Bladders vs poly tanks

[cruiser77]

We have just purchased a C&C 37R (totally excited), we will be making a lot of changes as she was used as a race boat and we are transforming her into a cruiser. As we go we will need some advice and help from all you folks!
First question, what is everyone's thoughts on bladders vs poly tanks, the good, the bad... all of it. TIA

[sailorboy1]

poly tank, no doubt in my mind that a tank is better than a bag!

[Cheechako]

I agree, poly tanks are great.

[Mike OReilly]

Yes, poly is better than a bag. That said on my previous boat I used a water bladder to cruise seasonally for seven years. The only problem I had was when I was removing it one year and damaged the fitting.

I’ve considered using a bladder as a replacement diesel tank. I may still do this. They’re not the best solution, but I think they can work.

[JPA Cate]

Totally agree with sailorboy1 on this. We've had bladders, and poly tanks, and s/s, and epoxy and glass.

The problems that we had with the bladders were mostly due to seam failure, but they failed in our use (crossing the Pacific) in two and a half weeks, and they were brand new, with a 5 yr guarantee. [The guarantee is really useless once you are constantly migratory.] Chafe can be a factor with bladders, but if you lay them on indoor/outdoor carpeting, that will help some. The best ones we had were the custom made hypalon ones that came with the boat; the worst were Tedlar-lined and we bought them from WM, who did honor the warranty.

For replacement tanks, there are poly ones in many sizes. They are easy to monitor, and if you get ones with a cleaning port, then they are cleanable, too. The ones we had did not give a flavor to the water.

We had custom s/s tanks built for our previous Insatiable in NZ, and if we had it to do over, we'd add a cleaning port and possibly a sight glass, but they were built in 1990, and as far as I know, the present owner of the boat has not replaced them. They were really good value. They should not rest on the hull, but be spaced off of it, for air circulation.

Welcome aboard CF.

Ann

[atmartin]

We picked a 20 gal bladder to add some capacity before heading south. It didn't fail, but I was less than happy with it. When we picked up some contaminated water (locals said well was fine; wasn't fine after percolating in tanks for a few days), it was a huge pain to clean compared to our monel tank. Had to remove it from the boat.

Also, if you try to shove them in a somewhat restricted area without a vent the flexible tanks develop what I can only describe as "springiness" (not strong on the fluid mechanics). But basically, as you fill the tanks, the pressure of the incoming water deforms the bladder and it pushes back, which can make getting those last few gallons in a real pain and that matters in some areas of the world.

It's been replaced with a poly tank. I'd only use a bladder as a temporary measure.

[cruiser77]

This is all really helpful and informative. Thank you very much and we look forward to reading more!

[JPA Cate]

There is one use for bladder tanks that was handy for some friends of ours who came out into the pacific. They put it in the dinghy to take on water ashore, disinfeccted the water, then pumped from the bladder into their tanks, and through a charcoal filter for the drinking water, on an as needed basic. It saved them lugging jerry jugs of water from places where you cannot go alongside to take on water.

Ann

[UNCIVILIZED]

I think that one of the better uses for bladder tanks is when a metal tank has seams which are failing, or it has a small leak, & that to replace it would entail destroying/removing much of the boat's interior furniture. In this instance you put the bladder tank inside of the metal one, after checking for any sharp edges or chafe points.

Otherwise, barring a crazy installation scenario, go with poly over bladders. Though whenever possible, I'm a BIG fan of built in clean out ports on tanks. More for fuel tanks than other types, but they're a great feature to have, & something of a necessity on some tanks.

Ann, do you guys prefer poly tanks over epoxy & glass, & if so why & for what applications?

EDIT: Sometimes bladder tanks are nice to have to enable you to carry extra water or fuel for an extended crossing. Using up the contents of the bladder tanks first, & then stowing them once you switch over to your regular tanks. As on a few boats we've attached them to the deck or cockpit sole, with exactly this purpose in mind. Just mind your boat's center of gravity when doing so.

[HopCar]

Now that everybody has told you to go with plastic tanks, here is where to buy your water and holding tanks. They offer almost 500 shapes and sizes.
https://ronco-plastics.com

[AndyEss]

For boats originally designed and built around rigid tanks, they obviously work well. As a retro fit in your case, bladders have some advantages - they can fit into far many more irregular spaces we have all over our boats. Most importantly you can position them along the boat's centerline in the bilge, where their weight adds to boat stability, and lessens any tendency to induce heel.
If you are stuck by space issues to mounting a rigid tank high up above the CG, that will decrease stability, and probably induce heel due to lack of symmetrical loading.
I like the bladder tanks on my new (to me), used boat as the space they fill would not be useful for storing items that could be damaged by exposure to salty bilge water. Full, they add well over 2000 lbs of weight low down beneath the cabin sole.

[Rex Delay]

Some time ago my poly tanks failed. Replacement tanks which matched the original and the hull shape were over $1k each. I put in bladder tanks for $100 each with the idea that if they fail every 3-4 yrs, I am still ahead. That was 8 yrs. ago and they are still in excellent condition.

[UNCIVILIZED]

Originally Posted by AndyEss

For boats originally designed and built around rigid tanks, they obviously work well. As a retro fit in your case, bladders have some advantages - they can fit into far many more irregular spaces we have all over our boats. Most importantly you can position them along the boat's centerline in the bilge, where their weight adds to boat stability, and lessens any tendency to induce heel.
If you are stuck by space issues to mounting a rigid tank high up above the CG, that will decrease stability, and probably induce heel due to lack of symmetrical loading.
I like the bladder tanks on my new (to me), used boat as the space they fill would not be useful for storing items that could be damaged by exposure to salty bilge water. Full, they add well over 2000 lbs of weight low down beneath the cabin sole.

What did you do to address the issue of keeping them in place should you suffer a knockdown? As well as protecting them from puncture & abrasion from items that get dropped into the bilge? Like the occassional screw, or tools. With the former item likely to wind up lodged somewhere underneath of them at times.

[Mike OReilly]

Originally Posted by Rex Delay

Some time ago my poly tanks failed. Replacement tanks which matched the original and the hull shape were over $1k each. I put in bladder tanks for $100 each with the idea that if they fail every 3-4 yrs, I am still ahead. That was 8 yrs. ago and they are still in excellent condition.

Good to hear this. I have integral steel diesel tanks built deep into the bilge. One (the small one) has already failed a pressure test and is decommissioned. I assume the other one will fail eventually. If I ever get around to it, my plan is to cut the top off the decommissioned tank, clean and remove all sharp points, then insert a flexible diesel tank.

Like I said, in my previous boat we used a flexible water tank (after the previous owner mistakenly filled the water tank with gasoline). I used the old poly tank as the supporting structure for the flexible one. In years of seasonal use the only problem was self-inflicted.

I don’t think they can be as good a proper solid tanks, but I was able to use one with zero problems for years.

[GILow]

The most horrible job I have ever had to perform on the boat was chopping out a hardened bladder tank that had been poked into one of the inbuilt keel tanks through the inspection hatch. I cannot describe how foul it had become with the old sour water trapped around the outside. The bladder itself had gone rock hard and I had to carve it out in pieces using a tree saw. I, personally, will never use a bladder tank on our boat.