Automatic pool covers, thoughts?

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Covers designed to hold a snow load actually sit on top of the water. A tarp with water bags rests on the water all the time its on the pool. A spring anchored safety cover is designed to flex enough with a snow load to sit on top of the water.
An auto cover mounted on rails isn't designed to flex and rest on the water. With any weight of a snow load, it would most likely collapse under the weight.
 
If you look at the pictures of the CoverPools cover, it sits very low to the water and the great majority of the cover rests directly on the water. They also say to not lower the water level in the winter. I presume that they say that so that the water will continue to support the cover during the winter. As long as you leave the water high so the cover can rest on the water, it should be able to handle snow loading just fine. You might have other problems with the water level being high, but the cover will be fine.
 
Jason,
I cant agree with you on that at all. Even with the water level fairly high, a heavy load will displace the water enough to pull that cover far enough down where the tracks will bend and buckle. At the very least, it would probably warp it enough to make it unusable. I know a couple of people up here that have auto covers and the installers told them under no circumstances let it go over the winter. They just arent designed to hold the weight, period. On a 500 sq ft pool with a 10-1 water to snow ratio, you have close to 10,000 pounds on the cover. With no springs to give, I wouldn't chance ruining a 5k cover.
 
A top track can look like that shown in this link at Pool Covers, Inc. where the rolled up cover goes into a bench.

As for the weight issue, I know that my pool cover (from Pool Covers, Inc., but an undertrack cover) can hold the weight of several people standing on the cover -- after all, that is why it is a safety cover. My pool builder remarked how one of his daughters had a sleepover on the pool cover -- again, not recommended, but it demonstrates that they don't collapse easily. If the weight is evenly distributed, it is less of an issue for puncture or local stretching and also less of an issue at the edges as well. Yes, the weight does displace some water. Though snow varies in density, some has one foot of snow being around 1-2 inches of rain equivalent. At 2 inches that is a weight of 711 pounds [EDIT] WRONG! It's really 5317 pounds [EDIT] over a 16' x 32' area or 1.4 pounds per square foot [EDIT] WRONG! It's really 10.4 pounds per square foot [EDIT] which isn't very much. In terms of force along the side, assuming 32' tracks, that's about 11 pounds per foot of track (roughly 1 pound per inch) [EDIT] WRONG! It's really 83 pounds per foot of track (roughly 7 pounds per inch) which is quite high [END-EDIT]. This probably is not enough to tear/stretch, though again wouldn't be normally recommended. However, we really need to look at the buoyancy effect. [EDIT] WRONG! So buoyancy effects must be significant and I calculate those in this post below. [END-EDIT]

The buoyancy effect of the water is equal to the weight of the water displaced so basically if you have slack in the cover, as they almost always do, then 1-2" of rain (or equivalent weight of snow) has the water level rise on the sides to match the height of water on the cover and the cover sinks by a relatively small amount such that there is probably no tension at all on the sides so long as there was enough slack to begin with.

The pool cover people said to use a pool cover pump to remove rain off of the cover, but it's not a disaster if I don't and the rain overflows after rising to around 1" or so.
 
chem geek said:
At 2 inches that is a weight of 711 pounds over a 16' x 32' area or 1.4 pounds per square foot which isn't very much. .
Click to expand...

Can you show your work?

For 22 inches of snow at 10-1 water to snow, that's 2.2 inches of water. For a 20x41 pool, thats 820 sq feet of surface area. So at 2.2 inches of water, that would occupy 150 cubic feet. There is 7.4 gallons in a cubic foot, and a gallon of water weighs 8.3 pounds. Thats a total of ~9400 pounds on the cover or 11 pounds per sq foot. If no water was drained and the cover set right on the water, it would still displace enough water to cause significant stress on the rails, IMO
But, this would not be a real world situation. In feeze/snow areas, if you dont drain the water at least a foot, the ice will pop the tiles off the pool at the water line. If you have no tile,theres still an issue in that ice would still build up enough to potentially pop the coping off the beam if you have an edge that hangs over the water.
I still maintain that an autocover is not designed to carry a winter snow load. If it didnt collapse the fisrt few snows, over time the entire assembly would become loose i suspect and you would have problems. At $5000 + for an auto cover, i wouldnt take the risk.


If someone in snow country has one and has no issues with a couple feet of snow on it, let me know and i'll stand corrected. :wink:
 
Interesting.......I will shoot a photo of my pool here in Indiana as it sits today. It will be sometime later when I arrive back at the house, but I can assure you that my CoverStar is holding up about 12-15" of snow just fine. As a matter of fact, I emailed my pool builder after reading this topic yesterday and he told me there was no any issue at all. He has been building pools for 25+ years and Autocovers since they were initially marketed.

I will attach a photo later tonight.....

Brian
 
One last note.....I did have 3" of water over the entire surface of the cover last summer. We received an enormous amount of rain in a short period of time and my cover pump was not placed on the pool. Again, there was no damage.

Jason is correct, we cannot let any water out of our pool in the winter. I maintain the same water level year round and as Jason referenced, the water is supporting what is on the cover. If someone walks on the cover, that displacement is directly under their feet and it does put stress on the cover. But as the water or snow falls on the cover, the weight is distributed evenly and supported by the water.
 
hardwareguy said:
I maintain the same water level year round and as Jason referenced, .
Click to expand...

Well, I guess I stand corrected then; it is possible not ruin one. I dont think we could get away with not lowering the water level up here. If we kept the water high enough so that 2-3 feet of snow would float without damaging the cover, the ice would do more damage to the pool. Trade off I guess. :?
 

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bk406 said:
chem geek said:
At 2 inches that is a weight of 711 pounds over a 16' x 32' area or 1.4 pounds per square foot which isn't very much. .
Click to expand...

Can you show your work?
Click to expand...
I made a mistake since I forgot to convert cubic feet into gallons before using 8.33 pounds per gallon. So your number is correct and for my example 2 inches is a weight of 5317 gallons or 10.4 pounds per square foot (I've edited/corrected my earlier post). That does sound like a lot more, but apparently the buoyancy effect must help out a lot. So if your water level is too low, then the cover won't hold much water at all without having problems. However, with a sufficient water level and enough slack, it won't be a problem.

Obviously, if the slack were 4" so 2" on each side then this clearly works with no stress whatsoever as the cover is in a U shape flat over the pool water and then turning up at the sides 90 degrees. The question is what happens with the more usual slack of around 1-1/2 to 2" (for an undertrack like mine; an overtrack would have more slack so that the cover was mostly on the water). The cover will go at a diagonal to the water and then be flat. In my own pool, I'd say that the cover is "on" the water within 2 feet from each edge, but with extra slack (i.e. not taut). If taut, then perhaps it's around 1 foot from each edge. So the question is how much the cover level drops when 2" of water is on top. The answer is it drops such that the pool water underneath on the sides rises to meet the 2" higher level. Assuming the 16' width with 1' on each side not touching the water initially, this is found as follows:

If "x" is the number of inches the water in the pool drops due to the cover with water on top of it while "y" is the rise in the pool water level at the sides where the cover is off the pool, then
x*14 = y*2 since the water displaced in the middle must equal that which rose at the sides
Old + 2 - x = Old + y since the level of water on the cover must equal the level at the sides

x*14 = (2-x)*2 so 16*x = 2 so x = 1/8" which means that y = 2" - 1/8" = 1-7/8"

So even ignoring the angled entry of the cover to the pool, a drop of 1/8" would at most require a slack of 1/4". So the felt weight of the water on the cover will only be that amount where the cover is not touching the water so only at some inches near the side and even then there won't be 2" of water on top since the cover will angle upwards there. I think one doesn't get serious tension until one uses up the slack completely.

By the way, when one walks out onto the cover it becomes fairly taught in the width area where you are walking, but that is because the displaced water is rising evenly throughout the pool (except where you are stepping) while your weight displacement is very localized so you use up much of the slack where you step and miss out on the overall buoyancy effect. This is not the case for rain or snow on the cover assuming it is fairly evenly distributed.
 
I get lost in your theory sometimes. But be that as it may, in all practicality:

1) the water level should be dropped lower than that of a functional pool in the winter time in areas that freeze and recieve lots of snow

2) I would not recommend using an auto cover as a winter cover in areas tthat recieve lots of snow

Beyond that, I suppose folks can do as they wish. As I said before, i wouldnt chance ruining a 5k+ cover when its just as easy to use a tarp or proper winter cover.
 
Many people use automatic covers as their winter cover. They work just fine in the winter as long as the cover has been designed for use as a winter cover, the pool is designed to allow the water level to remain high during the winter, the cover is installed correctly, and the pool is correctly winterized. None of that is especially common but none of it is particularly difficult either. There is no more risk with a properly done automatic cover than there would be for any other pool with any other kind of cover.

It is certainly much simpler to use an automatic cover than it is to use any other kind of cover, both during swim season and during the winter. Installing, removing, cleaning and storing a conventional winter cover are a couple of non-trivial projects that are almost completely eliminated by an automatic cover. You do have to pay thousands of dollars extra for that convenience, which some people are more than happy to do.
 
Not too mention it isn't a 5k cover, that is the entire cost of all the moving parts and install. The cover is not much more than the cost of a winter cover in m2 terms. Some good points raised though about winter water levels and certainly something to consider before making my decision on which one to purchase
 

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