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Old 29-01-2012, 10:52   #31
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Re: Replace Fuel Tank Advice

The tanks I've seen have had issues with corrosion or abrasion from the OUTSIDE. So , inspecting the inside will buy you little. You could look fine in there and have areas the thickness of paper!
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Old 29-01-2012, 10:56   #32
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Re: Replace Fuel Tank Advice

Some suggestions have been made to just keep using the existing tanks, since they are not presently leaking. The water tankage, yes, if it develops a leak, a little fresh water in your bilge is the result. A diesel leak, almost always a "weeping" leak, would be more serious, but should be announced by the distinctive smell and contamination in the bilge water, allowing quick remediation before a spill into the ocean.
Since I do inspect and test tanks to Transport Canada standards, maybe consider this. If your fuel tank has no leaks, and appears to be in good condition, have it pressure tested. The tank should be able to maintain 4 lbs psi for say, 30 minutes, without any drop whatsoever, provided all tank openings are sealed airtight. Replace fittings and fuel lines which appear older, and it is unlikely you should have any problems with the tank for years to come. The test will detect any tiny leaks you may be unaware of, and stresses the tank to help insure integrity of the welds, seams ect. Passing a thorough visual inspection, internal cleaning and pressure test allows me to re-certify a tank for road use, for a five year period. I have no authority or experience with marine fuel tanks, so this advice is subject to verification from someone who is qualified to do so. Further, this is for diesel tanks only, and pressure testing should be done by qualified persons.
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Old 29-01-2012, 11:33   #33
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Re: Replace Fuel Tank Advice

I agree on adding inspection ports. I also think it may be desireable to have the port straddle a baffel. On ours, the baffels are not attached to the tank top, only the sides and bottom. Having the port span the baffel makes it possible to inspect both sides.

Our tanks are five at about 80 gallons each. They are welded 316 SS and about 1/8 inch thick. The boat was built in 1984. No leaks. Inspection ports are 12 X 18 inches and larger so you can get your head in. We opened all tanks and removed many years worth of sludge that looked like rotted garden slugs. I can't imagine not having large inspection ports. Once the inches thick gook was scraped out by putty blade we used a pressure washer modified to snake over the baffels. All connecting piping was 1 inch black iron and rusted heavily. We discarded all of the valves and pipe. I used my access at our machine shop to make new 316L SS pipe stubs and replace all valves with new red brass gate valves. Interconnects now are 1 inch USCG hose. When we were done cleaning the tanks the insides were shiny.

I think you could hire steam and solvent cleaning of the tanks if a hatch was opened up. This could let a good welder in with a heliarc to re-weld the seams. I don't know about coatings but I wonder if an Epoxy lining might also be added. As noted above, usually only the bottom seams are most prone to damage. I found that Sherman WIlliams has several affordable coatings designated for continuous imersion for water and fuel tanks. I use their white epoxy to coat the bilge as I finish areas around the boat. You can see this in the before - after of the crappy old steel pipe.

I like the SS tanks. The important point though is that you really need the ability to get inside, not just look inside.
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Old 30-01-2012, 14:50   #34
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Re: Replace Fuel Tank Advice

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Originally Posted by colemj View Post
I have been waiting for an answer to this. Everyone says to do it, but I don't know anyone who actually has.

For a tank of any decent size, it will have baffles and make putting in a bladder impossible. Another issue is management of fittings, chafing, etc while inside another tank. If the tank is so inaccessible as to not being able to get it out, then it will be extremely difficult to get a bladder into it.

I have put these bladders in boats before (open, extra spaces - not inside existing tanks), and they are stiff, have preformed shape and are not readily workable to pop into a hole and fit to a tank. They need to be tightly secured in all dimensions and free to expand in ways a fixed tank would not.

It is really only possible for small open tanks in accessible places - if at that.

I think it is one of those urban myth type things that everyone believes and propagates but hasn't experienced or spent any thought about the validity of the prospect.

Mark

I've been putting some thought into this problem, as I too have old, massive fuel tanks. They're fine now but I'm trying to anticipate the day when they go south on me. In regards too a bladder tank being placed inside an exisiting tank; while I've never seen it done I believe it is possible. There is a particular type of newer bladder tank that may work well for this, though the lack of baffling obviously means it's not an option for larger tanks. I can't remember the product name right now, but it is basically a flexible bladder tank which is double-walled. The space between the walls is filled with a heat activated resin. You install the tank in the desired space and inflate it so it fits the shape precisely. Then you turn on a heat lamp inside the bladder and let it cure for a few days. The result is an "instant" hard tank that conforms to whatever shape is at hand. I believe with some research and prep this could be made to work inside an existing tank. Perhaps you could even do more than one inside a very large tank to provide "baffles". I'm sure someone here knows what I'm talking about, it's been around for a while now and I've seen it done several times.
However, I think there is a better option. My opinion on this may be the result of a general bias toward fiberglass, as I am a pro laminator. I have built many boats with integral fiberglass tanks, and they are remarkably easy to build. I think if you can cut off the top of an existing tank, remove the baffles, clean it nicely, etc, then you can use it for both a convenient mold for a fiberglass tank and a great structural reinforcement for same. Just build a new solid fiberglass tank inside the old one, tab in baffles, glass on a lid, cut inspection ports and install hardware, and voila, a new tank built in place without removing the old one. Obviously this would only work in certain situations, ie top of the tank accessible without removing as much stuff as you would need to remove the whole tank, tank not totally rusted out, etc. But for me I think this will be the solution, and I have put a lot of thought into designing how it would work. Would be a fairly cheap fix that would last, I think. Just my 2c. For me it would be a big problem solver, I have 2 225 gal. fuel tanks that would be a real pain to remove. Even cutting them up for removal without cutting into a stringer would be hard.
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Old 30-01-2012, 17:31   #35
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Re: Replace Fuel Tank Advice

I like the pressure testing as an altermative... It sounds like a long term liveaboard cruising boat from the OP. I would definitely lean toward replacing or removing and inspecting the tank. The problem is that once one starts leaking.... it's not like you can immediately take care of the problem! Before you do anything, you have to get rid of the fuel in the tank. That is a big messy task in itself, pump, drums, long hoses electricity etc. Until you do that, your boat is filling with diesel and related smell. If you are on a week long crossing you may be dumping a lot of fuel and living with a big time smell until you arrive. May also get a pretty bad reception when you enter also!
For one thing, consider if you need all that diesel stored .... the fuel just gets old if you store too much on board. Maybe a smaller tank would be best and more economical.
That depends on if you are rounding the globe , or cruising the Carribean.
Bladder tanks are tempting, but in the end expensive and not a super easy task either. I've seen huge ones on a flat bed truck with fuel... so they must be safe. If you are panicing over a couple boat bucks for basic safety like this, ($2000)... well... you've got a lot to learn about boating! There are people on this board considering buying boats that they know need a $10000 bottom job! (10 boat bucks)
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Old 08-02-2012, 16:32   #36
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Re: Replace Fuel Tank Advice

We're in the middle of a re-power project, and "while we were at it"...those famous words, we checked the fuel tank...75 gallons, 22 yours old. When the boat was built, the area behind the tank was foamed, and over the years, the foam had wicked up water and pitted the back of the tank, most of the way through. So, we have new aluminum tanks, wouldn't do plastic or a bladder.

Tanks were about $1000, all the carpentry was about $4,000.
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Old 21-11-2012, 13:40   #37
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Re: Replace Fuel Tank Advice

One thing I know is that a boat can burn you in two ways. Monetarily is a given. The other is fuel fires. It ain't like you can pull over and get out. You are going up with it or swimming with eyes full of tears. Seriously boating has plenty of dangers and messing about with the fuel is just plain silliness. Don't play with it and treat is as if it is a timebomb. It is.
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Old 21-11-2012, 19:41   #38
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Re: Replace Fuel Tank Advice

Hi:

Timely topic for me as fuel tank removal and inspection is on the agenda. My tank is metal, though unsure of material at this point.

I don't know if there is an inspection port as I need to remove the tank to get access to the top surface. The tank will come out, this much I know, and without having to destroy anything (pretty sure).

So first question is what would I use to make an inspection port? Is there a screw out part specifically for this task? Or is it just a gasketed piece of material.

Next question. Is there anything better than disconnecting a fuel line after the lift pump and Racor filter, and just powering the fuel into three of four 5 gallon plastic containers? Service the tank and fuel system over the winter and then pour it all back in again.

I certainly agree, one doesn't want a leak in the boat. I spilled about a cup of diesel in my shop closet 2 years ago and can still smell it.

Cheers

Boulter
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Old 28-11-2012, 20:05   #39
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Re: Replace Fuel Tank Advice

Take a look at this for an inspection port: https://www.fisheriessupply.com/seab...s-plate-system

I emptied my tank the same way you describe. It worked well.

Greg
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Old 28-11-2012, 20:15   #40
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Re: Replace Fuel Tank Advice

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Originally Posted by CarinaPDX View Post
Take a look at this for an inspection port: https://www.fisheriessupply.com/seab...s-plate-system

I emptied my tank the same way you describe. It worked well.

Greg
Thank you. The port you referenced is about is as much as a new tank. Ouch.

Boulter
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Old 28-11-2012, 20:22   #41
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Re: Replace Fuel Tank Advice

You didn't say what the tank is made of. You could certainly find something cheap of plastic if it is a plastic tank. If the tank were new then threaded weld-on nuts could have been attached on the inside for a cover, but once assembled it is too late - and too dangerous - to add them.

If you are handy you could make your own version of the referenced plates, but personally I don't think it is worth the time. Sorry.

Greg
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Old 28-11-2012, 20:32   #42
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Quote:
Originally Posted by HHNTR111
We're in the middle of a re-power project, and "while we were at it"...those famous words, we checked the fuel tank...75 gallons, 22 yours old. When the boat was built, the area behind the tank was foamed, and over the years, the foam had wicked up water and pitted the back of the tank, most of the way through. So, we have new aluminum tanks, wouldn't do plastic or a bladder.

Tanks were about $1000, all the carpentry was about $4,000.
High quality plastic tanks like Tek Tanks in the UK are the best material in my experience. Aluminium. Is a poor choice , stainless is OK.

Dave
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Old 29-11-2012, 19:02   #43
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Re: Replace Fuel Tank Advice

The same tank access plates are cheaper here; depending on shipping I guess.

SeaBuilt Tank Access Plates - Fittings, Parts & Accessories - Fuel System - Engine Systems - Downwind Marine
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