Pitting on rudders and exhaust funnels?

[Skuza]

Noticed some pitting on the rudders and the underwater exhaust funnels this year that I never really noticed before. Looks like rust blisters about 1/8" in size. The props and shaft struts are fine though. I'm wondering if this is due to the age of the boat now ('98) or if this is a grounding problem? How do you check if it is a grounding problem and why would it just be the rudders and exhaust funnels? Our boat is in freshwater (Lake St. Clair). I have never noticed this before or maybe I never eally payed attention. There is an '02ish 41 that appears normal yet but is that due to it being newer? I have pics but not handy. I'll try and get them posted.

 

[Asureyez]

Time to check your bonding system in the ER.

The likely issue will be galvanic errosion on these bronze parts.

Take screw driver, flashlight, small wire brush, some 1/4, 5/16 and 3/8 terminal eyes for #8 wire with crimper, in to the bilge. Crawl around in the aft ER and find the BUSS blocks where all those green bonding wires run to and then make sure they are corrosion free, you'll have at least three or four of these BUSS blocks. Clean up any corrosion and coat with Dielectric grease. Trace all Green bonding wires to confirm they are making soild connection and the terminal ends are in good shape.

You will find grounding wires running from each through hull fitting, each sea strainer, each rudder stock, each exhaust backing plate, each strut backing plate each main engine, the generator and tranny.

These grounding BUSS blocks will then be led to the hull zinc posts which should be in the bilge at the center of the stern below the waterline. The 460 zinc is through bolted under the generator, yours will be in a similar spot low and center in the aft bilge.

It is common to find terminal ends corroded through wires adrift, or dangling on one strand. Make sure the hull zinc is in good shape and make repairs accordingly and the loss of bronze should stop. :smt038 Don't do it and you'll loose the boat to Neptune one fine day.:smt100