Hamilton Navy Scuba vs Tissot Seastar

What both watches share

It is worth being clear about how much of this comparison is a tie, because it is most of it. Both watches are 40mm across. Both have a sapphirecrystal — the Seastar's with an anti-reflective treatment. Both run a Swiss automatic rated at roughly 80 hours of power reserve: the H-10 in the Hamilton, the Powermatic 80 in the Tissot. Both brands belong to the same parent group, and both calibers descend from the same ETA architecture.

That 80-hour figure is the single biggest practical difference between either of these and a Japanese automatic at half the money. Take a Seiko or Orient off on Friday evening and it is dead by Sunday; take either of these off and it is still running on Monday morning. Our power reserve guide covers why that matters more than it sounds, and the 80-hour list ranks everything we track that manages it.

It is also worth knowing how the 80 hours is achieved, because it is a trade rather than an engineering coup. The Powermatic 80 is the ETA C07.111, a development of the ETA 2824-2 whose frequency was deliberately lowered from 4Hz to 3Hz — 21,600 vibrations an hour, the same rate as a Seiko 4R36 — to buy the longer run. Powermatic 80 explained goes through it properly.

Difference one: 300m against 100m

This is the headline and it is not close. Tissot rates the Seastar 1000 at 300m with a screw-down crown. Hamilton rates the Khaki Navy Scuba at 100m. Both are styled as dive watches; only one carries a rating in dive-watch territory.

What that means in practice is narrower than the numbers suggest. A 100m rating covers swimming, snorkeling and anything you will do at the surface without thinking about it. A 300m rating covers actual scuba use and gives you a margin most owners will never touch. So if you are choosing between these two for a watch that will see a pool and a shower, the Hamilton's 100m is not a real limitation — it is only a limitation relative to what the name "Scuba" implies. Our water-resistance guide sets out what each rating actually permits.

The honest version of this difference: the Seastar is the better watch on paper and the Hamilton is the more honest about what its case is for. If you want to understand the Tissot's rating against its own stablemate, PRX vs Seastar is the in-brand decision.

Difference two: the 300m watch is the thinner watch

This is the finding this page exists for, and it runs against the grain of how dive watches are supposed to work. Tissot publishes 12.48mm for the Seastar 1000. Hamilton publishes 12.95mm for the Khaki Navy Scuba. Same 40mm diameter, same 20mm lug width on both — and the watch rated for 300 meters is roughly half a millimeter slimmer than the one rated for 100.

That matters because thickness is the specification that decides whether a dive-styled watch actually gets worn. A tall 40mm watch catches cuffs, rides up the wrist and feels like more watch than its diameter promised. The usual trade is that you accept that bulk in exchange for depth rating. The Seastar declines the trade: 12.48mm is slim for a 300m case, slimmer than a great many 200m Japanese divers, and it undercuts the Navy Scuba's central argument for itself.

Which leaves the Hamilton making a different case, and a legitimate one: it is the less tool-like watch. The Seastar carries a rotating dive bezel that takes up dial real estate and reads unmistakably as diving equipment. The Navy Scuba is quieter about what it is. That is a design preference, not a specification, and it is worth being clear that it is the main thing the Hamilton is winning on here. Both take 20mm straps, so either re-straps easily — see how to change a watch strap if that is part of your plan.

Difference three: what neither of them will tell you

Both makers leave the same two blanks, and it is worth naming them because the price implies otherwise.

Neither publishes a daily accuracy tolerance. Not for the H-10, not for the Powermatic 80. You are paying Swiss money for an undisclosed rate. Meanwhile Orient publishes -15/+25 seconds a day for the F6922 in a watch costing a fraction as much, and Seiko publishes -35/+45 for its 4R family. That inversion is one of the genuinely odd facts about this price band, and the accuracy shortlist is built entirely from calibers that do publish a figure. If you want a rate that is actually certified rather than merely published, that is COSC certification, and neither of these has it.

Neither publishes a lug-to-lug. Both thickness figures help, but the measurement that actually predicts overhang is missing from both. With two 40mm cases of unknown reach, the reliable approach is to buy where you can return it — or to look at a watch whose maker does publish it. Watch size and fit explains why that number beats diameter, and the 40mm roundup ranks this whole category on it.

The third contender, and why it is here

The Orient AC0Q Diver is on this page because it exposes what the Swiss premium does and does not buy. It is 39.9mm with a published 46.5mm lug-to-lug — the only fit figure any of these three makers publishes — a sapphire crystal, a 200m case, and the in-house F6722, which hacks and hand-winds. It costs a fraction of either Swiss watch.

On water resistance it beats the Hamilton outright and loses to the Tissot. On fit disclosure it beats both. What it gives up is the 80-hour reserve — the F6722 is a conventional Japanese caliber in that respect — along with Swiss finishing and the service network that comes with it. The AC0Q review has the detail, and the affordable diver list puts it against the rest of the Japanese field.

The verdict

• You are choosing on specification → the Tissot Seastar 1000. It wins on water resistance by a factor of three and wins on thickness too, at 12.48mm against 12.95mm, with anti-reflective sapphire, a screw-down crown and 80 hours. On published numbers this is simply the better watch.
• You want dive looks without a dive bezel → the Hamilton Khaki Navy Scuba. Buy it for the cleaner, less tool-like dial and because 100m is more than enough for the life the watch will actually have — not because it wears smaller, which on the published figures it does not.
• You want the dive rating and not the Swiss badge → the Orient AC0Q Diver. Double the Hamilton's rating, the only published lug-to-lug of the three, and a fraction of the money.

If the Swiss tier is where you have landed either way, the best Swiss automatics under $1,000 ranks the field these two sit in, and Tissot vs Hamilton settles the brand question underneath this model one.