DIY Fresh water tank ?

[waynes world]

Hi all.

I am planning out where to fit a FW tank in my project boat. Before i decide if to splash out on a custom made one i am thinking on saving a fortune to make my own, like i usually do. . Now i can weld SSteel, and happy to learn to plastic weld for the HDPE type but then cost will still be near as high as getting one made. Materials cost are high for both SSteel and HDPE.

So i am thinking on making a GRP tank. I know the first choice, well from what i have been told is to use a Isophthalic resin. Only problem is the post cure temps which are high temps, to get an oven to fit a 600+ liter tank in is not easy.

What have you guys used to finish off a GRP FW tank. There are a few ways to go but i wonder if there is a certain taint to the water from what you have used or how you sterilised it for potable water..

Captain Faffer

 

[bobtooke]

Line with a WRAS approved epoxy. After correct curing, venting, disinfection and flush there should be no residual chemical in the water.

Having said that, I reckon a poly tank or bladder tank will probably work out a hell of a lot cheaper than making a GRP one unless you need a specific difficult shape?

 

[waynes world]

Line with a WRAS approved epoxy. After correct curing, venting, disinfection and flush there should be no residual chemical in the water.

Having said that, I reckon a poly tank or bladder tank will probably work out a hell of a lot cheaper than making a GRP one unless you need a specific difficult shape?

The Loyds approved Poly resin is WRSA also. I have been looking for a bladder tank earlier today but i cant find one the size i need. It is not a basic shape but V shape, follows the hull shape up the 150mm from the lower chine.

 

[greeny]

Think along the lines of wooden box with liner inside. Or GRP if you like.
Ok you got it already.

 

[LadyInBed]

What access do you have to the space?
If you have full top access I would get a box made up in stainless. Whether to have an access hatch or a full bolt down top is open to debate, an access hatch is easier to seal but a full lid is better for inspection and cleaning.

 

[sarabande]

Wayne

that's quite a big tank, very roughly 550 litres. If you are making it up yourself, perhaps worth considering baffles to reduce the 'free surface effect" of water sloshing to and fro, and also inspection ports for cleaning. An alternative is to go for 2 or even 3 tanks to make up the volume, which means you can choose 1 tank as the main, and 1 or 2 reserves.

I'd be happier working in HDPE with a thermostatic hot air gun (my welding is crap) , as if you have to make any modifications you can do it without a disc grinder and sparks. You can often find HDPE slabs in charity shops where they hide as chopping boards, and I have seen large (2m by 2m sheets in recycling yards. Sometime you find used water tanks on ebay e.g.

105L Litre Upright Plastic Water Storage Tank - Valeting Window Cleaning Camping | eBay

and this looks good

500 litre baffle water tank valeting window cleaning etc | in Airdrie, North Lanarkshire | Gumtree

 

[Momac]

Will you include baffles - to stiffen the tank ?

600 litres seems a generous capacity although I am used to lumpy water motor boats . Our water tank is 250 litres and we manage okay with that as a couple and don't mind a sensible turnover of water ........ we don't live on the boat.

Perhaps consider two smaller tanks if that would be be easier /stiffer construction?

May I suggest some built in storage for wine bottles (or other drinks bottles) as part of the build as this saves on carrying water

Edit ,Posted at the same moment as the post above

 

[waynes world]

What access do you have to the space?
If you have full top access I would get a box made up in stainless. Whether to have an access hatch or a full bolt down top is open to debate, an access hatch is easier to seal but a full lid is better for inspection and cleaning.

The top access will be as large as i can get in, which will be around 120cm x 60cm and near central. It would be bolt down.

Wayne

that's quite a big tank, very roughly 550 litres. If you are making it up yourself, perhaps worth considering baffles to reduce the 'free surface effect" of water sloshing to and fro, and also inspection ports for cleaning. An alternative is to go for 2 or even 3 tanks to make up the volume, which means you can choose 1 tank as the main, and 1 or 2 reserves.

I'd be happier working in HDPE with a thermostatic hot air gun (my welding is crap) , as if you have to make any modifications you can do it without a disc grinder and sparks. You can often find HDPE slabs in charity shops where they hide as chopping boards, and I have seen large (2m by 2m sheets in recycling yards. Sometime you find used water tanks on ebay e.g.

105L Litre Upright Plastic Water Storage Tank - Valeting Window Cleaning Camping | eBay

and this looks good

500 litre baffle water tank valeting window cleaning etc | in Airdrie, North Lanarkshire | Gumtree

I want it big as possible, this is not that large to a lot of live aboards on the canals. Bigger the better, just for less top ups.
Oh yes it will be a properly built tank even though it would be a DIY tank, baffled and braced etc.
I have been looking at prices of HDPE sheets and rough cost will be £300-£350 for a slight smaller tank of 175cm x 100cm. When i was looking the other day i priced it up at over £600 for materials. they were 2m x 1m sheets though . One way i can do it is have this one under the centre deck and another flexi tank in the bow of 100 liters as back up.

I can use the ready made tanks but i want to save and use as much space as possible and the set out doesnt allow for these size/shape tanks.

Will you include baffles - to stiffen the tank ?

600 litres seems a generous capacity although I am used to lumpy water motor boats . Our water tank is 250 litres and we manage okay with that as a couple and don't mind a sensible turnover of water ........ we don't live on the boat.

Perhaps consider two smaller tanks if that would be be easier /stiffer construction?

May I suggest some built in storage for wine bottles (or other drinks bottles) as part of the build as this saves on carrying water

Edit ,Posted at the same moment as the post above

As to Saraband reply above


I know i may sound picky but when i design and build my boats i have it fixed to what i want and need. If i can do it i will within reason of cost and altering the design to much. I would like to learn plastic welding, and that was my first choice for the DIY tank. I have time to learn and practice and i have been told it is not that difficult to do so if i find a good priced welding gun, i mean not into hundreds of pounds and get some scraps ill give it ago.

Ill go look at welding gear

Thanks all for input.

 

[markhomer]

I can give you good advice on sterilising your tank on completion , its cwhat I do , but will share my secrets with you , send me a PM .. cheers

 

[AntarcticPilot]

My Moody 31 has a freshwater tank under one of the saloon berths - as far as I can see, it is simply the space between the hull and internal mouldings. It may be lined, but taking the top of is a big job (the entire top panel comes off, with screws spaced about every 6" round it!) and as the water tastes OK, we've never bothered on the grounds that what the eye can't see, the heart won't grieve over (for those who worry, we boil all drinking water, even if it comes from the tap at home - my wife is from Hong Kong where it is regarded as a sensible precaution. She also worked for a while for a local water company!)

 

[waynes world]

I can give you good advice on sterilising your tank on completion , its cwhat I do , but will share my secrets with you , send me a PM .. cheers

I am just looking at HDPE welding as we speak, materials are not far from GRP but for buying a gun. £250 materials and around £100 for a gun.

Although i will take you up in your offer if i go GRP Thanks kida

 

[Quandary]

Most Moodys were built by Marine Projects who used black upvc water tanks, I would be very surprised if yours is not one of those.

 

[Sandy]

Like AntarcticPilot we boil 99.99% of the water drunk onboard. The other 0.01% goes in my whisky.

 

[Graham376]

Most Moodys were built by Marine Projects who used black upvc water tanks, I would be very surprised if yours is not one of those.

Not so, many of the earlier models including my previous M346, had grp tanks as described above.

 

[waynes world]

Ok OK

I hate it when SWMBO is right.

I just like to make things

It does make sense this i guess. If i get two of these they will fit the under deck area nice as they take the space i have nicely. just plumb them as one

Plastimo Flexible Fresh Water Tank - 200ltr - Freshwater Flexible Tanks - Discount Marine Chandlery and Sailing Equipment. Bargain Boat Spares and Clothing

And the bow tank of 120l and then we have near the litres we want

i just want to make things

still save a lot of money to spend elsewhere on the boat

ah well

 

[LadyInBed]

Plastimo Flexible Fresh Water Tank

Make sure to put plenty of padding around it, you don't want it to chafe.

 

[waynes world]

Make sure to put plenty of padding around it, you don't want it to chafe.

I have though to line a box for it with EDPM or similar.

 

[duncan99210]

Just a word to the wise about flexible tanks. They’re fine but.......

When the bow water tank developed a crack in the top, leading to much water sloshing round outside the tank, I tried several different “fixes”, none of which survived first contact with water. So I removed the top of the tank and fitted a 120 litre flexible Plastimo tank. Worked fine for a couple of seasons, the we were filling it at the start of the third season and put the hose nozzle into the deck fitting and turned it on.... a few minutes later, there was a resounding pop as the mains pressure overwhelmed the tank and it split.

I replaced it with another (thankfully a Lefkas chandlers had one in stock) and now use a hose straight into the fitting so as to avoid any pressure build up. It’s now been about 5 years now, so I’d not hesitate to use them, just be careful filling: remember they don’t have a vent pipe fitted so you need to make sure there’s no way for the pressure to build up whilst filling. Make sure the tank can‘t move otherwise you will get chafe and holes in the bladder.

 

[lw395]

Sara's link had an ad for these people embedded:
280 Litre Potable Water Tank Flat
Cheap, and proper potable, but not very boat shaped?
You might fit two smaller tanks in?

 

[waynes world]

Sara's link had an ad for these people embedded:
280 Litre Potable Water Tank Flat
Cheap, and proper potable, but not very boat shaped?
You might fit two smaller tanks in?

It will fit but then i loose at least 200l of water.