otter board

noun Nautical.
  1. one of a pair of large, heavy, square or rectangular plates or boards of metal or weighted wood attached to the trawl lines on each side of the mouth of a trawl net to maintain lateral spread during trawling.

Origin of otter board

First recorded in 1765–75
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018