GB Rowing boss David Tanner is convinced this year's experimentation has strengthened Britain's medal chances for London 2012 - even if it costs them on the podium at this weekend's World Championships.

Andrew Triggs Hodge and Pete Reed, Olympic champions in the men's four last summer, moved into the pair at the start of this year while three-time silver medallist Katherine Grainger has spent the season competing in the single scull.

All three are in semi-final action on Thursday but have found their new classes a major challenge, particularly Grainger who failed to win a medal at either the Munich or Lucerne World Cup events.

But Tanner has no regrets about sanctioning the experiments because, with 2012 in mind, he believes the experience has already made them better athletes and British rowing a stronger long-term force.

As an example, Tanner points towards the new-look women's quad, featuring university students Ro Bradbury and Sarah Cowburn, who qualified for the finals on Wednesday.

"I am really chipper the women's quad came through," said Tanner, GB Rowing's performance director.

"When we put it together we weren't sure if the boat would work. We knew of Ro and Sarah's quality but they are at university and have not been with us all year.

"That is the flipside of Katherine being in the single. If she was sat in the boat, we wouldn't have had to chance our arm with one of the youngsters.

"The men's quad (who had to withdraw from competition due to injury) is also one of our most exciting projects.

"You have to look at it strategically. This is the first time at the worlds we have had a boat in every Olympic class.

"It is not an absolute priority - quality is more important than quantity - but it is important at the start of an Olympiad to have that breadth. We have had the chance to blood new people.

"The tough thing is going to be medal-winning performances. That is where the experimentation, where we haven't just gone for the safer bets, could make a difference.

"Whatever the outcome on Sunday this has been a really positive thing to do."

Grainger is likely to return to a crew boat next season, although no decision has yet been taken on what lies ahead for her or for the men's pair.

Whatever call is made, Tanner is convinced that all of them will have improved over the past 12 months.

"You sometimes learn a bit more by having your backside kicked than by cruising," said Tanner.

"Katherine doesn't enjoy being beaten but she has enjoyed the challenge of the year.

"The experience of the pair (Hodge and Reed) this season has also been a tough one but this is where top people find where they are.

"They have found it a big challenge but they have taken it on. They have had to learn to row a different class of boat.

"At the very top level there is a specialism in that boat, which I believe they have learned. They have made real progress and that will serve them well.

"From a team point of view the men's pair are our flagship and it is important they do well - but looking ahead this experience is invaluable."

While being realistic, Tanner is not writing off Britain's hopes of leaving Poznan with a healthy medal haul given there are seven GB crews in semi-final action on Thursday and five already in finals.

The women's quad were joined in qualifying for the finals by the women's eight, who were back at full strength after Tina Stiller recovered from illness, and the men's lightweight pair of Ross Hunter and Oliver Mahony.

The semi-finals begin on Thursday with single-sculler Alan Campbell boasting genuine medal chances after the most consistent season of his career to date.

Campbell performed heroics in Beijing to reach the final just three weeks after undergoing a knee operation - but his target here is most definitely a podium finish.

Gold-medal favourite New Zealander Mahe Drysdale is in the other semi-final and, while he is up against Olaf Tufte, Campbell has beaten the Olympic champion twice this year.

"He has been great this year and it is time he was on the podium," said Tanner.

The main disappointment on Wednesday came from the men's lightweight four, another new project, who missed their target of a top-12 finish by failing to qualify for the main semi-finals.