New water tank time

[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.

Thoughts?

 

[syjos]

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.

Thoughts?

I have built tanks using epoxy, either WEST or System Three. I use plain epoxy, normal mix ratio, for the build but use Interlux Interprotect 2000 for coating the interior.

I use 1708 and marine ply for coring. I install internal baffles for strength and to alleviate free surface effect on large tanks.

Makes sure to install some sort of inspection plate so the interior can be inspected.

I spoke with a client last winter who had me build his water and holding tanks out of FG over 25 years ago. He had opened the inspection plates for an interior inspection and reported the interior in good condition.

 

[rslifkin]

I have built tanks using epoxy, either WEST or System Three. I use plain epoxy, normal mix ratio, for the build but use Interlux Interprotect 2000 for coating the interior.

I use 1708 and marine ply for coring. I install internal baffles for strength and to alleviate free surface effect on large tanks.

Makes sure to install some sort of inspection plate so the interior can be inspected.

I spoke with a client last winter who had me build his water and holding tanks out of FG over 25 years ago. He had opened the inspection plates for an interior inspection and reported the interior in good condition.

That's good feedback. I was thinking foam core, just for the ability to trim to shape easily with a knife. The core will only be needed in the baffles, end plates, top, and the middle 6 inches of the bottom to put a lid on the keel sump below (to allow water to pass under the tank). The bulk of the bottom will be the hull with a couple layers of glass/epoxy added. Same goes for using the stringers as the sides.

I'll be able to put in an inspection plate into one part of the tank, but some of it is under the fuel tanks, so not all of the tank is accessible.

Any reason for using Interprotect? Nothing makes me think it's better for potable water contact than regular epoxy.

 

[syjos]

That's good feedback. I was thinking foam core, just for the ability to trim to shape easily with a knife. The core will only be needed in the baffles, end plates, top, and the middle 6 inches of the bottom to put a lid on the keel sump below (to allow water to pass under the tank). The bulk of the bottom will be the hull with a couple layers of glass/epoxy added. Same goes for using the stringers as the sides.

I'll be able to put in an inspection plate into one part of the tank, but some of it is under the fuel tanks, so not all of the tank is accessible.

Any reason for using Interprotect? Nothing makes me think it's better for potable water contact than regular epoxy.

Interprotect has some sort of additive mixed into it that makes the epoxy more water resistant. I think epoxy by itself would be waterproof enough. I applied the Interprotect as a belt and suspenders sort of guarantee that water will not permeate the epoxy. I used marine plywood for core so the precaution. With foam core, water intrusion would not be an issue.

I install coring on all 6 sides of tanks and the baffles. If the tank rests on the hull bottom, the bottom would not require a core.

I construct the plywood tank in the boat, using spacers to define the outside dimension after glassing. I take the plywood tank out and laminate FG onto the plywood in my shop.

I've also built fuel tanks using the same process.

 

[rslifkin]

I'm not planning to make the tank removable, as it will be too long to get out of the boat in 1 piece. So the stringers and hull will be an integral part of the tank structure. The stringers are hollow glass boxes, so they're already 3/8" thick before I add a couple of layers for extra strength and adequate epoxy coating for waterproofing. I don't see a reason to add core there.

 

[cks]

Very interesting discussion.
Is there any issue with paints regarding being NSF certified safe for potable water?

 

[rslifkin]

Very interesting discussion.
Is there any issue with paints regarding being NSF certified safe for potable water?

That's been one of my biggest hangups on the fiberglass tank thing. After some more digging, it looks like the previously mentioned Brewcoat is approved for food contact, but doesn't have the NSF-61 cert. However, I found an alternative. Aquatapoxy A61 looks to be NSF-61 approved for tanks 50 gallons and up. So that over a good epoxy base (given plenty of cure time both before and after coating) should be good in terms of not leaching stuff into the water (both in terms of health and taste concerns).

 

[Portage_Bay]

I've also built fuel tanks using the same process.

I'm curious how long ago you built the FG fuel tanks and how they're holding up. I'll eventually face fuel tank replacement and would consider making my own with your method.

 

[Jeff F]

I have a similar space that I'm planning to convert to extra fuel tankage, and my plan is to have custom bladders made to fit the space, with a liner between the glass and the bladder for protection. I can get a bladder in the space far more easily than a rigid tank.

ATL makes custom bladders, and it looks like they do water as well as fuel.

http://atlinc.com/potable-drinking-water-bladder-tanks.html

 

[syjos]

I'm curious how long ago you built the FG fuel tanks and how they're holding up. I'll eventually face fuel tank replacement and would consider making my own with your method.

Tanks were built in the late 90's.

Last time I had contact with client was about 4 to 5 years ago. The client had opened the inspection plates at 10 years and emailed me that the tank interior was in good condition.

 

[Portage_Bay]

Syjos,

Good to know. Thank you. How did you build connections for fuel, vent and tank senders?

 

[HeadMistress]

I started out thinking plastic tanks, but due to the shape and size of the space, it'll have to be 2 tanks...

Not necessarily. Ronco Plastics 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 marine Tanks Their tank drawings organized by capacity are here: Ronco Plastics marine Tanks
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

 

[Slowmo]

In addition to what Peggie mentions you can have custom plastic tanks made in pretty much whatever shape you need. I guess it depends whether its easier to build in place or slide in a prebuilt tank.

Not sure where your tanks are but water is heavy so be aware that doubling your water storage may affect your boat's trim. Our Tolly 40 is similarly sized to yours and I can see the effect of empty vs full water tanks. Ours are in the stern.

If space is tight you might also consider using some 'dead space' just to add a third tank. I know some Catalina 381's have an island queen in the stern...what is under that? Also, our Tollycraft 40 has a 'dead space' between the inner stringers under the aft stateroom floor large enough for another 75G or so.

 

[syjos]

I used stainless steel thru-hulls.

Glued them in with epoxy and glassed over them using hardware bonding technique.

 

[sailormike]

we had to do the same thing and I had Duraweld I think that was the companies name I made a post about it. they custom welded me a plastic tank with baffles. Its quality is amazing

 

[rslifkin]

My boat has the island king aft. The fuel tanks are under the bunk, water tank is under that between the center stringers (extending further forward than the fuel tanks). The shape of that space is what prompted the fiberglass thought, as I can use the full width and height of the space easily.

Trim wise, water doesn't make a big difference, only a small one. Fuel is centered a bit further aft and makes a much bigger trim difference. I figure a lighter tank structure helps there by offsetting some of the extra weight. Plus, I don't need to keep the tank full all the time if trim is a concern. We can easily fill it to half until it's time to travel and we need the extra water.

For plastic tanks, the 2 tank problem still applies with custom tanks. A single tank would be 8 or 9 feet long (original one is 6), but there's no way to get a tank that long into the space.

 

[Bmarler]

I started out thinking plastic tanks, but due to the shape and size of the space, it'll have to be 2 tanks...

Not necessarily. Ronco Plastics 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 marine Tanks Their tank drawings organized by capacity are here: Ronco Plastics marine Tanks
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

i had ronco do holding tanks for me, they were absolutely fantastic to work with. tanks are top notch.
i wouldn't worry about having two tanks for water, i have two now and it's no problem. just a little extra plumbing.

 

[rslifkin]

i wouldn't worry about having two tanks for water, i have two now and it's no problem. just a little extra plumbing.

I'm not so much concerned about the extra plumbing to connect the 2 tanks, but that it would involve putting connections in a totally inaccessible area (getting back in there would require another round of de-fueling, disassembling the aft bunk and moving the fuel tanks).

 

[Bmarler]

I'm not so much concerned about the extra plumbing to connect the 2 tanks, but that it would involve putting connections in a totally inaccessible area (getting back in there would require another round of de-fueling, disassembling the aft bunk and moving the fuel tanks).

understood, i wouldn't want to have fittings that i couldn't access either.

 

[DDW]

I have custom made fiberglass tanks in my sailboat. Even after 10 years, the water still has a....peculiar.... taste if it sits in the tanks for more than a couple of weeks. When we built them we could find no tank coating NSF certified for any tank less than about 1000 gallons. The issue is surface to volume ratio and leeching. Can be solved by a charcoal filter after the tanks, but from this experience I would do plastic tanks without a very good reason to do otherwise.

I am in the same position, will need to replace a 150 gallon aluminum tank in the trawler sometime soon (full of the mystery white crystals) and Ronco does not make the sizes I'd ideally need. The issue there is they put the tank in before the deck went on (which should be a flogging offence for any boatbuilder) so old tank will need to get cut up and new tank(s) go in in pieces.

 

[rslifkin]

For a little perspective on what's involved in getting to the water tank space on this boat, here are a few pictures.

The first picture is the aft bunk after removing the top to show the fuel tanks. The water tank is along the centerline between the stringers. It starts under about the mid-point of the fuel tanks and extends forward about 3 feet beyond the forward edge of the bunk (which puts about 16" of the tank forward of a bulkhead, but there's access to the front of the tank) through a panel in a closet. The floor between the center stringers will need to be cut out for access.

The second picture shows a view looking under the port side fuel tank to see the back end of the water tank. The space gets taller as you go further forward, so the original tank is tapered a bit. Because of that and the shape of the space, it's easy to see just how much space is wasted with off the shelf tanks (and even a bit on the sides for mounting custom tanks).

The stuff running under and alongside the current tank is all due for re-routing and/or replacement anyway, so they'd be re-run in conduits along the side. With plastic tanks the conduits would be clamped in place, with an integral tank I'd just glass the conduits right into the side of the tank against the stringers.

 

[AusCan]

Building an integral tank tank has several advantages.

It uses all the available space efficiently.
One side is done for you already. (the hull)
It adds a degree of safety if that part of the hull is ever holed. You'll only get salt water in your water tank, rather than sinking your boat.

 

[rslifkin]

One side is done for you already. (the hull)

In my case, I almost have 3 sides done for me as I'd build right out to the stringers. The bottom is there except for needing to bridge across the top of the keel sump. So I'd just have to glass over the existing structure, then add baffles, end plates, cover the keel sump and add a top.

 

[CarlinLA]

Greetings...

Here is a link to a thread that I initiated in 2016 about changing out water tanks. I used Ronco tanks and the thread has several pictures of their facility and the process for installing ports.

I got in a lot of trouble back then from the forum about my method of anchoring the tanks... I sold the boat thereafter and I do hope my installation has been up to snuff for the use of the vessel since then...

In any event - here is the link...

https://www.trawlerforum.com/forums/s3/water-tanks-repair-replace-opinions-25283.html

Best to all... I'm currently boatless... living vicariously through others.

Carl

 

[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.

 

[FF]

Your local plumbing supply (not a box store)will have a catalog of galvanized water tanks . A large variety of sizes , so you might be able to get a couple to fit .

 

[rslifkin]

Your local plumbing supply (not a box store)will have a catalog of galvanized water tanks . A large variety of sizes , so you might be able to get a couple to fit .

That's an interesting thought, but the biggest issue is the height taper in the space. The tank shown in the picture is 10" tall at the front, but only 7.5" at the back (although there's some amount of wasted height due to how it's all put together). Plus, if I go any longer than the current tank, I have to use 2 tanks (with hidden connections) unless I build the tank in place. The 6.5 foot long original tank is pushing the limit of what can be carried in and out of the boat.

 

[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 tank 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.

 

[syjos]

Great job!

I like the details you put in.

 

[rslifkin]

Great job!

I like the details you put in.

Thanks!