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Old 03-12-2018, 09:00 AM   #7
Dougcole
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City: Carrabelle, FL
Vessel Name: Morgan
Vessel Model: '05 Mainship 40T
Join Date: Jan 2008
Posts: 2,162
Quote:
Originally Posted by djmarchand View Post
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
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.
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