Fisher CZ-21 Dual-Frequency Underwater Metal Detector with 10.5" Concentric Waterproof Coil

The Fisher CZ-21, known to divers as the CZ21 QuickSilver, is a dual-frequency underwater metal detector submersible to 250 feet, built for scuba divers and surf hunters who work saltwater beaches, freshwater lakes, and deep dive sites. This version ships with the larger 10.5-inch concentric waterproof coil, which covers more ground per sweep and reaches a little deeper on open sand than the 8-inch, making it the choice for wide beach and open-bottom hunting. Where single-frequency VLF detectors chatter in wet salt and black sand, the CZ-21's Fourier Domain signal processing keeps targets clear. It is one of the underwater and waterproof metal detectors professionals still rank at the top for saltwater work.

What's included

• Fisher CZ-21 detector with 10.5-inch concentric waterproof search coil
• Submersible headphones
• Two-year Fisher manufacturer warranty

Why divers and surf hunters choose the CZ-21

• Dual frequency that ignores salt. It transmits 5 kHz and 15 kHz at the same time and reads both through Fourier Domain processing, so wet salt does not false the machine the way it hammers single-frequency detectors.
• Submersible to 250 feet. Covers every surf zone and most recreational dive sites, with no depth anxiety.
• More coverage from the 10.5-inch coil. The larger coil sweeps more ground and reaches a bit deeper on open sand, ideal for clearing wide beaches and flats.
• Manual ground balance for iron-heavy sites. Zeroes out soil minerals so you hear targets in trashy freshwater swim areas and old beach fills.
• Removable control housing. Detach the box, clip it to your belt or BC, and work the coil on an extended arm in current or tight spaces.

Where the CZ-21 with a 10.5-inch coil performs best

Open beaches and sand flats

The 10.5-inch coil is at its best on wide, open ground where coverage and depth matter more than tight separation. On dry sand, wet sand, and the wash, the larger footprint clears more area per sweep and helps you reach deeper coins, rings, and relics. The 250-foot rating means the same machine follows you from the towel line into the surf without a second thought.

Lake and river diving

Freshwater sites with iron trash, like old swim areas, sunken docks, and flooded homesteads, benefit from the manual ground balance and all-metal auto-tune mode. Ground balance zeroes out mineralization so you hear targets, not soil, and all-metal mode gives maximum depth on open sand flats and mud bottoms. The large-target alert boosts faint signals, which helps at depth and in low visibility.

Scuba and deep dive sites

Our team has taken the CZ-21 to 60 feet on wrecks and old ferry crossings. The dual frequency keeps working in high-conductivity saltwater without the drift you get from pulse induction machines that were not designed for discrimination. Touch-button controls and VCO no-motion pinpointing let you mark a target, set the detector on the bottom, and dig without losing the signal.

Which coil should you choose, 8 inch or 10.5 inch?

Both coils are genuine CZ-21 waterproof concentric coils. Pick by where you hunt.

Consideration	8-inch coil	10.5-inch coil (this page)
Ground coverage	Less per sweep	More per sweep
Depth on open sand	Good	Slightly deeper
Maneuverability in trash	Better separation	Bulkier in tight trash
Best for	Trashier sites, tight spots, pier pilings	Open beaches, sand flats, dive bottoms

Short version: choose the 10.5-inch coil for open ground and maximum coverage, or the 8-inch coil for trashier, tighter sites.

Specifications

• Operating Frequencies: 5 kHz and 15 kHz (dual frequency, simultaneous)
• Coil: 10.5" concentric waterproof search coil
• Waterproof Rating: Submersible to 250 ft
• Audio: 3-tone target ID (low, mid, high)
• Ground Balance: Manual
• Detect Modes: All-metal auto-tune, discrimination
• Pinpointing: VCO no-motion
• Control Housing: Removable for belt-mount
• Headphones: Submersible headphones included
• Country of Manufacture: USA (Texas)
• Warranty: Two years

Why buy from Serious Detecting

As an authorized Fisher dealer, every CZ-21 ships with a genuine two-year manufacturer warranty backed by Fisher's US support and service. Our team has run Fisher metal detectors in surf, lakes, and dive sites across the country, so we can walk you through coil choice, ground balance, and audio tuning for your conditions. Comparing machines in the $1,000 to $3,000 range? We will help you match the right tool to your sites. Free shipping, 30-day returns, and a price-match guarantee.