It seems that I am always buying shock cords. That's not really surprising as I have them holding tarps over my boat, log splitter, lawn tractor, and whatever else I want to keep protected from the weather.

The problem is the sunlight, which degrades the elastic portion until it is all frazzled out and has lost its springiness. Before long, the cord is worthless, but being a devoted packrat, I cut the coily metal ends off before throwing the cord portion away.

This Instructable makes use of the left over ends and results in a cord tensioner that really works well. Frequently, you want at least a part of your tarp secured firmly instead of flopping around in the wind; this will do it for you.

Step 1: To Begin With...

As I said, cut the deteriorated cord from the old tie-down and take the two ends off.

Take a piece of 1/4" or whatever size 550 cord you have, of whatever length you need and melt the ends to keep it from fraying out. While it is soft, I mash the ends to make them somewhat pointed.

Make a wooden (although I used a PVC trim board scrap) slide, about 1x3" and drill two holes in it as shown. Use the same size drill bit as the cord; that's why I make the cord ends pointy - so they feed through the holes easier.

Step 2: Construction...

Run one end of the 550 cord through a hole and through the bottom end of the metal hook. Tie a Figure 8 knot in the end to make the size larger and pull it tightly into the spring part of the hook body.

Run the other end throught the block then using one of two methods through the second hook and back through the block, where you tie another Figure 8 knot.

The easiest method of affixing the second hook is to merely run the cord through the bottom and out the top, as shown. The best way is to insert a small eyebolt through the bottom of the hook, run it through a washer, and make it fast with a nylon insert nut. Either way works but the second is best.

Step 3: Putting It to Use...

Use the tensioner as you would a shock cord, one hook through each of two gromets or however it works out for you. Then grab the block and pull it tight.

This project works well and if the cord begins to slack up, just yank it tight again.

{The picture above is misleading because of the seam in my boat's deck but you can figure it out.)