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Seiko SBBN035 (Tuna) vs Seiko SRP641K1 (Baby Tuna) Head-to-Head Comparison

Seiko SBBN035 (Tuna) vs Seiko SRP641K1 (Baby Tuna) Head-to-Head Comparison

Steve Powell

The Seiko “Tuna” wristwatch is valued by many professional divers. For one, this dive watch can withstand intense underwater pressure. It’s also stealthy, tactical, and long-lasting. However, it can be difficult to choose between one Seiko “Tuna” and the Seiko “Baby Tuna.”

While the original Seiko dive watch was developed in 1975, this Japanese manufacturer has continued to market new and useful dive tools. The Seiko “Tuna” is their professional-grade dive watch. Whereas, the “Baby Tuna” is a small, budget-friendly alternative. While both watches look alike, there are plenty of key differences that set them apart.

In this roundup, we put the Seiko “Tuna” SBBN035 and the Seiko “Baby Tuna” SRP641K1 side by side. We’ll highlight the differences between these two extraordinary wristwatches.

Seiko “Tuna” SBBN035

  • Movement: Seiko Quartz 7C46
  • Water Resistance: 984 feet
  • Watch Materials: Stainless steel and Hardlex
  • Strap Material: Silicone
  • Size: 47.7 millimeters
Seiko “Baby Tuna” SRP641K1

  • Movement: Seiko Automatic 4R36
  • Water Resistance: 984 feet
  • Watch Materials: Stainless steel and Hardlex
  • Strap Material: Silicone
  • Size: 47.7 millimeters

Seiko “Tuna” SBBN035

The Seiko “Tuna” SBBN035, or the Seiko Prospex Marinemaster Quartz is a professional-grade dive watch with a thick encapsulated case. The watch has earned itself the nickname “Ninja” because of its all-black exterior. It has a sleek black ion finish and a jet black silicone strap. All of the watch’s exterior elements, including its face, back, bezel, dials, and buckle, are black. Meanwhile, the numbers, dials, markers, and hands are white.

The Seiko “Tuna” displays the time and date. The one-way bezel features an Arabic and stick dial. Numeral indicators appear at each ten-second mark on the outside bezel. The day and date window are located in the center of the right side. It boasts an abbreviated day of the week followed by the day of the month. The main dial consists of stick and dot markers. Small ticks are used to indicate the minutes. Meanwhile, bold shapes are used to indicate the hours.

Seiko PROSPEX Marinemaster Quartz Professional Men's Watch SBBN035 Seiko PROSPEX Marinemaster Quartz Professional Men's Watch SBBN035
  • Suitable for saturation diving as deep as 984 feet
  • Movement: 7C46 Caliber
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More on the “Tuna’s” Appearance

While the “Tuna’s” black and white facade keeps things simple, the watch has a few noteworthy elements. For one, the watch face has two bold logos. The top of the watch face boasts an all-caps logo that reads, “SEIKO.” Meanwhile, the bottom reads “MARINE MASTER PROFESSIONAL 300m.” Below that, there is a strip of text that reads “JAPAN 7C46 -OACO HR 2.” These lines indicate where the watch was manufactured and what type of movement it contains. The watch’s hands and indexes are made to glow in the dark thanks to their Lumi Brite coatings.

The watch boasts a stainless steel case with a super-hard black ion coating. The back and crown are screwed down. There is a dual-curved glass crystal over the dial. The case and crystal are 14.7 millimeters thick, giving them their tuna can resemblance. On top of that, the watch face measures 47.7 millimeters high and 47.7 millimeters wide.

Movement

The Seiko features a 7C46 quartz movement. This particular watch movement is revered by professional divers. The movement is capable of powering through deep underwater dives. In fact, it is capable of providing accurate time as deep as 984 feet. It also has a high capacity to resist shock, heat, and magnetic pressure. The watch’s dense, protective case further enables it to perform accurately in adverse conditions.

Limitations

According to the manufacturer, the watch can maintain a 15-second accuracy per month. As such, there’s rarely any need to make adjustments.

The 7c46 watch movement contains seven quartz jewels and a long-lasting battery. These elements work together to power up the watches gears. The battery is guaranteed to last 5 years. It has a built-in end-of-life feature that develops a 2-second tick pattern when it is running low.

It’s easy to replace the battery and perform other maintenance tasks. The watch’s back can be unscrewed for quick cleanings and repairs. The “Tuna’s” premium design makes it easy to take apart and put back together.

Fit and Comfort

We’re big fans of the “Tuna’s” lug-less design. The watch’s silicone band seems to stream out of the back of the dial. As such, it assumes the natural contour of your wrist without any effort or adjustment. The watch’s black ion coating also has a pleasantly soft feel. On top of its impressive comfort, the watch is resistant to superficial scratches, nicks, and dings. Of course, the silicone strap is also soft and flexible. We cannot think of a better material choice for underwater adventures.

Pros

  • Dual—curved durable glass crystal
  • Suitable for underwater diving
  • Stainless steel back with black ion coating
  • Silicone watch band
  • Lumi Brite hands and indexes
  • Suitable for saturation diving as deep as 984 feet
  • All black with a white Arabic and stick dial
  • One-way bezel
  • Screw case back and crown
  • Magnetic resistance
  • 5-year battery life
  • Shock resistant
  • End of life warning feature

Cons

  • Only one color option
  • Expensive
  • Bulky

Seiko “Baby Tuna” SRP641K1

The Seiko Prospex “Baby Tuna” SRP641K1 is 200-meter men’s diving watch. It features a self-winding 4R36 movement and a dense capsule. With a 47-millimeter diameter and 14-millimeter thickness, it has earned itself the nickname “Baby Tuna.” While small in size, there are a lot of elements that make this watch a major contender for serious scuba sessions and underwater adventures. In this section, we’ll explore all that the SRP641K1 has to offer!

Seiko SRP641K1 Men's Prospex Automatic Dive Seiko SRP641K1 Men's Prospex Automatic Dive
  • Water resistant at depths up to 656 feet
  • Refined tactical look that is suitable for diving
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The Seiko SRP641K1 has a black stainless steel dial with a Hardlex crystal overhead. Like the “Tuna,” the “Baby Tuna” is almost all black. It features a black one-way bezel, a black polyurethane band, and a black bulk. The dial face is black with high-contrast white markings.

The watch’s bezel boasts Arabic and tick markings. The clock’s dial also features dots, ticks, and Arabic numbers. The minute hands are marked with thin gold ticks, with thicker lines for the five-minute increments. There is a date and day window to the left of 3 o’clock. The window features an abbreviated day of the week followed by the of the month.

The clock boasts extremely bold ticks that indicate five-second increments. These ticks are bold, white, and outlined in gold. There are Arabic numbers written above them. The Seiko logo is written in all-caps. Below it, it reads “AUTOMATIC DIVER’S 200m.” These words are written in gold print. The crown and pusher are covered a gold coating that matches the print.

More on the Seiko’s Appearance

Overall, the Seiko SRP641K1 has a refined tactical look that’s suitable for diving. The black base color enables the white and gold details to pop out without appearing too cluttered. Meanwhile, the Lumi Brite hands and markers provide ample illumination in low light conditions. The polyurethane band has a slight crimp that makes it easy to grip underwater.

Movement

The Seiko SRP641K1 boasts a 4R36 quartz movement. This automatic movement can be hacked and hand-wound, making it a popular choice with tinkerers According to the manufacturer, this watch’s movement maintains its accuracy within 30 seconds per day. However, this accuracy differs depending on the watch’s exposure levels. Because inaccuracies can add up quickly, we recommend adjusting it daily.

The SRP641K1’s movement can maintain its torque as deep as 656 feet under the ocean. It is also resistant to shock and extreme temperatures. The movement contains a whopping 24 jewels. Unlike its predecessor, it is capable of providing the time, day, and date.

Limitations

We don’t recommend taking the SRP641K1 deeper than 656 feet. What’s more, we recommend making daily adjustments to ensure the watch is accurate at all times. When doing this, take advantage of the watch’s hand-winding and hacking features.

Fit and Comfort

We love the feel of the SRP641K1’s polyurethane wrist band. It has slight crimps that enable you to twist it back and forth when driving diving. The material is soft, flexible, and, most importantly, durable. We took it on several dives and were unable to reveal any weaknesses. Even the surface of the coated stainless steel and the Hardlex crystal failed to pick up any noticeable blemishes.

Pros

  • Hardlex crystal
  • 4R36 movement
  • Polyurethane strap
  • One-way bezel
  • Date and day display
  • Arabic numerals and ticks
  • Black ion coating
  • Stainless steel back
  • Lumi Brite hands and ticks
  • Hackable
  • Durable buckle
  • Suitable for diving
  • Water resistant at depths up to 656 feet
  • 14 millimeters thick
  • Affordable

Cons

  • Difficult to take apart
  • Limited diving depth

Buyer’s Guide: Seiko “Tuna” SBBN035 vs Seiko “Baby Tuna” SRP641K1

Now that we’ve introduced you to the Seiko “Tuna” and the “Baby Tuna,” it’s time for us to put these two watches back to back. As you can see, these timepieces have dramatically different price points. What’s more, they have different underwater capacities. Still, you’ll find that both watches are attractive and accurate. Of course, it’s worth knowing all the details before you invest in the pricier “Tuna.”

Aesthetics

At first glance, it’s easy to see that these two watches are cousins. For one, they both boast thick tuna can-like cases. Both of the watches are also predominantly black. What’s more, they both have one-way notched bezels with Arabic numbers and white tick marks. With all that said, there are plenty of noteworthy differences between the two timepieces.

Bezel

A closer look at the watches’ bezels reveals some obvious inconsistencies. For one, the SBBN035’s bezel alternating white ticks and Arabic numbers every five seconds. The ticks are placed at the five-second intervals. Whereas, the numbers are placed at the 10-second intervals. Small white dots indicate the seconds between them.

On the other hand, the SRP641K1 boasts white ticks every five seconds and white Arabic numbers every 15 seconds. White dots are indicating the seconds between 15 and 50 seconds. However, white ticks are indicating the seconds between zero and five seconds. In our opinion, the inconsistencies on the “Baby Tuna’s” bezel leave something to be desired.

Dial

There are also some major differences between SBBN035 and the SRP641K1’s dials. The “Tuna’s” dial features a small yet defined second marker dial. The seconds are marked with white ticks. The inside dial features bold circular marks that indicate the hours. There is a triangular marker at noon and an oblong marker at 6 o’clock. The day/date window is written in fine white text with a black background.

See Also

On the other hand, the SRP641K1’s second marker dial consists of large white ticks with Arabic numbers on top of them. These ticks are placed every five seconds. There are no numbers at the 12 o’clock and 6 o’clock positions. The ticks are outlined in gold.

Overall, we found the “Tuna’s” dial to be easier to read and more elegant. The “Baby Tuna’s” dial appeared cluttered and undefined. While we expected the gold highlights to improve the watch’s aesthetics, they appeared to be too egregious for a diving watch.

Both watches illuminated well in low-light conditions. The dial and hands on both watches were covered in Lumi Brite. With that said, both watches require sunlight exposure to glow.

With all this said, if we had to make a buying decision on the dial and bezel alone, we’d go with the “Tuna.” A dive watch’s readability is paramount. In the “Tuna’s” case, the dial and bezel are less cluttered and more refined.

Movements

Now, let’s explore these two watches’ movements. The movement is the internal mechanism inside of a watch. They control the action of the gears. What’s more, they are somewhat responsible for a watch’s accuracy.

The “Tuna” boasts 7C46 quartz movement. It features seven jewels and a long-lasting battery. According to the experts, this watch only veers off course by a few seconds each month. What’s more, the watch’s battery can last as long as seven years.

On the other hand, the “Baby Tuna” features a 4R36 automatic movement. This movement contains 24 jewels. According to the manufacturer, it can be hand-wound and hacked. While inexpensive, many experienced divers say that it fits the bill. It’s one of the few automatic movements that offers the time, day, and date.

Overall, you get what you pay for with both the “Tuna” and the “Baby Tuna”. Both movements are incredibly accurate. What’s more, they are capable of maintaining their torque in intense underwater conditions. Neither watch is set off by heat, cold, magnets, nor shock. While the “Tuna” has greater accuracy, the “Baby Tuna’s” timekeeping capacities aren’t far off from its pricier predecessor.

Dive Potential

Here’s where we dig into the watches’ abilities to perform under pressure. The “Tuna” is capable of telling time as deep as 984 feet. Meanwhile, the “Baby Tuna” can tell time at a depth of 656 feet. The difference of roughly 300 feet may not seem significant to amateur divers. However, the difference is highly significant in professional settings.

If you’re serious about diving, consider choosing the “Tuna.” This watch has a larger range. If you’re stationed on a submarine or doing some series underwater expeditions, the “Tuna’ is the obvious option. Otherwise, the “Baby Tuna” may fit the bill!

Feel and Design

While we talked a lot about the look of these watches’ bezels and dials, we wanted to go into greater detail about their overall design and feel.

Seiko PROSPEX Marinemaster Quartz Professional Men's Watch SBBN035 Seiko PROSPEX Marinemaster Quartz Professional Men's Watch SBBN035
  • Suitable for saturation diving as deep as 984 feet
  • Movement: 7C46 Caliber
Check Price

The “Tuna” boasts a bulky case with lug-free attachment points. The watch’s silicone band features a bumpy exterior and a durable plastic buckle. There are several holes in the band, making adjustments easy. The inside of the silicone band boasts a snag-resistant lining. The watches are easy to adjust and comfortable underwater.

The “Baby Tuna” has a similar design. However, there are some key differences. For one, the band is made from polyurethane. While it feels similar to silicone, we feel that it is less resistant to wear. The watch also has more noticeable lugs. While these elements change the look of the watch, they do not take away from its comfort. Like the “Tuna,” the “Baby Tuna’s” band features a bumpy texture. This makes it easier to adjust underwater.

Similarities

While there are certainly a few differences between the “Tuna” and “Baby Tuna,” these two watches have a lot in common too. For one, they are both tested against water pressure, moisture, heat, cold, helium, and magnetic pressure.

Both watches also have a similar shape and feel. Seiko has stayed true to their original watch design. As such, they have made sure to include signature details in nearly every element of this watch. We’re pretty sure that their tuna can-inspired nicknames say it all.

Final Thoughts

While a deeper look revealed some key differences between the “Tuna” and “Baby Tuna,” it’s clear to see that these dive watches are part of the same family. They both are highly competent timekeeping devices that can function under extreme conditions. What’s more, they’re both black with tune can-like cases.

With all that said, we knew we owed it to you to choose a favorite. Overall, we preferred the look and performance of the “Tuna.” This impressive watch is capable of reaching intense underwater locations. It’s made from extremely durable and long-lasting materials, including crystal, silicone, quartz, and stainless steel. The watch’s bezel and dial are also clear and concise. As such, the watch is easy to read in low light.

Seiko SRP641K1 Men's Prospex Automatic Dive Seiko SRP641K1 Men's Prospex Automatic Dive
  • Water resistant at depths up to 656 feet
  • Refined tactical look that is suitable for diving
Check Price

Of course, the “Baby Tuna” is also a desirable timepiece. It’s perfect for divers on a limited budget or individuals who don’t plan on escaping to outlandish underwater destinations. While there are certainly a few shortcomings in terms of the watch’s design and performance, it’s still a prized option for underwater adventurers.

We hope you enjoyed our side-by-side comparison of the Seiko “Tuna” SBBN035 and Seiko “Baby Tuna” SRP641K1. We aimed to eliminate the guesswork involved in choosing the perfect dive watch. Did you recently purchase one of these dive watches? If so, let us know in the comments below!

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