Boatnerd Discussion Forum

The Anderson, Callaway and Clarke all have been retrofitted at some point with air ducts that protrude out the port side of their stacks. See the attached photos. Does anyone know when these were added, and the specific purpose for them? It appears that they were added sometime between 1986 and 1991.
Thanks in advance for any information.

Aerial photo by Eric Treece. Other photos by Roger LeLievre.