Deconstruction Blancpain Fifty Fathoms by The Naked Watchmaker

The Fifty Fathoms divers watch was originally designed in 1953. A deconstruction of the original model can be viewed by clicking here.  The modern version has evolved from the original design, to what is today a technically superior version from the movement through to the execution of the case. This version was launched in 2007.


Ref 5015-1130-52

Functions, Date, Seconds, Antimagnetic cage, One-way rotating bezel. Stainless Steel case. Case thickness 15.50 mm Case diameter 45.00 mm Water resistance 30.00 bar.

Power reserve 5 days / 120 hours 3 Stem positions; 1 winding the barrel 2 quick date correction 3 time setting.


The bezel turns anti-clockwise only. The watch is tested to be water resistant to a depth of 300 metres. Both the watch glass and insert on the bezel are made from sapphire.

The strap or bracelet is held onto the case by a screw system instead of spring bars.

Although versions of the Fifty Fathoms are being made with sapphire case backs to view the movement, the most standard versions are solid metal as shown below.

A soft iron cage is used to protect the balance spring from being magnetised and affecting the timekeeping.

case_drawings__page_14_of_15_ (1).jpg

The case back and iron cage removed, showing the 1315 calibre, held inside the case circled by a movement ring.

The calibre 1315 was developed over a period of 3 years.

The calibre 1315 was developed over a period of 3 years.

Calibre 1315

Movement Self-winding (single direction) Calibre thickness 5.65 mm Calibre diameter 30.60 mm  Jewels 35 Components 227 Frequency 4 Hz / 28’800 A/h Components 227.


Recto-verso of the dial with rear showing the riveted index feet. Indexes filled with Super-LumiNova

The seconds, minute and hour hands, are all filled with SLN as with the dial. The faceted surfaces on the minute and hour hands insure that regardless of how light catches the hands they can always be easily viewed.


The 1315 calibre with the automatic mass removed. The jewels are larger in diameter than conventionally found on most calibres. The overall finishing is clean, simple and consistent with a well-conceived and executed calibre. The basic calibre is both precise and a ‘work-horse’ movement able to be adapted from sports watches such as with the Fifty Fathoms through to the more intricate Villeret models with multiple modules and additional complications.


The automatic block still in place in the centre of the image, held by three screws. The rotor arbor which supports the rotor mass is seen in the centre and pivots in a ceramic ring which doesn’t require lubrication. The rotor is heavy and traditionally its arbour will wear over time. The combination of ceramic and highly polished hardened steel together on the larger pivoting surface of the arbour allows for strength, longevity and reduced friction.


The rotor (with tungsten carbide rim) removed from the movement.

The rotor block removed, recto-verso. The lower jewel for the rotor arbour is ‘massive’ compared to the others to compensate for the excessive pressures it is subjected to when the watch suffers impacts.

The rotor block with the lower bridge removed showing its gear train and ‘click’. The rotor winds in one direction. Due to the construction and finish of the pinions and pivots, combined with the jewels and ceramic bearing the automatic is highly efficient.

The movement with the central automatic block (assembly) removed.

A simplified exploded view of the movement.

 The calibre was developed over a period of 3 years.

The calibre was developed over a period of 3 years.

_MG_5369fifty -Edit-2.jpg

The barrel bridge holding in place the three barrels.

The intermediate winding pinions for the first ratchet wheel

In 2003 for the Fiftieth Anniversary of the Fifty Fathoms, Blancpain introduced the first divers wristwatch with a bezel including a sapphire insert with Super-LumiNova indexes. The same execution is shown below:


The winding crown screws onto the case tube and has multiple seals. The overall construction and design is one of the sturdiest of any existing divers watch.


The case construction prior to the rotating bezel being added.


The construction of the case including bezel and winding crown is synonymous with one of the strongest available on the market today. The extended power reserve on the movement differentiates this diver’s watch from others. The readability of the dial and the bezel both with Super-LumiNova detail is another element that defines this piece. Although quality is a subjective point of view, amongst all of the diver’s watches I have handled, this one, combined with its faraday-like cage, distinguishes itself.

Article by The Naked Watchmaker

Text and photos are the property of The Naked Watchmaker©

This site uses Akismet to reduce spam. Learn how your comment data is processed.