A fake Fifty Fathoms Full Moon is a replica of Blancpain's Fifty Fathoms Bathyscaphe Quantième Complet, the dive watch that adds a complete calendar and a moon phase at 6 o'clock. The case shape, bezel, and dial layout get copied, but the movement underneath decides how close the watch comes to the original. A working moon disc and a clean date pointer matter more than any engraving on the rotor.
Which Blancpain watch is called the Full Moon?
Blancpain has never sold a watch named the Fifty Fathoms Full Moon. Buyers and sellers use that phrase for the Fifty Fathoms Bathyscaphe Quantième Complet, which puts a complete calendar and a moon phase inside a dive watch case.
Bathyscaphe Quantième Complet basics
- Case: 43mm in steel or titanium, about 13.5mm thick
- Dial: sunburst blue, black, grey, or green with a moon window at 6 o'clock
- Complications: day, date, month, and moon phase
- Movement: automatic with a four-day power reserve
- Crystal and case back: sapphire on both faces
Earlier moon phase Fifty Fathoms models
Older complete calendar pieces in the Fifty Fathoms line used 40mm cases and a different subdial arrangement. Listings that mix reference numbers from those years with photos of the 43mm model deserve a second look before you pay.
What movement powers a replica Fifty Fathoms moon phase?
Three setups cover most of the market. Each one changes the price, the case thickness, and the way the moon disc moves.
Quartz with a printed moon disc
Cheap builds run on quartz and hide the movement behind a solid case back. The moon window still turns, but the seconds hand ticks and the case sits thin next to the original.
Automatic plus a calendar module
Mid-tier replicas stack a moon phase module on a base automatic such as a Miyota 9015 or a copy of an ETA 2836. Expect 1.5mm to 2mm of extra thickness and a moon disc that advances in small steps each day.
Decorated clone movements
The top builds engrave and plate the movement to look like Blancpain's in-house calibre. Timekeeping stays much the same as the mid tier, so you pay for finishing and a rotor that looks right through a sapphire case back.
How do you spot a good replica?
Moon disc and date pointer
The moon disc should sit centered in its window and the date hand should point at the printed numerals on the dial edge without scraping them. Ask for photos at more than one calendar date, because a disc that lines up on the 15th can drift by the 28th.
Bezel and case finishing
- Bezel insert: sapphire or ceramic on the original, printed aluminum or soft ceramic on cheap replicas
- Bezel action: firm clicks with no side-to-side play
- Case flanks: brushed surfaces with polished bevels and sharp edges
- Crown guards: even on both sides, no tool marks
Dial, hands, and lume
Printing should stay sharp under a loupe and the lume on the hands should match the hour markers. Budget builds often show a green tint where the original glows blue, and lume that fades in 20 minutes.
Crystal and reflections
The original uses sapphire with anti-reflective coating on both faces, which leaves a faint blue or purple sheen. A cloudy, milky reflection points to mineral glass. Check that the case back is sapphire too, since a mineral back picks up scratches in weeks.
What should you confirm with the seller?
- Measured case size and thickness, not a copied spec sheet
- Movement name and whether the moon phase tracks the 29.5-day cycle
- Water resistance rating, plus the fact that most replicas handle splashes only
- Strap or bracelet details, including clasp markings
- Photos of the actual watch rather than catalog images
- Return window and a payment method with buyer protection
What do these replicas cost?
- Quartz entry level: $60 to $120
- Automatic with a moon phase module: $180 to $350
- Top build with a decorated movement and sapphire: $400 to $700
A genuine Bathyscaphe Quantième Complet sells in the five-figure range, so a replica runs about 2% to 5% of the real price. That gap explains why buyers accept a quartz tick or extra case thickness as a trade.
Common questions about the Fifty Fathoms moon phase replica
Does the moon phase on a replica work?
On quartz and automatic replicas, yes. The disc advances on a 29.5-day cycle, the same length as a real lunar month. On the cheapest builds the window is printed and never moves, so confirm that point before paying.
Is a 43mm Fifty Fathoms moon phase too big?
A 43mm case with a dive bezel wears larger than the number suggests, and it suits a wrist of 17cm and up. Smaller wrists are better served by the older 40mm references or a Bathyscaphe three-hander at 38mm.
Can a watchmaker tell it is a replica?
Yes. A trained eye spots the movement, the bezel insert, and the dial printing within seconds of opening the case back. Replicas are built to look right on the wrist, not to pass an inspection.
Which dial color looks closest to the original?
Blue and black are the safest choices because the sunburst finish hides small printing flaws. Green and grey dials show misalignment on the moon disc and the date track more, so they demand better photos from the seller.
Quick summary
Match the replica to the reference you want, ask for real photos, and check the moon window and date pointer first. Movement type sets the price, and sapphire on both faces is the one upgrade worth paying for.