How to fix: Thru-hull transducer water leak in bilge

[pallantejm]

I am trying to discover the source of water filling up the bilge. I have narrowed it down to a potential seal leak near an Airmar thru-hull transducer/depth sounder.



The previous owner had a plastic P310 Airmar installed and after a couple days I get a bucket-full worth of water in the bilge. The level remains the same once it reaches a certain point.



I was curious as to what would be the best way to approach fixing this, as the boat is in-water at a marina. (Can this even be fixed in-water?) What is the best way to replace a leaky seal on these guys without flooding the boat?

[S/V Adeline]

The only thru hull transducers I have experience with required removal and installation from the outside. While I know it is possible to swap them out in water, past dealings with Murphy and his/her infernal laws would keep me from trying unless a haul out was just impossible.
I would not want to attempt it unless a sling was nearby and available if things went south.

[coopec43]

I did a search on "underwater sealant leaking through hull fittings" and came up with a number of links which could well be helpful.