I am building a model of the Presto, a Clyde built steamer that ran the blockade during the US Civil War.  I made the rudder to scale and it looks fine.  The problem is the boat has a pretty large turning radius.  I assume this is because the scale rudder is too small.  I've heard of removeable rudder extensions. 
Can someone explain how I could make one of these?  If you have pictures that would be even better.
I'll appreciate it! 

You can either make a removable rudder extension held on with a couple of small bolts, or do as Stuart Badger did with his model of the Connaught, and make a perspex rudder - The real rudder shape is painted on, with the extension left clear..... It worked extremely well on Connaught!

A photo explains it better than words:

Regards
Eddy

Thanks Eddy! 

One trick I saw is to drill a couple of holes in the bottom edge of the scale rudder.
Make an extension piece that fits to the underside of the rudder and again drill two holes in the top edge of the extension piece to match the rudder.
(It's generally better to make the rudder deeper rather than longer if practical)

In the top of the extension piece glue two short lengths of brass rod, or in a small model two pieces of copper electrical wire.
They should be just about long enough to extend to the ends of the holes in the underside of the scale rudder.
Don't kink the brass/copper as it will make it hard to fit. But introduce a very slight bend.
The friction will be enough to hold the extension in place while the model is in the water and can be removed to display the model.

Alan