steerboard

plural steerboards

1. A kind of old-fashioned rudder for a boat.

   And on the stern, as you will see, she does not have a steerboard or rudder of the Norse kind.

   2016, Nicholas Salaman, The White Ship

   2 more examples

   THE STEERBOARD This idea worked well for the Vikings but proves disappointing for modern yachts. […] Diagram B: The blade area has to be large on a steerboard jury-rig.

   1981, MotorBoating, volume 148, number 6, page 52

   The boat didn't use a steerboard. The centre mast was rotated using a cogwheel. One handle lifted the cogwheel up and the other handle rotated the mast until it needed to be locked in place.

   2018, R. G. Johnston, Vinland: Viking Resurrection