Over the course of several years, I have grappled with water leakages from flexible water tanks by the brands Plastimo and Nuova Rade.
When I purchased my third-hand boat, it was outfitted with four 150L flexible water tanks from Plastimo. The setup was symmetrical, with both the starboard and port sides mirroring each other (a design symmetry also applied to the two diesel tanks). No issues concerning water leakages were evident upon assuming ownership; the water installation was relatively recent.
On each side, a "lower tank" was positioned between the diesel tank and the hull. This space presents a challenge to utilize effectively using standard rigid water tanks. An "upper tank" was resting on top of the diesel tank. The upper tanks were nearly ready for use, lacking only a single connection. Since the seller's water needs hadn't exceeded 300L of water, these tanks remained untouched. The space available for the upper tanks would seem ideal for one or more rigid tanks featuring rectangular surfaces, but the flexible tank, when empty, allows for easy access to the diesel tank and lower tank - I believe a firmly installed rigid tank would make such access considerably more difficult.
The Plastimo tanks eventually succumbed to leaks, the seams yielding under pressure, particularly along the corners. When the initial tank sprung a leak, I dismissed it as a solitary mishap and promptly replaced it with another unit of the same size and brand. As more tanks developed leaks, I continued just replacing them. "Fool me once, shame on you - fool me twice, shame on me" - in hindsight, I question my inclination to replace tanks without delving into the root cause of the leaks. Perhaps driven by a desire to continue sailing without investing substantial time and effort into a water system overhaul, I chose a path of convenience.
Eventually it was time for a change, but I was not yet ready to discard the concept of flexible tanks. The tanks from Nuova Rade seemed to me to be more robust. I was also under the impression that smaller tanks would exert less force on the linings, reducing the risk of problems. The four 150L tanks from Plastimo was intended to be replaced with eight 100L tanks from Nuova Rade (unintentionally, I ended up with 6x100L + 200L). Despite these efforts, the challenge of water leakages persisted. I encountered significant leakage problems at the connections of the new tanks. Managing seven tanks, each with two connections, posed a formidable troubleshooting ordeal.
Three years on (and more than a handful of thousand nautical miles), two of the Nuova Rade tanks have been removed as the tank itself developed leaks.
I've encountered a minor problem with the tanks - sometimes it's been difficult getting the tanks completely empty. The outlets are placed a bit towards the corner of the tank. There may be water still on the tank, but when sucking water from the tank, the layers of plastic by the outlet clings together. This was more of a problem with Plastimo than Nuova Rade, but the latter has the same problem if the outlet comes too high.
The main problem I've had is LEAKS! Water, water, wherever there shouldn't be water - and sometimes no water left for drinking or doing dishes. The leakages have either been from the connections (the Nuova Rade tanks have been particularly troublesome) or from the tanks themselves (more prevalent problem with Plastimo).
I have done two omportant observations. First, the leaks seem to show up after trips in rough sea. Typically I'm looking into things in the harbour, maybe I'll tighten up some connections, then I fill up the tanks, I observe no leakages, everything seems to be OK - but as soon as I'm sailing somewhere things starts leaking again. Second, the upper tanks seem to be more prone to leakage compared to their lower counterparts. I believe it's because there is more space for movement for the upper tanks, while the lower tanks seems to benefit from the steadying presence of the diesel tank and the hull, being more or less wedged in place there.
The Nuova Rade tanks comes with two important instructions printed on the tank itself - it reads "do not overfill" and "do not overtighten" (the connections). I don't think there was more installation instructions than that.
Those instructions are a bit vague. What torque constitutes appropriate connection tightness? What is the precise filling capacity for the 100L tank? 90L? 100.0L? Should one meticulously measure the water input? Typically one would be filling the tank until water gracefully spills over the rim, signaling its completion - I suppose that's already considered to be "overfilling"?
I interpret it as "if those tanks starts leaking, it's always the customers fault, because either the connections are undertightened or overtightened or too much water has been filled on the tank". In hindsight, this is a big red flag that should have swayed me to look for a third brand when replacing the Plastimo tanks. Fortunately the Norwegian consumer purchase law is quite good for the ordinary consumer, so in theory I should have good possibilities on getting my money refunded. I already got my money back for the replacement Plastimo tanks bought.
If those tanks are so bad, why don't more people complain? for one thing, the leakages may be triggered by rough sea - and many boaters only use their boats in sheltered waters under fair skies, and may be happy with their tanks, never experiencing any leaks.
I think those water tanks to be sold with warnings visible already during the ordering. A clear caution such as "recommended for sheltered waters use only" would have unveiled my future of daily water-removal endeavors in hard-to-reach corners, alongside the futility of complaints. This proactive step could have illuminated the constraints, allowing me to make an informed choice before purchasing. Without it, as long as the product is sold as a water tank from a chandlery (as opposed to a caravan or cottage supplies outlet) bereft of any cautionary notes, it should be expected to remain steadfast and leak-proof even amidst the capricious dance of the waves.
From my vantage point, from the two brands I've tested, the Plastimo tanks emerge as a less appealing choice. The tanks are too fragile, and the intricacies of an inner tank and outer lining, complicate leak diagnosis.
According to this forum thread there are satisfied owners of flexible water tanks - even the Plastimo tanks - and the thread suggests that "installation is everyhing". At cruisersforum there seems to be only praises about the flexible water tanks, but everyone has ensured the tanks are protected against movement.
First the "minor" problem of tanks not being properly emptied. Effectively emptying the tanks demands strategic outlet positioning at the lowest conceivable point. Should a residual pool persist in the tank, a pragmatic solution lies in gently elevating parts of the tank – putting something under it, or lifting it by ropes, or just using hands. Maintaining a "residue reservoir" of water for emergencies may seem advantageous, but hygiene compels a periodic complete tank drainage, especially during cleaning endeavors involving chlorine, vinegar, or other agents. (Then again, perhaps residual water is an even bigger problem with fixed rigid tanks, as they may be less amenable to tilting or lifting).
According to my observations, the four attachment points on the tanks is not sufficient for supporting the tank - the tank should be allowed to nestle against secure surfaces. If one wants to utilize some big empty space for flexible water tanks, it may be an idea to build some supporting walls first. Given the constraints of tight spaces where these tanks often find themselves, excessive movement may not perturb many users, hence again explaining that the number of complaints on those tanks are relatively few. If I will continue using flexible water tanks, I will ensure they won't have much room to move.
The leaks in the connections on Nuova Rade may be due to a too thinny O-ring and a suboptimal fit towards the screw. As a minimum, one needs to ensure the O-ring and all surfaces are completely clean, and ensure that there is an impeccable well-aligned good fit on the connections before one starts screwing - it's important to keep in mind that it's the O-ring that should keep the water in place, and the screw is just there to ensure there is enough tension on the O-ring. It says "do not overtighten" on the tank, my experiences have indicated that undertightening often begets more complications. My personal workaround entails replacing the O-ring with a judicious application of hemp and paste.
Every tank should have it's own tap, so the tanks can be emptied one by one and so leaky tanks can be isolated. In particular, tanks that have different heights (including port and starboard tanks on a monohull sailboat) should not be staying connected as it will increase the pressure on the lower tank.
If topfilling the tanks, it may be important to tap out some water before attaching the lid, so the inlet tubes will be filled with air instead of water.
One should also aim to mitigate potential damage stemming from leaks. Water leaking from just anywhere on the tanks should run in one direction to a designated place where some water is allowable, and where a bilge pump can readily remove the water should there be a major leak. I still have some way to go fixing the layout of my vessel.
My exploration of water bladders has encompassed A LOT of frustrations, time wasted cleaning up water and doing research, crawling in unaccessible places on the boat, as well as secondary problems due to moist. The obvious conclusion would probably be that anyone aiming to sail in unsheltered waters should steer away from flexible water tanks - and particularly the Plastimo tanks. At the very least, one should be very careful with the planning and installation if installing flexible tanks.
While I can't negate the allure of a rigid tank, the allure of flexibility continue to beackon, and I do have a hope of achieving a dry boat without giving up on the very idea of flexible tanks. I still have some plans to try and make a better installation of the tanks I still have - and see if it's possible to repair those that are leaking. Perhaps I'll try a third brand - but it should definitively be bought in Norway, due to the strong consumer protection embedded in the laws.
An alternative to replacing the capacity with rigid water tanks could probably be to install a water maker, but it's rather expensive and also demands quite much energy and would probably add to the maintenance burden as well.
This article has been written by a human, with some help of ChatGPT 3.5 in proofreading and suggestions.
Comments may be sent to t-fwt@solveig.oslo.no
I've purchased a Vetus water bladder now. My plan is to yet another time replace all of my water tanks with Vetus tanks. They give a much better impression:
Tank looks more sturdy (or perhaps it's just the "brand new" vs "old and slightly worn out" effect).
Both the inlet and outlet at the top of the tank. My previous tanks had the outlet on the bottom of the tank, causing the tank to rest on the top of the plumbing. This may create quite a lot of forces and movement on a small area of the tank. Outlet at the top of the tank may work due to the vacuum effect. In practice, it didn't work out very well on my old tanks - since they were always leaking, the outlet would suck air rather than water when the outlet would be placed higher than the water. Also, the outlet would become blocked by the lining of the tank. The Vetus tank has spacers preventing this from happening.
Tank had a paper leaflet with installation instructions. One of the things it emphasizes is that the tank should be leaning towards walls at the sides - my water tanks at the top of the diesel tanks never had any good sideways support (so I need to scrap the idea of having water tanks on the top of the diesel tanks, or construct some sideway support for it).
"Do not overfill" is specified a bit better, maximum pressure 16 kPa, equivalent to water standing at 1.5 meters in the inlet tube.
The water tube should be connected only with a hose clamp, the fitting is semipermanently installed on the tank. The Nuova Rade tanks has a rather flimsy setup with a wide screw fitting that is permanently welded to the tank, and then the hose fitting should be screwed onto the tank. This causes potentially causes three points that can leak, the welding between the tank and the screw fitting, the connection between the screw fitting and the hose fitting, and finally the connection between the hose and the hose fitting. I never saw the latter leak, but the design of the Nuova Rade screw fitting left much to be desired - I never managed to keep it tight over a longer time period or over streches with lots of waves. The Nuova Rade also had an instruction "do not overtighten" applying to the screw connection - perhaps because the welding of the screw connection didn't withstand much forces. The Vetus connection looks much more sturdy. The disadvantage is that it's harder to inspect the inside of the tank.
Still some things that concerns me:
Max 16 kPa, that means it should withstand water standing ~1.6 meter up the water inlet tube. With a tube that is ~1.8 meters long and frequently filling water until it runs over, it means the tanks will be briefly exposed to more than 16 kPa. Water thrown forth and back in the tank may also give a lot more force than a static 16 kPa pressure.
The instructions says that the tank should be placed in a ventilated room, and that there should be a gap between the water tank and the bilge. To me that seems to be read like "expect the tank to be leaking, sooner or later".