Introduction:
Call them flexible tanks or bladder tanks; they may well be the answer to your water storage problem. These tanks can be easily retrofitted to almost any boat. A few possible reasons for doing so are to:
• Replace leaking metal or plastic tanks
• Replace integral (built-in tanks)
• Add additional water capacity
• Provide ballast that can also be used for drinking
These tanks are available in many different sizes and several different configurations. In this article, I’ll cover the general design of the tanks, proper location, correct installation techniques and some first hand experiences.
There are three main manufacturers of flexible tanks for recreational marine use today. They are Nauta, Plastimo and Vetus (see sidebar #1). The tanks are roughly comparable as is the installation process. Tank capacities range from roughly 14 gallons to 58 gallons. Most tanks are rectangular with some manufacturers offering a triangular shaped tank for installation in the bow. Several manufacturers also offer the option of making a custom sized tank (up to 1000 gallon capacity) for your specific space. Tanks are somewhat expensive, ranging from $76 to over $280, depending on the size and configuration. Custom tanks would obviously be more expensive.
Tank Design:
Tanks need to be flexible, chafe and cut resistant and keep the water tasting fresh. This is accomplished using a multi-part construction. The outside layer is wear-resistant polymer or rubber; the middle layer is high-strength fabric, while the inner layer is designed to be taste-free.
Some manufactures use a nitrile rubber and nylon fabric for the outer layers and vulcanize the tank to ensure strength and water tightness. Others use a welded construction.
One important feature on flexible tanks is the use of a doubler strip on the inner seam. This strengthens the joint between the two sides of the tank and prevents leaks. This strength is important when you consider that, while the tanks themselves are light, the contents can add up to a considerable weight.
The tanks come with an inlet elbow, usually for 1-1/2” hose and an outlet elbow, for 1/2” or 5/8” hose. Remember, a vent line is unnecessary for a flexible tank as it simply collapses as the water is drained. Most tanks have the outlet elbow installed with the inlet still to be installed. While a little scary at first thought, the installation process is quite straight forward. This allows you to place the inlet in the most appropriate location.
Tank Location:
The location of the flexible tank is subject to some of the same considerations that any rigid tank requires. They should be placed low in the hull, near the center of the boat and be accessible for running the hose connections.
Beyond that, flexible tanks require a bit more thought and preparation. The enemies of flexible tanks are chafe and cutting. Often, a likely location is found, a small access hole cut and the tank stuffed into the space. The boat owner is then surprised a short time later when the new tank starts leaking.
You need to carefully inspect and prepare the site of the new tank. Usually the tank will lie against the inside surface of the hull and up against a bulkhead or stringer. Check carefully to make sure there are no splinters in the wood surfaces or jagged strands of fiberglass on the hull. Either will make quick work of the tank. The best practice is to glue a sheet of neoprene or other closed-cell foam rubber to the surfaces where the tank will rest.
The location of the tank should also provide good access for installation, inspection and removal. The great thing about flexible tanks is that they are flexible and can (and should) be easily removed for cleaning, inspection and winter storage.
When considering the location of the tank, be aware of how the shape changes from an empty tank to a full tank and make proper allowances in the routing of the inlet and outlet hoses. Make some provision for proper ventilation of the tank compartment. Otherwise condensation on the cool tank will collect and promote mold and mildew. Incidentally, the tank should be placed above the maximum bilge water level,
Lastly, make sure that the place you plan on installing the tank will be strong enough to support the weight of the tank when filled as the forces from a full tank and pitching boat are substantial.
Tank Installation:
With the tank location selected, you can move on to the actual tank installation. Place the empty tank in its chosen location. You will need to install the inlet elbow, so note the best location and the orientation of the nipple. You want as straight a run for the inlet as practical while considering the movement of the tank when empty or filled. Take into consideration minimizing stress on the tank and limiting chafe on the hoses.
With the inlet located, install the fitting in the proper orientation. Notice from the photo that there is a groove on the elbow fitting and a matching raised area on the ring that matches the groove. This interlocking feature helps trap the tank fabric and helps make a waterproof seal.
I placed a garden hose in the inlet to fill the tank and test my installation. I duct-taped the hose in place to minimize leakage and also closed off the outlet with tape. I inadvertently did too good a job taping the hose in place. Before I knew it, I had pressurized the tank to full city water pressure. It survived with no leaks, but the manufacturers recommend not pressurizing the tanks. That means don’t hook your water system up to dockside water pressure.
The tanks come with a heavy-duty grommet in each corner. These should be used to locate the tank and keep it from creeping or moving about. Again, consider the weight of the filled tank and use appropriate mountings. Hang the top edge of the tank from a substantial beam or cleat, using stainless steel eyebolts for example. Remember that the tank will expand equally around the seam, so allow room behind the grommet/seam line.
Tank Care:
If properly installed, your flexible tank will require minimal care. Upon installation, sterilize the tank and then flush it thoroughly. One manufacturer suggests sterilizing their tanks by letting a solution of 2-1/2 gallons of water and 1/2 gallon white vinegar sit in the tank for two weeks. They recommend doing this once a year, preferably at the beginning of the season.
If you end up with polluted water in your tank or the tank is badly polluted with algae, you can use a bleach solution to clean the tank and hoses out. Be sure to flush the tank completely afterwords.
If you like, you can remove the tank for winterization. If you do, leave the inlets and outlets open and store in a cool, dry and dark place. Manufacturers don’t recommend using standard potable water antifreezes (although someone did suggest trying vodka).
Inspect the tank and hoses, at least annually, for any leaks, wear or chafe and make any corrections necessary. Make sure hose clamps are in good shape Other than that, you’re good to go.
First Hand Experience:
In my case, the tanks were installed in a 1974 Columbia 34 Mk II. The original water tank was built in under the port settee. In fact the settee cushion sat directly on top of the water tank. The one tank was built in place of fiberglass with a top cover screwed on with about 50 bolts and sealed, almost, with silicone sealant. The inside of the hull formed the tank bottom and side.
The water inlet was on the top of the tank: to fill the tank, you had to drag a hose down the companionway and lift up the settee cushion, very inconvenient.
I replaced the settee tank with a 58-gallon tank and added another 18.5-gallon tank. Both tanks can now be filled from the deck inlet. A simple plywood cover replaced the tank top, allowing inspection and removal of the tanks if necessary.
To protect the hoses from chafe, I made simple collars from StarBoard (R) for the hoses to pass through. A clearance hole for the hose was cut in a square piece of the polymer. I rounded over the edges of the hole for the hose and bolted it in place. A collar like this prevents any chafe on the hose from a sharp corner on a bulkhead or partition.
All the tank fittings were installed and tested in about half a day. The actual tank installation took about two weeks from start to finish. The results? Good tasting water with a fraction of the problems associated with finding and installing hard tanks.
Tank Manufacturers:
Nauta
Imtra Corporation
30 Barnet Blvd.
New Bedford MA 02745
Phone: 508-995-7000
Fax: 800-989-2580
E-mail: info@imtra.com
Website: www.imtra.com
Plastimo
Plastimo USA
7455 16th Street East
Suite 107
Sarasota FL 34243
Phone: (86) 383-1888
Fax: (866) 214-1400
E-mail: info@plastimousa.com
Website: www.plastimousa.com
Vetus
Vetus Den Ouden, Inc.
P.O.Box 8712
Baltimore MD 21240-0712
Phone: (410) 712-0740
Fax: (410) 712-0985
E-mail: vetus@aol.com
Website: www.vetus.com
Installing Tank Fittings
Tools required: scissors, marker, slip joint pliers (the manufacturer recommends using a pin wrench, not the pliers).
Tank fitting components, left to right; elbow, sealing washer, and nut. Notice the sealing groove in the elbow fitting and the raised area on the ring; these will help establish a watertight seal.
Mark the orientation of the elbow and size of the opening: trace around the inside of the sealing ring for the correct opening size.
Cut the opening: Pinch the tank wall to make sure you have just one tank wall and then snip an initial opening. Then cut the opening out with scissors. Be sure not to cut the opposite tank wall.
Inserting elbow: It will be a bit of a stretch and you may have to work it in slowly. It can be done so don’t make the opening any bigger.
Finished installation: Place the ring over the elbow with the raised area down, then the nut. I tightened the nut with slip-joint pliers (not recommended by the manufacturer). Tighten again in two days and again in four days as the ring and groove seal
No offense, but i suggest admin adding a google+ button for easy share!
Posted by: elliptical reviews | December 12, 2011 at 06:47 AM
Paul,
Very helpful.
I will have to consider the structural requirements for containing the bladders, as well as arranging in the irregular spaces below p&s berths.
Thanks for the info!!
Posted by: Pete Malone | February 13, 2009 at 05:15 AM