In the hotly contested Finn class, where Britain's Ben Ainslie is vying for a fourth consecutive Olympic gold, his Danish rival Hogh-Christensen maintained his overnight lead.
The Dane overcame a disastrous start after he collided with a committee boat on the line to finish seventh and lead the class after four races with just 11 points.
"Ben is one of many. I can't focus too much on him," he said when asked about being chased by Ainslie.
Ainslie said he was "not happy at all" after his sixth and 12th positions left him third equal with three others.
"I need to go away and get it right for the rest of the week," the 35-year-old Briton added.
Australia's Tom Slingsby dominated in the Laser on Monday, putting himself 30 points clear of gold medal holder Paul Goodison after two races.
Slingsby, who had a disappointing Olympics at Qingdao in 2008, is on top form this year and defeated Britain's Goodison at a warm-up regatta in Weymouth in June.
The Briton finished a disappointing 10th and 23rd, leaving himself with plenty of work to do. The event will be won by the helmsman with the least points after 10 races and a final medals race among the top 10 finishers in which points count double.
Slingsby said he is expecting to see more of Goodison, who he predicts "will come back strong".
Slingsby was "really happy" with his start, despite a second place in the first race after a slip let in Juan Ignacio Maegli from Guatemala who finished with a first and a 10th.
Colin Cheng of Singapore enjoyed early success with fourth place in the first race. Cheng, who is based in Sydney, has been in Weymouth every year for the past four years and "likes the strong winds" the waters off the English south coast resort offer the Olympic sailors.
In the women's Laser Radial class, a smaller sailed version of the hugely popular Laser dinghy, Ireland's Annalise Murphy came home first in both races.
British favourites in the men's keelboat Star class Iain Percy and Andrew Simpson, gold medallists in Beijing, had a good day with a third and a second putting them in joint first after four races.
Only two points separate the first four boats, which include the Swedish pair of Fredrik Loof and Max Salminen and the Brazilian duo Robert Scheidt and Bruno Prada.
The turbo-charged 49er skiff class saw more Danish success, with Allan Norregaard and Peter Lang coming out of the first two races with just six points. The Danes led the field early on in the first race, held on the spectator-friendly Nothe course.
But they failed to hold off the French crew who came through on the fourth leg and finished first at the line.
Danish skipper Norregaard calculated there was a 30 degree shift in the wind at one stage in the first race and suffered a bad start in the second. But from the rear of the 20-strong fleet they recovered to gain fourth position.