Buy the best binoculars you can afford, perhaps having a cheaper second pair for general crew use. Strong, waterproof binoculars with a rubber coating are best on boats to protect against inevitable bumps. Binoculars are categorized by their magnification and the size of the object lens, which determines how much light is admitted. A pair of 7 x 50 binoculars makes a good choice. A magnification higher than 7 makes the binoculars difficult to hold steady, unless they have built-in stabilization, and an object lens smaller than 2 in (50mm) will not work well in low light levels. Some types have a built-in compass and/or a range finder.
When using binoculars on a moving boat, try to brace the lower half of your body and allow the upper half to move with the roll to keep the binoculars as steady as possible. The boat’s companionway is often a good place to position yourself, as it allows you to brace yourself at waist height. If you wear glasses, make sure the binoculars have rubber eyepieces that fit snugly against the glasses and exclude extraneous light.
Steve Sleight’s The Complete Sailing Manual covers every aspect of sailing and seamanship, whatever your level of experience. Full of hundreds of pages of tips and advice like the information above, The Complete Sailing Manual is sure to help every sailor. Purchase it at Practical Sailor.