Stainless steel tanks - type and thickness?

[dalex]

Folks,
It has come to pass that I am weary of filling up my port tank every 40 miles, so am going to have 2 tanks made. I am looking to get 2x 70gallon tanks, and shoehorn them under the floor of my 305 statesman. Questions: What thickness and grade of stainless steel should I ask for?
Should I just have ordinary steel ones made?
My trusty steed is adequately slung along by 2x AD41's with duoprops. I know I can get from Ipswich to Lowestoft on 20 gallons per engine, but due to a blocked pickup tube in the other tank, could not run both engines from one tank. I couldn't get back without refuelling first, unless I do so at 7 knots and a wavy course on the good engine. I am pretty sure I have solved the reason why both would not run from the starboard tank. For those interested, the pickup tube seemed to be partially blocked.. until acted on by an externally, unbalanced force. In my case this was the air line at my local supermarket. One or two squeezes on the trigger, and a really satisfying bang from the opposite end, and the tube is crystal clear. I often wonder where the bit went, when it flew out, though. There was quite a queue at the burger drive through, and if it landed between the baps I doubt anyone would notice....
Thing is, I have little confidence in the fuel system now, and the thought of fuel transfer mid north sea from jerry cans does nothing to inspire me.
Has anyone else ended up with a set of woefully inadequate tanks and solved the problem?
I did read of a certain gent using an oil drum, but one of those won't fit down t'hole in't floor /forums/images/graemlins/frown.gif

 

[Dave_Snelson]

IF you are going to use stainless then less that 1mm will do and probably 0.7mm.

However...have you thought of getting two polypropelyne tanks made by Tek Tanks . It would be loads cheaper, loads lighter and they do all sorts of shapes and sizes to suit. And the strength is fine.

With stainless & ali, you are wandering into the world of "bespoke" and that means expensive. I should know, coz I made just that mistake. /forums/images/graemlins/wink.gif

BTW - Tek Tanks will do custom made if you wish.

 

[DAKA]

Stainless is not suitable for your boat.

Stainless is too ridged and the weld seams will fracture.

A fast boat hitting a wave is adequate to rupture a stainless tank.

It is for this reason stainless steel tanks are now illegal in petrol boats.

Even slow boats have problems with stainless tanks during road transport the stainless tanks rupture.

Aluminum rots very quickly if it gets near bilge water.

In my opinion Mild steel is the only sensible material to use.

 

[PCUK]

SS tanks must now be CE marked and tested by the manufacturer so they will provide the correct thickness material for the job.

 

[thefatlady]

You must be joking! Stainless steel is fine for tanks.
I have had stainless tanks in fast planing boats with no problems, including nearly 2000 miles of road transport.

I also used to have dealings with a company which made stainless steel tanks for nuclear submarines. Imagine the possible shock loadings there and the consequences of failure!

I would be interested to know what legislation prohibits the use of stainless steel for petrol tanks.

 

[DAKA]

In 1997 I tried to get a stainless petrol Tank made.
I was clearly told by several manufacturers including one Boat manufacturer that it was illegal to put a stainless fuel tank in a petrol boat.
The same manufacturer now confirms it is possible as long as they are CE marked.
I do know that stainless fuel tanks in large boats fracture when moved by lorry. The problem is worst if the tanks are half full of diesel.
How do you empty 700 L ????????????

In my opinion Stainless steel is no good for fuel tanks in boats that can exceed 17 knts or that may at any time be transported by road ( low loader ).

 

[Dave_Snelson]

Only two years ago I was given the alternative of SS or ali from a manufacturer of boat tanks. I do not think they are illegal (SS that is).

Ali does not corrode providing you stop galvanic action. The surface of ali is self protecting and is an otherwise excellent material for marine use.

 

[DAKA]

Dave 1000 apologies, I stand corrected.
I have phoned the Boat Manufacturer who agree with you that it is not illegal as long as CE marked. ( most technical team are at lunch so not 100% sure)

In my opinion there has to be serious doubt about putting stainless in a Sealine 305, 310, etc as they are fast and can be moved by road as they change hands. (low loaders are the problem not nice soft suspension sports boat trailers, but sports boats flex and the SS tank doesn't)


Has anyone got a new boat Petrol or diesel where the Manufacturer fits stainless as new <????

 

[hlb]

Forgive me for sounding a bit numb. Whats the problem with your present set up. Apart from a now mended pipe?? Is one tank knackered and you have not mentioned it??
Or are tanks just to small.

Mild steel tanks should be fine. I'd ask the tank man about his recomendations though.

 

[thefatlady]

DAKA, I am talking about over 40ft, over 30kts, nearly 2000 miles of low-loader transport back and forth across Europe.

 

[DAKA]

Your boat could be well designed, your transport company could have a very careful driver or perhaps it is only when the lorry has to bounce a curve side, but stainless do fracture while in transport and usually when 1/2 full.

I wish you continued luck with both road transport and calm seas.

Personally I will stick to mild steel and look after it, IE/ fill to the top most of the time and especially over winter.

Was it a standard fit from new ?
I will have to concede if a major boat manufacturer thinks they are suitable, all the boat builders give such attention to detail when they design with the boat shows in mind.

 

[dalex]

Thanks for all the replies. Seems to me that my initial enthusiasm for stainless as being the very best solution, was somewhat previous....
I am aware of the brittle nature of welded stainless, and thought the grade used for fuel tanks would be somehow impervious to this type of failure.
Oh well....
My problem is threefold. 1) existing capacity falls way short of what I'd consider safe. Having the fuel split over 1 70 gallon tank and a 20 gallon tank is unsatisfactory as having to balance fuel from one to another reduces my immunity to cross contamination.
2) 70 gall tank is old, has no inspection hatch, and I'm pretty sure it is corroding inside as well as out. It's days are numbered. It is made from what appears to be galvanised steel, but may simply be mild steel painted with grey hammerite. I don't fancy putting a grinding wheel to it, to check!
3) I want to fit the very best I can, but don't have money to burn. I was under the impression that pricewise, stainless was comparable to welded polypropolene, so if stainless was the better option, I'd prefer that for it's strength and corrosion resistance.
I wonder now at this idealistic approach, and am gravitating towards thinking, sod it, go for something cheap, as i won't have the boat forever. Sad fact, but probably true in the sense I'll probably upgrade before the replacements rust.
I also now wonder, how much more likely condensation would form on the inside of a very cold steel tank, compared to a polyprop one.
I just re-read my first post, and didn't make it clear that one was 70 gallon, the other was 20 gallon. I cannot imagine what the previous owner was thinking in specifying such a small tank on a boat with these engines... and why put odd sizes in anyhow?
Just a thought, do I have to get any new tanks CE marked?

 

[Frontier]

I have just had two tanks made by Duratank. They are flexible tanks, Worth a look and the Duratank people are very helpful.

Only problem I have to solve is making a fuel sender, for which I plan to use a normal internal one on the outside with an extended arm and maybe a small wheel rather then the float to rest on top.

I could have got a special sender and new gauges but at about £500 per tank it seemed way over priced the tanks were actually less.



Durtank

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