Peggy, one of the items on my refit list for this winter is to get rid of the 5-gallon bladder that serves as the holding tank, as well as to have a Class 1 MSD installed. Two years ago, I replaced the water bladders with custom aluminum tanks after one of the bladders sprung a leak.
I had planned to convert the stbd water tank to a holding tank, but in reading through several posts on this forum, I became concerned about the effects of urine on aluminum. The service manager at the yard where I keep the boat on the hard for the winter provided me the following:
"I know there are some pretty strong articles out there advising against aluminum for holding tanks and the crux of what they say is true. Aluminum can corrode in the presence of sewage. That said, we have used aluminum for holding tanks for over twenty years. During that time we have made hundreds of holding tanks and to my knowledge, we have not had a single failure for any reason, including corrosion.
On the other hand, we have seen the tanks of other manufacturers fail. In some cases this is because of the way the tanks were mounted and they corroded from the outside. In some cases, they have failed from the inside and in at least one case, this appears to have been from the excessive use of bleach which was left in the tank.
One defense we use on aluminum holding tanks is to use a thicker than normal plate to allow for some corrosion without failure. We usually use 3/16" plate. For your water tanks, we used 1/8" plate which is thicker than most water tanks, but thinner than we would use for a holding tank. 1/8" is still thicker than most fabricators would use for a holding tank of this size, so there is still some margin for error.
Aluminum has been pretty successful for us over the years. I think the strong negative articles are overwrought, but we are, however, aware of the corrosion issue. Stainless can have corrosion problems as well and is more expensive by considerable. A plastic holding tank is a good alternative, but historically they have had two problems. 1) they were not easily made on a custom basis and so you had to take what you could get from a limited number of shapes. Usually these did not do well at maximizing capacity. 2) if not heavily made, they passed odor and occasionally cracked at the fittings.
Today, however, there is a company in British Columbia who will make custom tanks out of 3/8" -1/2" co-polymer plastic (very odor resistant) using a plastic welding process. Beautiful stuff and even with shipping and customs, the tanks are competitive with aluminum. It does take three weeks to have a tank made but other than that, this is a great alternative.
I would not be too concerned with converting the aluminum water tank to a holding tank. The main thing is not to leave sewage in the tank for long periods, always pump and wash out the tank after trips."
I plan to have a new water tank installed under the quarterberth to restore my freshwater capacity from the converted tank.
So, Head Mistress, what are your thoughts? Thanks in advance.
I had planned to convert the stbd water tank to a holding tank, but in reading through several posts on this forum, I became concerned about the effects of urine on aluminum. The service manager at the yard where I keep the boat on the hard for the winter provided me the following:
"I know there are some pretty strong articles out there advising against aluminum for holding tanks and the crux of what they say is true. Aluminum can corrode in the presence of sewage. That said, we have used aluminum for holding tanks for over twenty years. During that time we have made hundreds of holding tanks and to my knowledge, we have not had a single failure for any reason, including corrosion.
On the other hand, we have seen the tanks of other manufacturers fail. In some cases this is because of the way the tanks were mounted and they corroded from the outside. In some cases, they have failed from the inside and in at least one case, this appears to have been from the excessive use of bleach which was left in the tank.
One defense we use on aluminum holding tanks is to use a thicker than normal plate to allow for some corrosion without failure. We usually use 3/16" plate. For your water tanks, we used 1/8" plate which is thicker than most water tanks, but thinner than we would use for a holding tank. 1/8" is still thicker than most fabricators would use for a holding tank of this size, so there is still some margin for error.
Aluminum has been pretty successful for us over the years. I think the strong negative articles are overwrought, but we are, however, aware of the corrosion issue. Stainless can have corrosion problems as well and is more expensive by considerable. A plastic holding tank is a good alternative, but historically they have had two problems. 1) they were not easily made on a custom basis and so you had to take what you could get from a limited number of shapes. Usually these did not do well at maximizing capacity. 2) if not heavily made, they passed odor and occasionally cracked at the fittings.
Today, however, there is a company in British Columbia who will make custom tanks out of 3/8" -1/2" co-polymer plastic (very odor resistant) using a plastic welding process. Beautiful stuff and even with shipping and customs, the tanks are competitive with aluminum. It does take three weeks to have a tank made but other than that, this is a great alternative.
I would not be too concerned with converting the aluminum water tank to a holding tank. The main thing is not to leave sewage in the tank for long periods, always pump and wash out the tank after trips."
I plan to have a new water tank installed under the quarterberth to restore my freshwater capacity from the converted tank.
So, Head Mistress, what are your thoughts? Thanks in advance.
