Short answer
A fake Fifty Fathoms chronograph is a replica built to look like Blancpain's Bathyscaphe Chronograph Flyback or the older Fifty Fathoms Chronograph. Nearly all of them run a Chinese clone of the Valjoux 7750. That single fact shapes everything else you will notice in hand: a 4 Hz movement instead of Blancpain's 5 Hz F385, no flyback function, a case that often runs thicker than the genuine 43.6 mm reference, and pushers that feel vague next to a column wheel and vertical clutch. Prices land between roughly $150 and $450 depending on tier. In the US, importing or reselling one is a federal crime, so treat this as a reading guide, not a shopping list.
Start with the movement, because it decides the rest
The genuine Bathyscaphe Chronograph Flyback uses caliber F385: a 5 Hz (36,000 vph) automatic flyback chronograph with a column wheel, a vertical clutch, a silicon balance spring, and about 50 hours of reserve. A 7750 clone beats at 4 Hz (28,800 vph) and has neither a column wheel nor a vertical clutch. You can test the beat rate without opening anything. Film the running seconds hand with a phone at 240 fps and step through the frames. Eight visible jumps per second means 4 Hz. Ten means 5 Hz. It is the cheapest real check you have.
Then test the flyback, carefully. On a true flyback, you press the reset pusher while the chronograph is running and the hand snaps to zero and keeps running. Most replicas cannot do this. Do not mash the reset on a 7750 clone mid-run, since that can stall or damage the movement. If a seller will not let you try it, that answers the question for you.
Subdials, date position, and the layout trap
Look up the exact reference the listing claims and compare subdial placement to the photo. A 7750 family movement limits how faithfully a maker can place the 30-minute, 12-hour, and running-seconds registers, so some replicas shift them a millimeter or two, and some use a printed overlay plate that reads flat up close. The same goes for the date aperture. Check it against the reference, not against another replica.
Also sort out which watch you are actually looking at. Plenty of listings say "Fifty Fathoms chronograph" and show a Bathyscaphe, or the reverse. The two have different case sizes, different bezels, and different movements. A seller who cannot name the reference is a seller to walk past.
Case, bezel, and crystal
- Thickness and weight. Replicas tend to sit taller on the wrist, because the chrono module stacks on top of the base movement. Genuine steel references feel dense and balanced, not top heavy.
- Bezel insert. Genuine uses ceramic or sapphire. Cheap copies use coated glass or printed aluminum, and the markings dull within months.
- Crystal. The real watch has anti-reflective coating on both sides, which gives a faint blue tint at an angle. A replica usually coats one side or none, so you get glare where the original stays clear.
- Caseback engraving. Factory engraving is crisp and shallow with even depth. Laser etching looks fuzzy under a loupe, and the lettering often drifts.
- Lume. Genuine uses Super-LumiNova that glows hard and fades slowly. Replica lume is weak and often uneven between the dial and the bezel.
Water resistance and pushers
The real Fifty Fathoms line is rated to 300 m. Replicas get assembled with seals that are not tested to that standard, and chronograph pushers are the weak point on any diver. Assume nothing beyond splashes. Even sellers who advertise "50 m" are repeating a number nobody verified on a pressure rig. For a watch whose whole identity is diving, that gap matters more than any cosmetic detail.
Price tiers, briefly
Entry copies sit near $150 and show it: rough bezel action, printed dial text, and a stock undecorated movement. Mid tier runs $200 to $300 with a decorated rotor and better finishing. The top tier, around $350 to $450, adds a ceramic insert, sapphire with double AR coating, and a movement plate engraved to imitate F385. None of that changes the beat rate or adds a flyback. You are paying for surfaces, not mechanics.
The legal side in the US
Trafficking in counterfeit goods is a federal offense under 18 U.S.C. 2320, with penalties that reach years in prison, and Customs can seize infringing imports at the border. Trademark owners can also sue sellers for damages. Buying one for personal use is a smaller exposure than selling, but wholesale is selling by definition. If the plan is to move replicas through a storefront, a marketplace, or a flea market table, that is the part that carries real risk.
What I would check in order
- Beat rate on video at 240 fps.
- Flyback behavior, if the seller allows it.
- Subdial and date placement against the real reference.
- Bezel insert material and action.
- Crystal glare and caseback engraving under a loupe.
- Case thickness on a caliper next to published specs.
Any one of those can end the conversation. Taken together, they separate a decent copy from a $150 gamble, and they tell you plainly that no replica Fifty Fathoms chronograph is the watch it is pretending to be.