What is the best way to anchor a swim raft at the cottage?
Use 3/8″ steel chain instead of rope. It won’t deteriorate anytime soon, plus it will add some useful weight. As for the anchors, you’ll need some seriously heavy ones: each submerged anchor loses about one-third of its weight in the water. Don’t use concrete-filled tires, though—that’s an old approach we no longer recommend. The science isn’t conclusive, but tires may leach harmful chemicals into the water overtime. Tire-shaped forms, like the ones made by Techstar, are easy to roll around and weigh about 110 kg when you fill them with concrete. For a cheap, 45 kg DIY option, you can fill 19 L plastic storage pails with concrete. While the concrete is still wet, insert steel hooks into it to attach the chains. Make a bend in the shaft of each hook before inserting it, so it can’t be pulled out once the concrete dries.
If you know your raft’s approximate weight, you’ll know how many of these anchors you have to make – probably no more than four, with one for each corner. Be sure to cross-chain them: Criss-cross each pair of chains so that each corner is linked to the anchor under the adjacent corner. The chains should run at about 45° angles to the raft. If your raft still has a case of wanderlust, you can always add more anchors at each corner.