A hand-drawn picture of a controllable pitch propeller, drawn after a model from within the book "The Sailors Handbook" by Halsey C. Herreshoff.
<a href="//commons.wikimedia.org/wiki/User:KVDP" class="mw-redirect" title="User:KVDP">KVDP</a>
<span class="int-own-work" lang="en">Own work</span>