Rudder Design and Broaching

[joebobb]

I have an old, 25', round-bilge, semi-displacement hulled Pacemaker Alglas. I've heard a lot of scuttlebutt about these boats having a tendency to broach. I have never been in such treacherous water that I was in fear of that, but I have felt the boat to be a bit tender in a following sea.

During a vaguely related search on the Internet, I found Michael Kasten's website (www.kastenmarine.com) where he discusses some variables related to broaching. Combined with another site describing rudder sizes and designs on old Bertram's, this led me to wonder how significant the impact of rudder design could be on broaching (or more accurately, preventing it). My boat has a standard rudder shape (akin to a shark's fin, you might say). I have seen a later model of the same boat that had what is typically referred to as a "high-speed rudder"...where the rudder is basically a tapered quadrilateral.

What is the impact of rudder design/shape on control in a following sea? When is a "high-speed rudder" the appropriate choice for an inboard vessel? What are the differences in terms of performance, between a conventional rudder and a high-speed rudder? I would like to know if switching to a high-speed rudder might improve my vessel's response to the helm (and resistance to broaching) and how one goes about sizing a rudder.

Any information will be appreciated.

Regards,

Brian