Hi, Peggy, We previously discussed replacing my aft holding tank and the fact that no plastic tank was available from several companies. We were forced to replace it with another metal tank from the original manufacturer (Ezell) but one twice as thic)k and internally coated (for whatever good that may do. The installer said "Hey, guess why your tank crapped out... it wasn't grounded." Ezell also suggested grounding. Hunter, as you know does not ground or bond anything, as they are opposed to this idea. Well, do you think that grounding may prevent or slow down corrosion? Thanks. George
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Jim Rushing
No George
Grounding the tank will not change anything. There shouldn't be any stray currents flowing through the tank. The problem is not the thickness of the aluminium, but the welds. When you weld aluminium you lose the alclad protection and the acid eats through the welded bead eventually. If they can coat the inside of the tank completely, then it will buy you time until the coating breaks down. The other problem with the original tank is the small size. When I changed tanks, I went from 13 gallons to 25 gallons. That is a big difference for a boat that is on a lake and must pump out at a site.
Grounding the tank will not change anything. There shouldn't be any stray currents flowing through the tank. The problem is not the thickness of the aluminium, but the welds. When you weld aluminium you lose the alclad protection and the acid eats through the welded bead eventually. If they can coat the inside of the tank completely, then it will buy you time until the coating breaks down. The other problem with the original tank is the small size. When I changed tanks, I went from 13 gallons to 25 gallons. That is a big difference for a boat that is on a lake and must pump out at a site.
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Peggie Hall/Head Mistress
Grounding it can't hurt
Otoh, metal water and fuel tanks aren't grounded, and they last 20+ years...so I dunno how grounding a metal waste tank would slow down the rate at which urine eats through a metal waste tank. You may not have been able to find a stock plastic tank to fit...but there are custom plastic tank fabricators who can weld a tank to any specs--for the same, or prob'ly even less, that you paid for the metal tank. Several people here have gotten 'em from C.C. Tech (http://www.gocctech.com/marine/boat-tank.htm). But in your waters, for only a couple hundred $$ more, you could have gone with a LectraSan (CG certified Type I MSD that treats waste and discharges it overboard legally) and a small tank for use only on those rare occasions when you happen to visit a "no discharge" harbor or marina. I know we discussed this option, George...how come you didn't want to do it?
Otoh, metal water and fuel tanks aren't grounded, and they last 20+ years...so I dunno how grounding a metal waste tank would slow down the rate at which urine eats through a metal waste tank. You may not have been able to find a stock plastic tank to fit...but there are custom plastic tank fabricators who can weld a tank to any specs--for the same, or prob'ly even less, that you paid for the metal tank. Several people here have gotten 'em from C.C. Tech (http://www.gocctech.com/marine/boat-tank.htm). But in your waters, for only a couple hundred $$ more, you could have gone with a LectraSan (CG certified Type I MSD that treats waste and discharges it overboard legally) and a small tank for use only on those rare occasions when you happen to visit a "no discharge" harbor or marina. I know we discussed this option, George...how come you didn't want to do it?
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George Kornreich
Here's the problem:
Our marina is in a no-discharge zone, which extends for some distance in all directions. Also, there is no place to install the tank within 6 or even 8 feet of the head. The headroom where the existing tank is located is too low to accomodate the unit. Believe me, I wanted to take that option, but could not. OTOH, I plan to replace the forward tank with a lectrosan in the spring, as we have plenty of room for it there. We also explored the option of having a custom molded plastic tank made, but they (Ronco and others wanted to make a mold from our tank at my expense as they did not have one and didn't want to make it from our measurements, and the mold cost was far too expensive (of course after I paid for the mold they would be able to make the tank for others with no mold cost!) Here's an interesting tidbit... The forward tank is failing at all the screwholes on the TOP where the inspection plate and sensor are screwed in, not below where the tank is bathed in urine, so I think it might be electrolysis rather than caused by urine in this particular case. The aft tank failed at the weld of the pumpout fitting to the top of the side of the tank... the fitting just came off, so I don't know why that area failed either. Any ideas? The bottom of the tank we pulled was intact. I wish I were in San Diego too... Great place. George
Our marina is in a no-discharge zone, which extends for some distance in all directions. Also, there is no place to install the tank within 6 or even 8 feet of the head. The headroom where the existing tank is located is too low to accomodate the unit. Believe me, I wanted to take that option, but could not. OTOH, I plan to replace the forward tank with a lectrosan in the spring, as we have plenty of room for it there. We also explored the option of having a custom molded plastic tank made, but they (Ronco and others wanted to make a mold from our tank at my expense as they did not have one and didn't want to make it from our measurements, and the mold cost was far too expensive (of course after I paid for the mold they would be able to make the tank for others with no mold cost!) Here's an interesting tidbit... The forward tank is failing at all the screwholes on the TOP where the inspection plate and sensor are screwed in, not below where the tank is bathed in urine, so I think it might be electrolysis rather than caused by urine in this particular case. The aft tank failed at the weld of the pumpout fitting to the top of the side of the tank... the fitting just came off, so I don't know why that area failed either. Any ideas? The bottom of the tank we pulled was intact. I wish I were in San Diego too... Great place. George
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Peggie Hall/HeadMistress
Did you see the inside of the bottom of the tank?
It may have looked sound on the outside, but I'd bet money it was badly pitted on the inside. The top of the tank is exposed to urine too...when the tank is full, or when you heel...and to the corrosive gasses. It's gonna fail at the weakest point first, wherever that may be on the tank. Apparently you only explored the cost of custom MOLDED tanks...yes, that's prohibitively expensive. But custom WELDED plastic tanks don't require a mold...and while more expensive than stock molded tanks, are about the same as or less than custom welded metal...and are the only other good choice. It's a bit late to re-direct you...but hopefully others won't make the same mistake.
It may have looked sound on the outside, but I'd bet money it was badly pitted on the inside. The top of the tank is exposed to urine too...when the tank is full, or when you heel...and to the corrosive gasses. It's gonna fail at the weakest point first, wherever that may be on the tank. Apparently you only explored the cost of custom MOLDED tanks...yes, that's prohibitively expensive. But custom WELDED plastic tanks don't require a mold...and while more expensive than stock molded tanks, are about the same as or less than custom welded metal...and are the only other good choice. It's a bit late to re-direct you...but hopefully others won't make the same mistake.
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George Kornreich
But, Peggie
the companies I quiried about plastic tanks were the ones you referred me to. They didn't offer me the option of welded plastic tanks, however, and yes, I didn't know about that option. Well, if (when) the metal tanks fail again, I get to try the welded plastic tanks next time. Meanwhile, I guess I'll ground the new tank and at least hope to control the galvanic aspect of "tank decay." BTW, the normal pH of urine is 6-7.4, so not really so acidic, and usually neutral or possible basic. So it's not the acidity that may eat metal, but I don't know what does it either. Could it be the vinegar we us to treat the plumbing?
the companies I quiried about plastic tanks were the ones you referred me to. They didn't offer me the option of welded plastic tanks, however, and yes, I didn't know about that option. Well, if (when) the metal tanks fail again, I get to try the welded plastic tanks next time. Meanwhile, I guess I'll ground the new tank and at least hope to control the galvanic aspect of "tank decay." BTW, the normal pH of urine is 6-7.4, so not really so acidic, and usually neutral or possible basic. So it's not the acidity that may eat metal, but I don't know what does it either. Could it be the vinegar we us to treat the plumbing?
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Peggie Hall/HeadMistress
Don't confuse corrosive with acidic
pH has nothing to do with corrosiveness. Urine is corrosive but not acidic...white vinegar, which has a PH of 4, is acidic but not corrosive. As I said earlier, it can't HURT to ground the tank...whether it will help is something we won't know for at least 5 years...maybe longer. You must have missed suggestions from several people here to try C.C. Tech. They make welded plastic tanks.
pH has nothing to do with corrosiveness. Urine is corrosive but not acidic...white vinegar, which has a PH of 4, is acidic but not corrosive. As I said earlier, it can't HURT to ground the tank...whether it will help is something we won't know for at least 5 years...maybe longer. You must have missed suggestions from several people here to try C.C. Tech. They make welded plastic tanks.
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George Kornreich
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