Thanks for that. Where I was comming unstuck was that Catalina.bat was starting a new window and running the jvm in it. I modified Catalina to run the jvm in the same process, i.e. run java directly, and then I was able to pipe the output using the ">".
I was however, looking to see if I could use one of the configuratioin files, e.g. server.xml, to direct the output, using a logger, to a specified file without having to alter catalina.bat.