The most important point is impermeability! Binoculars that are "only" splash-proof are not recommended. The magnification should not be too high, because especially with stronger waves, the shaking of the hand is worsened the motion of the boat.
When it comes to aperture, we do not recommend binoculars that are too small. Of course, an important deciding factor is whether you will use the binoculars only for day-time tours and good light, or if you will be on the water for several days and nights. Navigation aids such as a compass or a reticle can be very useful.
We rate binoculars as "not recommended” for sailing if the exit pupil is less than 4 mm. In addition, binoculars for use at sea must in any case be waterproof.