To get a more detailed view, I downloaded the timetable the Thames Clipper web site. It was immediately clear that a limiting factor was that the RB6 Putney route currently only runs during the week which ruled out a weekend attempt.
So, looking at the weekday timetable, lets first consider starting at Woolwich in the morning:
The problem here is that the first boat arriving at the London Eye (Waterloo) pier isn't until 09:26 while the last boat to Putney has already passed it and is at St George Wharf (Vauxhall) at 09:10, so that's no good.
Next let's consider starting at Woolwich in the evening:
Here the problem is Millbank: the last RB6 that stops there is at 17:37 while the first evening boat from Woolwich (Royal Arsenal) is at 18:01.
How about the other direction? Let's look at starting at Putney in the morning:
There's a similar problem here: Millbank (which is clearly a pinch point on the route) has its first arrival at 10:05 but Woolwich (Royal Arsenal) has its last boat arriving at 09:27.
Things were looking pretty difficult and I was wondering if this was one of those mind-bendingly complex scenarios when I turned to the Putney in the evening page:
What's that? A route that goes through all the piers? Yes!
It starts at 17:15 at Putney and yes is scheduled to stop at Millbank (the last one!). Then its necessary to pick up Westminster and London Eye (Waterloo) so have to get off and change. Alas the next boat at 18:08 doesn't stop at Westminster (why?) so have to way until 18:32 (Embankment) or 18:40 (Westminster) to continue the journey.
This picks up all the stations to Canary Wharf at which point must alight to pick up the RB4 over to Doubletree Docklands:
Then back to Canary Wharf for the 19:37 to pick up all the remaining piers to Woolwich, arriving at 20:03, making a schedule journey time from Putney of 2 hours 48 minutes.
This RB4 over to Doubletree Docklands is the most critical connection: if the RB1 18:32 arrival is late then might not be able to take one of the two possible RB4 connections over to Doubletree Docklands. For example, if have to get the 19:34 over to Doubletree Docklands, I wouldn't manage to pick up the 19:37 and so end up on the 20:01, arriving 24 minutes later.
And there can indeed be delays or cancellations on Thames Clipper. Around that time I spotted these tweets:
If the RB4 was suspended (or indeed, any of the routes used) then you could call the whole thing off.
On the shortest day of the year, Friday 21st of December 2018 I headed off to the Putney Pier to take the Thames Clipper Challenge.
What do you think happened? Did I make it to Woolwich?
If so, how close to the target time was I?