Portions of this article first appeared in Cruising World magazine
Building Integral Water Tanks Into Your Boat
by James Baldwin
My troubles with water tanks go back a long way. When I
bought Atom, my 28-foot Pearson Triton
in 1979, it came equipped with one 23-gallon fiberglass water tank located under
the forward v-berth. Since this was nowhere near adequate for extended cruising,
I carried extra plastic water cans in every conceivable location and spent a lot
of time and backbreaking effort dragging them out to refill the main tank.
Eventually the tank worked loose from its mounts and started to rub against the
hull. When it began leaking in a place inaccessible to repair, I was forced to
consider replacing it.
Before making any modifications, I considered
my options. Even if I ripped apart the v-berth and pulled out the tank to repair
it, I would still have only a 23-gallon tank. I ruled out replacing it with a
prefabricated plastic tank or custom-built stainless steel tank because of the
cost and because a tank
of the shape and capacity I required would not fit through my companionway
hatch. Not only
could these tanks develop leaks that would be difficult to repair, they prevent
access to the hull. If the hull were damaged behind a rigid tank there would be
no way to stop the leak and the boat could sink. Flexible tanks were an option,
but the size and shape I wanted was not available and at the time I had no
experience or confidence in how they stand up to the possibility of chafe damage
or leaking fittings. Since I had in my mind to create sealed watertight bulkheads
wherever possible, the flexible tank seemed unnecessary.
My solution was to build an
integral tank into the boat incorporating the fiberglass hull and an existing
bulkhead in the v-shaped bow area as the tank’s bottom and sides. By adding
one more side and a top, I would have a tank of exactly the shape and capacity I
wanted, without some of the problems of standard tanks. It did require careful
design and (as I soon found out) a considerable amount of work.
BUILDING THE
INTEGRAL TANK
After emptying all lockers in
the forward cabin, I used a jig saw to cut out the entire top plywood bunk
surface to within 3-inches of where it was glassed to the hull, and set it aside
until later. I then removed and discarded the old tank and cleaned out the wet
mass of filth that had collected in the gap between the tank and the hull. Now
began the dirty work of grinding and laying up fiberglass that would make the
boat nearly uninhabitable for the next week. To begin with, I ground all
surfaces of the hull in the area of the new tank using an angle grinder and #36
grit discs. To protect myself from fiberglass dust during grinding, I wore a
full Tyvek suit with hood, goggles, and cartridge respirator.
Instead of making complicated
measurements and calculations, I made a rough guess as to the increased capacity
of the new tank by simply adding 4-inches to the height of the original tank.
Adding a small amount of height enormously increased the volume of the v-shaped
tank. With pencil and tape measure, I marked the location of the tank’s new
top along the sides of the hull and the existing aft plywood locker bulkhead,
which would now form the aft end of the tank. At the forward end of the tank I
installed a ¾-inch marine plywood bulkhead divider near the location of the
original tank’s forward end. This created a useful separate storage locker
between the tank and the chain locker. Using cardboard, I made templates for the
tank’s internal baffles and cut them out of ½-inch marine plywood. The
baffles were placed from bottom to top of the tank in an X-pattern. Holes in the
baffles allow the water to flow between the four chambers. The baffles must be
strong to restrict the potentially damaging force of water sloshing back and
forth in a partially full tank. They also must divide the tank into small enough
sections to reduce the noise of that sloshing water. There’s nothing worse
than trying to sleep in a bunk above a half full water tank that lacks
sufficient baffles when the boat is rolling in a swell.
After degreasing with acetone,
I heavily reinforced the baffles, hull, and aft bulkhead inside and out with
several layers of medium-weight fiberglass mat and epoxy resin. I worked on the
simple principle that if it looks strong it is strong.
I then made another cardboard
template for the top of the tank, cut it out of ½-inch plywood and trimmed it
to fit evenly along the hull and rest squarely on the top edges of the baffles.
In this top piece I cut a 12-inch square access hole in the center where the
baffles met which allowed clearance to reach a hand inside all four chambers.
Then I removed the top and gave its edges and inside surface three coats of
epoxy resin followed by two coats of nontoxic, drinking water safe epoxy paint.
(Check with your supplier about the suitability of their epoxy coatings for
potable water tanks or check the resource links below.
I gave the inside of the tank
a final sanding with the angle grinder to remove sharp strands of fiberglass,
and applied to all surfaces another two coats of nontoxic epoxy paint. At the
bottom of the tank’s aft bulkhead, I installed a plastic thru-hull fitting
suitable for a ½-inch water outlet hose. In the tank top I fitted another ½-inch
thru-hull for a vent hose and a 1 ½-inch thru-hull for the filler inlet. I
installed a clear hose sight gauge into the tank’s forward bulkhead that can
be viewed through the adjoining locker. I then replaced the top, sealed the gaps
along its perimeter with thickened epoxy putty, and strengthened the seam from
above with wide overlapping layers of fiberglass mat.
To finish the tank, I cut a
piece of plywood for the inspection port cover, sealed it with epoxy resin and
paint, fit a rubber gasket under it, and screwed it down on the tank top. I made
this inspection port instead of using the round plastic type from the marine
chandlers because they are not large enough and not reliably watertight. With
the tank finished, I moved on to replacing the top bunk panel that I had earlier
cut out. To add support, I glued strips of overhanging hardwood along the lower
edges of the bunk cutout, filled the gaps with epoxy adhesive, and fastened it
all from above with stainless steel screws. Before replacing the top I enlarged
its access hatch to provide easy access for the locker above the water tank. A
¾-inch lip, or cleat, fixed around the bottom of the cutout supports the hinged
locker hatch. Barrel bolts keep it secured in case of a knockdown at sea.
I ran the tank’s vent hose
into the chain locker and secured it to the bulkhead near the deck. A fine
screen placed on the end of the hose prevents insects entering the tank. Because
there was no simple, attractive way to run the tank’s filler hose through the
cabin to the deck, I installed the tank filler fitting flush on the top of the
bunk directly above the tank. (There were some unexpected advantages to this
that I will mention later.) From the tank outlet fitting I ran a food grade,
algae-inhibiting opaque PVC hose, under the cabin sole to the galley foot pump.
Now that the integral tank occupied the lower v-berth area, I had to re-route
the chain locker drain hose to pass over the top of the tank and then down to a
shut-off valve in the bilge. To ensure the chain locker would drain, I planned
for the top of the tank to be just below the level of the bottom of the chain
locker. This is something that should be checked before doing your own
installation unless your chain locker has a direct overboard drain. I passed
sleeves of short lengths of larger
diameter hose over all hoses where they passed through bulkheads to protect them
from chafe.
ADDING A SECOND TANK
Before using the tank, I
scrubbed it out with detergents and then baking soda and rinsed it thoroughly.
The capacity of the new 43-gallon tank is nearly double that of the original
tank. The extra 20 gallons I now carry add about 200 pounds of weight to the
forward end of the boat. To maintain balance required shifting other heavy
supplies further aft. Since the forward tank worked so well I later added a
second integral tank in the nearly inaccessible space between the cockpit floor
and the hull. Adding a 30-gallon tank in this otherwise unusable space helped
counterbalance the weight of the forward tank. On many boats a tank built in to
part of the bilge is another possibility. Although Atom
does sit noticeably lower in the water with this combined extra load of 500
pounds, I don’t keep the tanks full at all times. But it’s good to know I
can carry sufficient water when it’s needed for long passages or when visiting
places where water is not easily available. To keep on an even keel, I first use
the forward tank down to half full and then switch over to the aft tank until it
is empty and then switch back to the forward tank. On a passage we use about one
gallon per person each day for combined uses of drinking, cooking, and allowing
one quart of water for a rinse after a saltwater deck shower. When water
conservation is not a concern we each use an additional gallon per day, mainly
for longer showers. For fetching water from shore I have five 3-gallon plastic
cans that I keep stored in their own cockpit locker. I also have two 5-gallon
cans in the bilge and three 5-gallon cans that fit into what used to be Atom’s engine compartment before I converted to outboard drive.
This makes an adequate, ocean-crossing total capacity of 113 gallons.
There is added safety in
keeping water in two separate tanks in case one becomes contaminated or develops
a leak. Each tank has its outlet hose going to a shut-off valve before joining
the common inlet of the galley foot pump. On small cruising boats, I consider
pressure pumps unacceptable because of their power usage, noise, unreliability
and the way they encourage water wastage. Unless you enjoy washing your hands
one at a time (something I never learned how to do) I would not choose a galley
hand pump except as a back-up to a foot pump or as a saltwater pump for washing
dishes.
The problem of having the
forward tank’s water filler fitting below deck is that if you overfill the
tank, the water ends up spilling on the forward bunk. This disadvantage is
offset by the ability to refill the tank from rainwater collected on deck. On Atom
I fit the two deck scuppers with valves that allow me to divert the deck drains
to a hose below deck that I insert into the water tank. If the water filler were
mounted on deck I would have to fill containers down below and then haul them on
deck to pour them into the tank. There are times on passage when trying to
refill water on the deck of a small boat is impossible due to the extreme motion
and the possibility of having seawater enter the filler. Now I can safely refill
the tank by siphoning water into it from a can resting on the bunk. Since the
water tank filler fitting is located directly below the forward deck hatch, I
normally fill the tank from on deck using a funnel connected to a 4-foot length
of hose that I drop through the hatch into the open tank filler. To avoid
overfilling, I use the sight gauge to monitor the incoming water level.
CONCLUSIONS
Each tank cost me about $300 (in 1994) for materials including -
plywood (bought as off-cuts at a discount), fiberglass, epoxy, paint, and
fittings. Labor amounted to roughly 40 hours per tank. This is not an easy job
by any means, but it is within the ability of anyone experienced in general boat
repair. My tanks have worked so well that I’ve since constructed additional
tanks on other boats. Although all my tanks have not had the slightest problem,
I suspect some lightly built modern boats may not be suited to integral tanks
because of risk of tank bulkhead damage due to hull flexing. For them, flexible
tanks may be the way to go. Also, flexible tanks are much easier and cheaper to
install and most of my customers choose flexible tanks.
You might think a watermaker would be a reasonable
alternative to increased tank storage capacity. On a small, self-sufficient
cruiser such as mine, watermakers are out of the question because of their
expense, energy use, unreliability, and maintenance hassles. When your
watermaker does crap out in a place scarce of fresh water, like the Bahamas,
you’ll be thankful for the extra storage capacity.
There is also the concern about the possibility of causing
osmosis blisters by having water on both sides of the hull, as is the case near
the integral tank. My 46-year-old boat has had integral tanks for 15 years now
without any sign of blistering. After working for many years building and
repairing fiberglass boats, it seems that a fiberglass boat will blister or not,
chiefly depending on the quality of its lay-up and materials during construction and the
coatings used to seal it thereafter. If the boat you are adding tanks to is
showing signs of blistering, then of course that problem should be addressed
first, or the adding of integral tanks may accelerate the problem. Modern
barrier epoxies are for all practical purposes, impermeable to water. In short,
if your boat is not blistering, an epoxy-lined tank should not start the
problem.
There are several advantages of integral tanks over other
types of tanks. Integral tanks are more space efficient. They take less room and
hold more water than any other tank. They add massive strength to the hull. They
act as a watertight locker in case of collision. They fit in areas of the hull
where other tanks cannot. With an integral tank you can choose exactly the size
tank you want and not be constrained to use whatever size tank is commercially
available. Properly built integral
tanks are much less likely than other tanks to leak or need replacement. If you
get rolled they can’t break free and cause further damage or loss of precious
drinking water. Whichever type water tanks you choose, it’s worth remembering
that fresh water is your most important and most used resource and its storage
deserves careful thought.
Resources:
Article on West System water tank construction
http://www.epoxyworks.com/18/tanks.html
FDA-certified epoxy water tank barrier coat available at
www.epoxyproducts.com
http://www.epoxyproducts.com/nsp120.html
More potable epoxy tank coatings available at:
Newlander Armor Products, St. Petersburg, FL.
727-544-3303
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