If you have a pool and you live somewhere north of the country's most temperate zones, you no doubt have to close your pool for at least a few months a year. If you like to open it early and close it late, you probably have a solar blanket to help keep the water warmer both early and late in the season. Solar blankets can be difficult to pull off and put on again, though, so if you have this problem, you might want to make a reel to store it.
Use the tape measure to measure the width of your pool and add 1 foot. This will be the width of your tube, which will allow 6 inches on either side for the reels to straddle the sides.
Buy a pair of reels, aluminum tubing and screws. The length of tubing you get should be equal to the measured width above—the pool width plus 1 foot. You should get 4-inch tubing if the pool is more than 20 feet wide, but even if it's less than 20 feet, 4 inches is a good size to prevent the reel from sagging in the middle from the weight of the cover. Another good way to ensure rigidity in the tube is to use three lengths of tubing and fit one inside the other, fastening with screws. The overlapping tube sections will help reinforce each other and act to prevent sagging. Another advantage of using three tubes is that you can adjust the size of the assembly more easily—without cutting—by sliding the tubes apart as far as necessary. Of course, if you're going to fit one or more tubes inside another, the inside tube will have to be about 1/8 inch smaller in diameter (3-7/8 inches vs. 4 inches, for example). Finally, you'll also need straps to attach the blanket to the reel. It's probably best just to buy a universal strap kit at your local pool store or on the internet. They come complete with straps, grommets and all the other hardware needed to secure the blanket.
If the aluminum tubing is a single piece, fasten it to the reels to finish the assembly. This can be accomplished by simply drilling one or two holes in the tubing and, after inserting the tubing into the receptacle in the middle of the reel, screwing the screws into place tightly. If you have three tubes, you'll also need to secure the tubes together at the ends of both the inside and outside tubes. Drill three holes 1 inch from the ends of each tube equidistant around the circumference of the tube and corresponding holes in the adjoining tube where the screws at the end of the tube being joined will meet the middle of the adjoining tube. You will therefore need 14 to 16 screws: 12 to join the tubes and one or two for each end of the tube where it attaches to the reels.
Attach the blanket by drilling the required number of holes in the tubing, which should be about one strap for every foot inside the reels, and screwing the grommet end of the strap into the tubing. Then use the blanket end of the strap, which should come equipped to punch through the blanket, and secure it in place. You'll need one screw for each strap to attach it to the tube. Once you've finished, the blanket will be attached in enough locations that when you reel the reel in, the blanket will follow and wrap around the tubing for storage when it's not in the water.