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  • Water Resistance

    (Re-posting of a reference post from Sep 22, 2009 that seemed to be missing from the new vBulletin TKNZ Forum).
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    I often get into arguments (Dad tells me to call these 'Vibrant Discussions') over the Water Resist Rating of a watch..... 300m Baby Tuna says 300 but so does a Rolex Submariner..... which is more suited to water use - or just what does WR300, WR50 or ISO 300m He. actually mean??

    This guy here (Joakim Agren, thank you for letting us steal the work) from the Casio Forum says it just a little better than I can (perhaps he's educated)..... grab a beer Team.....


    'First we need to conclude what is water resistance in the watch world?

    In the watch world a watch need to get a IP code rating in order for the mark Water Resistant to appear anywhere on the watch body(notice though that the rating only apply to individual parts not to the whole watch so if a WR rating appears on the wrist band but not on the case it is not a valid mark for the watch case). So what is IP code rating? well IP stands for International Protection or Ingress Protection. There is different IP codes for different types of "Ingress" protection. In case of Water protection there is 2 certifications. The most common one is the IP code ISO 2281.

    ISO 2281:

    The International Organization for Standardization issued a standard for water resistant watches which also prohibits the term waterproof to be used with watches, which many countries have adopted. In order to pass for this certification it is not required for each and every individual watch to be subjected to tests, only lot sampling is required.This standard was only designed for watches intended for ordinary daily use during exercises under water for a short period under conditions where water pressure and temperature vary. The tests are:

    Immersion of the watch in 10 cm of water for 1 hour.

    Immersion of the watch in 10 cm of water with a force of 5 Newton perpendicular to the crown and pusher buttons (if any) for 10 minutes.

    Immersion of the watch in 10 cm of water at the following temperatures for 5 minutes each, 40°C(104F), 20°C (68F)and 40°C(104F) again, with the transition between temperatures not to exceed 5 minutes. No evidence of water intrusion or condensation is allowed.

    Immersion of the watch in a suitable pressure vessel and subjecting it to the rated pressure for 1 hour. No evidence of water intrusion or condensation is allowed.

    Exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.

    No magnetic or shock resistance properties are required.

    No negative pressure test is required.

    No strap attachment test is required.

    No corrosion test is required.

    So in short it means that the minimum requirement is that the watch will pass a 20 meter(66') test. However if the watch have a different rating then just plain Water resistant for instance a 30M, 50M,100M,200M etc rating then it needs to be tested in a a pressure chamber with a static overpressure equvivalent to the pressure at that depth.

    What about Divers watches?

    ISO also have a certificate for them to it is called:

    ISO 6425

    The difference from ISO 2281 is that here not only sampling is required but each and every watch must be tested to 125% to the rated depth so a 200M Divers watch must be tested down to 250M. And also the other tests are much more comprehensive. Here is the list for all the tests and requirements:

    ISO 6425 water resistance testing of a diver's watch consists of:

    Immersion of the watch in 30 cm of water for 50 hours.

    Immersion of the watch in water under 125% of the rated pressure with a force of 5 N perpendicular to the crown and pusher buttons (if any) for 10 minutes.

    Immersion of the watch in 30 cm of water at the following temperatures for 5 minutes each, 40°C (104F), 5°C(41F) and 40°C(104F) again, with the transition between temperatures not to exceed 1 minute. No evidence of water intrusion or condensation is allowed.

    Immersion of the watch in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 2 hours. The pressure must be applied within 1 minute. Subsequently the overpressure shall be reduced to 0.3 bar(negative pressure) within 1 minute and maintained at this pressure for 1 hour. No evidence of water intrusion or condensation is allowed.

    For mixed gas diving the watch has to be immersed in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 15 days in a (helium enriched) breathing gas mix. Subsequently the overpressure shall be reduced to normal pressure within 3 minutes. No evidence of water intrusion, condensation or problems caused by internal overpressure are allowed.

    An optional test originating from the ISO 2281 tests (but not required for obtaining ISO 6425 approval) is exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.

    Except the thermal shock resistance test all further ISO 6425 testing should be conducted at 18(64.4F) to 25°C(77F) temperature. The required 125% test pressure provides a safety margin against dynamic pressure increase events, water density variations (seawater is 2 to 5% denser than freshwater) and degradation of the seals.

    Additional requirements for mechanical watches are:

    Besides water resistance standards to a minimum of 100 meter (330 ft) depth rating ISO 6425 also provides minimum requirements for mechanical diver's watches (quartz and digital watches have slightly differing readability requirements) such as:

    The presence of a unidirectional bezel with at least at every 5 minutes elapsed minute markings and a pre-select marker to mark a specific minute marking.

    The presence of clearly distinguishable minute markings on the watch face.

    Adequate readability/visibility at 25 cm (9.84") in total darkness.

    The presence of an indication that the watch is running in total darkness. This is usually indicated by a running second hand with a luminous tip or tail.

    Magnetic resistance. This is tested by 3 expositions to a direct current magnetic field of 4,800 A/m. The watch must keep its accuracy to +/- 30 seconds/day as measured before the test despite the magnetic field.

    Shock resistance. This is tested by two shocks (one on the 9 o'clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3 kg hammer with an impact velocity of 4.43 m/sec. The change in rate allowed is +/- 60 seconds/day.

    Chemical resistance. This is tested by immersion in a 30 g/l NaCl solution for 24 hours to test its rust or corrosion resistance. This test water solution has a salinity comparable to normal seawater.

    Strap/band solidity. This is tested by applying a force of 200 N to each springbar (or attaching point) in opposite directions with no damage to the watch of attachment point.

    The presence of an End Of Life (EOL) indicator on battery powered watches.

    Watches conforming to ISO 6425 are marked with the word DIVER'S to distinguish diving watches from look a like watches that are not suitable for actual scuba diving.

    Most manufacturers recommend diving watches have their seals changed and the watch pressure tested by an authorized service and repair facility every three years or so.


    So what do all of this means?

    For ISO 2281 watches there is a gigantic range of underwater performance. The ISO 2281 certification does not indicate that a manufacturer must test a watch to failing point and rate it below its failing point, however it must be rated to the maximum pressure test it passed. Its totally up to the manufacturer to descide for each individual watch model exactly what level they want to test it at. So this means that a specific rating is merely a market descision and a way for manufacturers to rate watches differently plainly to justify different price points in their line up of watches. The International Standard Organisation (ISO) have however created a recommendation table that is often found in watch manuals and brochures:


    Water resistance rating Suitability:

    - Water Resistant 30 m or 50 m Suitable for water related work and fishing.NOT suitable for swimming or diving.

    - Water Resistant 100 m Suitable for recreational surfing, swimming, snorkeling, sailing and water sports. NOT suitable for diving.

    - Water Resistant 200 m Suitable for professional marine activity and serious surface water sports. NOT suitable for diving.

    - Diver's 100 m Minimum ISO standard (ISO 6425) for scuba diving at depths NOT requiring helium gas. Diver's 100 m and 150 m watches are generally old(er) watches.

    - Diver's 200 m or 300 m Suitable for scuba diving at depths NOT requiring helium gas. Typical ratings for contemporary diver's watches.

    - Diver's 300+ m helium safe Suitable for saturation diving (helium enriched environment). Watches designed for helium mixed-gas diving will have additional markings to point this out.

    This table of recommendations helps manufacturers to descide what rating to choose and therefor what pressure test level to use depending on the intended use of a watch that they had in mind for a specific model. So this means that if a manufacturers design and development team comes up with a new design to the managment team it is then up to the marketing and managment department of the company to descide first if they will release it to the pucblic and if so to descide what position in their line up it should have. Depending on that descision it will be subjected to different pressure in the over pressure test.

    Thats right people! the rating on the watch is merely a market descision and not an actual fact of the capacity of the watch in question. This means that the capacity between different watches with the same rating can be significant. one 30 meter watch can vary greatly in maximum capacity from another 30 meter watch(hence the low recommendation for 30-50 m watches in the table above), the same is true with 50 m and 100 m and even 200 m rated watches, infact sometimes the most extreme examples the difference is so great that one watch that is merely rated at 50 or even just 30 meters can compete in capacity with another watch from a different manufacturer that is rated to 100 meter. So the ratings actually don't mean much and is not neccessarly indicative of a watch performance underwater....

    That's a shocker is it not?

    To use some examples I use Casio and Suunto. For instance the Suunto Vector does have a great track record of durability and many people have used it harshly in the field and even used it to make shallow and medium dives down to 15-30 meters(50-100') and yeat it was only tested by Suunto for a 30 meter rating and according to the recommendation table that means that it should not be submersed at all. An even more absurd example is the new Suunto Core that also have only a 30 meter rating and yeat is equiped with so called stinger buttons that is made to be used under water and also it comes equiped with a depth gauge so clearly the module and case designers had higher goals for it. Then the marketing department within the company that descided that it should not compete for customers with their more expensive diving computers or the Suunto Observer and therefor only tested it for a lower rating, a different marketing descision and it could most likely have a 100 meter rating.

    This is one of the more extreme examples but it still holds true for all manufacturers. Rating is not an abosulte truth it is merely marketing descisions and the difference in performance between equally rated watches can be great. Other examples is Casio Pathfinder/ProTrek watches that seems very sturdily built and yeat most of them (PAW-1500 beeing the exception) is rated to 100M but would not surprise me if they would survive at 200 meters and therefor compete with many 200 meter watches when it comes to underwater performance.

    Another example is Casio G-Shock watches that is rated to 200 meter which is usually the highest rating under ISO 2281. They are inexpensive massproduced watches so if Casio descided to give it a ISO 6425 Divers rating it would increase the cost of manufacturing since then each and every watch has to be subjected to tests, this would increase the cost and hence the consumer price. Therefor (with the exception of the Frogman which is considered a premium G with a higher price point and special dive functions in the module) all G-Shocks are only rated according to ISO 2281 despite the fact that most of them would most likely pass the Divers test with flying colors and several of them would rival the Frogman in under water performance.... once again market descisions descides the rating..... it would not surprise me one bit if many G-Shocks could survive just fine at 300-400 meters water depth its just that they have never been tested by the manufacturer for that level of performance......

    The examples I have above are the positive ones where they are underated officially. But it ofcourse goes the other way around as well, most notably are the fragile jewellery and dress watches that probably just barely meet their ratings during the testing, but there is also some surprises for instance the Tissot T-Touch an advanced ana/digi ABC watch that orininally where rated at just 30 meter just like the Suunto's but that model even though it appears rather rugged looking seems to not be so strong considering the unsual high failure rates in water that model has had.

    So the final conclusion regarding ratings is that you should not trust them very much, they don't mean much and is often a mere marketing tool and the difference between models can be great. Infact most of the time we as consumers nor the manufacturers them self knows a particular models maximum performance.

    What About Dynamic Pressure?

    This perhaps is the biggest myth and urban legend of all. It was mostly created by the watch industry and then spread trough watch retailers and watch brochures and manuals then also trough word of mouth of course. It was not so widespread in the 80's but by the late 90's and early 2000 it had spread alot.

    Why they spread that myth to begin with probably have to do with weakening the warranty terms and the fact that they want to encourage people to be carefull with their watches.But also primarly due to marketing reasons that enables them to charge a extra premium for higher rated watches.

    Anyway the myth is about movement in water. Apparently as you move around in the water especially your arms an extra pressure gets applied to the watch and the deeper in the water you go the higher this extra presssure will get due to the movement. I have read statements that these movements can add several Bars/ATM/PSI of pressure to a watch. Therefor it is not safe to take your watch anywhere near its stated deepth rating. I have read statements that you should not go any deeper then maximum 30 meter(100') with a 100 m rated watch or 60-70 meter (200-230') with a 200 m rated watch. 30-50 m rated watches should not be submersed at all.

    Whats the major problem here?

    First let me state that I was a firm believer of this "Dynamic Pressure" myth up untill just a few months ago. This whole journey into this topic for me was the presentation of the Suunto Core on Suuntos website prior to its actual release. I thought it looked fantastic and almost imediatly feel in love with it especially in combination with its seemingly superior feature set compared to the competion. Prior to the Core I pretty muched ruled out Suunto out of the realm of my interest frame when it came to ABC watches, not because of their active functions which in fact many times where even better then for instance the PathFinders/ProTrek of the Casio line up, but because I saw them as fragile crap due to their poor 30 M water resistance rating(the Observer with 100 m rating was an exception but did not appeal to me for other reasons). But when the Core was presented on Suuntos website it seem to have it all including a 100 meter rating.

    But when it was closer to the Core's release I suddenly noticed that the specs had changed on Suuntos website now it was suddenly rated to 30 M just like its predeccesor the Vector so I was very dissapointed and descided to mail Suunto to get it clarified. Apparently they did a misstake before and that 30 m was the correct fact. But by that time I had already worked up enough interest for the model so that I contemplated buying it anyway, all that I demanded from it was that I could do some surface swimming with it then I would be happy. So I mailed Suunto and asked again if i could use it when swimming. And the answer was yes!

    This confused me because what I knew prior to this told me that 30 m and 50 m watches should not be used for submersive water activitys such as swimming, what confused me even further was the fact that the Core came equipped with specially designed stinger buttons called UW(Under water buttons by Suunto) also the demo on the website showed it was also equipped with a cool depth gauge down to 10 meters which further suggested this was a watch that could be used under water.

    At first this lead me to believe that Suunto since it is a special company that has a very scientific image that pride themself with preciscion instruments for professionals was more honest with their rating and therefor took Dynamic pressure into account for their rating and gave their watches a more honest rating then the rest for the watch industry so therefor a 30 M Suunto was the equvivalent to a 100 Meter watch from other manufacturers.

    But this turned out to be a wrong assumption, I later found out that they just test their watches according to the standard ISO 2281 just like the rest of them.

    So because I was a believer of the dynamic pressure theory all I was left with was a big mystery, how come a 30 m rated watch was seemingly adapted for underwater use?

    This mystery lead me to seek out the answer and learn more about water resistance and the effects of dynamic pressure specifically. I did found some important pieces to the puzzle here in this forum from older forum posts but also from Wikipedia and also some Swedish scientists that I had enquired about this mather.

    What I did found out shattered the dynamic pressure theory to pieces. It simply was nothing more then a lie turned into an urban legend and myth.

    Apparently pressure can only be applied to an object as the result of added mass/weight that is applied to the object(in this case added depth with an increased weight of the water pillar above you) in question, or as a result of expansion or due to electro magnetism, another possible source of pressure is some external forcing preventing expansion or inversion. Another source is gravitational pull due to accceleration or decceleration but that reason is somewhat tied in to reason number one the one about added mass.

    So what kind of forces can a swimmer/diver apply to his/hers watch? first we have the depth ofcourse. If we use a watch similar in size to a Raysman. Lets say we are at 100 meter depth. The size of the watch is about 5cmX5cm thats 25cm2 in surface area. 1m is 100 cm so 100m is 10.000cm 10.000X25= 250.000 Cm2 of water above the watch that is pressuring against it. The weight of that water is 1000.000/250.000= 250Kg(550 ibs) of pressure against the watch at that deptht. This is known as the hydrostatic pressure.

    The diver(staying at the same depth) can only change that pressure against his watch in 2 ways either by moving his arms up or down but the maximum reach of ones arms is very limited usually not more then perhaps 120cm(4') or so.... that is only a change in pressure of 0.12 bars or 3Kg(6.7ibs) of pressure, very little difference not much more then 1% compared to the rest of the pressure at that given depth.

    Second way to increase pressure at the watch is trough speed/acceleration. Either by swimming or by moving our arms up and down. The maximum speed we can move our arms in free air is often not more then 3-6 feet per second and it moves even slower under water. And when it comes to Swim speed even an Olympic swimmer usually cant swim any faster then 6-7 feet per second. If we add the maximum output of that we get up to 10 feet or 3 meters of acceleration per second which is the equvivalant of about 10Km/h or 6.25 mph. That aint very much force/pressure in water. Someone smart here at the forum(CycloneFever) calculated this and I quote:

    "Without repeating all the calculations here (they involve denominators and the greek alphabet and are PITA to type out), at a depth of 330ft(100 m) and moving your arm at 3 ft/sec, the dynamic pressure is in the order of magnitude of 0.14 feet of head or 0.04% of the depth. Even assuming you could move your arm at 20 ft/sec (14 mph!) the dynamic pressure is only about 6.2 feet of additional depth (<2%)."

    So with this we can conclude that the Dynamic pressure is normaly a small force for a diver and do not limit your watch capacity very much. It only reduces it whit a couple of meters at most.

    So what can we conclude:

    1. The Standardisation does not indicate a watch maximum capacity.
    2. The rating is given by the manufacturer mostly due to marketing reasons and often the maximum capacity of a watch is seldom tested.
    3. The difference between different watches with the same rating can be huge....
    4. Dynamic Pressure is mostly just fear mongering and a myth.'



    So, we see the humble Seiko Baby Tuna is rated as more suited to the Sea than a Rolex Submariner!
    Harlan
    Timekeeper Watch Club
    Auckland, New Zealand, Pacific Ocean, Earth
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