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. Instead of using concrete blocks, make your own. Lay some polyethylene sheeting down on a flat surface, get some used 14″ tires and fill them (the tire insides and the centres) 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. The resulting anchors should weigh about 115 kilograms each, but because they’re tires, they can easily be moved via tilting and rolling.
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.