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Old 20 June 2014, 15:49   #21
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Replace the aluminium tank with a 'plastic' one.
I am with you,, would never go ali or stainless. ,,, no chance.
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Old 21 June 2014, 11:58   #22
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I am with you,, would never go ali or stainless. ,,, no chance.

I'm amazed- plastic really?? I was going to replace with stainless- why plastic over stainless? This is a 90 litre tank. The battery tray sits on it and various cables pass over and down the side of it- I would worry about chafing a plastic tank ...
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Old 21 June 2014, 12:05   #23
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Always go into my builds


Removed to date 4 leaking metal tanks. Say no more ,
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Old 21 June 2014, 14:33   #24
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That first pic showing the ducting come up under the console. Have to got a photo of the back of the boat? Fitting it to mine and any ideas would help
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Old 21 June 2014, 15:31   #25
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That first pic showing the ducting come up under the console. Have to got a photo of the back of the boat? Fitting it to mine and any ideas would help
Got nothing on my I pad. But generally I go about here
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Old 22 June 2014, 11:45   #26
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Quote:
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I'm amazed- plastic really?? I was going to replace with stainless- why plastic over stainless? This is a 90 litre tank. The battery tray sits on it and various cables pass over and down the side of it- I would worry about chafing a plastic tank ...
I had a 60 gallon aluminium gasoline tank. It developed holes. The areas near the holes were also wafer/paper thin.
Now have a plastic one.

Remember to have the uplift pipes at the stern of the tank. When riding even slightly bow up (when nearing and empty tank the fuel 'collects at the back. If you have the fuel uplifts at the bow you do not get to use all the fuel when planing.


Remember also stainless steel is just that 'Stain less' not 'stain free' or 'corrosion free'. Stainless steel also suffers from pocket or crevice corrosion (lack of oxygen).

Types of Stainless Corrosion

According to the DOD Technical Bulletin Corrosion Detection and Prevention there are 8 separate types of corrosion, with only a few having a major impact on stainless steel. Please be advised the descriptions below are extremely brief and written in laymen terms. Before acting on any particular application, qualified advice particular to such application should be obtained.

1. Uniform Attack - also known as general corrosion, this type of corrosion occurs when there is an overall breakdown of the passive film. The entire surface of the metal will show a uniform sponge like appearance. Halogens penetrate the passive film of stainless and allow corrosion to occur. These halogens are easily recognizable, because they end with "-ine". Fluorine, chlorine, bromine, iodine and astatine are some of the most active.

2. Crevice Corrosion - this is a problem with stainless fasteners used in seawater applications, because of the low PH of salt water. Chlorides pit the passivated surface, where the low PH saltwater attacks the exposed metal. Lacking the oxygen to re-passivate, corrosion continues. As is signified by its name, this corrosion is most common in oxygen restricted crevices, such as under a bolt head.

3. Pitting - See Galvanic Corrosion. Stainless that had had its passivation penetrated in a small spot becomes an anodic, with the passivated part remaining a cathodic, causing a pit type corrosion.

4. Galvanic Corrosion - Placing 2 dissimilar metals in a electrolyte produces an electrical current. A battery incorporates this simple philosophy in a controlled environment. The current flows from the anodic metal and towards the cathodic metal, and in the process slowly removes material from the anodic metal. Seawater makes a good electrolyte, and thus, galvanic corrosion is a common problem in this environment. 18-8 series stainless fasteners that work fine on fresh water boats, may experience accelerated galvanic corrosion in seawater boats, and thus it is suggested you examine 316 stainless.
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Old 22 June 2014, 14:49   #27
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Plus metal tanks have a colder surface. That means water vapour in the air space above the fuel will touch it, condense and run into the fuel.

So if you run with less than half a tank in less than ideal temperatures you may be slowly adding a pool of water to the bottom of the tank. May take a couple of years or more to accumulate but would take longer with plastic.
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Old 11 February 2015, 08:56   #28
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Thanks all for the input.

Today I took the plunge and chopped the console/seat off. I used a Ryobi 18V multi-tool like those shown above, and it took only a matter of minutes to remove.

My old tank is aluminium (built in Feb 1990 it says on it!) and lies flush with the deck. Part of cause of corrosion I am sure as there is a thin gap between the deck and the tank that holds seawater.

I am attracted by a 'plastic' tank, but can't find one of suitable dimensions off-the-shelf. My old tank is a not a plain rectangle cross-section as the photo below shows:


I shall start another thread with some questions about cutting a hole in the deck to accommodate a larger tank
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Old 11 February 2015, 13:08   #29
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Plastic tanks are crap , most are designed as removable tanks, held in place with a couple of straps. Go ally, if your old one is a 1990, then it's lasted the best part of 25 years. If your really worried, get it stove enameled.

I've been fitting ally tanks to boat for 20+ years, never had a problem with them.
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Old 12 February 2015, 08:09   #30
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thanks for the replies. I see the argument for plastic and for Aluminium.

I've started a new thread about replacing the tank now that I've got the console off.
Tornado 5.5 fitting under deck fuel tank?


spoiler alert: I chose Aluminium.
A plastic one -for me - would be a compromise on shape, would require big hole in deck and leave no space for me to protect it from chafing from cables/stored items. The old aluminium tank did last 25 years and would be perfect fit.
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