The Essential Guide to Underwater Metal Detectors

Historically, underwater metal detectors are responsible for some of the biggest and most famous treasures ever found.  The Atocha spanish ship wreck for example had 24 tons of silver and 125 gold bars on board when it sank in 1622. The Atocha was found by a guy named Mel Fisher more than 300 years later in 1985 with his underwater metal detector. That treasure today would be worth about US$1Billion and there are even bigger treasures still out there!

Modern treasure found with an underwater metal detector (By Author)

You’ll be glad to know that modern beach and underwater detectors have come a long way since 1985. They are now deeper seeking, light weight, powerful and affordable all at the same time meaning treasure hunting has become possible for everyone!

Today, underwater metal detectors are used by everyday people and professionals to search for lost coins, jewellery, artefacts, phones, cameras, watches and of course treasure troves in creeks, rivers, oceans and old swimming holes to name a few.

In this article, we’ve compiled everything you need to know about underwater metal detectors! With thousands of hours racked up metal detecting underwater, using a range of different detectors we have some great insights to share and hope it will help you on your treasure hunting journey.

Forget what you might have heard in the past, and read on to find out about detectors that will help you find treasures below the waterline!

Waterproof VS Underwater Metal Detectors

Many people think that any ‘waterproof metal detector’ would make a suitable ‘underwater metal detector’ however, this isn’t the case and we’ll explain why now. In some cases these ‘waterproof’ detectors are simply rain proof, can be washed down, or handle the occasional dunking… but these are not the kind of detectors we are here to talk about today. A dedicated underwater metal detector is one that will give you a serious shot at finding coins, rings and treasure in a variety of underwater conditions and will stand the test of time.

There are actually a few very unique characteristics that set underwater metal detectors apart from everyday waterproof detectors! These special attributes are why true underwater detectors work well in both saltwater and freshwater environments, from depths of just a few feet to a few hundred feet. It’s also why they are responsible for finding more treasure than any other type of metal detector in the world.

A weekend of PulseDive treasure, read our PulseDive review here and check out some footage of the PulseDive in action here

Types of Underwater Metal Detectors

Undeniably, the most important characteristic of a good beach or underwater metal detector is its ability to see through salt water as if it wasn’t there.  To the surprise of many new detectorists, salt water at the beach is one of the most difficult obstacles to overcome when beach and underwater detecting. Why? Because saltwater, just like metal, is electrically conductive with the result being that many metal detectors will actually start reacting when in or even near salt water. This is because they’re detecting the conductive salt water just like they detect conductive metal of all kinds!  

The amount of stories you read about people discovering that their brand new detector won't work at the beach is incredible! Therefore we recommend you pay close attention when looking for a beach and underwater metal detector.  If your detector is randomly beeping (falsing) and making a host of other unpredictable noises in saltwater, it's a sure sign that it's either; not set up optimally for saltwater detecting or isn't well suited for it.

The best underwater metal detectors employ one of two types of specialised circuitry that ignores the signals given off by salt water, they do this whilst still giving great detection depth on coins and rings and providing sensitivity to smaller targets like earrings and gold chains.  

Underwater metal detectors generally do this without the user having to tweak many settings making them very easy to use.  It is worth noting however that even the best saltwater metal detectors will lose some depth and sensitivity over wet salty sand and then lose a bit more when fully submerged in saltwater.

The two best underwater metal detector types:

• “Pulse Induction” (PulseDive, Seahunter and high end gold detectors)
  
  
• “Multi-Frequency VLF” (Excalibur, Equinox etc)

Both Pulse Induction and Multi-Frequency metal detectors can completely cancel out the noises from salt signals and make underwater metal detecting a lot easier. 

Author, Ed coming up for air - using a Pulse Induction Metal Detector.

How Waterproof should Underwater Metal Detectors be?

If you want to find underwater treasure like the pros, you will need a true underwater metal detector with a deep waterproof rating.  Underwater metal detectors like the PulseDive, Seahunter or Excalibur for example have waterproof ratings to 60m deep (or 200ft).  This 200ft rating certainly sounds like overkill considering most of us aren't going any deeper than 3m with our detectors, but the reality of underwater metal detecting is that the higher the depth rating, the higher level of reliability you’ll enjoy in an underwater environment, over a long period of time.

A depth of 60m underwater is a lot further than most professionals are likely to go, especially when you think that most people swimming at beaches only swim out to an area with about 3m in depth tops. Now, of course the detector manufacturers are very aware of this fact, but the reason they make detectors with these excessive ratings is a very good one. Underwater metal detecting - due to its nature - puts a lot of more stress on all the components compared to other waterproof devices like watches or cameras, making water ingress more likely.

It is possible to use waterproof metal detectors with a lesser rating of 3m+ for some underwater detecting, however the real intention for this type of waterproofing is for the occasional dunk and so that rogue waves aren't liable to drown your metal detector!

For long use underwater, we do recommend a metal detector with a higher waterproof rating like 60m (200ft), in the end it’ll last you a lot longer, be much more reliable and you won’t get caught out without a working detector on your next day out treasure hunting.

 Coins and lead found while snorkelling with an underwater metal detector.

How do you hear an Underwater Metal Detector?

Extremely important for underwater metal detecting or detecting in general is the ability to hear the detector when it detects a target! Most metal detectors have a loudspeaker built in with the option of wired or wireless headphones for when you don’t need the rest of the world to hear. Underwater metal detectors have special ways of doing this, which we’ll explain below.

Most run of the mill waterproof metal detectors have a waterproof speaker built in, these waterproof speakers are simply to stop water getting in and to the surprise of many they are not suitable for operation underwater!  Those types of waterproof detectors require you to buy separate waterproof headphones for them if you want to use them underwater, however most dedicated underwater metal detectors include specialised headphones or have other ways of alerting the user when it finds a target.

For example, underwater metal detectors such as the Excalibur and Seahunter have wired, fully waterproof headphones which use ‘piezo transducers’ instead of normal speakers in the ear cups, these types of headphones are not affected by the effects of deep water and will not be crushed by water pressure at depth.  The volume from these types of underwater headphones is good underwater and aren’t negatively affected by the higher pressures experienced underwater.

Other underwater metal detectors such as the PulseDive use a couple of different methods to alert the operator to a metal object!  The PulseDive uses a mixture of beeping and vibration in the handle to alert the user to a metal object, it does this with a small in-built piezo speaker for the beeping sounds and a rumble motor for vibration. The PulseDive’s audio can be heard underwater from up to 20m away but can be used silently with just vibration for extra stealth or just audio to save on battery.

The advantage to these types of audio/vibration alerts is that it provides freedom from cables by eliminating the need to wear headphones. This also means you won’t be obviously noticeable when walking to the beach, snorkelling or scuba diving. In fact the PulseDive is so subtle that most people won’t notice it at all!

Investigating an 18 carat antique gold ring just found with the PulseDive. 
Check out our PulseDive review HERE

Small Underwater Metal Detectors

If you’ve done your research on the most popular diving and underwater metal detectors you’ll find that all of them come with some type of short shaft or diving shaft option.  These shafts serve one purpose and one purpose only.  To reduce drag from the water!

Unlike air, water is a lot harder to move through so it's very common to make underwater metal detectors as short and streamlined as possible to reduce the drag from the water.

Underwater metal detectors like the seahunter and excalibur come with an optional short/diving shaft whilst hand-held versions like the Pulse dive are already very short and slice through the water very easily.

Reducing drag on your underwater metal detector is possibly the most neglected aspect of underwater metal detecting,  Reducing drag increases swinging and detecting speed.  Faster swing speed means more ground covered, more covered ground covered equals more targets found, which equals more treasure!

To sum it up, if you can swing 20% faster and cover 20% more ground, then you are going to average 20% more finds and 20% more treasure!

An example of the kinds of finds that can be uncovered underwater!

Underwater Metal Detector controls

Underwater metal detectors have to deal with extremely harsh conditions. The high pressure salt environment means that these detectors use specialised highly waterproof sealed controls that are very reliable and robust.  

Knob type controls are the most commonly found controls on underwater metal detectors and offer a very simple to understand, very waterproof option for tuning your metal detector.  Knob type controls however are susceptible to breaking off if bumped hard enough and require that the o-rings are inspected and replaced every few years.   The only current alternative controls for underwater detectors are stiffer membrane buttons which are harder to push in and therefore less easily pressed and are pushed in by deeper water pressures.

The Pulsedive underwater detector uses these stiffer membrane style buttons which will not be pressed in unless further than 10m underwater.  The PulseDive however is waterproof to 60m so the manufacturer chose to incorporate a clever feature called “Dive Mode” into the detector.  Dive mode allows deep diving users to lock the buttons so that they do not operate at all. The user can then control the detector by changing the orientation. For example, if the detector is upside down it will be off and if it’s right side up it will turn it on again.

Author, Ed Burnett scouting for a new detecting spot underwater.

Buying an Underwater Metal Detector

Like with any product, warranty is an important consideration especially if that product comes at a high cost and underwater metal detectors are no exception!

Even more important than salt water functionality or waterproof rating is overall functioning reliability! To ensure you have a reliable metal detector, choose from the well known brands with trusted warranty programs like Nokta, Garrett and Minelab. Warranty on detectors being used underwater is especially important because water ingress and other forms of damage are not uncommon due to the harsh environments we throw at these underwater metal detectors.

Make sure that there is a service/repair centre in your country for the brand you are looking to buy and ensure that you buy from a trusted dealer within your own country.  Buying within your own country will ensure that the detector is covered by warranty.  Please note that many manufacturers will not warranty/service detectors outside of the country they were purchased meaning you may have to send your metal detector overseas to be repaired which can be extremely costly and time consuming!

In Conclusion

We hope this article has helped by providing a clear overview of underwater metal detectors and the most important things to think about when buying your very own. The feeling of being underwater, whether just snorkelling or diving with gear and finding lost items with an underwater metal detector is simply amazing!

Let us know if you have any questions or feedback in the comments below, or contact us anytime, and happy underwater treasure hunting! - Ed.