Fix / seal / re mount transducer before going out again.
with sika marine sealant
Even a couple inches under the water at rest has a surprisingly amount of pressure to force water into transom.
Check bungs have O rings to seal.. missing O rings most common reason for leaking. They need to be done up firm.. not tight.
There should be nil water in the bulges after a day, even 2 days out on the water.
Issue could be with resent rain, if bow down on the trailer has a lot water in... espec if bungs where in.
We dropped the sons boat in on the weekend, as he backed it/ slide off the trailer he could hear the water up in the bulges. Once the boat started moving it drained back into the rear bilge, must have been a good wheel borrow full.
If O rings all good, wqas stored bow high on the trailer , bungs out. You can fill the bulges with water on the trailer... just bulge height, dont over do it as the weight can effect the structure. Then leave and look around the hull, in particular the screws that hold the keel strip on, after a few hrs or over next couple days