The practical answer to a "fake Fifty Fathoms full moon" search is that the watch people are chasing is a moon phase diver, and the pick that survives scrutiny is either a genuine or pre-owned Blancpain Bathyscaphe Quantième Complet Phases de Lune, or a legal moon phase watch from another established brand. Judge every candidate on four points: whether the moon disc actually tracks a 29.5 day cycle, how the case, bezel and dial printing are finished, whether the watch can still be serviced in ten years, and what legal exposure you accept as a buyer in the United States.
What the Phrase Refers To
Blancpain's Fifty Fathoms family is built around dive watch cases, and the moon phase found its way onto the Bathyscaphe Quantième Complet line, which pairs a complete calendar with a moon phase aperture. That combination is rare. A dive watch normally sacrifices complications for legibility and water resistance, so the moon phase model carries day, date and month indications plus an aperture, all behind a rotating bezel and a screw-down crown. Most searches for a "full moon" Fifty Fathoms are really searches for this reference or a copy of it.
Why This Model Is Hard to Copy Well
The moon phase is the weak point of any counterfeit. The disc has to advance on a geared cycle that stays accurate for months, and cheap copies often use a decorated calendar wheel that simply rotates once a day. Look at the moon itself: on a well made watch the two moons are printed or applied with defined craters and a clean overlap against a dark sky, while low grade copies show flat white circles with soft edges. The calendar mechanism adds thickness, so a copy built on a thin base movement tends to sit flatter than the real watch or stack its pushers at the wrong height. Finishing on the case flanks and the bezel insert usually tells the rest of the story.
Option One: Genuine or Pre-Owned Blancpain
- Pros: correct moon phase gearing, serviceable movement, documented water resistance, real resale value, no customs risk.
- Cons: high entry cost, waiting lists or a hunt through the pre-owned market, servicing is not cheap.
Best for the buyer who wants the real thing once and plans to keep it for decades.
Option Two: Legal Moon Phase Watches From Other Brands
- Pros: honest movements you can have repaired, a wide range of case sizes, no trademark problem, and a moon phase complication that actually works.
- Cons: none of them will look identical to the Blancpain, and finishing at lower tiers is simpler.
Best for the buyer who loves the moon phase idea more than the badge, and wants a watch they can wear in water without worry.
Option Three: The Counterfeit "Clone"
- Pros: short term appearance of the real design, low upfront spend.
- Cons: no warranty or parts support, moon phase that drifts or stops, gaskets that fail, and possible seizure at the border.
Best for nobody who plans to keep a watch. A counterfeit moon phase diver is the hardest category to get right and the easiest to spot across a table.
Legal and Practical Risk in the US
Counterfeit watches are subject to seizure at import, and trademark owners can record their marks with customs authorities to make interception easier. Beyond the legal side, a copy has no service network. When the calendar module jams or the moon disc slips, a local watchmaker often refuses the job because parts do not exist. That turns a cheap purchase into a paperweight.
Bottom Line
If you want the look of a Fifty Fathoms moon phase, buy a genuine reference, a pre-owned example, or a legal moon phase watch from a brand that will still be around to fix it. The counterfeit route fails exactly where this watch is most interesting: the complication itself.