While most draw and swing bridges on the ICW will correspond on channel 13 of VHF radios, the bridges in South Carolina will not. They operate on Channel 9!
Another distinguishing feature of the South Carolina bridges is they do not open on a set schedule. Most bridges along the waterway will open on the hour. If you are there at that time, you will get to pass and continue on your way. If you are not there at that time, you will have to wait for the next opening to occur. This means that if you arrive 5 minutes late, you will have to wait for 55 minutes until the bridge opens again.
Timing the bridges becomes very important as it can allow you to cover many more miles in a day instead of waiting around all day long. It is also important to time the bridges with the tides. The current in the ICW can be pretty fierce, especially near bridges where the waterway narrows and the speed of the current increases. If you miss a bridge, you might have to fight a 2 knot current for the next hour, motoring through nearly 2 miles of water while not moving an inch over ground!
Now, back to South Carolina. The bridges here open on demand. As you approach the bridge, you simply radio the bridge on Ch 9 and let them know that you would like to request an opening. The bridge tender wants to know what your boats name is, and where it hails from.
If you don't give this information when you hail the bridge, the bridge tender will ask you for it. To speed up the conversation, all you need to do is identify yourself with your vessel name and port and that you are requesting an opening.
For example: "Hello Swing Bridge, this is Southbound Sailing Vessel Wisdom from Baltimore Maryland requesting a bridge opening when you feel that I am close enough"
To this the bridge tender will respond and acknowledge your call, thank you for the information, and let you know when he feels you are close enough. When he begins to open the bridge, he will radio you and let you know so you can pick up the pace a little bit and get through quicker as to not hold up traffic as much.
So, you don't have to time the bridges in South Carolina, as they open on demand, but they do operate on a different channel (9 instead of 13).