I managed to run aground and put some scratches in my fish finder transducer. I'm not sure if the damage is interfering with the readings, there's a lot of 'frass' on the screen, but I'm not sure if it's because of the scratches or just the temperature of the water. Still, I would like to fix the scratches if possible. Would sanding the bottom of the transducer work, or is there some other method? It's a transom mount skimmer transducer.

My suggestion would be to contact Lowrance's tech support people and explain to them what happened, I don't think I would start sanding till you run it by them.

You can also drop the unit off at 1 of our stores (Boater's World, we'll cover the shipping) and we'll send it back to the manufacturer for analysis, you'll get the unit back in 10 days to 2 weeks, max.

Cabela's and bass pros have all the transducers you could ever want at a OK price.
Look athe transducer and see if the scratches have cracks then let water in, they dont have to be all the way in if there is not enough plastic between the guts and the flat botom every time you put the boat in the water conensation well do the exact thing you described....also check the cable where it goes into the transducer, a broken or cracked cable can let mositure in....Try to find someone who has the same sonar as you and do the swap test...if his does the same on your boat...its about $50 for a new transducer....DJ