Which material for permanent tank?

Questions about modifying a design

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jamundsen
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Re: Which material for permanent tank?

Postby jamundsen » Wed Dec 02, 2015 5:47 am

I'm in the process of removing my Moeller tank.
I think they are fine for smaller amounts but mine was a 58 gallon tank. Mine expanded making it almost impossible to get out plus it deformed causing a significant loss in quantity of fuel it was able to hold. I am ordering a custom aluminum tank. I'll prime and paint it prior to install.
As far as water in the fuel now that may be an issue. Back when I flew night freight in Michigan we added 1% alcohol by volume and eliminated the water problem. I don't know how that would work with some of the marine engines. The Continental aircraft engines were approved for it but some of our engines in boats may not have the right hoses, etc.
So far I've not had any water in my fuel even when it had sat around for several years . That may be from the Stable I added to the fuel.
John Amundsen
Monte Carlo
Lakeland,Fl

Work tends to get in the way of boat building

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Bill Edmundson
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Re: Which material for permanent tank?

Postby Bill Edmundson » Wed Dec 02, 2015 6:04 am

With aluminum tanks, put strips of webbing under the tank. This makes a little air gap so it can dry under there.

Bill
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Bill Edmundson
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Re: Which material for permanent tank?

Postby Bill Edmundson » Wed Dec 02, 2015 6:52 am

I think mine are 5052. I'm not sure. Maybe Kevin Morin will check in. He's the metal man.

Bill
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kens
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Re: Which material for permanent tank?

Postby kens » Wed Dec 02, 2015 10:39 am

here is a link to a fabricator in Jupiter, Fl.
there is some links on the website about installation and safety.
http://www.custommarinefueltanks.com
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Bill Edmundson
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Re: Which material for permanent tank?

Postby Bill Edmundson » Thu Dec 03, 2015 7:42 am

I just checked my RDS tanks. They're 5052-H32. I don't know what the H32 means.

Bill
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Kevin Morin
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Re: Which material for permanent tank?

Postby Kevin Morin » Wed Jan 06, 2016 5:19 pm

Sorry to miss this thread when it was newer, just reading the site today and found the metal tanks questions.

This is not a small topic! The many considerations are important so I'll start a thread on the Metal category and begin to try to establish some guidelines for welded aluminum tanks there?

Moderators, if this Metal Topic should be here, in reply to this thread, please move that post where it belongs. I was focusing on the Metal Aspect of the topic to start that discussion.

Cheers,
Kevin Morin
Kenai Ak
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kens
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Re: Which material for permanent tank?

Postby kens » Sun Aug 07, 2016 6:44 pm

I think you did good for yourself.
I priced a similar tank in Florida and it came out to about $600.
Aluminum is the best way to go.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

jcallends
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Re: Which material for permanent tank?

Postby jcallends » Mon Aug 08, 2016 6:28 am

Probably an oops but 4mm is closer to 3/16".

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Bill Edmundson
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Re: Which material for permanent tank?

Postby Bill Edmundson » Mon Aug 08, 2016 6:49 am

wolters

Nice job. Be sure to look up how to mount the tank. You probably have already. But, aluminum needs air. So you need something like fiberglass strips under it to keep a little air gap.

Bill
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Kevin Morin
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Re: Which material for permanent tank?

Postby Kevin Morin » Mon Aug 08, 2016 10:26 am

wolters, sure would be nice if the tank was etched to remove the mill scale which will promote corrosion in a short time. As mentioned the tank would be best mounted in isolation from the structure, looks like it may lay between hull longs? If the tabs on the top are to locate the tank which will lay on some support (?) they seem adequate but only if the tank will Not be suspended from those tabs?

If the 45 gallons weighs 270lb and the tank weighs another 55 lb then the tabs would be suspending 80 lb. each and that load will be on the underside welds to pull on the tank wall sides- (I don't see wall doublers or gussets on the tanks sides?) along a 2-3" length. If the tank were suspended with those loads and momentum/inertia in a head sea will increase that load a bit... I'd say it would be better if the tank's wt. was bedded to the bottom on inert material.

One product that works good for aluminum tank bedding is ribbed vinyl carpet runner - made into strips, rib side to the tanks' wall- that bed/isolate the tank and that can drain condensate or any 'dew' collected on the tank then drained down to the bedding/isolation barrier. By orienting the ribs in this non-reactive sheet material so they drain into the bilge, the bedding/isolation film can allow the water to drain off and not form a widely spread thin film on the bottom and become acidic. Thin films of water held against bare aluminum almost always become a source of corrosion when they de-aerate and shift ph.

It sure would be helpful to those reading about tanks to see the interior tank plumbing, baffles, and construction process of your build?

Cheers,
Kevin Morin
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Bill Edmundson
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Re: Which material for permanent tank?

Postby Bill Edmundson » Mon Aug 08, 2016 11:41 am

I had not thought of the ribbed vinyl. That would work.

Bill
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Roberta
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Re: Which material for permanent tank?

Postby Roberta » Mon Aug 08, 2016 1:02 pm

I agree with Kevin on not using those tabs to suspend the tank. You can use them as locators and drill holes in them for pins. Looks like the tank is meant to fit between the stringers. The flat bottom portion may fit on the keel but I'm unsure on doing that. Maybe someone with more knowledge would know. Otherwise a cradle could be made. I made a platform suspended in the stringers for my 40 gal. tank. I did use a plastic Moeller tank with a flat bottom. On the AL tank I had in the Zip, I used the carpet runner like Kevin suggested. It is readily available at places like Home Depot.

Roberta
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Re: Which material for permanent tank?

Postby Kevin Morin » Tue Aug 09, 2016 11:17 am

Wolters, a few remarks and an attempt to reply to questions.

wolters wrote:There are two longitudinal baffles inside.


The tank's bottom has the three panels, so the long wise seams will provide some panel reduction-stiffening, and the two longwise baffles will aid that. But... the slosh is not reduced for an aft- so... I'd want to make sure the fill hose was well sealed/connected as there will be some good hydraulic pressure because the fill downcomer is not on the bottom. Side to side (narrow direction) slosh or surface effect is not the direction I'd want to limit in that tank- I'd want some transverse baffles too, so reduce 1/2-1/4 full fore and aft movements while in a seaway?

Suction being that far off the bottom any water bottoms will be hard to remove? I'm not sure of the quality of fuel (water content) but there may be some bottoms to remove periodically as maintenance? An engine oil removal hand pump (bulb and tubes) will work to get out the bottoms. Water bottoms become acidic and since the tank is not etched inside the mill scale will promote corrosion if the bottoms are allowed to DE-areate?

The fill may "burb", being that shallow, but depending on the fill fitting and hose and vent or slosh cup in the fill line, that back flow of foam may not be a problem. Tanks seem like they may be 3/16" or nearly (4mm?) not 1/16"? That's plenty thick enough to hold up.

wolters wrote:I have thick rubber strips (10mm/5/8") to rest the tank on.


if the strips are neoprene rubber or have some other carbon content ("black rubber") that type of rubber has a galvanic potential to bare aluminum! (carbon to aluminum) So some rubber strips will form a "battery" and the aluminum will pit where the rubber and tank touch - if the interface gets wetted. If you don't have any evening condensation in humid air? (dew) and the tank won't get wet -ever- then no worries but vinyl is not reactive by itself, and the ribbed carpet runner type profiles keep the water from forming a wide area without ventilation or drainage due to capillary action.

All glue to attach bedding strips is not created equal, if you're using 3M 5200 that's one thing if almost any lesser quality- water can invade the interface space and if not drained corrosion will happen.

In another post I show a couple of tank mounts - to install a bigger tank (100 gal or more) as you'd install an engine- by using cantilevered/gusseted mounts that ride on the battens- that I refer to a hull longitudinals or "longs". Where engine beds are just heavy scantlings of battens or longs.

There is a discussion of aluminum corrosion on other threads, including an explanation of the roll of mill scale in this process. The issue is not an aluminum tank sitting free in the shop or garage, its being held against some other surface where a thin film of water can 'wick' into a tightly held space against the side, bottom or top of the tank's surface. Then water can become stripped of oxygen, and promote an crevice corrosion cell. If the tank were put on deck, and could drain/drip/shed water 100% dry all the time there would be little or no crevice corrosion from adjacent surfaces. But mill scale will still promote the "white flowers" pits which are just a limited version of the crevice corrosion on a tiny (but wide spread) scale.

The best to do is to use Zep-a-Lume (acid mixture designed to clean aluminum of mill scale and oxide) inside and out. Inside first, outside next. Rinse completely and let dry. If you're painting tank- good practice if the tank will live below decks in the bilge where it is damp or could be sloshed with bilge water in some conditions(?) - then while the rinse water is wet on the tank- coat with zinc chromate solution (Allodyne or equiv) and let dry. Check for color indication of the new oxide film (chrome oxide bonded to aluminum as nearly uniform as possible) and primer then topcoat. The reason is to keep the surface covered.

Wolters, marine aluminum is fine in salt water for a long time, it is when any water is held to the surface in a thin film (between two solids) and can become acidic that the corrosion begins. This is covered in the other posts. The coaming trims you've seen corrode may have been bedded to other metals? May have been improperly coated- bad paint job is worse than no paint job- or may have been an alloy that was misapplied? The dive tanks were spun/cast/forged- but not likely to have been 50 series and surely had not mill scale film left on them!!!

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin


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