1980s or 90s sci-fi novel about earth colonists on a new planet. They arrive in a sleeper ship called National Geographic. Many have "hibernation instability" after the trip. Colonists must deal with deadly reptiles called grendels.
This is probably The Legacy of Heorot, a collaborative novel written between Larry Niven, Steven Barnes, and Jerry Pournelle. It was published in 1987 and therefore fits your timeframe, and has the distinctive plot of the hibernation sickness (a result of using their suspended animation technology for too long), as well as the Grendels as the aliens. The colony ship is the Geographic and was funded by National Geographic society.
From the linked wikipedia article, discussion of the plot overview and suspended animation issues:
Two hundred colonists arrive on Avalon to found a new community, having made the 100-year journey from Earth in suspended animation on the starship Geographic (the expedition is funded by the National Geographic Society). The colonists, all selected for their outstanding physical and mental attributes, make a terrible discovery: though the suspended animation technology which permitted them to survive the journey worked well enough, it had unforeseeable side effects due to the unprecedented duration of its use. Their intelligence and reasoning skill are damaged. Some are only mildly afflicted, while others have intellectual disability; eight cannot be reanimated at all. The book opens with the colonists learning how to live without the sharp and nimble minds they all once had.
And discussion of the Grendels:
The autopsy reveals that grendels (as the creatures are now known) are crocodilian in appearance and behavior, with jaws that can crush steel. Their bones are significantly stronger than those of humans, as they are not based on calcium. They have a sense of smell better than a dog's. Studying its brain shows it is not fully sapient, but that it is not far off, and is at least as smart as a gorilla. Its claws are not just weapons, but exert enough traction for the creature to sprint up rocky cliffs. Though it is not a true amphibian – it cannot breathe water – it does possess an integral snorkel enabling it to move undetected beneath several feet of water. Its cardiovascular system and musculature give it strength and stamina far beyond that of humans, and that is without its primary evolutionary advantage: A super-oxygenated blood supplement.