundthe location of the fictitious center of pressure,affected by ground effect. Usuallyin flume-tank the longitudinal distance isaround 40% (see [1]) in sea trials we foundit was around 60% for both AR and Clarck-Y. With respect to zp, in AR is located inthe upper door plate above the cord, at 66%of the height, while in Clarck-Y it is on thelower plate, at approximately 55% of theheight.4 Discussion and conclusionsThis paper illustrates the performance andimpact on the seabed of an existing door(termed AR door) and a new door design(Clarck-Y door) for demersal fisheries, discussingthe differences between engineeringsea trials and flume-tank tests and alsothe differences between both trawl doors.We provided some results related to behaviourof otterboards such as the drag-, lift- and down-coefficient hydrodynamiccoefficients and the angle of attack. A valuableindicator of the impact of the otterboardon the seabed such as the reactionforce of the otterboards, was also calculated.The current paper is not new onlybecause it gives details on two unstudiedotterboards but it also undertakes a moredetailed and rigorous analysis using sea trialsdata, which is why it is been credited.In flume-tank tests both doors not only presenteda similar behaviour with attack anglebut also similar magnitude of drag-,lift- and efficiency coefficients. Meanwhilecomparing both doors in sea trials thereare important differences, for instance, ARdoor works with a higher drag- and liftforceas well as a larger spread but lower efficiency(CL/CD) than Clarck-Y door. As amain result of this work, we estimated valuesof attack-, heel- and pitch-angles andthe corresponding horizontal door spread,drag-, lift- and efficiency coefficients in seatrials condition for each warp attachmentposition to the otterboard. This is usefulinformation both for door manufacturersand fishermen: the maximum lift andthe optimum behaviour estimated for theAR otterboard were for the third attachmentwarp position. For Clarck-Y door, theestimated optimum condition might have1885