Does anyone have an opinion on the use of welded polypropylene tanks for holding tanks? For example those from Tripple M Plastics in ME? Is welded plastic suitable? Of course I mean properly welded. Tripple M adds baffles and pressure tests the tanks. triplemplastics.net Thanks, Dan Pfeiffer
Welded Plastic Tanks
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I would go with a molded one-piece plastic tank
I currently have a aluminum holding tank. I am going to replace it next year with a Ronco plastic tank. It is a one-piece injection molded tank. No seams. We were up in Canada one year, and saw 2 guys, actually 2 couples, working on a holding tank. They were out for a 2 week cruise and the plastic tank leaked at the seam. They had the tank out on the dock and epoxying it. It had cracked along an entire edge, right at the seam.
I currently have a aluminum holding tank. I am going to replace it next year with a Ronco plastic tank. It is a one-piece injection molded tank. No seams. We were up in Canada one year, and saw 2 guys, actually 2 couples, working on a holding tank. They were out for a 2 week cruise and the plastic tank leaked at the seam. They had the tank out on the dock and epoxying it. It had cracked along an entire edge, right at the seam.
More on Welded Tanks
Thanks JC. The annecdote is intersting. Do you know what kind of tank it was? Was it welded seams or chemically glued? What quality level tank? Hard to evaluate without knowing. I would be happy to use a roto-molded tank if I could find one that fit the space I want it in. I have been through the Ronco catalog. Any other places to look? How about a place that can do custom shapes in roto-mold? That is actually a question for another thread and I'll start one for that. JC, Can I ask you some questions about sailing around Bainbridge Is? Contact me at dan@pfeiffer.net Thanks, Dan Pfeiffer
Thanks JC. The annecdote is intersting. Do you know what kind of tank it was? Was it welded seams or chemically glued? What quality level tank? Hard to evaluate without knowing. I would be happy to use a roto-molded tank if I could find one that fit the space I want it in. I have been through the Ronco catalog. Any other places to look? How about a place that can do custom shapes in roto-mold? That is actually a question for another thread and I'll start one for that. JC, Can I ask you some questions about sailing around Bainbridge Is? Contact me at dan@pfeiffer.net Thanks, Dan Pfeiffer
A custom shaped molded tank is very expensive
I asked a local dealer about it once, and I quickly passed it up. Very very expensive.
I asked a local dealer about it once, and I quickly passed it up. Very very expensive.
We had the same challenge
because of the shape of the locker under our v-berth I needed a flat bottomed tank. Ronco had one but I was not prepared to pay that kind of cash (CDN - US exchange to boot) I checked into a custom tank from Barr Plastics and was floored at the price, it was over twice as much as the Ronco tank.
because of the shape of the locker under our v-berth I needed a flat bottomed tank. Ronco had one but I was not prepared to pay that kind of cash (CDN - US exchange to boot) I checked into a custom tank from Barr Plastics and was floored at the price, it was over twice as much as the Ronco tank.
Custom plastic tanks
I have a 1996 model 376 This boat has a factory aluminum 35 gal. waste tank. It needs to be stainless steel or plastic because the flush system uses salt water.The tank leaks because of corrosion. Aft stateroom cabinetry and bulkhead has to be cut out to remove the tank. Dura Cast tanks in Florida makes many plastic tanks for boat builders including Hunter.They can make a custom tank to the original dimensions for a bit over $200
I have a 1996 model 376 This boat has a factory aluminum 35 gal. waste tank. It needs to be stainless steel or plastic because the flush system uses salt water.The tank leaks because of corrosion. Aft stateroom cabinetry and bulkhead has to be cut out to remove the tank. Dura Cast tanks in Florida makes many plastic tanks for boat builders including Hunter.They can make a custom tank to the original dimensions for a bit over $200
Custom-welded is fine, in my exp
My opinion: If all other things were equal, I'd go with a single piece tank (one-piece rotomolded of the type that Ronco makes) to avoid potential for weak spots that welded seams might incur. But, the key words in your question are "properly welded." If properly welded, the welds in a custom-built welded tank should be strong enough to not fail for the given application. How do you know if they are properly welded? Good question, but that, I think, comes down to pressure-testing the tank, using thick-walled material (3/8” min), the reputation of the supplier and the quality of their manufacturing. Due to sizing requirements, your need for a welded custom-built tank outweighs the peace of mind that a one-piece (non-welded) Ronco stock tank would provide. But let's put it in perspective: if, uggh, there's a break, we're not talking about sinking boats here, just a mess! Also, keep in mind that if you were to buy a nice one-piece stock tank from Ronco, they will be customizing it for you to install fittings (threaded couplings for hoses, Beckson plate) based on your particular installation. So, you will end up with a one-piece roto-molded tank with welds in it anyway, although obviously not to the same extent as a tank welded together from flat panels. How do we know how good the fitting welds are on a one-piece Ronco tank? Ronco usese polyethylene. It seems that polypropylene is used in welded applications because it's easier to weld, but is just as effective for holding-tank use. As far as your question of a custom-shape in roto-mold. Yes, Ronco will do that for you. Three years ago they quoted me $600 to build the mold and then the cost of the tank on top of that (25 gal for a Hunter 37.5). Totaled about $800 for a custom-built roto-molded tank vs. $200 for one of their stock tanks. I didn't think it was worth the extra bucks compared to a custom welded tank. My experience is that it is not expensive to have a tank custom-built, using the welded method. A tank built to exactly replicate the one on the H37.5 cost me $375 about 3 years ago. That's a chunk more than the closest-sized Ronco stock tank, but that's cheap compared to most things we replace on a boat! I used C.C.Tech in Rhode Island to custom-build and was pleased with the product (a welded tank). I would not hesitate to have a tank custom-built again. TripleM Plastics may be very good too. Make sure they are using at least 3/8" thick poly (same thickness as Ronco).
My opinion: If all other things were equal, I'd go with a single piece tank (one-piece rotomolded of the type that Ronco makes) to avoid potential for weak spots that welded seams might incur. But, the key words in your question are "properly welded." If properly welded, the welds in a custom-built welded tank should be strong enough to not fail for the given application. How do you know if they are properly welded? Good question, but that, I think, comes down to pressure-testing the tank, using thick-walled material (3/8” min), the reputation of the supplier and the quality of their manufacturing. Due to sizing requirements, your need for a welded custom-built tank outweighs the peace of mind that a one-piece (non-welded) Ronco stock tank would provide. But let's put it in perspective: if, uggh, there's a break, we're not talking about sinking boats here, just a mess! Also, keep in mind that if you were to buy a nice one-piece stock tank from Ronco, they will be customizing it for you to install fittings (threaded couplings for hoses, Beckson plate) based on your particular installation. So, you will end up with a one-piece roto-molded tank with welds in it anyway, although obviously not to the same extent as a tank welded together from flat panels. How do we know how good the fitting welds are on a one-piece Ronco tank? Ronco usese polyethylene. It seems that polypropylene is used in welded applications because it's easier to weld, but is just as effective for holding-tank use. As far as your question of a custom-shape in roto-mold. Yes, Ronco will do that for you. Three years ago they quoted me $600 to build the mold and then the cost of the tank on top of that (25 gal for a Hunter 37.5). Totaled about $800 for a custom-built roto-molded tank vs. $200 for one of their stock tanks. I didn't think it was worth the extra bucks compared to a custom welded tank. My experience is that it is not expensive to have a tank custom-built, using the welded method. A tank built to exactly replicate the one on the H37.5 cost me $375 about 3 years ago. That's a chunk more than the closest-sized Ronco stock tank, but that's cheap compared to most things we replace on a boat! I used C.C.Tech in Rhode Island to custom-build and was pleased with the product (a welded tank). I would not hesitate to have a tank custom-built again. TripleM Plastics may be very good too. Make sure they are using at least 3/8" thick poly (same thickness as Ronco).
Good quality PP is ok...
(Btw, JC...PE tanks are ROTOmolded, not injection molded)... CC Tech and Triple M Plastics both seem to do a pretty good job. However, baffling a waste holding tank is not a good idea. You won't see any baffled rotomolded waste tanks or OEM supplied metal tanks, only custom aftermarket tanks that an owner wanted baffled. It's a bad idea because sludge buildup can plug limber holes and even buildup several inches, completely compartmentalizing the tank instead of only baffling it. I've had a number of calls from people who couldn't figure out why their tanks were still full after they'd pumped out...it was because the pumpout only emptied one compartment, the toilet discharged into another one...and the baffles had gotten plugged. Steve said, "It needs to be stainless steel or plastic because the flush system uses salt water.The tank leaks because of corrosion..." Corrosion will destroy any metal waste tank, including SS...but it's not salt water that does it, it's urine. Urine is so corrosive that salt water is benign in comparison. NO metal is recommended for waste holding. The recommended material is thickwalled (min 3/8") rotomolded polyethylene (PE)...the only other good choice is a high quality welded PE or PP tank. JC reported, "...plastic tank leaked at the seam. They had the tank out on the dock and epoxying it. It had cracked along an entire edge, right at the seam." Only one thing can cause that to a blocked tank vent that either a)caused the tank become so pressurized that continuing to use the toilet as it became harder and harder to pump finally burst it...or b) caused a particularly strong pumpout to pull enough of a vacuum to implode it. A couple of years ago, someone posted a story here about a couple who managed to burst a brand new stainless tank by continuing to pump the toilet past the point where it was all the owner could do to pump it at all. They'd just finished completely restoring the boat and were out for the first "shake down" cruise when it happened. If the tank in JC's story was plastic, they were wasting their time trying to repair it...nothing bonds permanently to PE.
(Btw, JC...PE tanks are ROTOmolded, not injection molded)... CC Tech and Triple M Plastics both seem to do a pretty good job. However, baffling a waste holding tank is not a good idea. You won't see any baffled rotomolded waste tanks or OEM supplied metal tanks, only custom aftermarket tanks that an owner wanted baffled. It's a bad idea because sludge buildup can plug limber holes and even buildup several inches, completely compartmentalizing the tank instead of only baffling it. I've had a number of calls from people who couldn't figure out why their tanks were still full after they'd pumped out...it was because the pumpout only emptied one compartment, the toilet discharged into another one...and the baffles had gotten plugged. Steve said, "It needs to be stainless steel or plastic because the flush system uses salt water.The tank leaks because of corrosion..." Corrosion will destroy any metal waste tank, including SS...but it's not salt water that does it, it's urine. Urine is so corrosive that salt water is benign in comparison. NO metal is recommended for waste holding. The recommended material is thickwalled (min 3/8") rotomolded polyethylene (PE)...the only other good choice is a high quality welded PE or PP tank. JC reported, "...plastic tank leaked at the seam. They had the tank out on the dock and epoxying it. It had cracked along an entire edge, right at the seam." Only one thing can cause that to a blocked tank vent that either a)caused the tank become so pressurized that continuing to use the toilet as it became harder and harder to pump finally burst it...or b) caused a particularly strong pumpout to pull enough of a vacuum to implode it. A couple of years ago, someone posted a story here about a couple who managed to burst a brand new stainless tank by continuing to pump the toilet past the point where it was all the owner could do to pump it at all. They'd just finished completely restoring the boat and were out for the first "shake down" cruise when it happened. If the tank in JC's story was plastic, they were wasting their time trying to repair it...nothing bonds permanently to PE.
Are you comfortable with welded PP?
Peggy, Are you comfortable with welded polypropylene tanks for integrity, strength and longevity? And are you comfortable with tanks form the two makers you referenced in particular? Thanks, Dan Pfeiffer
Peggy, Are you comfortable with welded polypropylene tanks for integrity, strength and longevity? And are you comfortable with tanks form the two makers you referenced in particular? Thanks, Dan Pfeiffer
I'm a lot MORE comfortable with it than I am with
metal or a bladder tank. I don't have any first hand experience with CC Tank or Triple M, but quite a few people on the dozen + sites I monitor have bought their tanks and have posted that they're very impressed with the quality and I haven't seen any negative comments about either one. So although my first preference is rotomolded PE, if we really can't find one in the Ronco catalog that'll work, 100% positive feedback from that many people is enough for me to feel comfortable in referring people to CC Tech and Triple M Plastics.
metal or a bladder tank. I don't have any first hand experience with CC Tank or Triple M, but quite a few people on the dozen + sites I monitor have bought their tanks and have posted that they're very impressed with the quality and I haven't seen any negative comments about either one. So although my first preference is rotomolded PE, if we really can't find one in the Ronco catalog that'll work, 100% positive feedback from that many people is enough for me to feel comfortable in referring people to CC Tech and Triple M Plastics.
Peggy: Re: Baffles
... thanks for your note regarding tank baffles in holding tanks. I forwarded it to Triple M Plastics with whom I just placed an order. In fact the stock aluminum tank in the 40.5 Hunter is baffled, and the welded-up Poly tank would too if they followed the manufacturer's spec's. I told them to use their best judgement re: baffles or not, but had the same concerns you outlined. Rick D.
... thanks for your note regarding tank baffles in holding tanks. I forwarded it to Triple M Plastics with whom I just placed an order. In fact the stock aluminum tank in the 40.5 Hunter is baffled, and the welded-up Poly tank would too if they followed the manufacturer's spec's. I told them to use their best judgement re: baffles or not, but had the same concerns you outlined. Rick D.
Bonding
"If the tank in JC's story was plastic, they were wasting their time trying to repair it...nothing bonds permanently to PE." With all due respect . . . . . . DP-8005 Scotch-WeldTM DP-8005 is a solvent-free, two-part, acrylic-based, structural plastic adhesive designed to structurally bond polyolefins to themselves and to many other substrates. It uses a one-step process that requires no pre-treatment of the substrates other than removing dirt and oil. Like Polyolefins themselves, DP-8005 provides very good chemical resistance. Similar to most polypropylenes and polyethylenes, maximum continuous service temperature for DP-8005 should be kept under about 212ºF (100ºC).
"If the tank in JC's story was plastic, they were wasting their time trying to repair it...nothing bonds permanently to PE." With all due respect . . . . . . DP-8005 Scotch-WeldTM DP-8005 is a solvent-free, two-part, acrylic-based, structural plastic adhesive designed to structurally bond polyolefins to themselves and to many other substrates. It uses a one-step process that requires no pre-treatment of the substrates other than removing dirt and oil. Like Polyolefins themselves, DP-8005 provides very good chemical resistance. Similar to most polypropylenes and polyethylenes, maximum continuous service temperature for DP-8005 should be kept under about 212ºF (100ºC).
It'll hold in some applications, but...
Spoken like someone who works for 3M.
Success in mending cracked tanks is mixed. If the crack is in a location that doesn't have any stress trying to open the crack again--for instance a spinwelded fitting that's leaking, it'll hold...but it hasn't proven to be very successful in permanently resealing cracks in locations that have pressure trying to push the crack apart again. It holds for a while (so will Marine Tex)...but the crack inevitably opens up again. The only thing that does work is heat welding, done by someone who knows how to do it...but in 20 years in this business, I've found a lot of plastics fabricators who'll work on a water tank, but not one who'll work on a used waste tank.
Spoken like someone who works for 3M.
Success in mending cracked tanks is mixed. If the crack is in a location that doesn't have any stress trying to open the crack again--for instance a spinwelded fitting that's leaking, it'll hold...but it hasn't proven to be very successful in permanently resealing cracks in locations that have pressure trying to push the crack apart again. It holds for a while (so will Marine Tex)...but the crack inevitably opens up again. The only thing that does work is heat welding, done by someone who knows how to do it...but in 20 years in this business, I've found a lot of plastics fabricators who'll work on a water tank, but not one who'll work on a used waste tank.Well, to set it straight, and some more details
The 2 couples we saw trying to epoxy the welded plastic holding tank were a bit ticked. They wanted to go sailing, but gotta have a tank. They just cleaned out the boat, and were trying to get some fiberglass cloth to stick to the tank with epoxy. They just wanted to finish the 2 weeks of sailing, and get the boat home, then replace the *$#*& tank with a new one. Poor people.... I really felt badly for them.
The 2 couples we saw trying to epoxy the welded plastic holding tank were a bit ticked. They wanted to go sailing, but gotta have a tank. They just cleaned out the boat, and were trying to get some fiberglass cloth to stick to the tank with epoxy. They just wanted to finish the 2 weeks of sailing, and get the boat home, then replace the *$#*& tank with a new one. Poor people.... I really felt badly for them.
Unfortunately, I suspect it was their own fault...
And an excellent illustration of why it's so important to maintain the tank vent to prevent it from becoming blocked. For some reason, when a toilet starts getting harder and harder to pump, "burps," or owners start seeing backup in the bowl, it never occurs to 'em that the problem is a blocked tank vent. They assume it's a clog and keep pumping to try to clear it...pressurizing the tank until something has to give--either a major eruption in the toilet, or a cracked tank. And welded tanks aren't the only ones that crack...even the best rotomolded tanks will with enough pressure.
And an excellent illustration of why it's so important to maintain the tank vent to prevent it from becoming blocked. For some reason, when a toilet starts getting harder and harder to pump, "burps," or owners start seeing backup in the bowl, it never occurs to 'em that the problem is a blocked tank vent. They assume it's a clog and keep pumping to try to clear it...pressurizing the tank until something has to give--either a major eruption in the toilet, or a cracked tank. And welded tanks aren't the only ones that crack...even the best rotomolded tanks will with enough pressure.
Inflatable/Bladder tank
Before i bought my bladder tank made by Vetus, i checked with many live-aboards that had them for many years. Everyone said they had no problems with them. On this i gambled. We live aboard and bought their 60? gallon tank and had no problems with it either from leaking or odors. We have had it now for 5 years and we do a lot of sailing and sometimes in rough weather. Prior to that, we had purchased a 30 gallon bladder type water tank and also no problems. BTW, at the time, Defender had it listed for much less than Vetus. We ordered it from Defender.
Before i bought my bladder tank made by Vetus, i checked with many live-aboards that had them for many years. Everyone said they had no problems with them. On this i gambled. We live aboard and bought their 60? gallon tank and had no problems with it either from leaking or odors. We have had it now for 5 years and we do a lot of sailing and sometimes in rough weather. Prior to that, we had purchased a 30 gallon bladder type water tank and also no problems. BTW, at the time, Defender had it listed for much less than Vetus. We ordered it from Defender.
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