A few of the guys at K&J Magnetics have gone fishing; magnet fishing, that is! Join us as we try using magnets to grab metal objects hidden underwater.

What’s magnet fishing?

At left, an MMS-C magnet screwed onto an MMS-D magnet, with the rope tied in between. At right, a single MMS-G magnet.

Magnet fishing uses a strong magnet to try and grab ferrous metal objects that are hidden or lost underwater. If you want to try grabbing something lost on the bottom of a lake, pond, or river, a magnet on a rope might do the trick.

What magnets should be used? As mentioned in our article about Mounting Magnets, many of our customers have reported success using strong Mounting Magnets. They are durable, and you can easily tie them onto the end of a rope.

Our MMS-G magnets are popular, with an eye-hook for attaching a rope or cable. Some of our customers have reported good results using an MMS-C and MMS-D magnet screwed together, with the rope/cable/cord tied on the space between them. The idea is that this combination might be more likely to catch onto an object below the water’s surface.

For long term underwater use, consider Plastic Coated Magnets for a waterproof solution.

What magnets did K&J use for this fishing trip?

Three incredibly powerful, 3" diameter MMS-B-Z0 magnets, bolted to an aluminum extrusion. This strength is probably too much for magnet fishing.

We picked 2” diameter MMS-C-Y0 and MMS-D-Y0 magnets, and screwed one to the other. Then we tied a rope between them. Make sure you torque the two magnets tightly together. If they come unscrewed underwater, the rope won’t hold them!

Not satisfied with this, we figured that we should show up at the lake with some bigger, stronger magnets that would be ridiculously strong. For the monster magnet picker-upper, we bolted three MMS-B-Z0 magnets across a length of aluminum extrusion, and tied that to our rope. This setup is a lot more powerful, so we did worry about it getting attached to something that would exceed our ability to pull up with a rope.

This setup is more poweful than you really want for magnet fishing. We don't recommend it. We only used it here in the spirit of so many TV shows and blog articles that go over the top with extra strength. It's like the Mythbusters guys blowing stuff up at the end, simply because they can. If we had accidentally stuck these magnets to the steel frame of a dock, the magnets might still be there now. Choose magnets that you'll be able to pull free with your rope!

From the dock

Magnet Fishing! The steel bottle opener sticks firmly to the magnet.

We started our tests from a dock at a local lake. To make sure we would have at least one successful “find,” we tossed a steel bottle opener into shallow water near the dock.

With the MMS-C-Y0 and MMS-D-Y0 magnets secured to the end of a rope, we tossed the magnets in hoping to grab the opener. These magnets are strong, or we’re lucky, because we were able to grab the opener easily on the first toss. It works!

Granted, this was in shallow water. On such a sunny day, we could see the opener lying on the bottom. Still, it’s proof that magnets like these are a handy way to pick up a dropped object.

Next, we tossed the bigger magnets off the end of the dock, searching for whatever we could find. On one of our first throws, we captured a big pipe elbow and a large fishing hook. The heavy, rusty pipe was an easy grab for the powerful magnets. A few snails nestled inside the pipe came along for the ride.

A 45° pipe elbow and large fishing hook stuck to the magnets.

From a boat

A socket once dropped by a sad boat mechanic, found by guys with a magnet on a string.

To cover more distance, we set out in kayaks to drag the magnets across more lake-bottom. With the magnets dangling on 50+ feet of rope, we went hunting for treasure on the bottom of the lake.

The experience wasn’t completely problem-free. When going by a rocky area, the magnet and rope sometimes got caught in the rocks. In a kayak, it was easy to back up and go yank the magnet out. In a motorboat, we might have simply broken the rope.

There’s lots of stuff sitting on a lake bottom that could trap a magnet on a rope. Be careful, but also be prepared to lose a magnet.

Most of what we found in our limited, 2-hour fishing trip was closer in towards shore. Near the marina, we found a socket that must have been dropped by an unfortunate boat mechanic some time ago.

Perhaps our most interesting find was something that we were not able to pull up. We located something strong using the smaller mounting magnets. When we pulled slowly up on the rope, the magnets broke free. The magnetic hold wasn’t strong enough to pull the object up.

The object appeared fixed on the bottom. We could find it repeatedly using the magnets. We tried to pull it up using the big 3” magnets, as shown towards the end of the video below. The magnets grabbed onto it well, but still were not strong enough to retrieve the object.

What was that thing? It could have been a boat anchor, firmly wedged into the gunk on the bottom. Our guess was a steel cable strung across the bottom of the lake. It was near some docks, so maybe the cable had something to do with those.

The pull of the magnets wasn’t strong enough to pull the object loose from the bottom. Remember, the pull force you get from a magnet depends on what you’re sticking it to. A powerful MMS-B-Z0 magnet can pull with hundreds of pounds of force when sticking to a solid steel surface (like the one that holds up a person in this video). If the steel object is smaller, though, the force could be a lot less. You won’t see 300 lb of force from the magnet to a paperclip.

What we learned while magnet fishing

Like treasure hunting with a metal detector, magnet fishing is not for the impatient. It’s a big lake and a small magnet, so you might not find much very quickly.

We also learned that there's lots of iron junk on the bottom of a lake! Rusted bits of metal, steel cable, and many rocks that contain iron often stick to the magnets. Periodically, we scraped off iron-bearing dirt and rocks from the magnets. If you’re going magnet fishing, bring a pair of sturdy work gloves to scrape the mess off without cutting yourself on something rusty.

It's not easy to scrape magnetic gunk off the powerful magnets...

Why would anyone want to do this?

The magnet fishers we hear from seem to fall into two groups: Treasure Hunters and Tool Droppers.

Treasure Hunters hope to find interesting things. Sometimes the found objects can be historically interesting. Rarely, something valuable might be found. While some trips might not find anything of interest, it’s still a good excuse to go sit by the water for a while.

Tool Droppers are after objects that haven’t been in the water quite so long. Maybe that boat mechanic would have liked to pick up his dropped socket. With a strong magnet and a little rope, that 15 feet of water isn’t a problem.

Naturally, we don’t think a toolbox is complete without a magnet or two in it. We always have a few magnets in our toolboxes. We are continually surprised at how often a small, powerful magnet comes in handy. Popular magnets to stash in the toolbox include the D68PC-RB (for identifying poles), the D6C (for magnetizing screwdrivers and other stuff), the TT-8 telescoping pickup tool and of course a single MMS-G-X8 or MMS-G-Y0 if you plan on going magnet fishing soon.

Good luck fishing!