https://creativecommons.org/publicdomain/zero/1.0/https://www.rawpixel.com/image/4025236
A bulbous bow is an extension of the hull just below the waterline.
It has many subtle shape variations but it’s basically a rounded front portion that flares out slightly as it blends into the traditional displacement hull construction. These forward protrusions are about twice as long as the width of the base and they would usually not extend forward past the top of the bow. The basic principal is to create a low pressure zone to eliminate the bow wave and reduce drag. Original public domain image from Flickr
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