This useful strap is wide and specially padded and will allow binoculars to remain bouyant if dropped into deep water. The strap is bright yellow to aid visibility and is suitable for all waterproof binoculars.

What if my binocular is too heavey for this strap - won't they sink anyway if they go over the side of the boat?

Yes of course, if the binocular is heavier than the bouyancy lift of the strap then they will sink. However, provided the water is not too deep, the strap will aid recovery (by boat hook or drag line etc) by creating a large easy-to-grab loop that floats above the binocular.