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Old 29-10-2011, 18:53   #1
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PVC Taboo - Myth or Reality ?

I finally own my dream boat, but part of that dream never included the smell of permeated sanitation pipes. In fact I didn't know such a problem could happen. I've scoured many threads here for advice on the major re-piping job ahead of me. This is a fantastic community. I think I'm pretty well educated now. I've already gutted all the pipes in my aft head. I'm committed.

Here's my question - it seems so obvious to me to use PVC fittings and pipe like I've used for years on home projects, but there is an occasional reference in threads on CF that PVC is taboo on a boat. No one ever goes deep, but the supposition is that it's too rigid for the flexible world of a boat, so it should be avoided. Since I haven't seen here, nor ever of heard anywhere, of a failure of a PVC system on a boat (and you know they are out there, but people may be afraid to admit it), I have to question the validity of that common supposition. Is this a job for the Mythbusters?

PVC has so many advantages - seriously cheap, seriously easy to work with, huge availability of fittings, joints stronger than the pipe itself, indestructible strength, never permeates, never rots, etc. I'm a fan at home for sure. My design would include some runs of flex sanitation hose here and there for the complex bendy bits, giving some stress relief when the boat flexes (if that's a real concern). I have a specific problem area where as the holding tank fills the discharge hose also fills for a couple feet, which is just begging to be a regular permeation problem. Can I use PVC there at least please?

PVC users please speak up! Any failures? Any success stories?

Thanks

JR
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Old 29-10-2011, 19:23   #2
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Re: PVC taboo - myth or reality?

I would like to hear an answer to this one as well. Marine sanitation just showed me some new marine hose that is supposed to be impermeable, but its not flexible, so you have to do elbows which means more joints. It's also expensive. PVC sure would be cheaper and easier.
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Old 29-10-2011, 19:44   #3
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Re: PVC taboo - myth or reality?

Maybe Peggie or a materials expert will chime in here, but I see no reason you can't use PVC so long as you have sections of flexible hose to relieve the stresses of movement.
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Old 29-10-2011, 19:48   #4
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Re: PVC taboo - myth or reality?

Most large yacht builders do use quite a bit of PVC instead of hose in sanitation system, but it's only recommended for use in long straight runs, which aren't very common in most sailboats <50-60'. A lot of bends require a lot of unions and fittings, all secured with glue pvc cement)...then there's the need to provide shock absorption and protection from flex, which require using about a foot of hose to connect pipe to fixed objects (toilet, tanks, pumps, thru-hulls etc).

Hose, otoh, is pretty easy to install and doesn't need all those glued connections etc. And at least one sanitation hose--Trident 101--is just about bullet proof against odor and isn't THAT much more expensive than PVC.

So yes, there are advantages to hard PVC over hose...and there can be a run or two in which it can work. But in most installations, the disadvantages outweigh the advantages as a total replacement for hose.
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Old 29-10-2011, 19:49   #5
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Re: PVC taboo - myth or reality?

PVC is plenty flexible for use on a boat. Just don't put it where someone can step on it or otherwise torque it severely. The normal motion and flexing of a boat isn't that big and if it is, inflate the liferaft. If you are really concerned, use schedule 80 instead of schedule 40 pipe and fittings. FWIW, the LectraSan comes complete with PVC fittings.
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Old 29-10-2011, 19:50   #6
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Re: PVC taboo - myth or reality?

Every one of those sections of hose creates at least one connection, some of 'em TWO connectionsl
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Old 29-10-2011, 19:52   #7
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Re: PVC taboo - myth or reality?

Fittings and pipe are two entirely different things!
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Old 29-10-2011, 19:56   #8
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Re: PVC taboo - myth or reality?

I have never seen a properly glued PVC joint leak.
From what I understand, the glues solvent weld the parts together so they are like one.

There is really no pressure in the pipes.
You can also buy rubber clamp couplings meant for sewer use inside your house with which you can soft join PVC piping.
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Old 29-10-2011, 20:12   #9
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Re: PVC taboo - myth or reality?

We have full PVC in our 28 foot yacht with a holding tank. We have given our boat a hiding in the sea and I can categorically say flex is not a problem. Neither are the glued/welded joins, I respect that many people on this forum stand up for flex pipe but they may not be authorities on PVC.

EVERYONE!!!! told me the PVC would fail, It has not!!!!

PVC is FANTASTIC for smell removal, Flex is not an issue with it as it can flex a small amount which is more than the amount of flex your boat should have anyway so you are covered. Yes it can be harder to put together than using flex pipe, but it is soooo worth it. ZERO SMELL!!!! ie repeat ZERO SMELL!!!!


The only downside we have found is if you want to make any changes down the track its more like surgery than applying a band-aid. We started with a manual pump to empty the tank but the smell came thru the rubber diaphragm. we now have a 12v pump to do that job and due to it not having any rubber parts open to the interior, their is no smell issues.

If i was tidying a boat up to flick off I would use flex pipe. if I was planning on using the boat as either a second home/ longterm cruiser I would invest the time (and save some cash) and run full PVC.

We used Pressure rated 40mm pipe. This is thicker wall thickness than the normal down pipe, the bends are tight 90's and not smooth flowing 90's. However this does not effect the operation at all.

I will try and post some photos of our system. Its simple, it was very low cost, it does not smell, it does flex if needed, it will most likely outlast the rest of the boat, it is absolutely one of the best things i ever did to our yacht!

You will not regret it, just remember to apply to much joint goo and they will not leak, the goo does smell like strong chemicals but will set hard after a few hours and can be painted over to deal with the smell. Also when you build the system, dry fit everything together and draw a mark over each join so that you can glue them on the right angle.

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Old 29-10-2011, 20:19   #10
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Re: PVC taboo - myth or reality?

You just don't want to use PVC in situations where if it failed it could sink the boat. PVC is too brittle. A hose you can step on or drop something on it and not break it.
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Old 29-10-2011, 20:43   #11
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Re: PVC taboo - myth or reality?

Quote:
Originally Posted by David M View Post
You just don't want to use PVC in situations where if it failed it could sink the boat. PVC is too brittle. A hose you can step on or drop something on it and not break it.
I would agree with this to a point, PVC pressure pipe is VERY strong, I would agree with the statement above if you are talking about the normal down pipe. Pressure pipe is approximately twice as thick, I can jump on it without any deflection (offcuts, not my boat piping). Once the joints a re glued they are Much less likely to come off than a flex pipe with twin hose clamps as the plastic joins melt together and become one piece.

Replace your sea cocks, as these are the best line of defence for a broken PVC pipe, dead hose-clamp, split flex pipe etc. Put your sea cocks in a place where you can turn them off in a nano second.

Flexi pipe has its place, Not all installs can use PVC, nor is it worth it on every boat. BUT, in some situations (liveaboards, cruisers, etc) I would seriously think about if it can be done as it is such a god send.

Damien
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Old 29-10-2011, 20:56   #12
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Re: PVC taboo - myth or reality?

You can also bend PVC pipe easily with a heat gun to avoid using excess fittings. I have done this quite often with electrical conduits which are also PVC. If I had to do it again I would use thick wall PVC. Peggy I think it is considerably cheaper then the trident hose. The hose at defender costs for $3.89 a foot up to $7.99 a foot The PVC at home depot was 4.99 to $5.61 for a 20' stick. I don't think that it was the thick wall but even if it were 3 times as much it would be considerably cheaper on a per foot basis.
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Old 29-10-2011, 20:59   #13
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Re: PVC taboo - myth or reality?

When we priced ours out non smelly flex pipe was $50 per meter (3.3ft) and a 6m length of the heavy PVC was $4.60 each. Bends were about $1.50 each. We are in Australia which is a very high cost country to rebuild a boat.
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Old 29-10-2011, 20:59   #14
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Re: PVC taboo - myth or reality?

The typical PVC flex tube sold for marine use cements into rigid PVC couplings fine. As above, I'd be wary of rigid PVC that could sink the boat if fractured.
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Old 29-10-2011, 21:09   #15
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Re: PVC taboo - myth or reality?

All fantastic input. I'm so glad I asked. I'm feeling better about using it.

The worry that if you drop something on it it will break seems extreme. The same sort of drop would also likely break your hull. Don't do that!

I have two good examples of why I love PVC. I live on an old farm with a number of small out buildings. A couple years ago I had to move one small building all of 12 feet to get out of the way of some new construction. To move it I jacked it up, laid 2x8 lumber on the ground like a track to the new location, and then used 1 1/2" PVC as rollers between the track and the lower sill frame of the building. It was heavy enough to actually visually deform the round PVC into an oval shape. I pushed the building with a tractor and it gently rolled along on the pipes. Voila, new location, and none of the PVC broke or shattered in any way. It's tough stuff.

My second example is at our ski house. We have an old wooden hot tub on a first story deck. It is heated from the boiler down in the basement. There's about a 40 foot run of PVC connecting the tub to the boiler which goes through many twists and turns, drops about 12 feet, has ball valves, a big two speed pump that sends vibrations through everything, runs at about 15 psi, has frozen, is always changing temperature dramatically, is exposed to sub-zero temps at least 20 times a year, and high winds put some flex in the deck sometimes to the point of noticeably sloshing the water around in the tub. It has never failed.

I'm not afraid to use it on the boat, but agree that as an extra degree of safety will use Schedule 80 (the heavy duty version) anywhere below the water line.

Peggie, I agree that Trident 101 is excellent, and I've bought a 50' roll for this job particularly to get up from the bilge to the deck fitting along the curved hull. Flex pipe is the only answer here. But it is 10x the price of PVC. Also just the clamps on any joint cost more than a PVC fitting.
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