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Rudder and Box Material Recommendations?


Ken_StJohn

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Here is a link to a very good article on making rudders and centerboards. Good techniques and information.

http://mothboat.tripod.com/CMBA/Building/foils.htm

Now then, do you really need it? If you are into pure racing performance, then the information above is really good. Otherwise good background.

The stock design for both the rudder and rudder box is fine. Not a whole lot you can do with a 3/4" thick board other than shaping it with a rounded leading edge and a tapered trailing edge. Jsut try to take as much care as you can to make the surfaces fair and smoothly flowing. As far as materials are concerned, we are back to the discussion on how the lumber is cut and its stability/resistance to warping, strength, etc. Again the choice of quarter sawn or vertical grain lumber will be your best choice. Otherwise knot free, close, straight grain lumber will work the next best. It is going to want to float, hence the hold down line. Some builders have inset a plug of Lead into the rudder to offset the tendency to float. Making it neutral buoyancy or slightly negative. Necessary, NO, but helpful and a lot less hassle to work with. Thre are some good articles on how to do this that we can refer you to if you want to persue that course.

It isn't necessary to wrap the rudder in glass although it will strengthen the trailing edge and help maintain the leading and trailing edges. Soaking the rudder blank with HOT, Boiled linseed oil, will help strengthen the leading and trailing edges as will thinned epoxy or CPES. It will take some abuse and the better care you take of the leading and trailing edges the better your rudder will work for you.

Light weight is also an advantage if it is strong wood. Mahogany is a good choice as is Redwood and Cedar. I happened to have an old sign that was Old growth, high ring count, vertical grain Douglas Fir. I made a second rudder with it to a foil such as suggested in the article above. It is thicker 1 7/16" thick. But I also have a stock 3/4" thick rudder to compare to it. It is quartersawn Western Hemlock. It could also be Mahogany, Spruce or Douglas Fir or Redwood, Western Red Cedar or many other woods. But I would avoid white pine, poplar, red oak and many of the heavier hardwoods. These three that I mention don't really have any place in boat building. They don't hold up well at all.

Again the same discussion on plywood for the rudder box and lumber for the spacers. You want really good exterior/marine plywood as it is going to be under a great deal of stress and you really don't want any possibility of voids or glue issues down the road. The more laminations the better the stresses are balanced.

You can go to commercially made pintles and geudgeons rather than the eye bolts, but if fabricated well, the stock design will be just as smooth if not smoother in operation and for a lot less money. There are several ways to get it to have nice tolerances and really smooth operation.

Commonly available hardware store items and a little patience in fitting will make the stock design work well.

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Ken,

I happened to have some quartersawn White Oak planks left over from a Mission Furniture project which I used for my rudder. :D Quite possibly the strongest piece of material anywhere on the boat. It was a bit of a bear to shape, but you only have to do that once. Got a nice foil on it, following (I think) the link that Barry provided.

For the rudder box, I used the ply recommended in the plans. Thoroughly painted the inside and edges before final assembly. Remember that only the bottom 2 to 3 inches of the rudder box is in the water.

--John M.

Alaskan-in-Exile

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Thanks, guys! I just got back from a shopping safari with some really good looking straight grained poplar. I will have to use ACX for the box but, I intend to treat it first with wetting/penetrating epoxy. Thanks for your suggestions and advice!

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