in ometer ▁or ▁based ▁on ▁USB L , ▁where ▁a ▁ris er ▁angle ▁monitoring ▁trans ponder ▁is ▁fitted ▁to ▁the ▁ris er ▁and ▁a ▁remote ▁incl in ometer ▁unit ▁is ▁installed ▁on ▁the ▁B low ▁Out ▁Pre vent er ▁( B OP ) ▁and ▁inter rog ated ▁through ▁the ▁ship ' s ▁H PR . ▁ ▁Light ▁t aut ▁wire , ▁L TW ▁or ▁L W TW . ▁The ▁oldest ▁position ▁reference ▁system ▁used ▁for ▁D P ▁is ▁still ▁very ▁accurate ▁in ▁relatively ▁shall ow ▁water . ▁A ▁cl ump weight ▁is ▁lower ed ▁to ▁the ▁se ab ed . ▁By ▁meas uring ▁the ▁amount ▁of ▁wire ▁paid ▁out ▁and ▁the ▁angle ▁of ▁the ▁wire ▁by ▁a ▁g im bal ▁head , ▁the ▁relative ▁position ▁can ▁be ▁calculated . ▁Care ▁should ▁be ▁taken ▁not ▁to ▁let ▁the ▁wire ▁angle ▁become ▁too ▁large ▁to ▁avoid ▁drag ging . ▁For ▁deeper ▁water ▁the ▁system ▁is ▁less ▁fav ou rable , ▁as ▁current ▁will ▁curve ▁the ▁wire . ▁There ▁are ▁however ▁systems ▁that ▁counter act ▁this ▁with ▁a ▁g im bal ▁head ▁on ▁the ▁cl ump weight . ▁Hor izontal ▁L TW ' s ▁are ▁also ▁used ▁when ▁operating ▁close ▁to ▁a ▁structure . ▁Object s ▁falling ▁on ▁the ▁wire ▁are ▁a ▁risk ▁here . ▁F an be am ▁and ▁Cy Scan . ▁These ▁are ▁las er ▁based ▁position ▁reference ▁systems . ▁They ▁are ▁very ▁straightforward ▁system , ▁as ▁only ▁a ▁pr ism ▁cluster ▁or ▁t ape ▁target ▁needs ▁to ▁be ▁installed ▁on ▁a ▁nearby ▁structure