Exhuast hose damage from battery off gas

A section of the exhaust hose is showing signs of some damage where it runs close to my house battery bank. The reinforcing wire in that section of the hose is starting to rust. The damaged section is about two feet long, only on one side of the hose and the rest of the hose is prefect. So I'm pretty sure it is from the batteries in my house bank which are 4 6V lead acid batteries. The batts are 2 years old and in good shape with no swelling, corrosion, problems holding a charge etc. I'd rather not replace the batteries at this time or go with some sort of AGM. I'm happy with my set up.

Even the damaged section of the hose pretty sound still, it's not soft at all or anything like that, but I'm concerned about it. It's a really big project to replace the whole hose, as I will have to move the genset to reach the muffler in the lazerette.

So here are my questions for the board:

1. Have you seen this type of thing before? Could it be related to something else?

2. Anything I could do to stop it from taking any more damage? Some sort of cover around the hose? Tape? Periodic cleaning?

3. The batts are in an open tray. Should I build a new tray with a lid?

4. Is it possible/advisable to replace just that section of the hose by splicing a new piece in?

Thanks as always.

Nothing wrong with splicing in a fresh section of hose. Get two pieces of FG exhaust tube maybe 6-8" long and eight clamps and a new piece of hose. Or a longer piece of FG tube to span the whole length of the damaged hose.

Maybe the batts cooked at some point prior to your ownership. Batts in good shape with good charging don't off-gas much, but will if you run them down and back up on charge. Any natural ventilation in the compartment?

I had the same problem, it turned out to be the exhaust risers were not swirling the water correctly. Fixed by replacing the risers with OEM factory risers instead of the knock off risers that the PO had installed.

Yes, the batteries were going downhill when I bought the boat, replacing them was one of my first projects.

I don't think it is my elbows/mixers. I replaced those a year ago and wouldn't the damage be to the entire hose, not just one section?

I have a 2007 Mainship 40 T and had the same problem. I replaced the entire run. Mine used two different size hoses. The batteries were spent when I purchased my boat. Be sure to check your battery shelf. I had to replace one of mine.

I will second Ski's theory and fix. If the damaged run is straight, just splice in a piece of fiberglass exhaust tube. Centek makes them.

The offgassing theory is strange, but your evidence certainly points to that cause. It may have been the old batteries, but also could be your charger is putting out too much current at the float stage or staying in the absorption stage too long.

Are you using electrolyte water? Good batteries and chargers should only need water adding once or twice each year. If you have to add significant water, check the float voltage after the charger has been on for a while and the batteries are topped off (charge wise). Check the voltage at the battery terminals. Should be in the mid 13s.

FWIW, I think the mechanism for how the battery off gas affected the steel hose reinforcing is the batteries off gassed significantly either because they had turned bad or a bad charger. When they offgassed it carried tiny aerosol droplets of sulfuric acid with the gas which settled on the hose, permeated to the reinforcing steel and corroded it.

An advantage of splicing in a section of fiberglass tube is that the offgas aerosol will not affect the fiberglass.

David

djmarchand said:

I will second Ski's theory and fix. If the damaged run is straight, just splice in a piece of fiberglass exhaust tube. Centek makes them.

The offgassing theory is strange, but your evidence certainly points to that cause. It may have been the old batteries, but also could be your charger is putting out too much current at the float stage or staying in the absorption stage too long.

Are you using electrolyte water? Good batteries and chargers should only need water adding once or twice each year. If you have to add significant water, check the float voltage after the charger has been on for a while and the batteries are topped off (charge wise). Check the voltage at the battery terminals. Should be in the mid 13s.

FWIW, I think the mechanism for how the battery off gas affected the steel hose reinforcing is the batteries off gassed significantly either because they had turned bad or a bad charger. When they offgassed it carried tiny aerosol droplets of sulfuric acid with the gas which settled on the hose, permeated to the reinforcing steel and corroded it.

An advantage of splicing in a section of fiberglass tube is that the offgas aerosol will not affect the fiberglass.

David

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Thanks, all of you, for your input. I replaced the old batteries after they had a catastrophic failure. They swelled, leaked acid, and wouldn't take any charge at all. The battery charger failed at the same time, I believe that it was overcharging, but to be completely honest, I can't remember exactly what was wrong with it. I replaced the charger at the same time as the batteries. Obviously, I should have done that job sooner.


The damage is just on the port side hose, not on the stb side. When I bought the boat it had 2 8D's both on the port side under that hose. They served as both the house bank and as starting batteries. When I did the charger/battery replacement I put in the 4 6V GC's as a house bank on the port side and a single 4D on the stb side as a starting batt for both engines. I did some rewiring that put all of the house loads onto the house bank.

So what you say makes a lot of sense.

I also like the suggestion of splicing in a section of fiberglass tubing. It's easier, cheaper and impervious to the gas. It's a straight run there. I'll do some internet searching for tubing.

Wondering if when the old batteries failed, some of the vaporized water and acid got on the exhaust hose and just took a while to corrode it.

Ted

Dumb question, but will centek 4" OD fiberglass exhaust tubing slip inside 4" ID Trident Corrugated exhaust hose?

Not sure the extent of the damage or why you think the batteries were involved. I've certainly had hoses age (most notable symptom was some rust appearing on the surface from the wire within). Nothing to do with batteries.

A picture might help.

Dougcole said:

Dumb question, but will centek 4" OD fiberglass exhaust tubing slip inside 4" ID Trident Corrugated exhaust hose?

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Almost certainly, yes. They are made to do just that.

David

Yep, FG tube is 4" measured on OD. Exhaust hose is 4" measured on ID. Made to fit together.