Today was the milestone of milestones - we passed the half way mark.
I now have one km less to swim than I have already swum. Tomorrow will be 10 or 11km less. From now on, it's a countdown to the finish line. I know that I can swim the same distance that I've already swum, so I know that I can get to the end.
Yes, I'm tired and my muscles are sore and aching, but knowing my goal is now within reach does a huge amount to spur me on. Mostly though, it's sheer stubbornness.
Today was also the epitome of a perfect swim. There was beautiful weather - a flat sea with no wind and one of the strongest currents I've ever come across on a neap tide. This was because I am swimming around an area called The Shambles; a shallow section of the seabed that forces water around it at an accelerated speed.
Luckily, it's going in the right direction for the swim, so I can piggyback off this natural phenomenon and cover distances that would ordinarily only be possible if I were an Olympic swimmer on a spring tide.
As the expedition yacht, Aquila, was being serviced this afternoon, we had arranged to hire a sport fisher - a smaller and faster boat - to zoom us out to the start point in less than quarter of the time it usually would.
We were joined by my friend, Cheong-Ann Png, who is a senior lawyer for the Asian Development Bank. We swam across the Channel in a relay 20 years ago tomorrow and I hadn't seen him since. It was wonderful to be supported by friends so generous with their time.
We also had surprise guests with us, Major General Tim Toyne Sewell and his wife, Jenny. Tim was my expedition leader on many previous swims and they decided to pop on board for some moral support. He swam behind me for part of the swim certainly kept me in line.
It was an absolute pleasure to host them and it was even more of a joy to watch Tim, 78, swallow dive off the very top of the boat.
As he dived off, he shouted: "There is still some life left in the old bugger!"
Today was an ode to those of us still young at heart.