If you look up in the dictionary you will find a definition of a "dog" A dog is a device which is used to block or hold something. A dogger is the man that attaches and removes or loosens a dog. In this instance a dogger on a carriage is on a sawmill that uses a circular saw to cut slaps or boards from a log. The log is dogged to carriage which runs back and forth to cut the boards from a log. Once the log is cut and the carriage returns the log must be loosened so it can be turned 90% to make the next cut. The dog is then replaced to hold the log for the next cut, thus the man or men depending on the size of the log is called a dogger turning the log on the carriage. On small logs the log may not be turned but just made tight to the carriage for the next cut. That is what a dogger on a carriage did.