if this sounds snarky, forgive me, but i couldn't think of another way to say it:
i'm rather surprised anyone has to ask. the main tow drops the string, goes through, stops just clear of the gates, and waits. lock cycles back. tug meanwhile positions at the back of the string, pushes first barge into lock. before next barge moves too far, first is uncoupled from string and if momentum isn't enough [odds are it will be] is warped into chamber. lock cycles. tow backs, picks up barge and hauls out. lock cycles back. rinse and repeat until the string is through. if need be, run tug into lock to reposition for next barge train.
and yes, you will have the needed ropes on each barge, with experienced longshoremen handling them - you don't leave any vessel bobbing free in a lock chamber with water swirling in or out. the bollards serve for the warping as well as guiding the barge while it's moving under power.
if you were paying attention, you'll have noticed 2 assumptions: that this is a single-flight lock, and there is traffic in only one direction at a time. in a multi-flight lock, you _are_ going to have to warp the barges through the interior gates, and at that point a winch is going to be the way to go, but for a single flight it would be more hindrance than help. simply too much unnecessary cable handling.
if the canal is busy enough that trains often pass at locks, but not busy enough that it's found worth while to build a second chamber and make it bidirectional, you have two options: save time, or save water. the faster passage will actually happen if the later arrival simply waits for the lock to clear, just as they would now. if water conservation is an issue, and you need to have a vessel move on each cycle of the lock whenever possible, then you have to take the time to move each string into position to couple or uncouple its next barge, and then clear so the other string can have its turn. some of that can happen as the lock cycles, but you will still have a delay getting the next barge into the chamber.
PeterZ wrote:Weird Harold wrote:How do you get around locks that will fit either the tug or a barge but nor both?
Tugs that push the barge into position to be winched in. Then winch the barge to position on the other side to be hauled through the next leg of the trip.
Ok, thinking it through, a mule or another tug organizing the barges into groups to be towed together would be most effective. I would think that a tug would be cheaper and more flexible than a steam mule and all the track that requires.