Sep 15, 2019
Guest Author

Tips for underwater metal detecting for treasure hunting and archaeology

Tips for underwater metal detecting

Metal detecting is an amazing hobby. It helps us unearth many relics and know more about the history of our ancestors. Many want to take it to the next level and hunt underwater treasures. In this article, I will give a few tips that will help in your next diving adventure.

Do your homework

Before going for a hunt, you need to do some research and look for promising locations to increase your chances of finding something precious. This is especially important for shipwreck diving.

You have to gather as much information as you can about the ship. This includes the departure and arrival ports, the cargo and its trajectory. This type of diving is very difficult, needs experienced divers and a lot of expensive equipment. However, if you were lucky and found a Spanish shipwreck full of gold, you are going to be rich, very rich!

Pick the right metal detector

To pick the right metal detector you have to take into consideration the depth you want to dive to and whether the water is salt or fresh. There are two types of metal detectors: VLF and PI. Each one of them has its pros and cons.

Technology type

VLF (very low frequency): the crashing majority of the devices on the market are VLF. Their operational frequency ranges from 4 to 30 kHz. They are very good at distinguishing between different metal types; this will save the diver a lot of time. He will know what type of metal is buried under the sand before even digging it.

If the machine indicates that the buried item is, for example, gold, he will (obviously) dig it. If not, he keeps looking for other interesting targets.

The problem is that this type of detectors isn’t suitable for saltwater. The mineralization will hinder its performance and it will emit many false signals making it useless. So it is recommended to use them only in freshwater.

The PI (pulse induction): is suitable for scuba diving in saltwater and can perform well when used with salt wet sand. The minerals don’t affect its depth range. Their downside is that they can’t discriminate; they will beep whenever they detect a metal. In this case, the diver has to dig in order to find out what is buried underneath the sand.

Operational depth

If you want to hunt shallow creeks and ponds, any metal detector (even cheap entry-level ones) can do the job. They can be submerged up to the control box.

If you want to go a little deeper (snorkeling), then you need a waterproof metal detector. You can get a reasonably priced device that can run up to 10 feet underwater. They are usually VLF machines. So they are suitable for freshwater.

If you are a professional scuba diver, then you need an underwater detector that can operate up to 200 feet. These are very expensive and meant for professional use.

Use the right accessories

In addition to the appropriate scuba diving equipment and to the metal detector, there are some tools that can make your hunt easier.

You can dig many targets with your hands but a sand scoop will make things easier and faster. It is recommended you choose a scoop with a wooden handle to reduce the weight.

You also need a pinpointer, which is a mini handheld detector with a limited range.

Metal detectors have onboard speakers. If you want more comfort, you can use waterproof headphones.

Maintain them in a good shape

Before going for a dive make sure there are no cracks in your devices. Check the O-rings frequently. Ensure they are in good shape and sand-free. Then lubricate them with silicone grease.

Use the right technique

It depends on the detector type. VLFs are motion detectors, you need to swing the coil from side to side in order to detect something. PIs are static detectors, they can detect metals even if they are motionless.

If you’re hunting shallow waters, relax and let the currents move you back and forth. Focus on low spots and around the rocks and scan them multiple times with your detector. The goodies are usually there.

Practice and practice more

Treasure hunting underwater is a lot more difficult than on land. Being a professional detectorist isn’t enough. You need to get sufficient training from professional divers. You can find many schools where you can get your diving certificate.

The same applies to divers who never used a metal detector. You need to learn how to use your device before going for a dive. This includes doing some air testing. This means passing some metal object in front of the search coil back and forth to get used the audio signals emitted by your machine. You need to read the user’s manual carefully and play with the settings to get used to them. I highly recommend that divers collaborate with detectorists to exchange skills.

About the Author

Rob Green is passionate about metal detecting, history, and archeology. He is also interested in shipwreck diving. You can follow him on his blog where you can find many tips and tricks about this hobby.

Seagrass Dive 2 31-08-2015

After checking the weather and tides, and the fact we were still going to be diving on lows we decided to go back to the same beach for the last dive of the weekend for another scan over the area for Seagrass (I think Elli was humouring me). The North coast was out anyway and we had to get the kit back to Seaways in Falmouth, and then to the Train Station in St Austell after lunch so Elli could go back to the hum-drum of London life. We were glad we did by the end of the dive, but my second biggest lesson was learnt for diving and equipment today, apologies for the long post.


We kitted up and headed down the beach, again Elli was towing the DSMB as I had my camera, after we had descended Elli was having difficulty with the reel, it had become caught, so we surfaced and untangled the line from around the reel as the vis wasn’t great that close to the shore. Then we prepared to descend again, and as I always do I went to hold my camera, even though we were only descending in about 2-2.5m, it was then I noticed my camera had become un-clipped and I only had the £16 extendable clip attached to my BCD that most dive shops sell hanging there. As this was my 40th birthday present a couple of years ago you can imagine my reaction, and Elli and I started scanning the bottom and surface for my camera, after a 10 minute look and no joy I walked back up the beach defeated and gutted, it was then that I looked at the clip, it wasn’t bent or broken and must have got caught, un-clipping itself from the housing.




As you can see from the photos there is nothing visibly wrong with the cable or clip, it even feels OK for the tension in the safety part of the clip, so this is just down to bad luck with it getting caught and un-clipped somehow, with the weight of the wet lens I had a feeling it would sink but wasn’t totally sure. I turned around and realised where I now stood  at the head of the beach was the same spot I started at a little earlier, grabbed my mask and fins and headed back down the beach along the same path we had taken, as I got out to roughly where we were when we dropped down, I looked down and saw it sat on the bottom, relieved doesn’t describe it and after shouting to Elli I had found it as she had waited patiently for me to get back in the water to look, I dropped down to pick it up, as I was coming back up I saw there was no water in the housing after its short drop and gentle rolling in the swell, am so glad we were on a shore dive.

Some may take from this to check their clips, and I would agree (rinse them properly, and vaseline them if needed, check them for damage or any looseness in the safety features of the clips), but more importantly I would say to check your reel, I am only a novice diver but if that had happened at depth Elli would have been dragged to the surface and I am mortified it got tangled so easily, and yes mortified that the clip came undone, nearly losing my camera. I’m still learning every dive but when I see other divers, the kit we use, such as reels, seem to be used for all depths (as is mine), but while it is extra cost, I think a reel for shallower dives is needed for me; around the coast of Cornwall the shore dives are generally around 8-15m and I am only qualified to 30m anyway, so I am going to be setting up reels for 15m and 30m (or just over), and keeping the one I have now set up as is (which is 50m). This just makes sense to me, not for the dive, but after when it comes to unreeling the line to rinse and dry it properly, stopping salt from building up in the line causing it to stick together, and then get tangled as happened to mine. I have also looked more closely at what I have around the D-ring on my BCD, as well as where the camera hangs when I am upright in the water and moved/removed, and secured more suitably anything that may cause it to become un-clipped again (I hope).

So back to the dive, after a few minutes sorting things out, we decided to carry on with the hunt for Seagrass, I had my hand stuck to my camera and it was back on the clip, Elli signaled she was good to go, and off we went dropping down into about 2 1/2m onto the sandy floor. After heading straight out from the beach for about a minute, Elli was waving at me and pointing down excitedly as us divers do, I went over with my best Starsky and Hutch head on to investigate as all I could see was organic debris floating by.

Pipe Fish

I’m not sure if this was a Lesser Pipefish (Syngnathus rostellatus)  because of the fan tail it had, or the same kind of fish as the 15 Spined Stickleback (Spinachia Spinachia) with the weird luminescent nest I had seen at Newquay before but it was a cool little critter, and a sign of things to come.

Pipe Fish

There was a lot of Hermit Crabs running around again but with over 15 species around the UK, I won’t be trying to identify them just yet.

Hermit Crab

We went straight out from the beach for about 25 minutes, the gentle current chasing the low carried us out and we only needed to kick  occasionally. Some people say going out over the sandy bays is boring as you don’t see much, the safe reefs to dive have a variety of life, but there is a large coastline around the South West (of the UK) and exploring it is half the fun of diving, even if you don’t see a lot as each dive is different.

Sandy seascape

On the way out we saw a few crabs which had picked up the scent of a dead Razor Shell and were heading toward it.

Slipper Crab


Razor shell

It was fairly large as well, would have been great to wait and take some pics of them feeding but time (and air) was getting on and after a near canceled dive, it was getting really interesting.

Sea Urchin

Elli found a dead Sea Urchin shell, it was in perfect condition so she put it in her pocket, as you do. Then as we were turning around we saw another crab mating (am pretty sure that is the male on the back) buried in the sand.


As we were heading back the battery light started flashing on my camera and then it switched off, after about 10 minutes, and lots more crabs, a flounder (the fish that got away) all not getting photographed, I tried to turn it on again as I saw Elli point at a rather large Crab and then she looked up and I saw her eyes light up, she raised her arm and pointed and as I looked to my right I suddenly saw what had caught her eye (as I had been staring at the camera, praying it would turn on for the Crab), a Barrel Jellyfish (Rhizostoma Pulmo) right in front of us.

Barrel Jellyfish

Barrel Jellyfish

Then the camera battery died again and I had just noticed a Cuttlefish stalking the Crab, I tried to slowly grab Elli to stop her moving toward it but was too late, it was gone and the cheap UK based ebay battery had drained. Elli grabbed my arm and frantically pointed again, so I crossed my fingers and pressed the on button, I looked across and managed to capture this shot of the snail Elli was pointing at before the camera turned straight off again, I didn’t try turning it back on and we headed back the last 10m or so to the beach.

Sea snail

When we were sorting the kit out at the car after, Elli pulled the Sea Urchin shell (dead, or empty in case you had forgotten) out of her BCD pocket, it hadn’t survived the short journey and had been crushed, was gutted for Elli as would have made a great memento. It was one of those really nice dives, even after a horrible start to it, and like last year it was a pleasure to dive with Elli, but please don’t go sticking your head down holes in warmer countries.

Elli met Lenny over the weekend and like everyone, fell in love with him, I had to stop her sneaking him out in her bag when we left for the train station, maybe next time.

Elli and Lenny

Sep 30, 2015

Seagrass Search Dive 1 31-08-2015

Elli and I were stuck as to where to dive next and had been to St Agnes and Newquay on the North coast but it was a bit choppy so we headed to the South coast and decided a nice easy dive at one of the secret little spots where it is almost always flat. It started out as just another dive, but we found Seagrass in the surf as we were walking out and decided to swim straight out, instead of following the reef round as I have done so many times before and it was on, a hunt to see if there was a Seagrass bed in the small bay.


We had done our buddy check on the beach and made our way into the water, it may seem daft to some to change the dive plan on entry, and normally at most other dive sites I would agree, yet we had near perfect conditions with no surf or surge, clear skies and a mass of sandy bay that we hadn’t explored before in front of us with a max depth of about 7m at low tide, the only concern was the vis. As I had my camera, Elli was towing the DSMB, we donned our fins, looked at each other to make sure we were OK and headed off, as we started to go down it was clear the vis wasn’t going to be great yet we were pleasantly surprised as to how patchy the areas of bad vis were and it was 5-8m in most places, there were tracks of higher particulate in some areas that were easy to spot and either avoid or move quickly through and the channels in the sand created by the currents gave us advanced warning of where those areas were.

So we bimbled along, never more than 3m apart and as most of you know there wasn’t a huge amount of life, well there would have been but it was hiding in the shallow water or out with the tide and waiting for it to turn with the large amount of food it would bring back in. One thing I noticed was the number of Lesser Weaver fish there were, seeing them dart from our path and bury themselves again made me glad this was too deep for land lubbers to stand, and as always there was a huge amount of Hermit Crabs that are common all over the Cornish coastline,they are actually quite interesting to watch, and it was a shame that a lot of my pics didn’t come out as well because we came across 3 fighting over homes, one had already left its home and was in the process of pulling a larger Crab out of his, they look very strange out of their shells and if you have ever accidentally stood on a snail would get the idea.

Hermit Crab

We were bimbling around for ages, heading straight out from the beach and apart from the odd bit of Seagrass floating freely in the current there was nothing on that dive, have to say I was gutted and we started to head back in, we saw more and more Hermit Crabs but not much else which was gutting, but then all of a sudden, and literally 20m or so from the beach, we were surrounded by silver flashes, now the pics aren’t very good, but it was my first shoal to be properly surrounded by, and no it wasn’t as impressive as a Sardine run but it was still awesome as they went round and round us as if they were taunting us and thinking we were Seals. My head was darting side to side and I was spinning over to keep track of them (like you do) and with poor lighting (the sun had gone behind clouds) this was the best of the pics, and I’m glad I didn’t get whiplash.

Fish shoal

So it was another dive down for Elli and while we didn’t see much life was worth it to cross the bay off the list of places to explore, something I have wanted to do for a long time and my Seagrass bed sightings are still limited to Swanpool down in Falmouth (and no Seahorses).