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