Introducing The NOMOS Glashütte Ahoi 38, White Dial – And A Closer Look At Caliber DUW 6101
The caliber DUW 6101 – it’s smarter than it looks, and it looked pretty smart to begin with.
Every once in a while in this business, you get a reminder that not only don’t you know everything, but you have actually missed something you should have noticed the first time around. So it is with me and the NOMOS caliber DUW 6101, which can be found unostentatiously going about its business inside a number of NOMOS watches since it was first introduced back in 2018. The DUW 6101 was the first Neomatik caliber to have a date indication, and while it might have seemed to be based on the 2015 DUW 3001, it was in many respects a new caliber – especially in the design of its quickset date mechanism.
To back up a little bit, the Ahoi is NOMOS’ take on a diver’s watch – well, at least in terms of water resistance; it’s rated to 200 meters but of course, since there’s no one-way bezel you can’t call it a diver’s watch. It is delivered on a water resistant woven strap (which NOMOS said, when the Ahoi launched as a 40mm watch, in 2013, was inspired the lanyards used for locker keys in German public swimming pools, which perhaps tells us a little more about the intended environment of the Ahoi) and in 2023, the Ahoi 38 was announced, with a modified version of the caliber 6101, and the 40mm Ahoi was discontinued. Today’s announcement introduces a white dial which joins three other dial colors in the Ahoi family, and while it’s always nice to have options, there is more than meets the eye in the Ahoi 38.
The Ahoi 38 is as we have said not a dive watch but its construction, which includes crown guards, and a screw down crown with a red ring on the crown tube to warn you if you’re about to push your luck, is nonetheless clearly capable of living the life aquatic if necessary, and more power to NOMOS for making a high water resistance watch that doesn’t have all the usual dive watch tropes – there are plenty of those around if that’s what you want. At 38mm it is a diffidently sized timepiece but since it has very little bezel to speak of (which is a basic element of NOMOS design) it wears larger than the numbers would have you think.
The date window is quite large, so much so that the numbers hardly seem smaller than those on the dial, and the typeface is almost identical (sharp eyed NOMOS watchers will note that there are serifs on the dial Arabics but none on the date wheel). NOMOS generally sticks pretty closely to the Bauhaus basic principle of form following function and although occasionally the brand shows a slightly frisky side, highly abstract allusions to high speed German motorways is about as baroque as NOMOS generally gets.
It is when you get into what’s going on in the caliber 6101 that some of the real watchmaking content which has helped make NOMOS so much more than just another design brand (of which we have a glut these days, to put it mildly) becomes apparent.
The caliber DUW 6101 is produced in-house, up to and including the critical escapement components which NOMOS calls – I’m sure it feels, rather daringly – its Swing System; and which was introduced in 2014 as the climax of NOMOS’ move towards vertical integration and independence as a manufacture. The vast majority of the components are in house (there may be some question about the antishock system, jewels, and lubricants) and the movement is both quite thin and very large in diameter, measuring 33mm x 3.6mm (most automatic movements range in diameter from 26mm up to 30mm, the latter being the maximum diameter for watch movements allowed in the wristwatch category at the observatory trials). The version of the DUW 6101 used in the Ahoi 38mm is actually a slightly smaller version of the original from 2018, which is 35.2mm x 3.6mm, with much of the extra diameter taken up by the date ring. The movement was designed so that the date ring’s diameter could support a date window on the hour/minute chapter ring, and be better integrated visually than if it were closer to the center, as is often the case for date windows in larger watches.
The 6101 is one of the thinner automatic movements currently in production; for comparison, the ETA 2892 is also 3.6mm thick, and is usually consider a thin caliber, although not extra flat in the strictest sense; the date version of the famous AP caliber 2120, the 2121, is 3.05mm thick, with a non-quickset date and no small or center seconds. The DUW 6101 has a 42 hour power reserve, and most of the components, in pursuit of the objective of keeping the movement on the flat side, are suppressed to the same level under the 3/4 plate; this includes the automatic winding train. The DUW 6101 errs slightly on the side of sturdiness over absolute thinness, with a full balance bridge, and the omission of the “hanging” mainspring barrel characteristic of true extra flat and ultra thin movements.
Where things get really interesting, is in the quickset date mechanism. The date switching and quickset mechanisms were designed by NOMOS and I don’t think I’ve ever seen anything else quite like them.
Normally, in a watch with a conventional date mechanism, you are advised to not manually switch the date from the crown between roughly 10PM and 2AM although the specific advice on this may vary with the movement (Seiko in general recommends not trying to switch the date between 8PM and 2AM). The reason for this is that if you try to change the date when the date switching is in progress, you’ll be trying to advance the date wheel when the finger on the switching gear is in contact with the inner teeth of the date wheel, which can cause excessive wear or even breakage of the gear teeth.
NOMOS came up with a most ingenious mechanism for switching the date.
This is the date switching wheel – not to be confused with the five pronged star for quicksetting the date, which is on the other side of the movement (this is the view from the dial side). The switching mechanism is driven off the hour wheel of the movement, and is set up so that the triangular cam on top rotates four times a day. You might recognize the shape – it is in fact a Reuleaux triangle, that unusual polygon whose curved sides give it a constant diameter, and which we last saw in the Derek Pratt-designed remontoir inside the Urban Jürgensen UJ-1.
The triangle, in three of those rotations, engages with the stirrup inside which it rides, but it does not move it clockwise far enough to quite engage the inner gear tooth on the date wheel until the fourth rotation. On that rotation, the triangle pushes the stirrup far enough to the right that the tip of the stirrup engages the date wheel and as the engaging tip of the triangle falls off the stirrup, the next side of the triangle rotates into position, takes up the small amount of slack, and applies enough pressure to switch the date. NOMOS chose this design because it minimizes the amount of time that switching requires, and therefore the amount of time that the switching mechanism is in contact with the date wheel – NOMOS says that the entire process should take 30 minutes but in practice, it seems to take less than 20.
On the other side of the movement is the quickset mechanism.
The gear for switching the date forwards or backwards is the five-lobed, starfish shaped wheel next to the clutch mechanism for the keyless works. Underneath that wheel is a conventional gear which is directly turned by the date change gears in the keyless works proper. The upper star and lower gear are not rigidly connected; instead, they are separated by a washer spring, which exerts frictional force on the two wheels so that they turn together. However, if the date switching stirrup is engaged with the date wheel, there is additional resistance, which is enough to defeat the friction from the washer spring, and the star wheel will not be able to turn until the date change is complete. This protects the date wheel and switching stirrup from potential damage, as the owner will be unable to change the date while the actual date change is in progress. The use of the Reuleaux triangle means that the amount of time the quickset mechanism is blocked is minimized.
The entire movement is very well engineered and don’t take my word for it; in 2020, watchmaker Justin Koulapis, writing for the Horological Journal, found much to praise about the DUW 6101 to the tune of several thousand words and copious illustrations, including a sequence showing the actual action of the Reuleaux triangle against the stirrup, which is otherwise quite difficult to visualize. He wrote in part, “Overall, the movement presents a beautiful distinctive appearance … [the keyless works] give me even more reason to admire this watch [they are] compact, efficient, simple … the gold plated train wheels are beautifully low centre of gravity, making reassembly an absolute dream,” and much more. If serviceability, reliability, and longevity are as they should be, priorities for a watchmaker and goals for a watch movement, there would seem to be few ways to improve on the the DUW 6101.
And, on top of everything else, all this in a 200 meter depth rated watch, adjusted to six positions and (says NOMOS) to chronometer specs, which costs just $4,460. It is hard to imagine a better bargain in modern mechanical watchmaking, and while NOMOS is sometimes criticized for lack of imagination in its designs, there is something to be said for consistency and for sticking to what you’re good at (god knows it has worked just fine for a brand whose name rhymes with Molex). A fine watch, full of intelligent engineering, that’s got it where it counts.
The NOMOS Glashütte Ahoi 38 with white dial: Case, steel, with screw down crown and sapphire crystals front and back, 200 meter water resistance with red indicator showing an open crown on the crown tube; 38mm x 9.8mm. Not a dive watch but suitable for diving. Movement, DUW 6101, in house automatic with 42 hour power reserve, running at 21,600 vph, with bidirectional quickset date and safety mechanism for the quickset mechanism. Price, $4,460. The 1916 Company is proud to be an authorized retailer for NOMOS Glashütte; contact us for availability.