Replacement Stainless steel tank

[MaungaMoana]

Hi all

We are on a 1977 Tayana 37 which previous owner converted the 100gal stainless steel keel water tank to a diesel tank 2 years ago.

This tank recently started to leak due to corrosion and old age (as they do after 45 years...) so we would like to fabricate two independent tanks in its place one of diesel and the other for drinking water (we dont need 100 gallons of diesel)

Since custom plastic tank fabrication isnt available here we are thinking to go for both new tanks with stainless steel again.

My questions for others here

1) Original big tank was ~3mm thick. is there a concern going with 2mm stainless for the two independent tanks, (each will have one baffle)

2) is 304L (low carbon) stainless ok for this use? 316L is not easily available here also being extra brittle meaning each side will need to be welded instead of bent

3) Finger in the air cost that we were quoted was $1500 USD for the fabrication and materials of the two new tanks. Is this a fair price for such a thing?

I have added pictures the rough measurements of our current single tank which we would plan to simply create two side by side instead for context.

Would love any input from others and their opinions of best approach or the 'gotchas' that we might be missing

[wingssail]

You are lucky that you are able to easily access the tanks.

We have replaced our water tanks more than once and here is our experience:

If you use 2mm stainless you have to have very good baffling. The large panels of your tanks will tend to flex when filled (oil can effect) and this can quickly break the weld seams. The baffles must be strong and welded extra securely to prevent this.

Make sure you have good access panels between each baffle so you can clean the tank is needed.

I cannot say whether you can use 304 instead of 316, I think that being in a fresh water environment it should be OK. You'll want to keep the bilge dry.

Install good vents to make filling easier.

Make sure you plan for good tie downs

The price seems high to me. My recent 45 gallon custom tanks were fabricated locally (Mexico) for about $500 for a pair. Perhaps the shipping cost you mention is the difference.