Seiko dive watch- Seiko “Grandfather Tuna”

When you think of Seiko, do you think of diving watches? No? I can guarantee that you don’t. If you are like me, you are definitely familiar with dive watches like the Rolex Submariner for example. Or the Omega Seamaster PloProf? How about the Blancpain Fifty Fathoms?


Seiko Logo (Source: Seikowatches.com)

Rolex Submariner (Source: Rolex.com)

Blancpain Fifty Fathoms (Source: jomashop.com)

Omega Seamaster (Source: Amazon.com)




If you noticed, we have been exploring dive watches all along with our waffle straps, chocolate, and tire tread strap. If you are not familiar with the above luxury dive watches, you can click the links for the straps as they come with the watch models as well.

Seiko chocolate strap (Source: plus9time.com)

Tire tread strap (Source:plus9time.com)

Waffle strap (Source: Uncleseiko.com)

62MAS (Source: Fratellowatches.com)

So Seiko has been making dive watches ever since the Seiko reference 6217-8000 or also known as 62MAS model. However, an event led Seiko to create the perfect dive watch, which is today’s topic the Seiko reference 6150-7010 or the “Grandfather Tuna”.




During the 1950s to 1960s, professional saturation diving became popular with the advancement in technology such as the Rolex Oyster case (waterproof), the Omega Ploproof Shark Mesh strap and etc. Of course, Seiko also wanted to join in on the trend of diving watches.

Omega PloProf 1200M (Source: Amazon.com)

The problem with a lot of watches especially for professional saturation diving is that the helium gas in the helium and oxygen mixture tank has a tendency to enter the watch.

Removing crystal (Source:blog.esslinger.com)

This happens regularly during decompression when divers tend to go up because regular gasket construction cannot fully prevent helium from entering. So, what happens is that helium gas tends to enter the watch and stay in between the crystal and dial.

This is not an issue when diving down because the pressure of helium inside the watch is balanced by the atmospheric water pressure. However, when you dive upwards, as the water pressure decreases, the helium pressure is still inside.

Therefore, watch manufacturers like Rolex implemented the helium escape valves at the side. The purpose is to allow the helium gas to “escape” from the watch.

Read all about the helium escape valve by Rolex (Source:beckertime.com)

The issue is that when the helium gas cannot escape fast enough, the pressure will build up. Enough pressure will cause the crystal to pop!! and dislocated from the watch case. Ouch!!




In 1968, a saturation diver from Kure City in Hiroshima prefecture Japan wrote a letter of complaint to Seiko. In the letter, he described the weakness of Seiko dive watches and challenges it faced during helium saturation diving.

Ikuo Tokunaga Seiko Engineer (Source: gearpatrol.com)

Seiko watches probably faced the same problem with crystals popping out of the watch case. However, instead of making helium escape faster from the watch, Seiko did something else. Under the leadership of Seiko engineer, Mr. Ikuo Tokunaga, they decided to make the perfect diving watch.



Seiko Grandfather Tuna (source: fratellowatches.com)

Therefore, 20 patents and 7 years later, Seiko unveiled the perfect dive watch for helium saturation diving, the 1975 Seiko reference 6159-7010. Among watch collectors, it is also nicknamed the Seiko Grandfather Tuna. In the next post, we will learn more about why this watch is the ultimate diving watch from Seiko.

Seiko SBDX013 Emperor Tuna (Source: lazada.com.my)




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