Short answer
A replica Fifty Fathoms 38mm copies Blancpain's mid-size dive watch. Genuine 38 mm versions come from the Bathyscaphe line: steel or ceramic case, ceramic bezel insert, sapphire crystal, in-house caliber 1150, 100-hour power reserve, 300 m water rating. Copies use Asian automatic or quartz movements, carry no water rating, and measure 11 mm to 14 mm thick against about 10.5 mm on the original. Cases sold as 38 mm often measure 40 mm or more. Ask for caliper photos before you pay.
The genuine 38 mm reference
Blancpain launched the Fifty Fathoms in 1953 for French combat swimmers. The dive line splits into two families today. The Fifty Fathoms Automatique runs 42.3 mm and 45 mm. The Bathyscaphe runs 38 mm and 43.5 mm. The 38 mm Bathyscaphe in steel, reference 5100, is the model most 38 mm copies follow.
- Case: 38.0 mm, steel or ceramic
- Thickness: listed at 10.4 mm to 11.4 mm across sources, so confirm the reference
- Water rating: 300 m
- Movement: caliber 1150, automatic, 100-hour power reserve
- Crystal: sapphire, front and caseback
- Bezel: unidirectional, ceramic insert
- Lume: Super-LumiNova on hands and markers
- Lug width: 20 mm on 38 mm references, confirm with the seller
What sellers mean by 38 mm
Three case types appear under that label: the Bathyscaphe copy at 38 mm, vintage 1953 style copies in small sizes, and larger 42 to 45 mm cases listed with wrong numbers. Measure across the bezel at 3 and 9 o'clock and leave the crown out of the figure. A 38 mm copy should read 38.0 mm to 38.5 mm.
Movement options
Automatic copies use clones of the ETA 2824 or the Miyota 9015, or the low-cost 2813. Quartz copies cost less and sit thinner. Out of the box, automatic copies run 15 to 30 seconds a day in rate error. The 2813 holds about 40 hours of reserve. The 2824 clone holds about 38 hours. The 9015 clone holds about 42 hours.
Water resistance
Replica cases are not pressure tested. Gaskets can be dry or absent. Crown seals on screw-down tubes often leak. Do not swim or dive with a copy. A watchmaker can reseal and test a case for $30 to $80, but the result is whatever the test shows, not 300 m.
Dial, bezel and lume
Mid-tier copies use ceramic or aluminum bezel inserts. Low-end copies use painted metal. Lume on copies fades faster than Super-LumiNova BGW9. Check the 12 o'clock triangle against the dial marker. Check the date wheel alignment and the date change at midnight. Many Fifty Fathoms dials put the date window at 4:30, and copies follow that layout.
Fit and strap sizes
A 38 mm case suits wrists from 6.0 to 7.0 inches. Overall length from lug tip to lug tip decides how the watch sits, and that number differs between factories. Ask for it. The 38 mm case takes a 20 mm strap in most listings, which leaves a wide choice of rubber, leather and steel bands.
Checklist before you buy
- Caliper photo of the case at 3 and 9 o'clock.
- Photo of case thickness at the crystal edge.
- Movement photo with the rotor and balance visible.
- Lume shot taken in a dark room.
- Bezel click test and alignment at 12.
- Date flip test across midnight.
- Crown thread and screw-down feel.
- Return window and payment method in writing.
Care and service
Rinse the case with fresh water after contact with salt or sweat. Wipe the gaskets dry. Have an automatic serviced when the rate drifts past 40 seconds a day or the rotor sounds dry. Service on an Asian automatic runs $60 to $150 at an independent watchmaker.
Price bands
A 38 mm Fifty Fathoms copy runs about $120 to $250 for quartz or a basic automatic, $250 to $450 for a mid-tier automatic with a clone movement, and $450 to $800 for copies sold as Swiss or 1:1. Claims about Swiss parts are hard to verify. Ask for movement photos before you pay above $400.
Common faults and shipping
Common faults include extra case thickness, soft crown guard edges, thin lume on printed markers, dull bezel inserts, and casebacks with wrong engravings. Numbers on copies rarely match genuine formats. In the United States, Customs can seize shipments of counterfeit watches under federal trademark rules, so delivery is not guaranteed.