Our most fundamental tool as a visual lookout, other than our eyes and ears, are our binoculars. Equipping yourself with knowledge and information will help you choose the best pair at the best price. While each pair of binoculars is usually designed for a specific application, they are all built on a similar foundation of optical parameters and physical attributes.
What size do I need for general cruising?
Many years of trial and error have long settled the question of what is the "best" size optical binocular for maritime lookouts.
7x50 has been the gold standard since World War II, and with good reason. It is the single best compromise between magnification, light gathering and field of vision. It is also small enough to wear and carry comfortably for shipboard watch standing. Because they are traditionally used for seafaring, some 7x50 binoculars come with a built-in compass, which can be useful. If we are only going to have one pair of binoculars at sea, our 7x50 would be that pair.
However, if as a recreational mariner, we know that we are only going to be underway during daylight hours, with no exceptions, then most of the benefit of the large light-gathering 50mm objective lenses will be lost, by virtue of our pupils constricting and blocking most of that light. In this case, a pocket-size pair of 7x25—or even 10x25—binoculars might be a better option.
Especially for ocean voyages, it is rarely - though occasionally - nice to have a bit more magification and light-gathering than our 7x50. It's a bit of a luxury, but if I have the stowage to do so, a pair of 15x70 binoculars are realistically about the largest that would ever be useful on a recreational boat. These are made mostly for amateur stargazing, and frankly, on a clear moonless midnight watch far away from the city lights, I might well use them this way. In a manner consistent with safe watchkeeping, of course. But the 7x50 binos are pretty sufficient for this as well.
How much money should I really spend on binoculars for recreational boating?
Hopefully we will be using them quite a lot, but we will be doing so in a potentially rugged environment. My rule of thumb is to not take any hand-held tools on the boat that I would be heartbroken if they were launched over the side. With modern manufacturing, even the cheapest optics are probably sufficient to resolve what navigational lights a gill-netter is displaying.
Binoculars are important enough for redundancy to be a consideration. I would probably prefer two $200 binocs to one $400 pair. Ideally, every watch stander on the boat should have a pair of optical binoculars, pre-adjusted to their own eyesight and inter-pupillary distance.
What about night-vision binoculars?
They certainly have their place in the wheelhouse, although I would strongly recommend that if we are going to use them, an additional committed lookout should be stationed specifically for that purpose. By design, the person using the night-vision goggles will not have their eyesight night-adapted without them. Not so long ago night-vision binoculars and monoculars were prohibitively expensive, but today, many are available for less than $200.
Most importantly, remember to put those binoculars down once in a while. The naked eye is still your most dependable tool for a safe lookout.