The traditional marine binocular is a 7x50 and for good reason. The low magnification of a 7x binocular makes it easier to obtain steady views amidst the movement of the waves while the larger 50mm objective lens is ideal for seeing color and detail in low light.
Many marine binoculars will have individual focusing eyecups rather than a single, center focus wheel which is more typical. There are some design/durability benefits of not having an external focus bridge and in the case of marine binoculars (astronomy binoculars as well), the user is often viewing the horizon, so the need to constantly adjust the focus just isn’t there.
Many marine binoculars are available with a built in compass to aid in navigation.
For boaters who are looking for useable, high magnification binoculars, an imaged stabilized binocular is the best option. Imaged stabilized binoculars allow users to experience a comfortable view at a higher power without experiencing the negative effects of a rocking boat. Cannon, Fujinon, and Nikon all make image stabilized binoculars (link to image stabilized tag) well suited for marine use.
Link: Staff picks - Marine binoculars
Viewing wildlife from small boats, canoes
and kayaks is becoming increasingly popular. If you plan to use your
binoculars from a small watercraft, you'll appreciate waterproof
binoculars that can survive an accidental dunking and keep going strong.