I wanted to build a magnetic retrieval tool to recover ferrous objects underwater.  I tried various "fishing magnets" but most of those don't work very well.  They are simply not powerful enough.  Or too heavy to repeatedly cast into the water.  So I came up with a magnetic drag bar.  Pictured is a stainless steel knife retrieved from Mobile Bay on July 4, 2013 using the tool.

Step 1: Materials Needed

Materials Needed
550 paracord.
  50 ft length and rated at 100 lbs.  Available at local big box hardware store for about $4
Magnets. Two kinds are used in my project.  I salvaged the kidney bean shaped magnets from disassembled hard drives work was sending to the shredder.  "Free" other than the time to pull them.  I'm guessing 5 lb pull.  To augment, I ordered 12 additional ones from KJ Magnetics (part number: DX01-N52).  1 inch diameter, rated at 8.5 lbs pull.  Figure $35 - $40 shipped if you can find a coupon code or not.
Metal bar stock (steel or aluminum).  For $8, I got a 1/8 inch thick, 2 inch wide by 36 inch long steel bar from local big box hardware store.  I choose steel.  However, there's some good arguments for using aluminum underwater.
Newspaper. For painting on.  Pick up a store advertisement flyer.
Sandpaper - laying around from another project.  New say $4
Spraypaint - laying around from another project.  New say $7.
WaterWeld.  By the makers of JB Weld, it's a two part adhesive designed for use in and under water.  that one can use to glue metals together so it'll hold in a submerged environment.  Available at local big box hardware store.  Ask a store associate as it's not consistent as to which dept  (plumbing, or near the tape) even at the same name brand store in the same town.  $6

Material cost:  $64
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