Seiko Prospex SRP773 Turtle Diver - A beautiful case; Similar to the SRP775, SRP777 and SRP779, A Review

I have been following the progress of Seiko dive watches for some time now. I have in my collection quite a number of Seiko divers (you can view them here: http://easternwatch.blogspot.co.id/p/blog-page_4.html). However, it is one model of Seiko diver that I have not been able to get, the 6105, or more affectionately known as the "Turtle Diver".

Granted, it is still possible to get one in the secondary market but I try to keep my collection from pre-owned pieces. However, I am still open to homage pieces. For the 6309/6105, I got a homage by Athaya Vintage, the AV002 Lamafa.

For the last two years, Seiko have started to reissue (more like reinterpret) some of its classic models for the modern collector. This is very exciting for collectors such as myself as it gives me an opportunity to get watches that are no longer in production (Here are some of them which I was able to collect - SBEX001G, SNKN45K1 and SNKM79K1).

In November 2015, Seiko announced a modern reinterpretation of the classic turtle divers of the 1960s and 1970s. The reissue is more akin to the original 6309 than the 6105. More about it later.



The watch comes in four options. Both the SRP773K1 and SRP775K1 comes with bracelets where the former has a blue dial while the latter has a black dial and yellow/gold accents minute markers on the bezel. The SRP777K1 and SRP779K1 comes with black silicone strap and dial. The SRP779K1 has a Pepsi bezel. The watch comes with a Prospex designation.

Source: WUS. From the left: SRP775K1, SRP779K1, SRP773K1 and SRP777K1.


My personal choice is the SRP773K1 which was the unit that I got and being reviewed here.

The package that came with the watch is in two set of boxes, one inside the other. The outer box is a two piece cardboard white box construction which holds the main watch box (also white) as well as the manual and guarantee dockets. On both boxes, the “SEIKO” brand is prominently printed on the top in silver.


The watch has a width of 44.3 mm and a height of 14 mm. The lug width is 22 mm while the lug-to-lug distance is 48 mm. The iconic cushion case features a unidirectional bezel, an unsigned screw down crown, a water resistance of 200 meters, and a screw case back featuring the famous ‘Tsunami’ logo.

The glass protecting the dial is Seiko’s proprietary “Hardlex” crystal. This material is a Seiko in-house hardened mineral crystal and comes in at least two different varieties. Since this watch is under the Prospex line and is also an ISO certified diver (more about this later), the version of Hardlex for this watch is of stronger quality compared to what goes on Seiko 5 watches.

Although this material scratch easier than sapphire, it has much more flexible. For example, since sapphire is harder, it is more brittle: Hardlex resists impact much better than sapphire; it is easier to shape (into a dome) compared to sapphire; and the price is way cheaper. If given a choice, I am more inclined for sapphire crystal instead.

The watch comes with a day and date function located at the 3 o’clock position. The main hour markers are wide dots with while the 6 and 9 hour markers are obelisk shaped. The 12 o’clock marker has two obelisk shaped sections with a “sword” separating the two. On the sloped chapter ring are minute markers. I was made to understand that the set-up is similar to the original 6309. Another similarity is the short broad sword style hours hand and the arrow-like style minutes hand. Only the seconds hand is a more modern interpretation with where the “lollipop” is on the back instead of the front in the original 6309. All major indices as well as the two main hands (for the seconds hand, only the lollipop is lumed) are liberally painted with of Seiko’s “LumiBrite” paint.

There are five lines of text and logos on the dial. The “SEIKO” brand is the only text on the top half of the watch. On the bottom half of the dial you will be able to see the Prospex logo, the words “AUTOMATIC”, “DIVER’S 200m” and, in extremely fine font size, the words “4R36-O4Z4 R 2”. The first part of the last line refers to the movement used in the watch. The next part is something that I cannot decipher. It could refer to where it was made. If anyone of you knows, please feel free to leave a comment below.

Despite the many lines of graphics, the dial does not look cluttered and the whole thing looks balanced. In fact, the thick amount of LumiBrite paint gives a 3-dimentional effect to the dial which is obvious at any angle of view.


The bezel is unidirectional with 120 clicks. A luminous pip is located at 12 o’clock. There are minute markers and Arabic numbers at every 10 minutes mark. The bezel is sloped towards the crystal and it has a coin-edge side to facilitate gripping.

As highlighted earlier, the large screw down crown is devoid of any marks. Located at the 4 o’clock position, the crown has a finer coin-edge side and is approximately 7 mm wide. Under lockdown, the crown in partially protected by the watch casing. The crown has 3 working positions: the first is to wind-up the movement, the second to adjust the day and date, and the third to adjust the time.

The SRP773 has lug holes which were missing in the original 6309. This is a convenient way for changing straps and bracelets.

As highlighted earlier, the lug width is 22 mm. The bracelet that comes with this watch tapers to 20 mm at the centre clasp. It has a simple diver’s extension and four micro-adjustment points. The links are connected by a pin-collar retaining system. I had the opportunity to try out the other models under this series that came with the strap and I must say the silicone material used is so much smoother and much suppler than then original Seiko rubber straps.

Earlier I mentioned that this watch is an ISO certified diver. What I meant is that this watch conforms to the ISO 6425 international standards for diving watches. For more detail on this standard click here: ISO 6425.

This watch officially retails for RM2,014 in Malaysia. Depending on where you get it, discounts can be varied. Do shop around. I was able to get mine for RM1,450.

Under the rather clean screw-down case-back is the Seiko 4R36 caliber movement. Operating with 24 jewels and 21,600 bph (or 3 Hertz), it is an automatic movement with hand “windable” and seconds hand stop capabilities. It also powers day and date wheels and its main springs have 41 hours of power reserve. Based on specifications, it is rated for an acceptable error of -35/+45 seconds a day. In reality, the actually performance is far superior.

In some of the reviews I’ve read, two areas of contention were highlighted. The first was the use of Hardlex glass instead of sapphire crystal andthe second was the use of the 4R36 movement instead of the more refined 6R15 series movement.

For the first issue, I am more inclined to support the argument. Since the glass window is flat and under the more renowned Prospex series, having sapphire as the crystal would give it the added quality to differentiate it from other ‘common’ divers under the Seiko brand. However, from a product placement perspective, what Seiko did conforms to the differentiation strategy which it practices for its watches. For all intense and purposes, using Hardlex makes it even more “Seiko” as the Company can now boast that everything was made and concocted in their in-house factory. Unfortunately, it is hard for me to accept Hardlex as I view sapphire crystal as something of value. In practical terms, Hardlex is more ‘value-for-money’ compared to sapphire.

For the second issue, it is more complex. From a comparative perspective, below are some statistics about the two movements.

4R36	6R15
Beat at 21600 bph Lift angle is 53° Hack and handwind Automatic winding mechanism The acceptable daily rate for the 4R36 is: -35/+45 seconds a day, +/- 30 seconds day isochronism fault, +/- 30 maximum positional variation, 40 hours power reserve (SPRON110 mainspring).	Beat at 21600 bph Lift angle is 53° Hack and handwind Automatic winding mechanism The acceptable daily rate for the 6R15 is: -15/+25 seconds a day, +/- 10 seconds day isochronism fault, +/- 15 maximum positional variation, 50 hours power reserve (SPRON510 mainspring).

From the specifications above, the 6R15 is far better than the 4R36. The main differences in materials and construction between the two calibers are the balance spring, mainspring and the adjustment lever.

These are made from a special formulation of Seiko's SPRON material. The balance spring in the 6R15 is better suited to handle temperature and positional variations. The mainspring in the 6R15 has approximately 20% longer reserve and the spring unwinds more uniformly than the one in the 4R36.

These are the things that account for the tighter specifications on the 6R15. Most other parts are common to both calibers so there shouldn't be any disparity in quality, robustness or longevity.

For a perfectionist, the 6R15 is desirable. However, from a practical point of view (and taking into account overall costs), the 4R36 is more than able to perform what the watch was designed for. In this case, I am indifferent.



There are a number of reasons that I like the turtle case (or more commonly known as cushion case). The most obvious is the shape. It helps the wearer to use the watch with formal wear. The case slide smoothly under cuffs and reduces the possibility of snagging on things.

The shape of the lugs also contributes towards wearing comfort. The curvature designed into the lugs hugs the wrist naturally and it allows wearers with thinner wrist to carry the watch more confidently.

The last reason is the most subjective, the overall shape. It is hard to put it in words but to me, it looks so pleasing on my wrist. Compared to the typical round case watch, the turtle (cushion shaped) casing looks more in sync to a human wrist – it looks more natural. I just love it.

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