On our trips, Gerry and I have always single carried portages and have never really understood people that do the double or even the dreaded triple carry. If you need to make three trips you are on a LONG trip, really disorganized or more often then not, bringing way to much crap! I think it helps that we started out on the right foot by making smart choices about what gear was essential, then buying the lite weight version, while keeping luxury items to a minimum. We never wanted to do that "car camping without a car" we once did again and after having seen many people unsuccessfully try to do just that in the Algonquin interior (...you know, like the guys we have all seen on portages with the coolers that "clink") I don't see us changing anytime soon. But we are not getting any younger and I am sure there will come a time when we will have to look at doing the double and when we do the "the trip and a half method" is the way to go. I have heard the "trip and and a half method of portaging described many times, but never as well as this.
Makes sense to me!
The trip and a half Method:
Consider the case of 2 paddlers arriving at a 2k portage with a canoe and 2 packs. They walk the packs through first, and this trip takes them 20 minutes. One of them goes back for the canoe which takes 40mins for that round trip and a total time of 1 hour. The other paddler waits around for the 40 minutes.
If they did the trip and a half method they would walk the packs half way in 10 minutes. One would drop the pack and go back for the canoe while the second would complete the portage and then return for the pack. They would both complete the portage in 40mins thus saving 20mins.
In general, if somebody is waiting for a long time at the end of a portage they are doing something wrong.