Final answer:
Gulliver's boat almost tipped over due to the violent motion of formidable and powerful waves that swirled the boat perilously, nearly causing it to capsize.
Step-by-step explanation:
Gulliver's boat nearly capsized due to a series of powerful and formidable waves that caught the vessel, throwing it into tumultuous movements. As the waves approached, they always seemed on the verge of breaking and rolling over the small dingey, which caused anxiety among the crew.
At a critical moment, a large wave lifted the boat up the incline, and as it crested, the boat bounced over it, swung down the long back of the wave, and was tumultuously swirled, nearly becoming perpendicular to the water. The violent motion of these waves filled the boat with water, nearly tipping it over, and it took great effort for the crew to keep it from completely capsizing.