For almost half a century, the Amphibia dive watch has been produced by Vostok Watchmakers Inc continuously, with only styling changes. In fact, the term "Amphibia" should be considered as an integrated design and engineering solution, upon which this family of watches is based. Here is an attempt to analyse how the designers arrived at this design solution, which is very different from the numerous other diver watch designs over the years, and hopefully come to a conclusion of its merits or otherwise.
The objective of a dive watch is, of course, to prevent the ingress of water when submerged, and to keep the watch operating normally under increased water pressure. Many different approaches had been tried over the decades.
While there have been claims and counter-claims on which was the first dive watch, it is an undisputed fact that the Omega Marine, introduced in 1932, was one of the earliest. Here, an ostensibly regular watch is housed within an additional solid enclosure to effect water resistance. The pictures here show one of the reissues made in 2007.
In terms of design, it is not about making a watch water resistant, but more of putting a watch in a water resistant enclosure: think about putting a watch in a jam jar.
At around the same time, other manufacturers such as Panerai, Hamilton, Waltham, etc, also produced dive watches, where water resistance was an integral part of the watch itself. The American firms favoured the canteen crown: an additional screw-on cap over the crown to prevent water ingress through the stem tube. This design was also adopted by Zlatoust for its famous professional dive watch.
After WWII saw the advent of many other dive watches, such as Lip-Blanpain Fifty Fathom, Rolex Submariner: these came on the market in the 1950s. However, these were meant to be for professional, or serious diving enthusiasts, rather than for general consumption.
With the market ripe for dive watches for the masses, many other dive watches were designed and introduced, and Vostok wanted to get into this business as well. The design solution we know as Amphibia was very different from the others.
It goes without saying that a dive watch needs to have enhanced resistance against water ingress when fully submerged, and can withstand increased water pressure when dive deeper. As a watch needs to be assembled from numerous parts, there are three main areas where water can gain entry:
1. Crystal. The watch dial has to be read, so that a transparent crystal needs to be fitted to the front: it is this crystal mounting system that can allow water ingress.
2. Caseback. For assembly, the movement needs to be put into the watch case, and then sealed with the caseback.
3. Crown. The movement needs to be manipulated, such as winding and time setting from the outside, so a crown needs to be incorporated.
It is worth mentioning in passing that the Zlatoust diver eliminated the second factor by having no detachable caseback: the whole watch is assembled from the front crystal side, and the sealing of the crown is effected by a canteen crown. Made as a professional diver's instrument in limited numbers, manufacturing cost and ease of maintenance were not high on the list of priorities in its design considerations.
The Amphibia Design Approach
The two designers, Mikhail Novikov and Vera Belova, examined the existing dive watches on the market and noticed that the design approaches were somewhat in wanting. Basically they were using brute strength to counteract against water pressure, on a piece-meal basis. They rejected all these designs and came up with a most elegant, integrated technical solution which we shall examine in further detail.
The fundamental concept of the Amphibia design is not to use brute strength to fight water pressure, but instead utilizes water pressure to enhance water resistance. This design philosophy can be seen in the three aspects mentioned earlier.
It goes without saying that dive watches have comparatively thick and strong crystals, and dome crystals have the added benefits of being stronger. Novikov and Belova elected to use acrylic crystal, conventionally fitted into the front of the watch.
What we call acrylic is actually a transparent thermoplastic polymer, technically known as poly(methyl methacrylate), PMMA for short, better known under its propriety names Lucite, Plexiglass, and Perspex. The combibation of PMMA material and dome shape creates an interesting characteristic: while the dome shape can withstand significant pressure load on the convex - external - side, the slight flexibility also allows it to deform minutely, increasing its diameter when a pressure load is applied.
The Amphibia crystal profile - thickness, and both internal and external curves - was carefully calculated with respect to the mechanical characteristics of PMMA. In actual production each crystal needs to be individually machined to a high level of precision, so that it can fit into the watch case tightly, to effect the first phase of water resistance. When submerged, the increasing water pressure will flatten the crystal, making its circumference minutely greater along the way, which increases the effectiveness of the seal between the crystal and the watch case.
An added consideration is that, at a depth of 200m, water pressure reaches 20kg per square centimetre, this makes the crystal pushed in by about 0.5mm. During the design phase of the crystal profile, special care was given to allow for sufficient clearance, so that the inside surface of the crystal would not hit the hands mechanism.
On the other hand, conventional dive watch design merely tries to make the crystal as strong as practically possible and held down with as much strength as possible: hence the brute strength approach. This is particular true when flat mineral and synthetic sapphire crystals - now much in vogue - are employed, which cannot distort at all, but just shatter.
Additionally, the use of glass crystal, be it mineral glass or synthetic sapphire, would put it under tremendous stress if in dome form. When fitted into the front of the watch case, the perimeter is under tremendous radial load; in other words, the bezel holding the crystal is constantly squeezing the crystal as if to make its diameter smaller. This causes the crystal itself to be under very high stress internally, and if a tiny scratch is made on the surface, this becomes a stress razor for the stress to escape, in the form of the crystal exploding with huge force. An example is a modern watch known as the "Mini Fiddy", and its domed crystal exploding is not a particularly rare phenomenon. A crystal made of PMMA would completely avoid this problem.
Here is a picture of the Amphibia crystal as fitted to a Type 470 case, note the height of the crystal standing proud of the case, indicating its thickness.
As a comparison, this drawing (by WUS member cmoy) shows the cross section of an advanced dive watch design by Jenny Carribean, who owns the famous brand Doxa:
While its performance is fine, it shows the need for a massive screw down bezel ring to hold everything together, and no fewer than three O-rings to secure the crystal. How well the crystal is secured with a good seal against water ingress primarily depends on how well the threaded ring is screwed in and stayed in. Furthermore, the inherent issue with using O-rings in this manner is further discussed in the next section. It is an effective design, as long as the assembly was done correctly and the O-rings are in good order, and pretty much obligatory for its design where the whole watch is assembled from the front, like the Zlatoust diver. I feel sure that there exist other dive watches with a regular caseback employing similar systems for securing the crystal, but in this context it is not as elegant as the Amphibia approach.
The Amphibia caseback also takes advantage of water pressure to effect and enhance water resistance. In a nutshell, to make the caseback water resistant, it is all in two words: squashing rubber. But how much rubber is squashed, and how it is squashed, are also important.
A conventional dive watch employs a once-piece caseback, with a relatively slim rubber O-ring, normally fitted to the caseback, to effect water resistance. When screwed into the back of the case, the O-ring is compressed, making a seal.
However, this method has distinct drawbacks. When the caseback is screwed in, the compression of the O-ring is invariably coupled with a tangential shearing action along the perimeter. The nature of the screw thread is that, a small compression is achieved by a large degree of rotation, hence the O-ring has to be quite slim to allow for this magnitude of shear load. The use of O-ring grease helps to decrease the initial shear distortion, but it is part and parcel of this design, which also means that the overall seal surface is small. The significant distortion of the O-ring also necessitates its replacement every time the caseback is taken off, and also a need for it to be pressure tested to ensure the O-ring is still in good order. But if a larger flat gasket is used, then it would not give enough shear distortion to result in sufficient compression, so that is definitely a no-go.
The Amphibia design eliminates these issues in one stroke. The caseback drops into the back of the watch case, and has two keys which mate with keyways in the case, preventing the caseback from rotating altogether. Then a threaded locking ring is screwed in, this presses down the caseback on the comparatively huge flat rubber gasket, which bears only compression load. This way, the gasket can be very big, giving a total seal surface many times greater than what can be offered by the O-ring in conventional designs. Needless to say, the gasket has no wear whatsoever, and there is absolutely no need to replace it.
These are pictures of typical Amphibias showing the external appearance of the two-piece caseback, and how it appears when disassembled.
Under high water pressure, the caseback is still pushed in by a small amount. At 200m depth, the gasket is further compressed by about 20-30%. But this causes no problems at all: in fact it enhances water resistance. Novikov and Belova, however, found that regular rubber gaskets such as those used in Komandirskies, have an inherent problem. During surfacing, the decrease in pressure should allow the gasket to bounce back to its original thickness in real time, but the rubber material could not do so in time. New rubber processing methods were developed and a sintering system was settled on: the rubber material is first ground into a fine dust, then put under heat and high pressure. This makes the individual particles to fuse together, resulting in a uniform and smooth rubber sheet, from which gaskets are made by the process of die-cutting. This sintered rubber has the correct rebound performance, ensuring total water resistance during surfacing.
This picture shows the gasket removed from the case, showing it is a wide, flat piece of rubber.
The Amphibia two-piece caseback design is undoubtedly a significantly superior design than the conventional one-piece configuration. It is actually quite costly to build, requiring more parts, and expensive parts at that. But the performance benefit is unquestionable, and each time it is opened, there is no need to install a new part, and to perform a test to see if that new part actually works: if it does not, then the watch would be flooded, incurring further cost.
For most dive watches, the stem and stem tube are made to have as little clearance as possible, with the correct application of a suitable grease, a degree of water resistance can be achieved. A screw-down crown would make it even better.
A watch with standard keyless works offers two stem positions: pushed in it winds the movement, pulled out it adjusts the hands. But for a watch with a screw-down crown, the crown needs to be in three positions: the crown needs to go in further when screwed down, and a clutch has to be incorporated so that when the movement is fully wound, where the stem cannot turn anymore, the crown can still turn further to screw to the crown tube.
The conventional Swiss approach incorporates either an internal, or external thread in the crown tube, as shown respectively in the following drawings, kindly prepared by member lysanderxiii:
In both cases we can see the crown is internally spring loaded, to pull it away from the stem in order to keep the clutch engaged; only when the crown is being screwed home that the clutch is disengaged as the stem cannot go into the keyless works any further, despite the pressure of the spring. So the stem is under constant pressure, being pushed into the keyless works. At the same time, the joint between the stem and stem tube is very tight without offering leeway movement.
Originally designed to employ the "Mir" 2209 hand-wind Vostok movement, the designers could very well adopt these established approaches. But regular hand-winding has a possibility - however remote - that lateral pressure can distort the stem, unless the stem is made to be quite stout.
Many novices are alarmed by the characteristic "wobbly crown", but this is part of the design feature, with extra benefits.
Like the designs detailed before, the Amphibia crown and stem assembly incoporates a clutch between the two pieces, hidden inside the crown: they are coupled only when the crown is pulled slightly away from the stem, otherwise they are decoupled and the crown wobbles somewhat in relation to the stem. During winding - and time setting - the crown needs to be manually pulled away slightly as it does not incorporate an internal spring, eliminating the pressures imparted on the keyless works, and the inherent "wobble" prevents the stem from getting bent.
When the crown is screwed in, the clutch de-couples, which means the crown and case become one unit, and the movement and stem become another. In the unlikely event of serious shock, where the movement moves minutely within the case, this decoupling means that the stem would never bear any load, and the wide clearance between the stem and stem tube facilitates that. The conventional designs do not offer this built-in protection.
This picture shows the very slim stem and the comparative large crown.
Many terms has been used to describe Russian design and engineering: "crude but effective" is most often heard. It is pointless to question the effectiveness of the Amphibia design; in fact it is far more advanced than anything else. Using a clear vision to see the actual requirements, and then arriving at a most effective solution, is anything but crude; in fact it is the art of the designer at its highest order. By comparison, no matter how finely a one-piece caseback is made and decorated, it is still no more than a glorified jam jar lid. To be realistic, it is better to consider the Amphibia design as an example of design, rather than a "Russian" design, and judge its merits as such.
What if Novikov and Belova worked in Switzerland, and the Amphibia design was for a big-name Swiss manufacturer? What if Lip-Blancpain's Fifty Fathom was launched a few years later and employed the Amphibia design? These we can only speculate. One thing for sure: the Amphibia is a masterpiece, which demonstrates how designers should approach problems and requirements. It must be among the greatest watch designs in the parthenon of horological history, along with its talented creators. When superficial styling is confused with design, this serves as a fine case study of the essence of the design process itself.
P.S. I would welcome comments and suggestions, please visit this thread. Thank you.