Some things to look for in quality binos for marine use.
Waterproof binos: may or may not be appropriate. Think about your experiences on the boat.
Nitrogen-filled: This will prevent the binos from fogging up inside. This can happen if you make a rapid transition from a warm cabin to the cold outside. If you have been using non-nitrogen binos for years and never had a problem with this, then you probably don't need it.
Optics: Prism: BAK-4 Porro prisms are the best, unless you are talking about the very best roof prisms made by Zeiss or Swarovsky during the last 2 years. "Oversized" Porro prisms make it easier to align your eyes to the binoculars, especially at higher magnifications.
Optics: Coatings. You want broadband fully multicoated lenses and prisms for the best transmission of light. Fully multicoated means all air to glass (or nitrogen to glass) surfaces are multicoated, inside and out. If the binos do not claim to be fully multicoated, then they are not. If the manufacturer claims the binos are "muticoated", that means the lenses are multicoated on some surfaces. Multicoating results in better light transmission than "coated lenses" which means "single coat."
Light transmission: How effective are the lenses, coating and prisms at transmitting light? This is important in choosing binoculars that are best in low light or at night.
The Fujinon Polaris SX and some of the Steiner models can approach 95-96% light transmission. Of the Steiner binoculars, only the Nighthunter XP Series, Commander V, or Military R models reach this figure.
Be careful purchasing Chinese made binoculars. Lesser quality and higher quality binos can look identical (except for the brand name) unless you are expert at examining optics.
Oberwerk sells the highest quality binoculars made in China. The light transmission of these fully multicoated binos is 94%. Each binocular is individuly tested for perfect alignment in the US prior to shipment.
Steiner is famous for rugged build and that's why the military likes them. They carry a 30 year warranty. However, if you buy a model other than the three listed above, the optical quality will be equal to or less than that of the best Chinese made binos.
Oberwerk has a one year warranty, but will do repair and collimation (alignment) after warranty on an hourly basis. 30 day inspection period for reurn or exchange. The stores that sell them are listed at the web site.
Things to avoid: Built-in compass. Unless you really need to have it there.
Red "ruby" coating or mirrored coatings: Deep red coatings do nothing except mask bad color from poor lenses. Mirrored lenses relect light from the lens instead of sending it to your eye. They best multicoatings from Europe, Japan and the US appear violet to green in color, while the best Chinese multicoatings appear greenish to violet.