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Old 17-05-2015, 13:29   #46
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Join Date: Jun 2013
Boat: Luger, Southwind, 21
Posts: 368
Re: Solar hotwater and fiberglass tank?

Am I the only one, who's been burned, brushing against the hollow rub rail of a vessel. Could this not be plumbed into the solar water heating system. They need replacing from time to time anyway, no additional solar collector cost. :what:

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Old 17-05-2015, 16:06   #47
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Re: Solar hotwater and fiberglass tank?

Hello Canibul,

I don't think they hold six gallons. The tech sheet says only about 8 oz of water in the panel itself, plus whatever is in your external piping. That seems very little in the panel, but the piping is pretty small. The panel only weighs around 14 lbs and is just 2' by 2'. I looked into this before I bought them, because I was concerned with weight. I'm always looking for stuff that is light weight. It is a sailboat, and there is the tendency to keep adding equipment. The weights adds up.

As far as using a rub rail, I guess you could engineer that, if you put some effort into it. It is there to get bashed occasionally, and that might be an issue. You could just use a good quality black PVC in a coil attached to some kind of backer board, and make it removable if you like. I think you could get more than enough heat from 25 to 50 feet to warm the water in your hot water heater. Still, the Heliatos panels are pretty cheap, the circulation pumps, or slow solar pumps, are a bit pricy. You kind of need one no matter how you build your solar water heating system.

Someone ask why copper. I can't say a copper tank will last for decades, but way back when water heaters first appeared in houses, they built them from copper. I have seen some of them operating more than 65 years on. Also, copper is natural antimicrobial material. Water stored in it keeps better. Do some web searches and you can read about this. Copper is still an ideal material for potable water tanks and piping. It's hard to find any tanks or water heaters made of copper. Monel use to be popular for tanks, but cost drove them out of boats.

In building tanks, stainless steel, various plastics, fiberglass, and some aluminum alloys are used. Each has it's problems. Stainless steel is a pretty good material for many tanks, hot water tanks included. When it fails, it is often at the welds. This is called Intergranular Corrosion - all austentic stainless steels contain a small amount of carbon. At extremely high temperature, such as welding, the carbon forces local chrome to form chromium carbide around it, thus starving adjacent areas of the chrome it needs for its own corrosion protection. When welding, it is recommended you consider low carbon stainless such as 304L or 316L. Most marine tanks are made of these materials. Make sure it is of the (L) variety for low carbon. The welding rod must also be of this material. Even with these precautions the welds can fail, and leaking at the weld is not unusual. Still, they can last a long time. One other thing worth mentioning, you should probably not put chlorine in a stainless tank. It can cause chloride stress corrosion. In small amounts it might be fine, but who wants to find out how much is too much.

My boat it my home. I want the best I can get when it comes to equipment, so I went with copper. The Solaris line of water heaters are top of the line. If the budget is an issue, it is worth saying that I've had boats with every type of material a tank can be made of, and had good success. My current boat has fiberglass holding tanks, a fiberglass diesel day tank, an aluminum primary fuel tank, two fiberglass water tanks, and the Solaris copper hot water tank. I am very pleased with all. The fiberglass tanks are all custom made.

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fiberglass, solar, water

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