Aluminum Fuel Tank Cracked Weld

iddooer

Member
Sep 21, 2010
306
63
Seattle
Name
Lee
Boat
22' ThunderJet Outboard offshore
I was smelling fuel last time out and decided to see where it was coming from. I was hoping for a loose clamp or hole in one of the fuel lines. No such luck. I ended up having to remove the seats and the entire floor. What I found was about a 7” crack in the center of the weld on the upper edge on the right side of the tank. I also found more cracks along the stiffeners on the hull after removing the floor as well. I had the boat back at Thunderjets plant last year for some other cracks I found in the hull and now I found more. I was wondering if its even possible to reweld the crack on the tank or will I need to have it removed and replaced with a new one? Thunderjet said they would repair all the new cracks in the hull again since its covered by a lifetime warranty so at least that one good thing
 

G-Spot

Captain
  • Mar 14, 2008
    5,270
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    Salem/OR/USA
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    John
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    53’ Hatteras STEEL N TIME
    They can re-weld even on a fuel tank... dangerous if not properly evacuated and run Co while welding... the factory should abs probably will just drop a new tank in there...

    Although they have structural issues, they probably don’t manufacture their own tanks.... maybe...
     

    Deviant

    I Should Upgrade My Account
    Apr 8, 2010
    1,597
    770
    WA
    Name
    Tim
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    Arima SeaRanger 19
    I'm a metal guy/aircraft structural and when I was getting my airframe license and I remember reading a lot about welding aircraft fuel tanks.
    Vent, purge, inert gas and clean metal.
    Gotta ask if repairs are a bandaid on a arterial wound.
     

    aguachico

    I Post A Lot But I Can't Edit This
    Jul 20, 2004
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    El Lago Tijuana
    Name
    Art
    Boat
    Trident Yak- Grady White Seafarer
    A boat is mostly gas, flammable resin ... all stuffed into a small space. The fire escape is no picnic.
    If the original weld failed, maybe the boat design is bad.
     

    Walker Inc.

    I Post A Lot But I Can't Edit This
    Jun 24, 2013
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    Gig Harbor, WA
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    Patrick Walker
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    33 ft. Coldwater Walkaround
    Yes you can weld on a fuel tank. I just had it done on mine. The key is air circulation. I removed all the fuel from the tank. Pulled it. Removed sending unit, and pick up tubes. Removed fittings from the 2 vent line holes. I then duck taped my shop vac hose to the 1.5” fill barb and added another hose to move the vacuum about 12 feet from the tank and let it push air through the tank out in the field behind my house. After about 6 hours the gas smell was completely gone as the tank dried out. I then cut out the damaged area and Allied welded a patch on. No big deal. I acid washed and scotch brited the whole tank and it looked almost brand new. In typical Coldwater fashion the tank was way overbuilt out of all 1/4inch and weighed entirely way to much. Re-installed the tank and had the rear deck welded back in.

    Mine was caused by dis-similar metal and saltwater. Make sure your tank inspection hatches are sealed and there are not brass fittings in your aluminum pick up tube fittings!

    it was a great excuse to run all new 1.5” tank fill line, 5/8 vent hose, and 3/8 supply lines to the racors. Hoses were 2003 vintage.

    i also did away with my sending unit which eliminated a potential leak /failure point. The nmea fuel data is way more accurate anyway.
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    A-K

    Member
    Jun 14, 2015
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    Gig Harbor Washington
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    Aaron
    Boat
    Parker 2320
    When we purge piping systems go low to high if it’s argon because it’s heavier than air. Make sure you plan out the purge so you know it’s actually “working”. Let if fill slowly. If working on a bench don’t flip the tank and have your purge gas dump out. Then weld and go boom!
     

    Captain Decent

    The Bert makes ‘em Squirt
    Nov 2, 2017
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    Given blunderjets track record in this I would for damn sure replace the tank with one built by someone competent.

    the next crack could be on the bottom.
     
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    tacklejacked

    Capt./ Ho if I get to drive
    Jun 2, 2009
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    Seabeck
    Name
    Greg
    Boat
    22 Hewescraft Searunner ET HT
    At this point I would be pushing for a new boat...with an attorney involved...

    As for the tank....Welding around gas scares the hell out of me. That's all I got.
     

    bobberdoggin

    ‘Butt Kraken
    Mar 23, 2015
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    Name
    Thomas
    Boat
    22’ SeaSport Sportsman ‘Butt Kraken
    What I found was about a 7” crack in the center of the weld on the upper edge on the right side of the tank. I also found more cracks along the stiffeners on the hull after removing the floor as well.

    Some could be aluminum crater cracks. I would think it would be covered any warranty either way. It would be unusual to have that many welds with that condition though. Anyway, it's fixable as others have mentioned.

    If they are all actually fatigue cracks I would start to wonder how much of a pounding the boat is taking either on water or on the trailer. If that’s not happening, then probably some sort of fit up issue with their assembly of the boat causing excessive pressure on the welds that are cracking.

    I guess you can also have the welds independently inspected to see if there are any issues there.
     
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    acefuture

    @acecraftco
    Apr 3, 2019
    627
    595
    Costa Mesa, CA
    Name
    Ace
    Boat
    Always changing
    Short answer, yes it can be welded and fixed.

    Long answer, as many have already said, it's all about purging and cleaning the tank. I'm looking at potentially fixing my tank instead of welding a new one now. My process is I pulled the tank. Drained all fuel, filled it with water, dumped the water, and now have about 3" of water in it that I'm letting air dry. Then i'll hook up a vacuum similar to what Walker Inc. said and also try to back purge it with argon. I don't think i'll be able to get the full tank full of argon since its a 63 gallon, but it'll help.

    But the problem is really larger than cracked welds. If there's a cracked weld, or multiple cracked welds, it's caused by a structure issue. And fixing a cracked weld is just putting a bandaid on an issue that will arise again. Unless the guy who welded it was just hungover that day and left all the welds with craters and that's what caused the cracks. If you just reweld them, they'll crack again. So they need to find the root cause of why the cracks are happening and fix that first.
     
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    Vek

    Newbie
    Jan 17, 2008
    64
    19
    Blaine
    Name
    Jerry
    Boat
    28' Almar
    Float any fuel residue out and displace vapors with water. I had to extend the fill neck on my rear tank by slipping a piece of 1.5" tube inside the 2" 1.5" pipe (bracket builder error...made for a fun fill hose fitup before the fix), so I left the tank full of water after floating out any slick trace, in order to not have vapor in the tank while welding. Repair to tank wall would mean dry-out as described above since you couldn't leave it full of water.

    Cracks in the boat traces back to any of a number of causes of high stress. Stringer spacing, bulkhead spacing, plate thickness, stringer section properties, etc and so on. Wide stringer spacing means increasing plate thickness. Inadequate stringer section means tightening bulkhead spacing. Screw up any one of these and you're cracking. Aluminum has no "endurance limit" or stress level below which it won't fatigue crack, like steel generally does. So, maximize stress cycles before failure, which means keeping stress low, which means building a rigid boat: heavy plate, substantial stringers spaced close, bulkheads spaced to suit stringer section beef.

    There's enough tin boat representation on a site like this that one could compile an interesting knowledge base of make, model, size and hull framing. The three I'm familiar with are a 19' wolfboat, 26' hewes and 28' almar. The wolf hull plate is 3/16" 5052. Stringers are 4" 6061 channels on about 1' centers, so maybe 8" plate span between supports. The stringers are then trussed to the 3/16" deck plate. Bomber boats, those are, and the builder can weld pretty with wire. The hewes had 1/4" 5086 hull plate and one big box girder of plate on each side of the keel, if I remember right. Don't have specifics or measurements on that one, but don't hear many stories of problems. The almar has 1/4" 5086 hull with a 1/2" x 3" flat bar keel stringer and t-section stringers on 1' centers or so above that...should go measure.
     

    G-Spot

    Captain
  • Mar 14, 2008
    5,270
    2,313
    Salem/OR/USA
    Name
    John
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    53’ Hatteras STEEL N TIME
    Short answer, yes it can be welded and fixed.

    Long answer, as many have already said, it's all about purging and cleaning the tank. I'm looking at potentially fixing my tank instead of welding a new one now. My process is I pulled the tank. Drained all fuel, filled it with water, dumped the water, and now have about 3" of water in it that I'm letting air dry. Then i'll hook up a vacuum similar to what Walker Inc. said and also try to back purge it with argon. I don't think i'll be able to get the full tank full of argon since its a 63 gallon, but it'll help.

    But the problem is really larger than cracked welds. If there's a cracked weld, or multiple cracked welds, it's caused by a structure issue. And fixing a cracked weld is just putting a bandaid on an issue that will arise again. Unless the guy who welded it was just hungover that day and left all the welds with craters and that's what caused the cracks. If you just reweld them, they'll crack again. So they need to find the root cause of why the cracks are happening and fix that first.

    The two I did..... After purge, we hooked up a steel pipe in the exhaust of a car connected to a vacuum hose, to the fuel fill and let the vehicle idle for a long time filling the tank and left it running while welding.... easier than argon and worked good for me twice....
     

    iddooer

    Member
    Sep 21, 2010
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    63
    Seattle
    Name
    Lee
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    22' ThunderJet Outboard offshore
    Well it sure sounds like it can be done but after hearing all of this I’m thinking I’m just going to have a new tank installed. I’m not sure if they actually made it or not but with all the welds I’m seeing that are cracked I don’t want to take a chance and have it crack in a different location. I just pulled up some foam along the stiffener just aft from one of the cracks and noticed another crack that was buried under all that foam. I would hope they remove all the rest to inspect those areas that are under the foam for cracks prior to re installing the floor. I removed all the fuel and now waiting to hear back from thunderjet to get that thing back to them for repairs. Thanks for all or your input. I really appreciate the help. You guys are a wealth of info for sure
     

    G-Spot

    Captain
  • Mar 14, 2008
    5,270
    2,313
    Salem/OR/USA
    Name
    John
    Boat
    53’ Hatteras STEEL N TIME
    Well it sure sounds like it can be done but after hearing all of this I’m thinking I’m just going to have a new tank installed. I’m not sure if they actually made it or not but with all the welds I’m seeing that are cracked I don’t want to take a chance and have it crack in a different location. I just pulled up some foam along the stiffener just aft from one of the cracks and noticed another crack that was buried under all that foam. I would hope they remove all the rest to inspect those areas that are under the foam for cracks prior to re installing the floor. I removed all the fuel and now waiting to hear back from thunderjet to get that thing back to them for repairs. Thanks for all or your input. I really appreciate the help. You guys are a wealth of info for sure

    As mentioned above.... You may want to consider if you are pounding a little too much when running... Especially if you have suspension seats... It’s easy to get carried away... 20+ years ago I was a Tin boat guy and had suspension seats and never realized how bad I had been pounding until Inlet my friend drive once and didn’t have the benefit of the fancy seat! Wow!

    I also had an experience with my fuel tank cracking at the hanger mounts.... I fueled up and came out one day to the smell of gas... notice fuel dripping out of the drain. After a little research I found that the mounts had all cracked and the tank slid back a couple of inches rubbing a hole in the filler hose. With the boat title up on the trailer the filler hose had plenty of fuel to leak. My tank was still in tact, but had to weld new mounts on it...

    I have no idea how you run your boat, just a thought... Good Luck!
     

    iddooer

    Member
    Sep 21, 2010
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    Seattle
    Name
    Lee
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    22' ThunderJet Outboard offshore
    Overall lm pretty easy on it. I do have the suspension seats but I don’t really hammer down and hit the waves really hard. It’s not not I’m heading offshore when the weather goes to shit like the bigger boat do. I have to pick and choose my days and typically it’s not bad when I’m out there
     
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    Ugly Bayliner

    I Should Upgrade My Account
    Sep 18, 2008
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    Olympia, Wa USA
    Name
    Steve Ericsson
    Boat
    20' Ugly Bayliner
    Anyone who welds will tell you about welding fuel tanks - we’ve all done it, we’re all nervous about it. It can be done. I would look for why it happened. Is the tank hanging from plates welded to the top? If so it’s the plates are flexing with fuel weight and cracking the welds. They should be mounted on the sides. A buddy’s Hewewscraft was hanging and cracked, they switched it to gusseted plates so it wouldn’t flex.
     
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    iddooer

    Member
    Sep 21, 2010
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    Seattle
    Name
    Lee
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    22' ThunderJet Outboard offshore
    This tank is just laying on the bottom and has some cross beams with a support bar pushing down on the tank at ea cross beam location. It looks like a sheet of rubber between the lower side of the tank and the upper side of the hull. This tank seems pretty thin too. You can push on it and it will have an oil caning effect too.
     

    Captain Decent

    The Bert makes ‘em Squirt
    Nov 2, 2017
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    Ryan
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    The Bert Makes ’em Squirt
    If it’s sitting on rubber strips as they usually are you will have corrosion there as well. Left in the open the aluminum will weather very well but this rubber holds moisture against it constantly. The tanks in my Grady were all Swiss cheese where the hold downs were because they used that rubber.