Water tank sag

TylerG · May 10, 2021

My 2016 Heartland Mallard m29 has terrible water tank sag, in fact the tank literally fell off its hangers last year. I've fixed the hangers but now I'm trying to add support under the tank to stop the sagging.

I bought some 1" angle iron to span the frame with and then added 1/2 square tube steel between the two, however the tank still sags and puts a lot of pressure downwards on this metal. Did I buy too light of angle iron? How would I go about strengthening this up? I've thought about running 5/4 x 6" pressure treated planks under the tank sitting on the frame rails on other side. But I'm not sure what else I can do.

Original after rehanging. Boards were supposed to spread the weight across the straps better.

My "fix" before filling the tank with water

After filling with water

Material I purchased.

ABMax24 · May 10, 2021

Way too light of material. For the angle I'd be using 3"x3" x 1/4" as a minimum, I'd likely go 4"x4" x 1/4". This will also give a much thicker lip for the tank to sit on.

The pictures are unclear as to how the rear end of the tank is supported, does the tank just sit on the square tubing, or is there another support I can't see? If the design allows for it I'd likely use 2x2" x 3/16" angle instead of the 1" square tube, just bolt the L facing down if that makes sense.

On Edit: I see the hangers now. just replace the 1/2" square tube with the largest square tube that fits, looks like you should be able to get 1.5" x 1.5" x 3/16" in there, after upsizing the angle.

TylerG · May 10, 2021

ABMax24 said:
Way too light of material. For the angle I'd be using 3"x3" x 1/4" as a minimum, I'd likely go 4"x4" x 1/4". This will also give a much thicker lip for the tank to sit on.

The pictures are unclear as to how the rear end of the tank is supported, does the tank just sit on the square tubing, or is there another support I can't see? If the design allows for it I'd likely use 2x2" x 3/16" angle instead of the 1" square tube, just bolt the L facing down if that makes sense.

I can't have the angle on the bottom due to the underbelly material I need to put back into place. The tank is hung at the top with angle iron that is bolted thru the frame rails under the lips of the tank.

The underbelly material is just coreplast but I want to put it back to help keep critters out and the bottom properly sealed up.

I'm thinking either step up to 1/4 thick angle iron or weld a square tube across the back of the existing angle iron to add more strength to it.

ABMax24 · May 10, 2021

Everything else with what you did looks fine, that light material is just not up to the task.

snopro · May 10, 2021

I've seen tanks do that over time. They lose their structural integrity after years of heat and bouncing down roads full of water and none seem to be supported properly. Plastic weakens over time. It might be easier to just get a replacement tank. At some point a well placed rock bouncing under the trailer will hit it right and you are going to have wet road behind you.

ABMax24 · May 10, 2021

TylerG said:
I can't have the angle on the bottom due to the underbelly material I need to put back into place. The tank is hung at the top with angle iron that is bolted thru the frame rails under the lips of the tank.

The underbelly material is just coreplast but I want to put it back to help keep critters out and the bottom properly sealed up.

I'm thinking either step up to 1/4 thick angle iron or weld a square tube across the back of the existing angle iron to add more strength to it. //uploads.tapatalk-cdn.com/20210511/072d1808f239c40a4c747d31b7dd8a8c.jpg

Okay, that makes sense. Can you upsize the 1" angle and have it fit? Going to even 2" will give you significantly more strength than just adding wall thickness.

TylerG · May 10, 2021

snopro said:
I've seen tanks do that over time. They lose their structural integrity after years of heat and bouncing down roads full of water and none seem to be supported properly. Plastic weakens over time. It might be easier to just get a replacement tank. At some point a well placed rock bouncing under the trailer will hit it right and you are going to have wet road behind you.

The frustrating thing Ken is the trailer is only 5 years old. And that's one of the reasons I want to put the underbelly back in place.

TylerG · May 10, 2021

ABMax24 said:
Okay, that makes sense. Can you upsize the 1" angle and have it fit? Going to even 2" will give you significantly more strength than just adding wall thickness.

Yes I definitely can do that. And I'll see about some larger square tube for going across. I bolted it all together simply in case I ever need to drop the tank out of it.

It's 1/2" square tube in there now. I think I'll step it up to 1" as well.

ABMax24 · May 10, 2021

TylerG said:
Yes I definitely can do that. And I'll see about some larger square tube for going across. I bolted it all together simply in case I ever need to drop the tank out of it.

That's what I would do. 3" x 1/4" angle, as all the weight is on the angle, and it has a long span. You could even replace that square tube with just 1" x 1/8" and it would likely be fine, I didn't see that the original tube was 1/2" x 1/16", that's light stuff.

Once done you shouldn't have to touch it ever again.

TylerG · May 10, 2021

ABMax24 said:
That's what I would do. 4" x 1/4" angle, as all the weight is on the angle, and it has a long span. You could even replace that square tube with just 1" x 1/8" and it would likely be fine, I didn't see that the original tube was 1/2" x 1/16", that's light stuff.

Once done you shouldn't have to touch it ever again.

Thank you very much for all your expertise.

ABMax24 · May 10, 2021

TylerG said:
Thank you very much for all your expertise.

No problem.

I see my fat fingers got in the way, my last post was supposed to be 3". I'll fix it.

TylerG · May 10, 2021

ABMax24 said:
No problem.

I see my fat fingers got in the way, my last post was supposed to be 3". I'll fix it.

Thinking I might have someone weld the angle iron in and keep the 1" as removable pieces in case I ever need to remove the tank

Caper11 · May 11, 2021

Do you jam the end of the water hose in the fill neck when filling the tank???
I use a attachment on the end of my hose to fill so the air can escape properly during filling. Ballooning a water tank cam break floorboards as well.

fredw · May 11, 2021

Our tank was the same thing, we had welded a few more flat iron gussets to help support the bottom of the tank up.. and this also helps the angle iron keep up to the crapy frame if the plastic tank.. like Ken said they made the plastic to light and it dis forms over time.. they call this a ware time and not covered under your warranty..lol play book from brp

LUCKY 7 · May 11, 2021

AS a RV tech friend of mine told me " all the RV's are junk and all will leak and have issues, some quicker than others"

TylerG · May 11, 2021

Caper11 said:
Do you jam the end of the water hose in the fill neck when filling the tank???
I use a attachment on the end of my hose to fill so the air can escape properly during filling. Ballooning a water tank cam break floorboards as well.

Used to but bought one of those hoses too

blubbles · May 11, 2021

Depending on the hose setup for these, sometimes you need even longer hoses to fill the tanks. I find that filling with a much smaller line (3/8") that gets pushed in two or three feet into the fill hose seems to do a better job at filling the tanks than those adapters. Takes longer, but seems to actually get it full.

For sure worth looking at the bracing though.

ABMax24 · May 11, 2021

TylerG said:
Thinking I might have someone weld the angle iron in and keep the 1" as removable pieces in case I ever need to remove the tank

You could. Since the angle sits on the frame though it isn't needed, bolting would be as strong if the hole has already been drilled in the trailer frame, but it's just a matter of personal preference.

But maybe there isn't a hole already? I cant tell from the photo. If not then I'd weld it to avoid removing material from the frame.
.

TylerG · May 11, 2021

ABMax24 said:
You could. Since the angle sits on the frame though it isn't needed, bolting would be as strong if the hole has already been drilled in the trailer frame, but it's just a matter of personal preference.

But maybe there isn't a hole already? I cant tell from the photo. If not then I'd weld it to avoid removing material from the frame.
.

I have 1/4' holes in the frame holding the 1" angle iron in place.

TylerG · May 11, 2021

Materials picked up. Got a good deal from a local place in Spruce Grove called Stinger Fabrication.

3" angle iron 1/4" thick @ 68" x 2
1" square tube whatever they had @ 36" x 5

$100

Back to building tonight.

Water tank sag

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