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mosseater's avatar
mosseater
Explorer II
Apr 29, 2014

Holy sagging water tanks, Batman!

Since I was already having a venting problem with my FW tank, I decided this weekend to look and see why there seemed to be a bulge in my enclosed underbelly.

The venting problem was a pretty simple one. The vent tube was sagging about an inch below where it entered the tank, so there was about 10" of water it that had to be either sucked in or blown out before it could vent properly. A couple wireties solved that in short order.

The bulge was a different issue. SunnyBrook did a nice job installing and supporting the 50 gal. tank between two "Z" struts which were firmly anchored to the frame rails with the tank held captive between them on a 1 1/2" ledge. The problem comes with their rational to support under the tank with a piece of 1/2" OSB sitting on the ledge of the "Z" strut. That, in and of itself, isn't a problem, although it's marginally able to carry the load of 400 lbs of water without bowing. The root of the problem is with their complete lack of allowance for the condesation which forms between the tank and OSB, and slowly rots the OSB, taking with it all support. The wetter it gets, the more water it collects, and the more it rots. The whole center about 1' around was so spongey I could put my hand right through it.

The repair could have taken several paths, but I chose to change out the piece of OSB with 5/8" plywood, which I cut to fit as closely as I could. I bored a 3/4" weep hole in the middle and stapled two strips of plastic, one on either side of the weep hole, to aid in air circulation and drainage of condensation. After got the whole high- tech mess up and in place, I ran two banding straps under the plywood from one "Z" strut flange to the other to help support the tank and also keep the struts for torquing under load. I filled the tank before re-installing the underbelly to watch how it perfomed, and it barely bowed at all. I think it's going to last a long time.

It was also nice to be able to shore up some wiring with cable ties and get a good look at the innards of the beast. At least I know that problem won't rear it's ugly head at some inopportuned moment this season. If any of you folks have some question about the security of your tanks, I highly recommend you take a look. That's a lot of weight hanging under there!
  • Sorry, no pics. I lost my hosting site quite a while back and haven't gotten a new one yet.

    I had a heavier piece of plywood to put in, but it was too thick. And I also had all kinds of construction stuff laying down there. Putting the plastic underbelly back up was no picnic either!
  • Mine started to flex or bow when my drain valve got hit by something kicked up from the tire and started to leak. The leak got the 3/8" plywood wet and lose it's strength. My rig also had 3 metal straps under the flexing plywood. When I took the plywood out there were all sorts of construction leftovers between the plywood and the water tank. I replaced mine with 3/4" plywood and everything is working just fine- so far.
  • They have been doing it the same way for years and having trouble with it for as long…

    My FWT fell out from under my Sunnybrook trailer and skidded across the highway and smashed into a guard post… the piece of OSB when airborne like a Frisbee and very fortunately didn’t hit anything…

    Mine was repaired by making and bolting 3 pieces of heavy flat stock across the bottom of the tank… no way possible for it to fall after that or bow on the bottom…
  • Glad you caught it in time, can't imagine what a hassle it would be if it fell off during a big trip.
  • Nice work!

    I'm guessing the mfg. saved, what, $.50 per unit between OSB and plywood? Strapping a tank with the weight of water, and being transported, has to have some consideration, too. I've seen a few that looked less than up to the task.