Hi there bazzbug, u have 2 options:
Cut the transducer cable and join with an proper joining kit after u have pulled the wire through the gland,u will need an 16 mm gland and need to drill an 25 mm hole.
2nd, u drill 2 25 mm holes opposite each other about 75 mm apart in the length of the ski, cut an slot between the holes, fit the transducer, mount the bracket on the inside of the ski, seal with good sealer and on the inside eith the sealer that makes foam.
U will need to mount an 6 inch hatch on top of the ski to have access to the transducer.
Big holes though, but no leaks if u do it right. First time.