yet another rudder size question (or two)

[byankee]

I'm trying to design a rudder for my self-designed 14' flat bottom sailing skiff and I'm not sure how to proceed. I know that the rudder should be about 1/3 the area of the centerbaord, but I don't know how to distribute this area (i.e how to shape the board). My main inspiration comes from Sucher's Flat Bottom Boat book. In this book, the sailing skiffs shown have very shallow (i.e. 6"-10" below LWL) but wide rudders, but most contemporary skiffs have deep but narrow rudders. If it's of no real consequence either way, my preference would be to keep the board wide but shallow so it is protected by the skeg, but I do want the boat to sail decently. Can someone either explain the virtues and vices of each configuration or point me to a reference that does? Thanks.

[lewisboats]

Originally Posted by byankee

I'm trying to design a rudder for my self-designed 14' flat bottom sailing skiff and I'm not sure how to proceed. I know that the rudder should be about 1/3 the area of the centerbaord, but I don't know how to distribute this area (i.e how to shape the board). My main inspiration comes from Sucher's Flat Bottom Boat book. In this book, the sailing skiffs shown have very shallow (i.e. 6"-10" below LWL) but wide rudders, but most contemporary skiffs have deep but narrow rudders. If it's of no real consequence either way, my preference would be to keep the board wide but shallow so it is protected by the skeg, but I do want the boat to sail decently. Can someone either explain the virtues and vices of each configuration or point me to a reference that does? Thanks.

The deeper narrower rudder will be the more efficient one, providing more lift because of it's higher aspect ratio, especially if shaped correctly. Not to say that a shallow wide rudder won't get you where you are going, it just isn't as efficient at dooing it. My personal compromise would be to make a Pivoting rudder, that way you have the best of both worlds, shoal draft with the rudder up a bit and high efficiency with it down in deeper waters. You can spring (bungie) load it or weight it with a bit of lead. The usual way is to calculate up the area needed and cut a hole in the blade. Then you bevel the edges of the blade and maybe knock a couple of nails in to hold the lead securely. Lay the blade flat with the hole backed up and pour the lead, let it cool and then rasp/file it to shape.

Here are a few links for info:

http://www.duckworksmagazine.com/06/...rob/index4.htm
http://www.simplicityboats.com/leadpour.html
http://www.riverswest.org/RiversWest...ourgallery.htm
http://marina.fortunecity.com/breakw...715/index.htm#
http://www.glen-l.com/designs/sailboat/gl14-notes.html (this one has a nice rudder shape...1/3 2/3 plus width)
http://www.duckworksmagazine.com/04/...k-up/index.cfm
http://www.simplicityboats.com/rig_details.htm

Steve