So I am almost complete with my transom replacement. I have these things that are on the outside of my transom that connect directly to the mercathodes. There are four of them. All four of them are are roughly a four inch diameter circle, two have a 1" metal strip down the center and the other two have a 1 inch circle in the center that has a bunch of holes. Are these things really neccessary? I know that two of them were leaking water in the transom. I also don't see these on newer boats. Can i just leave them off? Does anyone know what they actually do or if they are even beneficial to have? I want to drill as few holes as possible in my new transom.

i was talking w/ my marina discussing redoing my transom due to possible rot. he said if i go thru w/ it, just glass over & dont reinstall the mercathodes. he said they were only good if leaving the boat in the water full time. he said the less holes in the transom the better. so when i eventually break down & do the work, i will not be putting them in mine.

you can leave those electrodes off and go with the transom assembly mount type mercathode system if you still want the protection of it. The transom assembly type replaces the zinc anode on the bottom that mounts to the hyd block. This is the most common setup. You can buy the complete mercathode setup online fairly cheap. Comes with the inside controller, wiring, and electrode.

Sounds great. My boat had both types. I will just stick with the transom mounted ones. This is great. Thanks guys.