Thursday, May 31, 2012

The long awaited Water Tank Blog

 Enough of this cheesy wedding stuff, back to the nit and grit of boat ownership!

As promised, here is a [very] detailed account of our water tank experiment thus far. Warning: this is a very long and rather technical blog. This is not because I feel you are overstimulated or need a nap. This is because the blogs of other boat owners have helped us tremendously with all of our first-time boat parent worries. It’s a “pay it forward” thing.

If you don’t know boats and are bored enough to read on, here is a boat glossary to help with some of the nonsensical words boat owners use.

Last December, I came home to John taking a saw to the inside of our boat, which I told you about here. We pulled the seat apart, cut up the water tank, dragged the pieces out of the boat, and then stood, hands on hips, staring into a very dusty and oddly shaped hole. We scratched our heads. This was going to be interesting.

We spent about a month with a useless gaping hole on the left side of the boat while we researched and discussed various replacement options. We measured and sketched and measured again. We got quotes from steelworkers and plasticmakers. We got advice from all of our friends, whether we asked for it or not. We decided what to do… Then we changed our minds. There were 2 primary complicating factors for us:

1. we live very far away from the steelworkers and plasticmakers and even the boat stores. Any prefabricated tank quote we had to almost double because of shipping. Anything we made ourselves would have to be meticulously planned out so we ordered all the right pieces in all the right quantities. No quick dashes to home depot when you realize you don’t have the right size paint brush…

2. Our tanks were put in place before they added the cabin top to the boat, and are therefore larger than the companionway. If we had a tank made, the dimensions would have to be perfect to both fit through the door and maximize tankage once in place. This was a daunting task (hence this somewhat arbitrary experiment). If we were, say, 2 inches off, we would have a lovely 7’ long $2,000 hood ornament on our bow, and a very grumpy Becca.

Matt, pondering our water tank space

 With the help of our very patient friend, Matt (an experienced sailor, boat builder, and good friend), we finally bit the bullet and put in an order with fisheries for everything we thought we’d need to build our own fiberglass water tank. We just barely got in before the barge deadline- otherwise it would have been 2 weeks before our materials left Vancouver.

 The order list looked something like this:
-5 gal West System epoxy resin
-1/2 gal cell-o-fill (filler, so the epoxy thickens and keeps shape)
-2 gal West System slow epoxy hardener
-20 oz West System micro-fiber adhesive filler (to make the epoxy more like glue)
-1 pt barrier coat additive
-1 4x8’ sheet marine plywood
-4x28’ roll of fiberglass,
-1 gal Blue Max liquid rubber
-1 pump kit (the pump kit makes measuring epoxy: hardener much easier—1 pump to 1 pump. I’d highly recommend it, no math, no mess, no measuring)
-1 resin roller
-1 bag mixing sticks
-1 syringe
-3 paint smoothers (an angled piece of hard plastic like a squeegee for the epoxy)
-3 deck plates
-3 1/2” plumbing fittings, one leading to the fill up, one leading to the pump (and then to the sinks), and one as a vent
-various paint brushes, rollers, gloves, masks, paint thinners, and rags

The dimensions of the tank make an odd looking trapezoid. It is 79” long and about 18” tall in the front. The aft end is 31” wide at the top and 10” wide at the bottom. By the forward end, the space narrows to 26” wide at the top and 7” wide at the bottom. The back is angled and rounded slightly. Including the baffles, there is about 70 square feet of surface area, and 100 gallons of volume capacity (if my rusty geometry skills are right).
About to saw off the tab

It was like Christmas morning, 5 days later, when our several palettes of goodies arrived. In the meantime, we had been vigorously grinding away the old fiberglass to create a nice, smooth surface, including cutting out and grinding down the two tabs on the hull side. (And that would be the Royal We—John did ALL of the grinding, and deserves credit for it—fiberglass dust is really pesky stuff)

The basic idea of this tank is to use the infrastructure already in place as the mould. So the hull on the outer side, the floor on the bottom, the bulkheads on either end, and the settee support on the inside. By laying fiberglass over those 5 sides continuously, all we have to add is a top and some baffles and we have the maximum size tank, with the fewest materials possible. Theoretically, at least.

So here’s what we did:

Step One- Tabs.    make strips of epoxy-hardened fiberglass that act as supports for the lid. To make them, we laid down a huge piece of plastic and set 2x4’s down as guides (to keep the fiberglass perfectly straight while it’s curing). Then we cut strips of fiberglass about 2” wide, slathered some epoxy down next to each board, laid a strip of fiberglass in the epoxy, slathered a whole bunch more epoxy over the top, laid a second strip of fiberglass, another slather of epoxy, and then smoothed it all out. We started with a paint smoother, then moved to the resin roller to make sure all the air bubbles were out. Then we had a beer.

Step Two- Funky plywood shapes.    The space we are filling with ‘tank’ runs the length of the settee and the depth from the edge of the bench to the hull. It extends under the storage compartments that would normally hide behind the back settee cushions. To waterproof this part of the tank’s “ceiling”, we cut a funky-shaped piece of marine plywood that –miraculously- fit snuggly in this “ceiling” space. We fiberglassed the bottom of the board with epoxy mixed with the barrier coat (to waterproof the epoxy) and hot glued it in place (the hot glue simply holds it there until it is fiberglassed in place)

You can see the tabs ready to support the lid
Step Three- Tabs Again.   When the tabs were dry and hard, we scraped and sanded the excess epoxy off the sides and ends, cut them to fit the four lengths we needed, and hot glued them in place, so half of it hung over to support the lid.

one of the newly filleted corners
Step Four- Filleting. Fiberglass does not like to bend into 90 degree angles, so we had to get rid of all of them. To do this we made a witch’s brew of epoxy, hardener, cell-o-fill, and micro fiber filler until it was the consistency of peanut butter and smoothed it along every edge inside the tank. It took three coats in some corners to get the angle obtuse enough to please the fiberglass gods. Then two sessions of concentrated sanding, making sure every little bump and drip are smoothed out (so we don’t end up with holes in the fiberglass). 

Here's Matt, rolling on the epoxy
Step Five-  The Big Step.     Matt came in to assist in this crucial step, where we laid sheets of fiberglass inside the entire tank and rolled on the barrier coat added epoxy. Finally, the big gaping hole started to look like a tank! Because it’s cold and
wet here, and ensuring the epoxy cures right is the very most importantest step of the whole process, we plugged in a few electric heaters and covered the whole setup with big blankets to keep it warm and dry while the epoxy cured. 

Step Six- The Lid.    We measured and cut (and then re-measured and cut a bit more) a piece of marine plywood for the lid of the tank, to fit perfectly inside the frame and rest lightly on top of the
tabs. Then we fiberglassed both sides, ensuring the bottom (inside) side had the barrier coat additive.

rolling out the airbubbles in the epoxy on the l
Step Seven- Make Baffles.    Baffles are blockades inside water tanks to baffle the water so the
molecules can’t band together and plan an escape, using momentum to throw themselves violently from one side of the tank to the other. In our case, they are 2 pieces of fiberglass cut to trisect the tank, with several holes to allow the passive water through. We made them just as we made the tabs, but bigger (epoxied 2 rectangles of fiberglass together for each one, let them cure, and cut them to fit). We added triangle supports for better structural integrity. Then we used the same filleting concoction along every touching edge, to glue them firmly in place.

Step Eight- Break. Take a month off and get married in Mexico. 

Step Nine- Add view ports.   We drilled three large strategically placed holes in the lid of the tank and epoxied the three view ports in place, making sure to coat the newly exposed wood very well. The three ports are centered over each of the three sections created by the baffles, so we can theoretically reach every corner of the tank to inspect and clean.


Step Ten- Access ports for the view ports.   We saved the original piece of plywood John cut out to rip out the old tank (the ‘seat’ part of the settee), so we simply cut three squares out to use as “doors” to the newly installed view ports. We also painted this piece, as it was old and sad looking.

Step Eleven- Plumb.   We drilled a ½” hole at the lowest bottomest point in the tank (where the old tank was plumbed as well) and silicone-d one of the fittings in place. Once it dried, John hose clamped the flexible piping to the fitting and teed it into our water system. Then we drilled another hole at the top of the tank and did the same thing to plumb it to the fill up port on the deck. The third fitting also leads to the deck, so the water has somewhere to go in case we overflow the tank.

Step Twelve- Clean.   It is up for debate how safe it is to drink out of an epoxy-covered surface. It seems to me it’s no worse than plastic or metal. But to minimize the potential effects, we scrubbed the tank really well. With vinegar, then soap, then more vinegar. When epoxy cures, it secretes a waxy stuff that can taint the water, so the idea is to scrub as much of that away as possible.

Step Thirteen- Gunky blue stuff.    It was recommended to us that we coat the tank in BlueMax liquid rubber. You can check it out here. It’s pretty cool stuff, and seemed like a smart addition to the tank. This was not actually on the original order, but a friend happened to have some for a project he hadn’t yet started, and let us buy it off him. It’s almost the consistency of silly putty, and the goal is to slather it on as thick as possible. We used paint brushes, but it was more like smearing and pushing than painting. We coated the entire interior including the baffles and lid, and used exactly 1 gallon. 

Step Fourteen- Wait.   There is a recommended 2-week curing time for the Blue Max, so we’re hanging out for now, drinking out of a 5-gallon jug like we have been for the last year, waiting for the grass to grow. (And the tank to dry). This waiting time works out well anyway, since we’ve just moved again and are orienting ourselves with a new job. In the meantime, we have placed the lid in place, put the settee back together, and sat on that side of the boat again for the first time in 7 months!

Step Fifteen- Finish!   The very last step is to give the tank one more good scrub, glue the lid in place with epoxy, and fill it up with water.

If you have leaky old aluminum water tanks, I hope this was helpful. If you have questions or want to talk more about what we did, please leave a comment- we’re more than happy to share the rest of our limited knowledge and experience.

If you don’t have a leaky old water tank and are not yet snoring on your keyboard, sorry for the long-winded somewhat technical ramble. And I bet you wish you did have a leaky old water tank, so you could grind fiberglass and smear goop like us :-)

***UPDATE 7/12: Do not use Blue Max on your fiberglass water tank! It does not stick to fiberglass, but is meant for concrete. I have spent way too many hours with my face jammed against the top of the tank, shoulder distending, fingers stretched to the very corners to "peel blue" from the entire inside of the tank.


  1. Chester would be proud! Even though epoxy and fiberglass were not part of tour!
    Love ya, Mom

  2. Thanks for sharing that well done project. You are lucky because you have a professional friends when it comes in making the boats.

  3. It is a very good blog. Thanks for sharing.

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  5. this is an excellent blog. It was very great to see such blog about water tanks and everything on plumbing world. Thanks for sharing some articles with regards on your job.

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  6. Thank you so much for all of your information about water tank. I have been having some problems with mine, and I really want to get it fixed fast. You have given me some really great suggestions! Thanks again for your help!