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In article , Peggie Hall
wrote: hard PVC is likely to crack, especially in cold weather. Not. (incompetently piped?) Incompetently piped is only one cause. Schedule 40 gets very brittle below 40F. Even a sharp rap against a dock can crack it. The kinds of stresses a boat can be subjected to in a storm at sea can crack sch 40 even in warm temps. PVC glue can crack, resulting in a leak. I really wonder about this. First, not all yachts have hulls that are all that flexible - steel boats in particular. Second, PVC *is* used on commercial fishing boats all the time, and it works well. Third, there are low temp plastics available. Fourth, PVC glue *can* crack, but rarely does if the joint is done properly - cleaned, primed then glued. It's a solvent cement rather than a glue. There are also other plastic products. I'm thinking of pressure rated black plastic pipe widely used on farms worldwide. The fittings are a bit on the bulky side but work very well. Some pipework on my country place has been exposed to UV and heat/cold cycles for 20 years now, under 10 metres of water head pressure. No leaks. Have you never worked with PVC fittings & layout? It is very fast & easy. You've obviously never had to pay for labor. 5 extra minutes per union on your own boat is one thing...multiply that by several hundred or even several thousand boats, and the cost to builders becomes prohibitive. Yeah, but that's a different argument. We all know builders of anything need to look at costings, esp when any potential problem is going to happen far enough in the future to be not theirs. In the case of blackwater wouldn't it last far longer & be more vapor-impermeable? More impermeable, yes. But the stresses on the glue in unions results in more maintenance (or repairs at sea). I really doubt this is true, if the hull is rigid enough and the pipework is well supported. Personally I think the whole business of running flex hose everywhere is plain crazy and a throwback to a time where the choices were flex hose or metal pipework. Put it this way - I spend some months of every year on an icebreaker bashing about in sea ice. It's COLD, the hull is cold, there's a hell of a lot of vibration, shuddering and shock loads that the average boat NEVER sees. There's a hell of a lot of PVC piping for the toilet systems, potable water systems etc etc on that ship. Sure, the final runs are all welded steel pipe, but the point is, we *don't* have massive and continual failures of the PVC pipework, despite cold and vibration. Haven't decided what I'll use, but flex hose will be considered only when I can't use something better. If the flex hose is better structurally than rigid pipework, why don't commercial vessels use it? PDW |
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