Seiko Baby Tuna Review (SRP641) – A Cheaper Version Of The Famous Seiko Tuna Watch


Hi guys! In this post, I’m going to write about the Seiko Baby Tuna Review (specifically the model no. SRP641 black color). It’s a diver’s watch from the Japanese brand and has a one of a kind look.

I mean, just look at how weird it is. It’s got this protective layer around the case (or what fans will refer to as the shroud) which serves to protect it from high impact.


Seiko SRP641 baby tuna black dial

Above is the Seiko Baby Tuna – the protective shroud around its case make it unique, very different than the other Sub-like diver’s watches


It’s because of this shroud the watch has a huge diameter of 47 mm, which certainly not a good fit for anyone with a small wrist.

But before we go to the review, let’s go a little way back to 1975, when Seiko first produced the Tuna watch (the watch that started it all).


History Of Seiko Tuna Diver’s Watch

In the 60s to 70s, the watch world was engulfed in a race to produce better diver’s watches – watches that can go deeper and deeper under water. Blancpain and Rolex sort of started the race and other watchmakers followed suit.

Seiko produced their first diver’s watch in 1965 with a 150 m water resistance. But of course, that’s not enough especially when the Swiss were producing watches with higher water resistance.

In 1975, the first Seiko Tuna (model no. 6159-7010, now called the Grandfather Tuna) was released. It features the shroud like protection layer around the case, giving it a very unique look.

Legend has it the “Tuna” name came to it because the watch looks like an opened tuna can lol! I can honestly say that Seiko fans have the best creativity in giving nicknames to their favorite watches such as Seiko Monster, Turtle, Sumo and others.

But apart from the shroud which gives it an extra protection against impact, the Tuna also has an increased water tightness and air tightness.


Seiko Tuna

Seiko Tuna has long been heralded as one of Seiko’s best diver’s watch around (and with the most distinct look!)


This results in it having a 600 m water resistance, as well as not needing a helium escape valve since it won’t allow helium (used in saturation dives) to get into the watch.

This is done by a special L-shaped gasket and construction that helped it being more air tight than normal watches.

The original Tuna also was made in Titanium, which Seiko claimed to be the world’s first diver’s watch made in the lightweight material.

Truly, the Seiko Tuna was a great watch in the history of the watchmaker. Throughout the years, Seiko has updated it with many variations (stainless steel case, gold plating, quartz version, etc.) to widen the model and appeal to wider segments of its customers.


Here Comes The Baby Tuna

Seiko Tuna can be said to be a higher grade of diver’s watches from the brand. It’s inside the Marine Master line up, and typically costs from $1,000 to $3,000 depending on the various specifications offered.

Tuna watches with Quartz movement will be cheaper, followed by automatic, hi-beat and spring drive movements. The titanium models will also costs premium compared to its stainless steel counterpart.

Realizing the popularity of this model, Seiko decided to make a cheaper version of the Tuna to cater to their fans with lower budget and positioned inside their Prospex (or Professional Specification) line up.

This so called “Baby Tuna” watches are smaller than the original Tuna, with lesser features and overall quality. The movement used is also the 4R36 automatic movement used in Seiko watches in the lower end of automatic watches ($200 to $300) price range.


Seiko Baby Tuna review

The Seiko Baby Tuna is what the nickname is – a baby to the original Tuna lol! But even though it’s the downgraded version of the legendary watch, this Baby Tuna still packs lots of punches in it

And unlike the original Tuna, this Baby Tuna does not have the Helium gas air tightness, which means it only suitable for air dives and not saturation dives.

But make no mistake, this watch is still a real diver’s watch. It has 200 m water resistance and complies to ISO 6425 diver’s watch standard – the same features that the other Seiko diver’s such as SKX007, Monster and Turtle have.

The best part about this Baby Tuna (aside from its more affordable price) is the distinctive shroud, which is a one of a kind thing that no other watch manufacturers do.

Well, without further ado, let’s check out the Seiko Baby Tuna review shall we.


Seiko SRP641 Baby Tuna Specification

Diameter: 47 mm
Thickness: 14 mm
Lug Width: 22 mm
Case: Black IP coated stainless steel with shroud case
Strap: Polyurethane strap

Dial: Black dial with gold accent
Watch Crystal: Hardlex crystal
Hands: Sword style hands with lume
Markers: Rectangular index markers with lume

Movement: Seiko Caliber 4R36 Automatic Self-Wind movement
Movement Features: Japanese made in-house movement, 24 Jewels, 21600 vibrations per hour or 6 beats per second, Hacking, Manual winding
Accuracy: +- 15 seconds per day
Power Reserve: 41 hours

Water Resistance: 200 m
Other Features: Day and date display, Unidirectional rotating bezel, Shroud for impact protection, Screw down crown, Seiko’s Lumibrite lume, Complied with ISO 6425 Diver’s watch standard

Best Place To Buy: Amazon, MSRP is $575


A Huge 47 mm Case – Thanks To The Shroud Layer

From the first look, we can see that the watch is quite big. At 47 mm diameter (excluding the crown) it’s well bigger than most other watches. And it’s easy to see that the bump in size is due to the shroud case.

The case is not built one-piece with the shroud. Instead, the shroud is put in place around the case by 3 screws around the watch.

The idea of having the shroud is to protect the watch from impact. But in my opinion, I don’t think any great impact will come from the sides as logically, most of the impact should come from the top of the watch, which already is well protected by the bezel and hardlex crystal.

So having the shroud is not that much of a help – after all hundreds of other diver’s watches don’t have them and are working fine.

But I do agree that having the shroud will give this Baby Tuna (as well as the Tuna) its distinctive look that makes them unique. So is the shroud a cosmetic thing? Well, I believe so. Let me know if you think otherwise in the comments section below =)


Seiko SRP641 on hand


The Seiko SRP641 comes with a black IP coated on its stainless steel case, though Seiko also produced a normal stainless steel version too. The watch is strapped to a polyurethane band via its 22 mm lugs.

Speaking of the lugs, the watch has short lugs to keep the lug to lug distance as minimal as possible to make the watch wearable by normal guys.

Overall, the case is a high quality case, as what we can expect from Seiko. The shroud do give it a very unique look and it’s highly likely you are the only one wearing this watch in your town (unless you are going for a diver’s meetings lol!).


Monster-Like Dial Design

The dial is black in color with gold accent around the markers, hands and signatures. And it’s really looking like the dial of Seiko Monster first generation.

I mean the big bulky markers and the bezel markings are almost the same. This makes this Baby Tuna to has quite a busy dial, even though it’s a large watch.

In comparison, the Tuna has circle markers and simpler dial layout which is something that I prefer.

But then again we need to understand that the Tuna is a high end diver’s watch and it’s improper for Seiko to simply copy the dial layout for the cheaper Baby Tuna.

They need to ensure the Tuna brand is not diluted further by making them look totally identical to each other.

That aside, the big over-sized markers and hands give ample of space to put some LumiBrite goodness on it. The result is a very clear and bright lume that’s even visible when the room is mildly dark. That’s Seiko’s lume for you!


Seiko SRP641 baby tuna lume

The lume on this Seiko SRP641 Baby Tuna is as bright as what you’d expect from Seiko


The watch also has the date and day display – very nifty and convenient for anyone wanting to use it everyday.

Apart from the gold accent of this SRP641, Seiko also produced a total black dial (SRP637) and black dial with yellow accent (SRP639).


Seiko SRP641 baby tuna side


200 m Water Resistance And ISO 6425 Compliance

As mentioned earlier, this Baby Tuna is a real diver’s watch with all the features. It’s after all inside the Prospex line up of Seiko, famed for its features.

The watch complies to ISO 6425 diver’s watch standard, which means it’s totally okay to use it for diving and other water activities.

Apart from the 200 m water resistance, the Baby Tuna also has unidirectional rotating bezel (to time elapsed diving time), screw down crown and Seiko’s diver’s polyurethane strap.

Seiko 4R36 Automatic Movement

Inside the Baby Tuna is a well-known automatic movement, the 4R36. It’s a staple in all of Seiko’s automatic watches in the $200 to $300 price range.

It’s made in-house with 24 jewels and has 21,600 vibrations per hour. This gives the sweeping second hand a 6 beats per second.

The movement also can be hacked and manual wind, further enhancing its usability. It also has a power reserve of 41 hours, a bit short of 2 days.


Seiko Tuna Vs Baby Tuna

So what’s the difference of Seiko Tuna vs its’ little brother, the Baby Tuna? I’ve compiled this list to give a glimpse of what’s the items that Seiko downgrades to make the Baby Tuna as affordable as it is now.

A showdown of the Tuna (above) and Baby Tuna (bottom). Well, we already know which one is going to win =P


In summary, the Seiko Tuna has:

1- Higher grade case in the Tuna. It’s larger (at 50 mm diameter) and better finished than the Baby Tuna. The Tuna also has Titanium versions and ceramic shroud versions which basically make the shroud scratch resistant.

2- Higher water resistant with versions of 300 m, 600 m and 1,000 m ratings.

3- Sapphire crystals instead of the not-so-scratch resistant hardlex.

4- Better movement. There are versions of higher grade automatic movement (with 8 beats per second) and even quartz (for those that like a very accurate watch). And there is also the Tuna watch with Spring Drive movement, Seiko’s top of the line movement with the best innovation in automatic watches giving the watch a super smooth gliding seconds hand.


Now, the Tuna will cost from $1,000 (the quartz version) to more than $3,000 (top of the line spring drive with titanium case), well more than the Baby Tuna retails on Amazon.

Does the increase in price substantiated the extra features? It’s definitely a difficult question. Let me know in the comments section what you think about the price difference of Tuna vs Baby Tuna and is it worth it to pay more for the watch.


Watch this video to see the Seiko Baby Tuna up close


Who Is This Watch For?

Smitten by the Tuna’s shroud case but feels that $1,000 is a bit too much to pay for a watch? Then the Baby Tuna is definitely a good choice. Sure, it got a few downgrade here and there but it’s a fact that the Baby Tuna is still a good value for money watch.

Serious diver’s can also find the Baby Tuna a great diving watch. The shroud gives an extra protection (though not much) against impact to the watch.


Who Should Not Get It?

While the Baby Tuna is a good diver’s watch with ISO 6425 standard, it’s not to be used for any saturation diving. Helium and oxygen mixture gas during saturation dives can seep into the watch and break it from inside once the diver returns up.

So for those wanting to do saturation diving, it’s important for you guys to use a watch with helium escape valve, or better yet, just get the Tuna =)

I also feel that the Baby Tuna is not as versatile as other diver’s watch such as the SKX007 and Sumo because of the bigger case with the shroud.

So if you are finding a watch to be worn for your office job, then you might need to find a different watch. But for casual and sports activities, this watch is the right one =)

Seiko Baby Tuna Pros and Cons


  • Distinctive shrouded case is a one-of-a-kind look and protects the case from impact
  • Great craftsmanship with the stainless steel case
  • ISO 6425 diver’s watch standard compliance
  • A good 200 m water resistance


  • Hardlex crystal is not great in preventing scratches


Like The Seiko Baby Tuna? Buy It Cheapest On Amazon!

If you want to buy the Seiko Baby Tuna, consider buying it for the cheapest price on Amazon. The MSRP for this watch is $575 while it’s listed for just aroun $250 to $300 on Amazon! Click the link below to check out the watch on Amazon.


->Click Here To Check Out The Seiko Baby Tuna (SRP641) On Amazon<-

Final Thoughts

The Seiko Baby Tuna tries to bring the much beloved Tuna to the masses, and it’s definitely a good strategy by Seiko. The watch captures the essence of the originial Tuna, especially the distinctive shrouded case.

At just $260, it’s definitely a much affordable watch compared to the Tuna that can cost thousands of dollars. I’ve heard many people say that this Baby Tuna is a stepping stone towards the Tuna lol. How true is that!




Hope you guys like this Seiko Baby Tuna review. Don’t forget to share this if you like it.

Drop your comments below. I love to hear what you guys think about the Baby Tuna =)


4 thoughts on “Seiko Baby Tuna Review (SRP641) – A Cheaper Version Of The Famous Seiko Tuna Watch”

    • I think most of these automatic divers are made in Japan. But if in doubt, it’s best to ask the seller directly to confirm things

  1. Watches are very powerful item for every responsible person who want to be presentable.

    But for sometime now mobile phone has come to take over because of the time in it but some of us we still stick to the old tradition.

    Seiko watch is one of the olders brand. I like it because it has date and month which alway gives you update. I like the black one. Thanks for this review.


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