Slow going in the intense heat of the sailing wilderness has been challenging for Blair Tuke and MAPFRE

It's slow going for Blair Tuke and his MAPFRE crew as they inch towards Hong Kong on leg four of the Volvo Ocean Race.

The boats have almost made their way out of an extended 'Doldrums' passage, that has seen them battling a total lack of wind as well as intense heat. The fleet is still seven-to-eight days away from arrival in south-east Asia.

Tuke, a member of the victorious America's Cup winning Team New Zealand, said the last week has been truly eye opening - some of the most challenging days of his career.

"Soon after we reached the Solomon Island we got becalmed for two-and-a-half days," Tuke told Newshub.

"It was super-hot downstairs - made it almost impossible to sleep for three-odd days.

"It was pretty hard going given we were only averaging about 2 knots over that period but it has improved somewhat since.

"It's certainly been a challenge that is for sure."

Tuke said the crew believe they have sailed through the worst of it - and hopes the excitement levels will pick up when the boats hit the 'trade' winds, which is most likely to be Friday evening  (NZT).

"Hopefully we are almost out of these conditions - we will wait and see but this has seemed like a super long leg after drifting around in the light winds."

"Once we get into the trade winds it will certainly become more about boat speed as we head towards the Philippines - it will be much nicer sailing and we will be able to push on towards the end."

At one point on Thursday (NZT) all seven boats were within seeing distance of each other as they struggled to navigate the tricky, calm conditions.

A few thunderstorms later and the ability to assess the opposition was over as the fleet separated. However, a drag race to Hong Kong is expected once the breeze fills in. 

Tuke said it's important to embrace the challenges presented by the conditions with each day throwing up something new.

Tuke noted that MAPFRE was probably due it's fair share of bad luck after sailing relatively trouble free through the first three legs.

"You have to enjoy challenges - the last four or five days have been super challenging for the crew.

"We have had a lot go our way since the start of the race - but we have really been up against it the last few days. We just have to stick together and keep going hard towards Hong Kong."

MAPFRE has two wins and a second from the first three legs, sitting atop the scoreboard on 29-points.