WT_2006_01: DOUBLE TEST: SINN U1 VS. SINN U2

DOUBLE TEST: SINN U1 VS. SINN U2
74 WatchTime February 2006

Advantages
+ The scratch-resistant bezel
won’t snap off
+ Scratch-resistant, non-reflective
coating
+ Attractive design
+ Stay-dry technology
Disadvantages
– High surcharge compared to
the price of the U1
Advantages
+ The scratch-resistant bezel
won't snap off
+ Scratch-resistant, non-reflective
coating
+ Excellent rate results
+ Favorable price
Disadvantages
– It takes time to get used to the
unusual design
photo: Marcus Krüger, Hamburg
Submarine
Steel
“Warsaw” is the code word for “caution” on the high seas.
A mariner expresses his experience and superiority with the
phrase “Warsaw nautical miles.” Now Sinn has built two
watches from submarine steel. They’re harder than all other
steel watches. Are they the perfect divers’ watches?
Along with its well-known pilots’ watches,
Sinn can also boast several impressive
timepieces for divers. The so-called “hydro
technique” made it possible to build a
quartz watch that can remain water-resistant
to virtually any depth. Its case is completely
filled with non-compressible oil. This technique
is also used in the company’s EZM 2, which the
professionals in the maritime unit of Germany’s
anti-terrorism police force, the GSG 9, use to
keep track of time during their missions.
Sinn’s accumulated know-how prompted
its technicians to begin developing even
tougher divers’ watches. The results are the U1
and U2, and it’s no mere coincidence that the
names of these watches sound as though they
could also be the names of U-boats.
In their search for materials from which to
craft the cases of these new divers’ watches,
Sinn chief Lothar Schmidt and his team found a
special type of steel that, for several reasons,
proved to be ideal for underwater wristwatches.
Expressly developed by Germany’s metallurgical
industry for U-boat construction, this alloy
is used in new submarines of the 212 A
class. This extraordinary alloy is highly resistant
to corrosion by saltwater, extremely strong and
BY JENS KOCH
unusually elastic. These attributes are crucial
because they help prevent a sub from springing
a leak under the extreme pressure of deep
dives or in the event of a collision. Furthermore,
the alloy cannot be magnetized, thus
protecting the vessel against magnetic sensors
in robotic mines.
The four 212 A U-boats that the German
navy ordered have been built and are undergoing
test operations at sea. Manufactured at the
Howaldtswerke Deutsche Werft (HDW) in Kiel,
they’re regarded as the world’s most advanced
conventional U-boats. They’re also the first
such vessels to be powered by fuel cells. This
means they can dive and stay underwater for
extremely long periods of time.
Sinn’s engineers were particularly interested
when they heard about this alloy’s ability to
resist the corrosive effects of saltwater. Watch
cases made of conventional steel alloys aren’t
suitable for long-term underwater use. The
ability to withstand corrosion from saltwater,
which can cause crater-shaped scars in a metal’s
surface, is measured in a unit called a
“PRE,” which stands for “pitting resistance.”
The maximum PRE value for stainless steel is
26, but a metal doesn’t deserve to be de-
February 2006 WatchTime 75

DOUBLE TEST: SINN U1 VS. SINN U2
scribed as “seawater resistant” unless its PRE
value is at least 32. U-boat steel has a PRE value
of 38, which is high enough for professional
divers. This steel won’t be damaged even if the
watch isn’t rinsed with freshwater after immersion
in the briny deep. But it’s not just corrosion
resistance that makes this alloy so interesting
for Sinn: this material can also be hardened
very well using the Tegiment process.
Sinn first experimented with hardened steel
on its Model 756. The first ice-hardened variation
achieved a value of 700 on the Vickers
hardness scale. That’s an enormous improvement
over the 316L steel alloy typically used in
watches: 316L steel tops out at 220 on the
Vickers scale. When Sinn’s specialists subjected
316L steel to the Tegiment technique, they
were able to increase its hardness to 1,200
Vickers. Applying the same procedure to Uboat
steel, they achieve a value of 1,500 Vickers.
This means that the surfaces of the U1 and
76 WatchTime February 2006
The green Viton insulator protects the ETA 2893-2 in the U2 (left) and the ETA 2824-2 in the U1.
U2 divers’ watches are nearly seven times harder
than the surfaces of ordinary steel wristwatches.
This hardening procedure is performed
only on the bezel because the Tegiment
process is very laborious and takes several
weeks to complete, but since the rotating
bezel covers the entire case, it gives the case all
necessary protection. Even before undergoing
the Tegiment process, the U-boat steel of
which the bezel, case and crown are made is
already 40% to 50% harder than the 316L alloy.
The case comes from SUG and is very nearly
perfectly made. We searched for tool marks
everywhere, even between the strap lugs, but
were unable to find any. The glass pearl blasted
surface is so fine it looks almost elegant.
Lothar Schmidt didn’t want to compromise
the scratch-resistance of the surfaces by using
the soft non-reflective coating that’s ordinarily
applied to watch crystals. Here, too, Schmidt
sought a better solution. As so often occurs in
the world of watchmaking, he found it in another
discipline altogether: namely, in the technology
used to improve the optical quality of
lenses. This laborious and costly technological
process creates a non-reflective layer with a
value of 1,800 Vickers, nearly as hard as the
2,000-Vickers value achieved by its sapphire
substrate. After proving itself on Sinn’s Model
900, this technique is now also used on the U1
and U2. Sinn pre-tenses its crystals before gluing
them into place, thus enabling the construction
to forego an unattractive white plastic
insulating ring. A 1.4-mm-wide glue crevice
ensures that the crystal never parts company
with the case, even under de-pressurized conditions.
Schmidt and his team also needed to be
sure that the extremely hard rotating bezel
would never get lost. Most manufacturers
press the bezel onto the case from above. If
you want to remove the bezel, all you do is ex-
Argon’s comparatively large atoms ensure that the smaller water molecules
cannot find any space for themselves inside the case.

DOUBLE TEST: SINN U1 VS. SINN U2
DATA
SINN U2
Manufacturer: Sinn Spezialuhren
GmbH & Co. KG, Im Füldchen 5-7, 60489
Frankfurt, Germany
Model: U2
Reference number: 1020.020
Functions: Hours, minutes, seconds, date;
uni-directionally rotating bezel; stop-seconds
function.
Movement: Self-winding ETA 2893-2;
diameter = 25.6 mm; height = 4.1 mm;
28,800 vibrations per hour; 21 jewels;
Incabloc shock absorption; power reserve of
about 42 hours.
Case: U-boat steel, glass pearl blasted; divers’ rotating
bezel is made of steel hardened to 1500
HV and is impossible to lose; threaded screw-in
back; domed sapphire crystal is non-reflective on
both its surfaces, 4.6 mm thick, and given extrahard
1800 HV non-reflective treatment on its
outer surface; argon filling; two copper sulfate
desiccant capsules; special oil for a temperature
range from -45° to +80° Celsius; water-resistant
to 2,000 meters.
Band and clasp: Rubber strap; secure folding
clasp made of steel with divers’ extension
piece.
Rate results:
(Deviations in seconds per 24 hours)
Dial up: +3
Dial down: +7
Crown up: -4
Crown down: +1
Crown left: –3
Crown right: –1
Greatest deviation of rate: 11
Average deviation: +0.5
Mean amplitude
Flat positions: 317°
Hanging positions: 274°
Dimensions: Diameter = 44 mm;
height = 15.45 mm; weight: 170 grams.
Price: $2,200
ert a little leverage and snap it free. But under
unfavorable conditions, a pressure-fit bezel of
this kind can be inadvertently snapped off the
case, for example, if a diver snags it on an underwater
rock.
To prevent this from happening, Sinn developed
an impossible-to-lose rotating bezel. An
open tension ring, which fits into a groove on
the bezel, is pressed by three little screws into a
corresponding groove on the case. This creates
a secure bond that can be readily (but never accidentally)
undone whenever desired. The bezel
runs smoothly on three elastically borne
78 WatchTime February 2006
The secure folding clasp with divers’ extension piece isn’t made from U-boat steel, but it’s
very durable anyway.
balls that also let the bezel click incrementally
into place. Here, too, Sinn has found a solution
that combines elegance and longevity.
The luminous index on the bezel consists of
an inlaid piece of artificial material that contains
Super-LumiNova. The large amount of luminous
substance here, as well as its copious
use on the hands and on the dial’s indices, assures
that these U-boat watches keep glowing
in the dark much longer than ordinary wristwatches.
Even shortly before sunrise, the time
can still be clearly read from the dials of Sinn’s
U-boat watches.
Lothar Schmidt isn’t just an engineer. He’s
also a perfectionist. His critical eye misses nothing,
not even seemingly minor details such as
insulators. Viton is the material of choice for
the insulators on Sinn’s U-boat watches. This
green material has a longer lifespan than conventional
black nitril insulators. Furthermore,
Viton allows only one-fourth as much gas and
atmospheric moisture to penetrate into the
watch’s interior. Last but not least, Viton is
more resistant to corrosion by many chemicals.
With so many attributes in its favor, one wonders
why all watch manufacturers haven’t
switched to Viton insulators. One reason is the
higher price of such insulators. Nitril rings can
be had for less than one euro; their Viton counterparts
cost more than one euro each. If insulating
rings aren’t available in the desired size,
several hundred euros must be spent to make
the tools needed to manufacture them. Lothar
Schmidt doesn’t shy away from the additional
DATA
SINN U1
Manufacturer: Sinn Spezialuhren
GmbH & Co. KG, Im Füldchen 5-7, 60489
Frankfurt, Germany
Model: U1
Reference number: 1010.010
Functions: Hours, minutes, seconds, date; unidirectionally
rotating bezel; stop-seconds function.
Movement: Self-winding ETA 2824-2;
diameter = 25.6 mm; height = 4.8 mm;
28,800 vibrations per hour; 25 jewels;
Incabloc shock absorption; power reserve of
about 40 hours.
Case: U-boat steel, glass pearl blasted; divers’ rotating
bezel is made of steel hardened to 1500
HV and is impossible to lose; threaded screw-in
back; sapphire crystal is non-reflective on both its
surfaces, 3.5 mm thick, and given extra-hard
1800 HV non-reflective treatment on its outer
surface; argon filling; water-resistant to 1,000
meters.
Band and clasp: Rubber strap; secure folding
clasp made of steel with divers’ extension
piece.
Rate results:
(Deviations in seconds per 24 hours)
Dial up: +5
Dial down: +4
Crown up: +3
Crown down: +4
Crown left: +4
Crown right: +4
Greatest deviation of rate: 2
Average deviation: +4
Mean amplitude
Flat positions: 305°
Hanging positions: 294°
Dimensions: Diameter = 44 mm;
height = 14.35 mm; weight: 170 grams.
Price: $1,200

expenses: he uses Viton on the back of the case, as well as for the crown’s
two O-ring insulators and its flat insulator.
The meaning of the first part of the names “U1” and “U2” isn’t hard to
guess: “U” stands for “U-boat steel.” But what do the numbers “1” and
“2” mean? They allude to the water-resistance. The U1 is water-resistant
to 1,000 meters. The U2 remains impenetrable down to twice that depth.
The U2 achieves this deep-diving water-resistance in part thanks to its 4.6mm-thick
sapphire crystal. This crystal is domed and significantly thicker
than the one on the U1, which is flat.
But there are other differences between the U1 and U2. From the start,
the U2 was conceived to be a timepiece for professional missions, so it
bears the additional designation “EZM 5.” Its design is derived from the
EZM watches, but has undergone further evolution. The guiding principle
behind this philosophy is to use unobtrusive colors to display information
of lesser importance.
As an instrument for use on professional missions, the U2 is also
equipped with an improved version of Sinn’s “stay-dry” technology. Its
case is filled with argon, one of the noble gases. Argon’s comparatively
large atoms ensure that the smaller water molecules cannot find any
space for themselves inside the case. If small amounts of water vapor
nonetheless manage to penetrate, they’re soon absorbed by the copper
sulfate inside three desiccant capsules. This means that infiltrating water
molecules can’t do any damage and it also assures that the crystal won’t
fog up when the watch undergoes a temperature change. The copper
sulfate is originally white, but it gradually changes to blue as it absorbs
moisture and approaches saturation. The window that lets you keep tabs
on the change to blue is no longer in the case (as it was on Sinn’s earlier
version), but is now integrated into the dial at the “6.” Without the aperture,
the case is even less permeable because any opening in a watch’s
case is a potential Achilles’s heel.
Another technical innovation lets Sinn guarantee this watch’s flawless
performance even when it’s exposed to extreme temperatures. Thanks to
the 66-228 oil that was developed expressly for Sinn, this watch continues
Plenty of Super-LumiNova keeps these U-boat watches glowing for
a long time.

DOUBLE TEST: SINN U1 VS. SINN U2
to run blithely at temperatures ranging from
–45° to +80° Celsius. Every U2 is tested for 24
hours at the lowest guaranteed temperature
inside a frigid chamber. This oil is used at all lubricated
locations, including the pallet jewels.
Although the company doesn’t explicitly say
so, Sinn uses this same special oil on most of its
other watches, including the U1.
The author wore the U2 during a 10-day
vacation. Man and machine swam in seawater
at a balmy 26° C., a temperature at which saltwater
really gets its teeth into ordinary steel
surfaces. We also dug through fine sand on
the beach and hiked in the mountains on hot
afternoons. The author survived well enough,
and his U2 came through with flying colors.
The rubber strap still looks brand new, too.
And even the business end of a screwdriver
couldn’t scratch the hardened steel bezel or
the non-reflective coating on the crystal.
The rubber strap fits solidly between the
lugs and contributes to the watch’s up-to-date
good looks. Sinn has taken a great leap forwards
here. Furthermore, the strap curves
downwards at an angle that makes it comfortable
for even a smaller wrist, despite the
watch’s 44-mm-diameter case. The dark gray
color of the steel radiates an aura of reliability.
We prefer the design of the U2; the U1 looks a
bit too boxy for our taste. On the other hand,
the U1 is king of the hill as far as its cost-benefit
ratio is concerned: $1,200 is an inarguably
low price to pay for a watch with this much
high-tech refinement packed into it. Furthermore,
the U1 contains the best-quality version
of ETA’s Caliber 2824-2. A rate deviation of just
two seconds among the several positions is
well within chronometer norms. On the wrist, it
gained a negligible two seconds per day. The
ETA 2893-2 inside the U2 didn’t perform quite
as well: it lost three seconds per 24 hours on
the wrist and posted a large difference of 11
seconds among the several positions. The surcharge
for the U2 buys you water-resistance to
a greater depth, “stay-dry” technology inside
the case, and the display of the time in a second
time zone. Though it costs more than the U1,
the $2,200 charged for the U2 is by no means
exorbitant for such an admirable union of functionality
and beauty. ■
80 WatchTime February 2006
TEST RESULTS
Sinn U2
Band and clasp (max. 10 points): Like those
on the U1; soft rubber strap; sturdy clasp with
divers’ extension piece; visually and functionally
well-designed. 8
Operation (5): The same good crown as on the
U1; along with the stop-seconds function and
the rapid adjustment for the date display, this
model also allows rapid adjustment for the display
of the time in a second time zone. 5
Case (10): Even more water-resistant than the
U1, with stay-dry technology inside the case,
which is very well-crafted and protected by an
extremely scratch-resistant, impossible-to-lose,
rotating bezel. 9
Design (15): The U2 is clearly designed to measure
time on underwater missions; it has an unobtrusive
24-hour display for the time in a second
zone and it boasts beautifully shaped, highly
functional hands and indices. The domed crystal
looks good on the U2; the crystal above the U1’s
dial is flat. 13
Legibility (5): Here, too, this is as good as it
gets. The second time zone display is also unmistakably
legible under daylight conditions. 5
Wearing comfort (10): The case is slightly slimmer
than that of the U1; the wearing comfort is
equally good. 9
Movement (20): The insignia on the rotor and
the wide temperature range for the oil are the
only changes made to ETA’s standard caliber. 12
Rate results (10): Eleven seconds of deviation
between the several positions could stand some
improvement. 7
Overall rating (15): Still a good price, but significantly
more costly than the U1 because of
the stay-dry technology and the greater depth
of water-resistance. 13
TOTAL: 81 points
TEST RESULTS
Sinn U1
Band and clasp (max. 10 points): The velvety
rubber strap and the sturdy folding clasp with
divers’ extension piece look good; they combine
high quality with a high degree of functionality.
8
Operation (5): When it’s unscrewed, the crown
disengages from the winding staff, turns easily
and can be readily pulled into the various positions;
the watch has a stop-seconds function and
the date display can be rapidly reset. 5
Case (10): The very well-crafted and extremely
water-resistant case evokes added enthusiasm
thanks to its extremely scratch-resistant, impossible-to-lose,
rotating bezel. 9
Design (15): The indices recall the silhouette of a
submarine moving toward the viewer; the design
is appropriate for a U-boat watch, but the styling
is a little too boxy. 12
Legibility (5): By day or by night, the legibility
couldn’t be better. 5
Wearing comfort (10): Despite its heaviness,
the watch is very comfortable on the wrist; the
crown can’t hurt the top of the wrist. 9
Movement (20): The unaltered ETA movement
is sturdy and reliable and has proven itself in
countless wristwatches. 11
Rate results (10): Superlative performance! A
mere two seconds’ deviation among the several
positions, and scarcely any decline in amplitude.
10
Overall rating (15): An uncommonly good
price for a timepiece with so much fine technology.
15
TOTAL: 84 points