Corrosion

[Boatin2]

Hi everyone, I have a couple questions about corrosion. When we pulled the boat in the fall there is some corrosion on the port side forward on the bottom. I plan on sanding and painting the bottom in the spring and am trying to get things together. Question 1. Would the corrosion typically be close to the source of the problem? If so it should be much easier to find and correct. Question 2. How do i repair the corrosion before I paint. Thanks, Mike

[jralbert]

In the years I've been watching this forum, reports of corrosion in that area are unusual. More likely - for me - rare. There is some interior wiring in that area that I would check out - such as a bilge pump or cabin lights. Make sure all the wires are secure and covered, not touching the hull. The 12v stray current is the biggest corrosion source.

[Boatin2]

It is fairly close to the fresh water pump. Who ever installed is used wire nuts on the connections. I rarely used it and it is sitting on a wood platform. Should I replace the nuts with butt splices and heat shrink tube? The anodes were new this season and look fairly pitted as well. Is this normal? How long should they last in fresh water? Sorry for all the questions I just want to make sure she doesn't dissolve around me.

[bill]

What kind of readings are you getting on you capac meter?
bill

[Boatin2]

Bill, when we first launched it was reading around .085. After we got to our marina I did some work an finished hooking up power to the fresh water pump and search light. Since then it hasn't been any higher than .065. I don't know if its because of what i wired up or the shore power. My dock neighbor that was in the slip next to me had to move because he said the power blew up on him? Mike

[Maestro]

Replacing those wire nuts is probably a good idea. Make sure your bilge pump wires and other wires are not submerged in the bilge water.

It would be interesting to see what your CAPAC reads "out at sea" as well as at other marinas. That would tell you if there's any electrical funny business happening around your dock. I have read stories on the old forum about other boats or even the docks themselves leaking voltage into the water due to bad wiring.

About your anode question:
Brand new anodes in fresh water can probably last 2-3 seasons but that can vary depending on your body of water and who's parked around you (stray current). I believe the general rule is to replace the anodes when about 50% of their mass has dissolved away. I bought brand new anodes for the summer of 2014 and before I splashed the boat in for 2015, I sanded the corrosion off the anodes with a random orbital sander. I put them back on the boat and the continued working great. They will get used again for summer 2016. If the anodes appear corroded, they're doing their job.

About your corrosion repair question:
There were entire topics and detailed conversations on the old forum about this. There is some here too if you search around. The short version of the story is to do it right, you need to sand the corroded area down to shiny metal. If there is pitting, you chemically etch the aluminum and apply a primer. Then, you fill the pits with PC-11 Marine epoxy and paint with antifouling bottom paint.

If you just wanted to repair a small area of corrosion, you could sand the area down to the bare metal and immediately clean with paint thinner or compressed air, then spray it with a couple coats of this stuff:
http://www.jamestowndistributors.com/us ... on+Aerosol

Then do the PC-11 for pits and actual bottom paint.

Hope this helps!

[jralbert]

Wire nuts don't belong in boats (well, I did use them to connect audio speakers in a couple of dry places because I didn't have another connector available at the time). And, of course, keep those connections out of the water.
Anodes: they are meant to wear down. If they are wearing rapidly, though, in fresh water, you have to check the source. Stray DC current is much more corrosive to alum boats than AC. The reason, I've read, is that the DC current is always moving in one direction, pulling electrons and metal away from the "less noble" surface to the more noble one. AC is going back and forth (alternating). So those electrons are marching to and fro.

[Boatin2]

Thanks guys. I appreciate any help.