Over the years, Whitby has produced a number of variations in the rudder construction.
The early Alberg 30's had wooden rudders, as seen here. Notice that you can see the metal straps that hold the planks together. The rudderstocks are visible at the forward edge of the rudder. The two notches at the bottom are for the bolts that hold the rudder to the rudderstock.
Hugh McCormack has more to say on the repair of wooden rudders.
This is the rudder on Andante, #152. You can see that it contains some reinforcing wooden strips and brass straps in the construction. If you look closely, you'll find that the reinforcement is not symmetrical between the two sides.
The rudder on Lorrie Rose, #133, is similar. The photos of the Lorrie Rose rudder show more detail.
This style of rudder has been described on the public-list, before. In brief, it appears that the brass strips form a skeleton for the rudder, and the wood strips make channels for the nuts attaching the brass. These rudders were used as early as hull #133 and as late as #249.
The photos by Bill Boyle of #129 may also be helpful for boats of this era.
Michael Grosh has contributed some photos showing the construction of the rudder on Checkmate, #220.
Here we have a rudder on a late-model boat (#543, built in 1973). This rudder has two molded fiberglass skins with the space between filled with syntactic foam. The edge was then faired with putty. The differences between this and earlier fiberglass rudders seems to be in the details of the inner construction.
In this rudder, the lower rudderpost is a solid piece of 1" diameter naval brass. The end of this was turned down on a lathe to 1/2" diameter to form the pin that holds the bottom of the rudder in the rudder shoe. (This wore/corroded off. The rudderpost has since been drilled and tapped for a 1/2" bolt used as a pin.) To keep the rudder from breaking free of the rudder post and turning on it, two 1/4" rods were inserted in holes drilled horizontally through the lower rudderpost. These rods were glassed to one side of the rudder.
This is a non-standard rudder--not built by Whitby. At one time Carl Alberg drew a sketch of a squared-off rudder for the Alberg 30, but I don't think any were produced that way. This one was probably the product of a previous owner of the boat.