Time for a new water tank

[rslifkin]

This winter's big project is to rip out my slightly leaky, too small aluminum water tank and replace it. I started out thinking plastic tanks, but due to the shape and size of the space, it'll have to be 2 tanks and I'll be stuck with an inaccessible connection between the tanks once everything is back together.

Currently, we carry 65 gallons of water. There's space for more, that's just the biggest single tank they could put in during construction. Plastic tanks would likely get me something in the 80-95 gallon range, but until I get the old tank out, I can't measure enough to know or order tanks.

I'm now thinking I should just build an integral fiberglass tank in the area where the current tank sits. My math says I can easily get 100-110 gallons in there, plus the tank will weigh less than either the current or plastic tanks (with their supporting structure). Plan would be to follow the West systems method of slightly hardener lean epoxy for the build. And then paint the inside with Brewcoat or similar.

Design idea for the integral tank would be using foam core for the end plates, baffles, top, and the small piece to bridge the top of the keel sump (so water can flow under the tank). The bottom of the tank will just be the hull with a few layers of epoxy / glass added, and the sides will be the stringers with the same treatment (stringers are already 3/8" thick glass on the sides, as they're hollow glass stringers).

Thoughts?

[peghall]

Check out Ronco Plastics...They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with. Their catalog is here Ronco Plastics tank drawings Their tank drawings organized by capacity are here Ronco Plastics tank drawings
When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fit your space.


--Peggie

[Cheechako]

I have never liked fiberglass water tanks. That's the last thing I wold do. Couldn't two plastic ones not be 'tied together', but each have tubing separately to a 3 way valve in an accessible place?

[rslifkin]

I've looked through the whole Ronco catalog, and that's where my estimate of capacity with plastic tanks comes from. The issue is that if I put in 2 tanks, unless I give up more capacity to leave space on the sides, I won't have room to run a hose along the tanks. So they'd have to be tied together (and I'd prefer them to act as 1 tank anyway). And I waste a few inches between the tanks for connections.

The other issue is, until I get the old tank out, I'm not sure how much height I have to work with. The space gets shorter as I go further aft, but until it's apart, I can only measure the front of the space. So I'd have to rip it apart, then order tanks and wait for them. And unless I get 2 completely custom tanks, I'll definitely end up with less capacity than I could get in fiberglass. If it's as short towards the back of the space as I fear, it's possible I may only be able to get 75 gallons of tanks in there. And I'd effectively have an 8 - 9 foot long tank with just a single baffle in the middle (the division between the tanks), which isn't ideal and puts more stress on the mounts.

As far as concerns with fiberglass, some of the issues should be mitigated by using a potable water safe coating on the inside on top of epoxy, so I shouldn't have to worry about osmosis or anything.

Part of the concern is just about capacity and making efficient use of space. This boat has a disproportionately tiny water tank. We have a 70 gallon holding tank, 420 gallons of fuel, and only 65 gallons of fresh water. So water is always our limiting resource. And there's no good space to add a second water tank without adding too much weight up forward, taking away needed space in the engine room, etc.

For perspective, this is a view from the rear of the water tank. It's buried under the floor, between the stringers, with half of the tank under the fuel tanks that sit on top of that floor.

[Cheechako]

The boats I had were factory built fiberglass tanks, so I dont know if they were done properly or not. We found the water undrinkable... only used it for washing. How would you even get under there to do the glassing and gel coat properly?

Is this a power boat? That's a ton of fuel! (well almost 2 tons actually!)
No space for a couple of water tanks above the bilge somewhere? V Berth? Engine room?
Buy a water maker and forget making tanks!

[rslifkin]

Originally Posted by Cheechako

The boats I had were factory built fiberglass tanks, so I dont know if they were done properly or not. We found the water undrinkable... only used it for washing. How would you even get under there to do the glassing and gel coat properly?

Is this a power boat? That's a ton of fuel! (well almost 2 tons actually!)
No space for a couple of water tanks above the bilge somewhere? V Berth? Engine room?
Buy a water maker and forget making tanks!

Yes, it's a powerboat. Just hauled for the winter a few days ago and off-loaded the remaining fuel that was in the tanks. Plan is to move the fuel tanks out of the way and cut the floor open for access, so other than the forward foot or so where access will be a little limited, I'll have good top-down access into that whole space.

Pretty much the only other good spaces for tanks would be the forward bilge (I could fit plenty of tankage in there, but weight distribution would be a serious problem) and the engine room, but anywhere in the engine room would be in the way when doing engine maintenance (the only good tank spot in there is consumed by the holding tank).

Most factory fiberglass tanks on older boats were built with the same polyester resin and gelcoat as the rest of the boat, which typically wasn't very suitable for contact with potable water. I'm hoping that epoxy and then a suitable coating on top (plus good carbon filtration after the tank) will avoid the water quality issues.

I have thought about a watermaker and smaller tanks, but I can't justify the cost. This isn't a boat that will ever cruise outside an area where we can obtain water easily enough, plus we're currently in fresh water. So spending thousands on a water maker just to avoid shoving a hose in a deck fill after a week or so doesn't make sense.

[ranger58sb]

Originally Posted by rslifkin

Pretty much the only other good spaces for tanks would be the forward bilge (I could fit plenty of tankage in there, but weight distribution would be a serious problem) and the engine room, but anywhere in the engine room would be in the way when doing engine maintenance (the only good tank spot in there is consumed by the holding tank).

Our previous boat had two freshwater tanks, outboard of the engines, connected with a hose from one side of the bilge to the other, one deck fill. Maybe you have outboard locations? Or fore and aft locations?

Or... maybe move the holding tank and put the new freshwater tank(s) where the holding tank was?

+1 for what Peggy said about Ronco and their tanks.

-Chris

[rslifkin]

Originally Posted by ranger42c

Our previous boat had two freshwater tanks, outboard of the engines, connected with a hose from one side of the bilge to the other, one deck fill. Maybe you have outboard locations? Or fore and aft locations?

Or... maybe move the holding tank and put the new freshwater tank(s) where the holding tank was?

+1 for what Peggy said about Ronco and their tanks.

-Chris

The only outboard locations are unfortunately not great. I'd either have to give up most of the drawers in the aft cabin and fill that space with tanks, or ruin the access to the outboard sides of my engines. The only reason it's decent currently is the lack of stuff mounted out there.

The current tank is in the centerline aft location. Unfortunately the lack of lazarette on this boat and having the fuel tanks under the aft bunk limits what places are left to put other tanks in.

[Scrimshaw4]

In the event you chose to build your own tank you need to think about the tank's interior coating. It needs to be a certified potable water coating. Be aware that there are a number of products that meet this requirement but are certified at different tank volumes. Ex. A coating certified for a 5K gallon tank can NOT be used in a 100 gallon tank. It all has to do with leaching ratio's. This holds true for fiberglass tanks. Metal and "manufactured drinking water" tanks have non-leaching surfaces. Just something to think about.

[MCOS]

Try looking for a flexible bladder tank. Find one approx shape and size of your space. Would not go with fiberglassing in hull unless you don't mind the off taste of the water. The out gassing of the epoxy takes quite a while and the water will have a off taste even after several years.

[rslifkin]

Originally Posted by Scrimshaw4

In the event you chose to build your own tank you need to think about the tank's interior coating. It needs to be a certified potable water coating. Be aware that there are a number of products that meet this requirement but are certified at different tank volumes. Ex. A coating certified for a 5K gallon tank can NOT be used in a 100 gallon tank. It all has to do with leaching ratio's. This holds true for fiberglass tanks. Metal and "manufactured drinking water" tanks have non-leaching surfaces. Just something to think about.

I have found a suitable coating, as that was one of my first concerns. Aquatapoxy A61 has the NSF-61 cert for tanks 50 gallons and up. So that should be no problem.

[rslifkin]

I've now got the tank area opened up for anyone curious about the space in question. The old tank shown in the picture extends about 18" under the floor at the left side of the picture. I'm figuring the new tank will start in a similar location (there's some access into that area through a panel in a closet) and extend back about 1.5 feet past the end of the current tank. Hoses and such will get re-routed as needed.

[rslifkin]

At this point, I think it's update time. The tank is almost finished. I'm in the process of making and installing the last top panel this week, then it's time to hook up the tank and start reassembling the boat. Based on how the tank measured out, it should hold right about 105 gallons (40 gallons more than the original tank). Once the boat is in the water I'll fill the tank with a flow meter in line to confirm capacity.

The basic construction method is foam cored fiberglass panels over the top of the keel sump (allowing water to pass under the tank) and for the baffles, end plates, and top panels. I glassed in tubes from the limber holes in the stringers down to the keel sump to allow water drainage from the stringers.

The hull bottom had a layer of fiberglass and epoxy added, as did the inboard sides of the center stringers. I glassed PVC conduits into the sides of the tank to accommodate fuel lines, etc. and allow for future replacement (replacement wasn't well accounted for in the original construction).

Fittings in the tank are stainless thru hulls from Groco and the interior of the tank is coated with Aquatapoxy A61 (potable water safe epoxy). The tank bottom slopes down a bit into the keel sump as the sump get taller towards the front of the tank, ensuring that the tank bottom is always sloped towards the water outlet regardless of boat trim.

Below are some pictures of the tear down and build (in chronological order). The last picture is the status as of yesterday. You can also see in some of the early pictures the plastic steering lines that were run through the keel sump at some point in the past when the original copper lines failed. I haven't relocated them yet, but I did include a pair of extra 1 inch conduits to accommodate moving those in the future.