flexible tanks

[captpete]

Anybody have experience with flexible tanks? I'm looking at vetus or plastimo units. Durability? Any downsides? Thanks in advance for any help.

[knottybuoyz]

We have two, fresh water and black water. Small, not very efficient space wise. Pumping out the holding tank is a pain as there's no vacuum break when it empties so it burps! *ewe* The space around the f/w tank always seems damp even though it's not leaking. If you've got an odd shape space for a tank they're probably the answer. Turtlepak also makes them.

[hellosailor]

As a holding tank you can't ventilate it, so it may create an odor problem.

When good tanks are installed carefully--so they won't chafe on rough spots in the fiberglass, etc., and you use an anti-chafe or padding material around them to make sure they won't chafe, and you secure them so they won't be sloshing around...Seems like the folks who treat them carefully get good life out of them.

I'd still use a fixed tank IF the space was going to be dedicated and available, but as a way to carry extra tankage when you need it, and make the space available when you don't, they're a great idea.

The military also drops thousands of gallons of fuel in flex tanks--better known as "blivets". If they can trust 'em with fuel, you can probably trust the small ones with water or waste.<G>

[swagman]

Hi Hellosailor,
Re your comment that a flexible tank can't be ventilated.......

Beg to differ. They can be, and if used for waste, MUST be.

The stuff that's carried in them is obviously organic. Cut it off from light and you'll get growth, which if NOT VENTED could cause the flexible tank to burst.

Any good quality flexible waste tank will have a vent fitting moulded to it.

Cheers
JOHN

[Dunkers]

I used a Plastimo 25 gallon water tank in my Achilles 24 to good effect. I still had sweet water after 33 days at sea when crossing the Atlantic. True they do "sweat" with condensation but if they are in a locker which drains to the bilge its no problem. There are several different shapes of tank which will make it easier to fit whatever space you have allocated for it.

[hellosailor]

Swagman, I didn't say that a blivet couldn't have a vent fitting--I said it couldn't be ventilated properly. In order to properly ventilate a holding tank, you need to ensure airflow over the entire surface area of the contents. The only way to do that, is to create an airspace over the entire contents, and since the flex tank is designed to collapse and ensure "zero air" in the tank...it also ensures there is no airspace over the contents, and no airflow over the contents.
So you can "vent" the tank, to relieve pressure, etc., but you cannot "ventilate" the tank in any conventional manner. Which is why Peg, who has been making boats smell clean for 20+ years, doesn't recommend them as holding tanks unless you have no other alternative.

[Charlie]

I believe it was on this forum but it could have been a different one. Someone made a suggestion that you plumb a fuel bladder and a water bladder to the same spot. Water on top. If you need extra fuel fill the fuel baldder if you need extra water use the water tank. sounded like a good idea to me.