Someone sent me these pictures anonymously in response to my older posts on trimaran rudder design (1, 2). They show Jim Brown’s skeg rudder design for the Searunner 31. This is the best design for offshore. It allows the boat to navigate at it’s shallowest draft and the rudder is always protected by the minikeel. Also, the unbalanced design will improve tracking, especially when surfing down steep waves at high speed (at the cost of reduced maneuverability at low speed).

We had a couple of white knuckle rides during which I was wishing for a rudder like this. Once when we sledding down 30 foot swells north of Punta Baja (often approaching 16 kts). I also blame the broach we experienced entering Bahia del Sol on our rudder.

Also, note the trim tab on the trailing edge. This is part of a self steering wind vane system. A small force applied to the trim tab by a wind vane or tiller master is amplified (by the passing water) into the larger force needed to deflect the main rudder (in the opposite deflection).

This entry was posted on Tuesday, February 3rd, 2009 at 9:29 pm and is filed under boat projects, TimeMachine. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a comment, or trackback from your own site.