all of our beach launched fishing boats around here simply silicone the transducer onto the single layer of glass in the well at the transom. Then it doesnt get damaged by rocks and shingle on the beach and the silicone is easy to remove if you need to. It will work perfectly well without silicone and without any nasty oil in a tube if you just throw a bucketfull of water in the drain well and toss the transducer in there! Helps if you wedge it upright of course
We used to do this with one of our fishing boats and then take the whole rig out when we went to Ireland with my mates boat so that we didnt have to run thru all that expensive paper on the one he had fitted-worked fine just thrown in a well full of water (transducer-not the top bit ! ). And No you dont need a shoot thru the hull type transducer to make it work
As a passing thought we dumped our last hummingbird as it didnt want to know at speed-replaced it with a cheap (£70) eagle cuda-brilliant, works at all speeds, the shallow water alarm is a godsend round here, and transducer is simply siliconed in the well! Got two now and they are both fine after over a years hard work.