Marine binoculars for boating

Choose 7x50 for use under way and 10x50 for steadier spots such as a mooring or the shore. The BoatUS Foundation found the human hand cannot hold binoculars steady enough for most maritime use beyond seven power (BoatUS).

A 7x50 also gives a 7.1 mm exit pupil against 5 mm for a 10x50, which helps at dusk. Our 7x50 guide explains why the size suits marine use.

Marine binoculars are made for use on the water, and some add a compass and range scale. Fujinon, for example, describes an airtight, waterproof, nitrogen-filled body for its Mariner line and offers a compass version with an internal light for reading the scale at night (Fujinon), and our 7x50 guide notes that 7x50 is widely used by sailors.

A regular waterproof 8x42 still works on a boat; it just lacks those extras.

Not all of them do, so look for an explicit float claim on the maker's page. Waterproof only means water stays out: Pentax rates its VD 4x20 to JIS Class 7, protected against immersion to 1 m, and notes it is not usable in the water.

Fujinon ships a flotation neck strap with its Mariner instead (Fujinon). None of the maker figures we show for this list includes a float claim, so add a floating strap if you use them near the rail.

It lets you take a bearing and estimate distance or size without lowering the binoculars. Fujinon says the scale in its compass models identifies an object's direction, measures distance and determines its size.

Compass models in this list include the Bushnell Marine 7x50, with an illuminated compass and rangefinding reticle (Bushnell), the Fujinon Polaris 7x50 FMTRC-SX, with a built-in compass and scale (Fujifilm), and the Steiner Navigator Pro 7x50 C, with an illuminated compass.

It stops fog forming inside the binoculars. Celestron describes the nitrogen fill as a dry, inert gas barrier against internal moisture and internal fogging (Celestron), so it does not keep spray off the outer lenses.

Read each protection line: Steiner lists its Military-Marine 10x50 as waterproof but not nitrogen filled.

Yes, if you want more than 7x while under way. The BoatUS Foundation names swell, engine vibration and boat speed as what shakes the view, and tested stabilized pairs to counter it (BoatUS).

Check the weather rating first: Canon's specification for the 10x30 IS II in this list gives no water resistance, and it runs on two AA batteries for about 9 hours of continuous viewing at 25°C (77°F).