Points are awarded for each run - one for first place, two for second and so on. The four riders with the lowest score from each heat qualify for the semi-finals.

With a little while to go in that 470 race, we may have enough time to focus on the BMX quarter-finals.

The riders go in four quarter-finals of eight, with each group of eight racing each other three times.

Mills and Clark currently sit fifth in this medal race, approaching the end of the third leg. Remember, if they finish the race, they win gold.

At around 18:00, Nicola Adams will step in the ring with huge rival Ren Cancan in the semi-finals of the women's flyweight boxing.

Then, at around 19:30, Jade Jones goes in the quarter-finals of the -57kq taekwondo.

So the sailing is under way, with three of the five legs completed in this women's 470 medal race. At some point in the next 20 minutes, Hannah Mills and Saskia Clark will seal a gold medal.

At 17:30, the BMX quarter-finals. World champion Liam Phillips and Kyle Evans line up for GB.

Image source, BBC Sport

The BBC TV team have just been catching up with Argentina's Santi Lange, who has become one of the stories of the Rio Olympics after winning gold in the Nacra 17 alongside Cecilia Carranza Saroli despite losing a lung to cancer last year. At 52, he is also the oldest gold medal winner of the Games.

His two sons are also racing in the 49er medal race later today, where GB's Alain Sign and Dylan Fletcher are fourth and can still make the podium. 

And there's a huge Brazilian story brewing in the 49er FX women's race where Martine Grael, alongside Kahena Kunze, could follow in her father's footsteps by winning an Olympic sailing gold. Torben Grael won two titles and his daughter's boat is one of four boats separated by a point at the top of the standings. 

BBC Radio 5 Live

Our colleagues at BBC Radio 5 live are hosting a special Olympic social programme tonight. It starts at 21:30 BST, with presenter Nihal Arthanayake being joined by Victoria Pendleton, Steve Parry and Steve Bunce. They're asking for your thoughts on the following questions:

1) Who will take over Usain Bolt's mantle as the poster boy or girl of track and field presuming the Jamacian superstar doesn't compete at Tokyo 2020?

2) What is your moment of the 2016 Games? And why?

3) What can other governing bodies in the UK learn from British Cycling?

You can also join in on Twitter, using #bbcrio2016, external

Annie Emmerson
BBC Sport triathlon expert & former GB triathlete

Alistair eluded to the fact he might not go to Tokyo but Jonny is a bit younger.

We might not see them going head to head ever again.

I wonder if Alistair will turn his attention to the longer distance races.

Tom Fordyce
Chief sports writer in Rio

That might seem like the result all expected, but these have been the most testing of four years for Alistair Brownlee - every season an injury, every season a doubt that he could ever stay fit for long enough to hit his peak once again. 

But no-one can suffer in a race like the double Olympic champion, no-one push themselves as hard. 

The greatest one-day racer in history has once again proved himself unbeatable when it matters most.

We'll be keeping right across that, bringing you the moment when the GB gold-medal tally ticks over to 21 (that's two more than you, China).

We'll also keep bringing reaction to the Brownlees bossing it, have some BMX action, a Nicola Adams semi-final and a Jade Jones quarter-final.

Yep, after a frustrating day yesterday, Hannah Mills and Saskia Clark are finally on the water, needing only to finish to claim gold in the women's 470.

There's wind, but not too much wind. It's the right kind of wind, which is blessed relief.

That was Magic Mike Henson, bringing home the British bacon for the Brownlee brothers. This is Stephan Shemilt, with another GB gold medal right around the corner.

Watch the best bits as Marcus Ellis and Chris Langridge won Great Britain's first Olympic badminton men's doubles medal, beating China's Hong Wei and Chai Biao to take bronze.

More from Alistair Brownlee speaking to BBC TV: "We have been pushing each other to the max. Jonny had the edge and I wasn’t sure I would win, I knew had to go through hell and I did.

"I was delighted at the finish. On that run I got the gap and I was thinking it is good but kept trying to focus and when I got onto the blue carpet I was so happy.

"I knew the gap was big and I had a chance to enjoy it, it will probably never happen again."