I guess I have an electrolysis problem

[Sun Chaser]

When I launched the boat in April I noticed the start of a hole in my transom housing. This hole is at the top of the housing above the water line. When I pulled the boat for the winter, I now have a hole in the transom housing. Where do I start to determine weather I have a boat problem or a problem with our electric in my marina.

Glenn

 

[Carpediem44DB]

Yikes! There are ways to simply measure the current in the water at your slip. I think a lot of it is kind of black magic. If you keep your boat plugged into shore power you will want to go thru the boats grounding system carefully and ensure it’s all I good shape and check to see if you have a good ground isolation device in your system.
Also ask around to see if other owners near you or even on the other end of the marina have noticed any increase in wear of their anodes recently.
Hope you figure it out. That will make boating really expensive really fast!

 

[tdschafer]

I had an issue with my old 260 DA one year in my marina where I was going through zincs at an alarming rate. Turned out the guy next to me had serious electric issues on his boat & was dumping current into the water. They ended up pulling his boat out of the water as it had damaged a few boats in his vicinity. I was lucky that I checked my zincs regularly.

 

[Lazy Daze]

Have you had the boat since new?

This is a REALLY odd place to have an issue. Do you have any issues anywhere else on the drive. For now, I'm going to assume "no", since you probably would have said something. That looks more like someone did a swivel pin repair and the repaired "hole" that they cut out to access the pin is simply starting to come apart. Sand that entire flat area and see what you see. It certainly could be something else, but this makes the most logical sense given the info at hand.

 

[BillK2632]

Agree it seems like an odd spot for corrosion. That is right where swivel pin repair work would be done. Corrosion usually stats around the prop shaft hub and any areas in close proximity to stainless steel.

 

[Sun Chaser]

Thanks for the replies. I've owned the boat since 2006. I am not aware that any work was done to the swivel pin. Since my boat is out of the water as well as the boats next to me, I will have to wait till next year to look for stray current around my boat. What I plan to do before launching the boat in the spring is buy the kit for repairing the swivel pin and at least cover up the hole with the plate they give you.

 

[SCORPIO]

How did your zincs look when you hauled out? Are you in fresh or salt water? Any other corrosion damage anywhere else on the drive?
To measure voltage in the water, get a silver/silver chloride electrode and a digital multimeter. You can simply attach the negative lead to the engine block and the Ag/AgCL electrode to the positive input of the meter and just dunk the electrode in the water about two to three feet deep and read the potential off the meter. There is a range of potentials in Mercs. manuals that will tell you what is 'safe' and what is going to cause corrosion. I do this several time each season so I have a baseline and can compare readings over time to see if something is changing. I had bad zinc wear two years ago and found out the guy two slips down had a garden variety extension cord powering his shore power inlet and the cord was in the (salt) water several hours every day. He got an approved marine shore cord this year and no issues for me.

 

[Sun Chaser]

I'm in salt water. Here is a picture of the zincs. I don't think they look too bad. The rest of the drive looks OK.

 

[JVM225]

That round zinc looks way too healthy compared to the other two. Is that what’s left of the zinc that is mounted above the prop?
I would start by making sure all of the ground connections are clean and tight. Everything should be bonded together and the ground block (with all the green wires attached) should attach to your engine block.
Also check the ground wire that goes from behind your dockside power inlet to your 110 panel on your boat.
The “Galvonic Isolator” will be located inline on the ground wire between the inlet and 110 panel.
You may also want to have an electrician check the condition of the receptacle and wiring you plug in to on your dock.

 

[Sublimetime]

I have seen this exact spot on two different boats exact same corrosion all the way thru.

Related or not- the bottom paint should have about a half inch of clearance all the way around the outdrive so the bottom paint does not touch the drive housing, which should be painted with a different type paint meant for aluminum

 

[Sun Chaser]

Thanks for the replies. The zinc in the center is the bearing carrier. The one on the right is the trim tab. I bought the probe for checking stray current but will not be able to use it till next spring. I'll also check out the boat the best I can before spring launch. I'm not going to replace the transom but will be buying a kit that will allow me to cover up the hole . As for bottom painting, I'm going to leave a gap around the outdrive.

 

[JVM225]

Make sure you have a sanded off clean surface to mate that “trim tab” zincs to when you install the new zincs in the Spring. It doesn’t look like it was doing too much for you compared to the other two in your picture.