We decided to catch the mid-morning high tide at Chiswick on a Monday in August - and paddle to Dar es Salaam.
At the Irish Embassy, a Mr O'Rourke was not impressed when I told him we needed our passports in a hurry, but he obliged and offered the following advice, "Don't be getting into any trouble."
I'd wanted to make some money writing en route, so had put out a press release - another mistake.
We had expected a group of fellow ANC Youth League members and university friends to see us off, but what happened was a media circus - even before we'd finished packing.
There were TV cameras, journalists and well wishers jostling with singing, chanting comrades, among them a future president and several individuals destined to become cabinet ministers in post-1994 South Africa.
Eventually we made it to the river, but by then the tide had well and truly turned.
Somehow we managed to get into the kayak, only to be held back by demands for more photographs.
Some items were getting in the way.
"Just throw them out," I whispered to Barbara, seated in the front cockpit.
And so we threw out the sail and, to our later regret, the portable barbecue.As we paddled away from the shore, Barbara pointed out that we were now hours too late to take full advantage of the tide.
"Never mind," I assured her. "Once we leave this lot behind, we'll find a quiet place to pull up and sort everything out."As evening fell, we found ourselves stranded on a pile of rocks in midstream.
It was only then that it began to dawn on us what a difference of up to 7m between low and high tides really meant. Also, how long it takes for the tide to turn.
It was dark before we again pushed off and we were exhausted as we made our way to a sloping stone bank beside the old coaling pier of the Blackwall Point power station. It was an awkward landing and we had to pull the kayak up the slope to the roadway at the top.
"Well, we've made it to Greenwich," I announced. "How do you know where we are?" asked Barbara.
Proudly, I showed her my map. "It's a bloody Michelin road map!" she exploded.
I quickly pointed out that it did show the river and the places along its banks.
"But it doesn't show where there are slipways or anything like that," Barbara complained.
As we struggled to strap the kayak onto its wheels, Barbara kept muttering under her breath. Finally, we wheeled the kayak off towards a pub - which had just closed.
We must have looked a sorry sight as the publican and his wife opened the door. We said we'd just come ashore after canoeing on the Thames. They peered at us rather incredulously, but let us put the kayak in their yard. We could sleep downstairs on the pub benches, they said.
We lay down and didn't stir until early the next morning when the publican rushed in.
"You're the people that's going to Africa," he said excitedly, waving a daily newspaper.
Oh hell, I thought, we've really done it. There would be no opportunity to stop, reflect, plan and prepare. No peace at all. At least Barbara was smiling.
"Yes," I said as confidently as I could, "this is our first stop."
•  This is an edited extract from Terry Bell's book, A hat, a kayak and dreams of Dar...