Here is how I did mine on the TI.
I do not like cables loose in the bottom of a boat so I used some electrical fittings to connect the transducer to the standard electrical gland I installed.
I used a standard 20mm gland, modified some fittings I got from Bunnings Hardware to screw into the gland and used some 20mm pvc conduit to fit is and cable tied up at the front hatch mast mounting point. I also put an elbow on the end to point down to stop excess water coming in...not really necessary but nice.
Pic 1 - 3 fittings used plus PVC conduit...cable gland (throw away the nut and use part 2 as nut), modified 25mm to 20mm reducer (couldn't find a 20mm threaded piece, 20mm threaded fitting to 20mm push in fitting for conduit.
(conduit runs from gland fitting that tightens rubber grommet on cable to mast column (about 1.5m)
Pic 2 - I used a lathe to take off the lip to make an internal threaded piece, can cut it off carefully with hacksaw if you don't have a lathe. This piece is now the new gland nut and couples the PVC conduit fitting to the gland. Can glue conduit into the fitting if you want...I didn't bother!!!
Pic 3 - To get power through because cable is short I drilled a hole just before it fits into coupling and fed wires out. Alternative (probably better) is to extend power wires and run through to front hatch???
Pic 4 - What it looks like from outside when finished (pocket to be re-installed) and cable to be run through...
When the conduit is installed it was run along the side wall off the bottom (natural flex caused this) so it sits against side wall. I put some goop on the tube to fix it to stop any flapping about.
Looks neat and tidy inside and out and is more waterproof than the Hobie way. Cost about $10-15 in parts but I had to buy 2 couplings per pack so have a spare one for my brother's boat...when he gets one!!!