Water tank welding

[V_King]

Thanks for all the responses. The aim to weld a SS water tank was after seeing youtube videos, showing the SS welding with MMA (Before I did not even know you can weld SS with MMA). It is not the most practical, but I love welding projects, hence the idea.

The boat is a simple box, used in inland waterways - a narrow boat. There is plenty of support and I was considering a simple cross shaped baffle inside anyways, just to help with welding and reduce sloshing effects.

But the SS weld seam cracking is a bit of a worry. Might need to reconsider other options. I am not a fan of plastic tanks. My water tank goes into the bow, and the old one I removed was square shape plastic tank, wasting a lot of precious space.

Are there any galvanising/zinc coating procedures, which are suitable for the drinking water, if I was to weld the water tank out of mild sheet?

 

[addjunkie]

Are there any galvanising/zinc coating procedures, which are suitable for the drinking water, if I was to weld the water tank out of mild sheet?

Steel tanks in the shipping industry used to be cement washed inside, they are now coated with some kind of spray on plastic.

Id steer clear of the galvanising...you could mould your own in fiberglass, that way it could be made to fit the space.

Or an oversized bag tank built and constrained inside a box structuremaximising the space.

If you build a metal tank, can you get it into the space?

 

[TomCGB]

What was the purpose of removing the previous tank? Are you significantly increasing the capacity of the tank compared to the original? Bear in mind any weight difference will effect the vessel's trim more significantly than you may think, especially since its a narrow boat. Because of the bow's distance from the longitudinal centre of flotation the trimming moment as a result of the tank will be higher. Trimming by the bow could affect your fuel consumption and your under keel clearance through shallow areas, however in the real world for the distance you are doing and the location it might not make much difference.

If you go for a fuel bag and still want a welding project, the bag will need supporting structurally.

 

[V_King]

The old water tank was small and crusty 25year old plastic tank with leaks through all the seams and some cracks. I want to utilize as much as possible of the bow volume. And I am not worried about the trim - the boat is stripped to the shell and will move the ballast around accordingly.

People with experience with sailing and living in boats suggest to steer away from plastic/grp/bag water tanks, due to the tendency of them developing a foul taste in the water, even with all the regular water treatments. I had a plastic water tank in in loft in my old house, and never liked the taste of water.

One guy in a sailing forum, has a whole bow as a water tank, but it needs recoating every 3-5 years with water tank coatings. Sounds as an attractive proposition, but the only place I could have inspection/service hatch is the bulkhead. Sealing a vertical inspection hatch is probably impossible.

need to carry on looking at my options

 

[Seadog]

I had a plastic water tank in in loft in my old house, and never liked the taste of water.

The water tasted foul because it was never intended for consumption, purely for washing. Not uncommon to find dead pigeons or rats floating around in them

 

[TomCGB]

I have never worked with narrow boats and don't know what their hull girder strength is like, but just be careful not to create too many large point loads far away from amidships. You don't want to end up with a loading condition that results in over hogging your hull.

Many of the smaller vessels I have worked with have their freshwater tanks forward, just as the chap you mentioned has. I think you are right about the vertical inspection hatch. Is there a chance of putting a hatch coaming on the focsle deck?

 

[addjunkie]

Large vessel tanks are often sealed on a vertical face. They just have a flange welded to the tank and the hatch is bolted with a rubber or teflon gasket.

 

[Member 66061]

One guy in a sailing forum, has a whole bow as a water tank, but it needs recoating every 3-5 years with water tank coatings. Sounds as an attractive proposition, but the only place I could have inspection/service hatch is the bulkhead. Sealing a vertical inspection hatch is probably impossible.

Sealing an inspection hatch shouldnt be an issue, its done on large storage tanks.

 

[Kent]

Nobody has mentioned it but as the tank is for drinking water you will need a nice finish on the weld inside the tank. When I worked in the food industry all s/s pipe welding had to be purged and tigged to leave a clean smooth weld inside the pipe. If there is any dross inside it could act as a breeding ground for bugs.
It would be very difficult to weld your tank with mma and not leave gaps or dross inside the weld. The best way would be to tack the tank together, purge it & weld with tig.

Good points but have you seen water supply gear under the roads etc. And practically all private water supply pressure tanks are mild steel and rust out in about 5 years along the diaphragm.