400 Sundancer water tNk crack and repair

Discussion in 'Sport Yachts/Yachts' started by peterkvs, Oct 27, 2014.

  1. peterkvs

    peterkvs Member GOLD Sponsor

    489
    Nov 11, 2012
    Guntersville, Alabama
    400 Sundancer 1999
    3116 Cats, 1000 hours
    400 Sundancer water tank crack and repair

    Last weekend I found water running into the bilge from the forward cabin area. Upon Inspection i learned that the 100 gallon L shaped tank under the aft bed was cracked in the inside corner of the L and the whole tank was surrounded by 6 inches of water. NOT GOOD! A new tank priced out at $1100 or so plus shipping and so I decided to try and see if I could fix it. After doing some research online I learned that the tank, made by Dura Cast was a Linear Medium Density Polyethylene. (LMDPE) This was good because if it had been a Cross Linked PE it would not have been weldable. So I stumbled onto a source of DIY repair kits for plastic and some videos that show you ho to do it. It looked easy enough and so I bought some tools and materials, watched the videos and fixed the tank. It took a day to remove the tank, repair it and reinstall it, and about $80 for the tools and materials.

    Youtube had two good videos on repairing PE and I used a combination of both techniques. One technique has you grind out the crack and then using a heatgun and a stick of PE slowly melt the tank and press the rod into the crack. I liked the look of this technique, and I had a heatgun, so I thought that I would go that approach. Then, I saw I video where they were fixing a kayak and used an iron to melt the PE and press into it stainless steel mesh so that it would reinforce the crack. Because my crack was a stress crack in the corner of the tank which was on the top of the tank, transitioned around the edge of the tank, traveled along the edge for an inch or so and then proceeded down the side of the tank, I knew that adding the reinforcing mesh was also going to be important.

    So here is the sequence of repair.

    Disassemble the entire aft berth.
    image.jpg

    Drain the tank, I removed the line to the pump in the engine room and let it drain into the bilge. This takes a long time. Then I lifted each end of the tank with a suction cup and put ratchet straps around the tank so that three of us could lift it out of the hole. It was a bugger because the tank still had an inch of water in it and the water under the tank had a good suction holding it in place. Once it was lifted, it was pretty easy to maneuver and get up onto the dock where I could work on it. You will need two or three friends to move it.
    image.jpg

    I cleaned the area of the crack with MEK and then took a right angle grinder with a 80 grit flapper wheel and ground the edges of the tank square and ground some of the surface of the tank off so that I had new fresh material to work with and no plastic with mold release on it. Then I took a dremel bit with a 3/16" round burr and ground down into the crack about 1/8"- 1/4" deep following the crack and extending beyond both ends.
    image.jpg

    Then I used the heat gun to preheat the crack until it was starting to look clear and getting soft. Once it was hot I used the heatgun to heat the tank and pushed the PE welding rod into the tank. You have to go slow, you heat the tank and press the rod into the tank and let the heat of the tank melt the rod into the tank. You get a good bond this way. I went over the crack with rod until it was flush.Then I used the iron to smooth the repaired area. Here is the youtube video I watched that showed me how to make the repair.

    Then I took the stainless mesh that came with the Canoe and Kayak repair kit that I bought from urethanesupply.com and used the iron from the kit along with my heat gun to press the mesh into the repair. I bent the mesh over the corner on an angle so that the mesh was on the bias and would easily bend to follow the contour of the corner of the tank. After I got the mesh pressed into the tank I use a combination of both methods with with iron and heat gun to completely cover the mesh with the PE welding rod and really encapsulate the mesh into the tank and reinforce the cracked area. Here is the video I watch to learn how to repair a crack with the reinforcement mesh.


    Once the repair was complete and cooling I was ready to install the tank. Here is a picture of the completed repair.
    image.jpg

    I cleaned with hole where the tank goes. It was nasty from being wet for perhaps a long period. Installation was the reverse of the removal. I removed all of the fittings and put them back in with new thread sealant. I filled the tank until it was completely full. I was very surprised to see how much the tank bulges after it is full and long before the overflow starts to spit out water. I would estimate that the tank bulged 1-2" in the center and so it is no wonder that the corners are cracking on these tanks. There is tons of stress there and thats not even when you are pounding over the waves. I also found that the adapter that went from the threaded pickup tube to the press on pipe connector was leaking. The oring in that fitting was as hard as a rock. Fortunately I had new one in my parts box and was able to replace it. Once I got the tank back in and filled up I was happy to see that there were no leaks and that the repair seemed to be holding well. Ill report back if I notice it leaking again. I hope to be vigilant and not fill the tank to its max so that I do not have to relive the crack repair experience. I am seriously considering adding a much lower overflow vent so that tank won't get overfilled.

    Here is a picture of the mayhem in the cabin. The admiral was a big help getting this all cleaned up and put back together.
    image.jpg

    I hope this helps the next poor guy with a leaky tank and the DIY curse.

    Pete
     
    Last edited: Jan 23, 2018
  2. RollerCoastr

    RollerCoastr Well-Known Member

    Nov 15, 2007
    Cedar Point, OH / Miami, FL / MacRay Harbor, MI
    1997 400DA
    340HP 7.4 Mercruiser Bluewaters
    Garmin 8212, 741 24HD, Intellian I2
    1999 280BR
    Twin 250HP Merc 350 Alpha Ones
    Are you kidding? This makes you the official 400DA HERO.

    Did you take the opportunity to rinse out the inside of the tank? I'm very careful about maintaining fresh water, but one of the extra motivations for me to repair the tank is the peace of mind of getting the inside as clean as possible.
     
  3. peterkvs

    peterkvs Member GOLD Sponsor

    489
    Nov 11, 2012
    Guntersville, Alabama
    400 Sundancer 1999
    3116 Cats, 1000 hours
    Thanks! I appreciate the kind words. Hopefully the repair will last and not just crack at the next weakest place. I'm very careful with the tank and it is spotless inside. We only use the tank for our water and thus go through 100 gallons or so a weekend. We don't try to conserve unless we are on the hook. I did completely drain the tank and there was zero residue inside the tank.

    Good luck with your repair.

    Pete
     
  4. Skuza

    Skuza Active Member

    Nov 1, 2006
    Lake St Clair, MI
    400 Sundancer
    7.4L Horizons
    I honestly had no idea that's where the tank was! I've heard about the famous 400DA "L" shaped tank and the leak but always thought it was behind the fridge! Thanks for the writeup!
     
  5. perryk123

    perryk123 Member

    42
    Nov 29, 2013
    Little Rock AR
    2004 Sea Ray 390 Sundancer
    T/ 8.1 496 370 HP Vdrives
    fyi

    if this issue persists, an economical fix would be to have a local welder replicate the tank using aluminum. you can even add a large clean out access, if you ever wanted to get in there. Had to do this years ago, as the tank was no longer available from manufacturer.

    i have also wondered if you can have one made from the same materials used for ballast bags on all these wakeboard boats
     
  6. stephens013

    stephens013 New Member

    171
    Oct 8, 2009
    Ft Walton Beach, Fl
    1997 400DA Sundancer
    3116 Cat; 340 PHP
    Outstanding
    thanks for the info
    I'm checking my tank tomorrow
     
  7. Steve500dancer

    Steve500dancer New Member

    865
    Jul 13, 2009
    Franklin Tennessee (Nashville area)
    1996 500 sundancer
    2001 340 sundancer sold
    2001 270 Rinker sold
    1996 240 sundancer sold
    Twin 6v92 Detroit deisels
    I am dealing with the same thing right now on my 96 500 DA. Unfortunately, my tank is a 150 gallons and is under the salon floor. I repaired two leaks a couple of years ago and now I have another leak somewhere. When the tank is 1/2 full I have no leaks until I am under way. I have to try and find the leak and it is very tough to get it. I am going to try and fill it up a little more and add food coloring and see if I can pin point the leak. It doesn't appear to be leaking from the last two repairs I made on the top of the tank. Once I add the food coloring I am going to use my GoPro on a stick and see if I can see where the red food coloring is leaking from. I can only hope that it is on the top again where I can get to it (with great difficulty) if it is on the bottom or sides I am going to have to replace it.

    I have spoken with Dura Cast and they were not much help at all. Their answer was..."hmmm it should not have done that" cracked at the support ribs that is. I am also sure that it happened from over filling. The 1 1/2" fill tube is no match for the 5/8" vent that has 25" of hose and exists under the kitchen sink. I think this is an incredibly poor design on dura casts part, these tanks can only take so much expansion and contraction before they fail. As a matter of fact I have a friend in Denmark with almost the same boat and he is having the exact same issue as me.m

    I am trying to see if I can source a bladder that can be installed the tank instead of having to cut out a big part of the salon floor. I used 3M 5200 for the previous two repairs.

    If anyone has any ideas on how to locate the leak or any other ideas please let me know.

    Thanks in advance
    Steve
     
  8. mwph

    mwph Active Member

    Jul 8, 2008
    Lake Guntersville, Tennessee River, Alabama
    1998 250 DA
    7.4L, B3
    Great write up Pete. Thanks for taking the time to post it.
    Is that the transient dock at The GYC? Looks awfully familiar.
     
  9. peterkvs

    peterkvs Member GOLD Sponsor

    489
    Nov 11, 2012
    Guntersville, Alabama
    400 Sundancer 1999
    3116 Cats, 1000 hours
    Yes it is the party/transient dock at the yacht club. Steve I like your bladder idea. I have installed bladders in aircraft wings and it all goes in through the fill hole. A biatch to get it in, but it would solve the problem nicely. You might look into fluorescent dye like they use in finding leaks in radiators and cooling systems. You can find the leak super easy with a black light. Not sure if the stuff is toxic or not or what it might take to rinse it out of your system. But it would make finding the leak easy.

    Pete
     
  10. Mazenk

    Mazenk New Member

    1
    May 24, 2016
    Newburyport
    1997 400 Sundancer
    CATS 3116
    Hi, thank you for the great write up. I am having the same issue (same crack location). I tried everything including plastic welding.. Like you said, the bulge is the issue, I too can't believe the amount of pressure with no relief from the overflow vent, very poor design. Is your fix still holding? Do you or anyone else knows how add a 4" access hole so it could be patched from inside to prevent the upward pressure?

    Thanks
     
  11. fwebster

    fwebster Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    Oct 6, 2006
    Middle Tennessee ; Panama City Beach, FL
    1996 450DA
    3116 Caterpillars
    You guys need to understand who you are dealing with here........Pete is a guy that cannot accept no. He even made his own pizza oven because he could make a better one than those commercially available.....and he likes good pizza.
     
  12. Skuza

    Skuza Active Member

    Nov 1, 2006
    Lake St Clair, MI
    400 Sundancer
    7.4L Horizons
    I repaired ours last year by plastic welding it. I also built braces along with particle board “plates” to hold the top of the tank. I did this to prevent the top of the tank from bulging and “working” the repaired area. People would be SHOCKED to see how much the tank bulges when it reaches the full point. At that point the vent cannot keep up with a wide open garden hose and it starts pressurizing the tank. I now am part of the 3/4 full MAX club.
     
  13. RollerCoastr

    RollerCoastr Well-Known Member

    Nov 15, 2007
    Cedar Point, OH / Miami, FL / MacRay Harbor, MI
    1997 400DA
    340HP 7.4 Mercruiser Bluewaters
    Garmin 8212, 741 24HD, Intellian I2
    1999 280BR
    Twin 250HP Merc 350 Alpha Ones
    I was thinking about that
    When I read the "your favorite SeaRay" thread, I think about how many things about the 400DA I like over similar SeaRays, but that tank is NOT one of those things! A true "what were they thinking?" item.
     
  14. Ezsteps

    Ezsteps Active Member PLATINUM Sponsor

    235
    Nov 14, 2015
    Lake St. Clair-- Michigan
    1999 400 Sundancer, YL310 Zodiac
    7.4 Mercuisers Horizons 380 hp, 9.9 hp Mercury
    Hello
    Hello Skuza, ready for summer yet? I am in the same club. 1/2 mostly to 3/4 MAX.
     
  15. Skuza

    Skuza Active Member

    Nov 1, 2006
    Lake St Clair, MI
    400 Sundancer
    7.4L Horizons
    The high bulge water warning light is your clue that something is up down there. I wrote it off for a while as a fluke till one day I checked the bilge at the bottom of the cabin steps. Bingo!
     
  16. bobeast

    bobeast Dance the Tide SILVER Sponsor

    298
    Oct 22, 2017
    Isleton, CA
    2002 310DA
    350 MPI w/V-drives
    For others who stumble across this thread, a cautionary tale: Surveyor found rotting stringers on my recent 310 purchase, which thankfully, the seller agreed to pay for. Total bill came in at around 12 boat bucks. During the repair, the yard called and told me they had found the reason for the rot. Apparently the fresh-water tank had been leaking for who knows how long.

    The obvious moral of this story is, if you discover a leaky water tank, do not pass go, do not go in search of a round tuit. Fix it yesterday.
     

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