Travel with full fresh water tank?

Gliddenwoods

Is it correct that the fresh water tank on my 2019 Tab 400 Boondock is behind the axle so traveling with a full tank of water will reduce the tongue weight? Thus it is a good practice to do so? Ignore possible negative impact on mpg and just focus on tongue weight reduction.

falcon1970

Yes, it sits just behind the axle.  However, it is not very far aft of the axle so even though a full fresh water tank weighs just over 250 pounds the moment arm is only about 12 inches to the cg of the tank.  The moment arm of the ball socket is 216 147 inches so you are only relieving about 13 20 pounds of tongue weight.  Having said all that, I also travel with a full fresh water tank.  Mostly cause my tongue weight is approaching 500 pounds and anything helps, but also because it is handy to have water if you stop at a Wal-Mart for the night.
By the way, either fill the tank or leave it empty.  There are no baffles in the tank so if it is only half full you might feel the effects (when you least expect or want it) of water sloshing from side to side.
By all the above reasoning I try to not travel with water in the gray tank--it adds weight to the tongue and it will slosh.
NOTE:  The cross outs have been corrected.  I read the wrong lines on my Weight and Balance sheet.

NorthIsUp

I keep that tank filled when starting out on an adventure because it gives me a few days worth of clean, filtered water from home, as well as a little bit of balancing action for the tongue weight.

I dump water on the last day of a trip before returning home, so I guess I really do it just for the fresh water, but feel good about the tongue weight when the vehicle and T@B are fully loaded.  

greggill

I agree with @NorthIsUp. I like my water from home and start out with a full tank. I never thought about the tongue weight factor. For the most part an extra 250 pounds isn't going to make or break me.

tabiphile

For an alternative perspective, we never tow with water in out tanks if we can avoid it. Unbaffled tanks filled with water can shift your load in very unpleasant and dangerous ways. IMHO, it's better to fill at or near your destination and empty before returning home. Carry a drinking water cooler if that is the need. There is little a brake controller can do to save you when the wind hits you while you are on a curve with your water load slopping from side to side tossing your load around.

falcon1970

@tabiphile
If the tank is full it won't/can't slosh.  However, if you are on a several day trip and use water from the tank you will eventually leave enough room in the tank for it to start sloshing.  And you are correct: you really don't want to have a half full water tank rocking your trailer from side to side--even with calm winds and no semi's blasting past.

N7SHG_Ham

There is a reason a tanker endorsement is required to pull tank trailers in the CDL world.

Cbusguy

We boondocks/dry camp most of the time.

We always travel with full fresh water tanks and on the trip home our grey and black tanks are various states of full.  I will generally use the water in the fresh tank to flush/fill black tank before we stop at the dump station on the way home.

Occasionally I have felt a surge under braking that I attributed to water in the tanks.  

Plan for it.   First, my vehicle is less at half of it's tow capacity and gross weight.  Second, the trailer is properly balanced and we experience zero sway without a sway bar, full tanks and loaded for the trip.   Use the trailer brakes many people don't bother.    I use them and adjust them every outing.

@N7SHG_Ham There is a pretty big difference between  80,000 pounds of liquid in a semi verse 200-300 mounted low in your trailer.  My 320 with all three tanks full is roughly 250 pounds. 

N7SHG_Ham

@Cbusguy true, but sloshing principals are same and why extra skill is required. It is 80,000 gross, not 80,000 of liquid.

Cbusguy

I think you are over stating the issue in our trailers, for a properly sized tow vehicle..

If you are at or above max max tongue weight or gross vehicle weight all bets are off

ColoradoJon

I, like @Cbusguy, primarily boondock and also travel with full or partially full tanks.  Never had a problem, but then again I tow with a full size truck.  For those towing with smaller vehicles water dynamics while towing might cause unwanted sway characteristics.

Michigan_Mike

I tow with a full size Chevy Silverado and normally carry some fresh water in the 400 tank to allow for hand washing and using the toilet as this saves time in eliminating the need to use rest stop facilities.  I think that water preferences are personal and respect that.  I have towed with a full tank when traveling to remote camping areas and am cognizant of the added weight, but have not experienced any adverse issues as my vehicle can handle the load.  I was actually surprised the last trip out west as my truck bed was jam packed, I had the cab full with belongings and the trailer was in tow and surprisingly my gas mileage was a tad bit better and I drove 1800 miles without any issues to our new home in New Mexico.   

N7SHG_Ham

Weight has a much smaller effect on MPG than winds and speeds, these Tabs are NOT aerodynamic at all despite popular opinion to the contrary. Packing water or not will have minimal impact on MPG. Assuming you have adequate tow vehicle then fill the tank and camp on.

While maybe a personal choice, you can't deny the physics of sloshing fluids in a moving vehicle. Whether it impacts your towing stability is largely depending on if you have a barely adequate or even inadequate tow vehicle vs some safety margin.

Proportionally a small tow vehicle with a tab could get pushed around almost like a big truck with a lot more liquid in a smooth bore tanker. It is more the forward and aft movement of the liquid in a tank truck, can push you right out in an intersection, especially with less than dry pavement when you hit the brakes.

lkc001

I usually tow with full water tanks when leaving home, as the family group always boondocks and there is no water conveniently available.  Also tow it home with either empty water & full gray & black, or some combination thereof.  I do not notice any sloshing issues, I do notice that the trailer is less "bouncy" with a full water tank.  I am also towing with a vehicle rated well above 3,500 tow capacity.  I dump at a small local municipality close to my home, which offers a minimal charge per year for dumping, plus it is a nice, new facility.  I like to take my unit there to dump & really backflush the tanks well.  

Marceline

Some of the clamshell models have a fresh water tank all the way at the back of trailer, very far behind the rear axle. Mine is like this so I travel with my tank pretty empty.