Having chosen the EchoPilot 2D for your boat the only remaining choice is: which transducer ismost appropriate. Our larger professional transducer comes with a bronze 2“ BSP thru-hullftting and with 3“ of useable thread is excellent for most larger boats.The standard transducer fts through a glass flled Polypropylene thru-hull with 1“ of useablethread. Most bottomed GRP hulls can take the standard transducer.If however you have a thick hull, or a signifcant degree of dead rise requiring wedges or chocksto keep the transducer vertical then the professional is the choice to make