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MARES HORIZON | SRP: AUD$6,590 Nicolas Remy: When Mares acquired rEvo Rebreathers in 2016, speculations went on about how Mares might leverage the expertise which rEvo had with technical rebreathers. Being a rEvo diver myself (and a big fan) since 2011, this move certainly picked my curiosity. The announcement came in 2019 - Mares revealed the Horizon, a recreational rebreather with rEvo similarities (back-mounted, clear chest, dual scrubbers) but also new features not found in existing recreational or technical rebreathers. I was very keen to try it, and the opportunity finally came in 2021. In this initial review, I will share my thoughts on the design and key differences I see vs other types of rebreathers, based on eight hours diving the Horizon. In an upcoming article, I will cover the certification process and share more detailed observations, as I will grow more familiar with Horizon. How does the Horizon compare with traditional scuba? Being a rebreather, the Horizon allows breathing again and again from the same gas, granting its user much more bottom time out of a given tank. Mares claims three to eight times more bottom time, which sounds right based on my initial dives and calculations. Rebreathing also means very few bubbles are released in the water (from the Horizon’s top cover, on the diver’s back), and there is no second stage regulator noise - all this helps getting closer to shy marine life. Another advantage of rebreathing is that your buoyancy doesn’t change as you inhale/exhale. This can be disconcerting at first (no more hopping up/down just by breath control), but advantageous over time - as a photographer, I don’t need to hold my breath anymore! Comfort is also enhanced as you breathe a warmer gas than the cold air coming from a tank. It helps keeping warmer on longer/colder dives. Finally, it is worth noting the Horizon is limited to 40m depth - visual and acoustic alarms will ensure you don’t forget! How does the Horizon compare with existing rebreathers? Firstly, let’s name the two types of rebreathers on the market. Their main difference is how oxygen molecules get added into the rebreather, to replace those consumed by the divers’ breathing: CCR (Closed Circuit Rebreather): a pure oxygen tank adds just the amount of oxygen consumed, meaning there is no extra gas to dump, no bubbles produced. SCR (Semi Closed Rebreather): a nitrox tank continuously
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delivers nitrox gas into the rebreather (controlled flow). More gas is added than what the body consumed, so bubbles are released in the water. The Horizon is a hybrid SCR, a different beast which complements a fixed nitrox flow with an electronically controlled valve, adding more nitrox as the diver’s oxygen consumption rises (varies with dive conditions and efforts). Consequently, the gas economy is better than traditional SCRs, but not as minimal as CCRs. Assume I dive at 30m for 30 minutes, in relaxed conditions, so my body only consumes one litre/minute of oxygen molecules. On traditional scuba, if my air consumption is 15 litres/minute (surface equivalent), I will consume 1,800-litres of Nx32 over those ten minutes, or 120 bars on a 15-litre tank. On my rEvo CCR, those 30 minutes will cost me only 30 litres of pure oxygen. Configuring my Horizon to breathe Nx32, those 30 minutes will take 255 litres of gas, or 17 bars on a
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