Champion New Zealand sculler Mahe Drysdale has few worries about being ambushed as he zeros in on his fifth title at the world rowing championships starting on Lake Karapiro near Cambridge on Sunday.

He's only too well aware exactly where his opposition will come from: redoubtable Beijing Olympic gold medallist Olaf Tufte, of Norway, the in-form Ondrej Synek from the Czech Republic, and Britain's 2009 world championship silver medallist Alan Campbell have all shown the credentials to steal the big-boned New Zealander's title.

There is more than enough competition there to keep Drysdale focused and motivated without worrying about an unknown sneaking into the mix.

More to the point, however, Drysdale remembers only too clearly how long it took him to work his way to the top of the gruelling and extremely competitive single sculls discipline.

"As a developing athlete, I know what it was like trying to get there," Drysdale told NZPA.

"It's frustrating, you see the same guys winning all the time."

He said it took about five years of hard work just to get to a level where he was competitive with the rest of the world.

As a rookie oarsman, Drysdale said he struggled to make that breakthrough to the top echelon.

"It was pretty frustrating, those first four years of doing all the work and not getting the results I thought I should be getting with the amount of work I was doing.

"It's just patience, but I'm a pretty impatient sort of guy."

The chances of an unknown catapulting on to the world scene may be unlikely, but Drysdale is still thorough in his assessment of his opposition, labelling Synek as the man to beat.

"Olaf hasn't had a good year so far, but you never know what he's going to produce. And Alan Campbell's getting more consistent as the years go on.

"Those guys are the guys who've been on the dais for the last five years, and I expect it'll be those three and me fighting it out for the medals again."

Having said that, Drysdale is still wary of narrowing his focus too much.

He mentions Canadian sculler Malcolm Howard, who stepped up a level in the single sculls this year, Belgian Tim Maeyens and Sweden's Lassi Karonen as potential finals material.

"But the thing in sculling is, it's quite rare for someone to come out of the woodwork from nowhere.

"You generally see them coming up, it would be very unlikely to see someone that wasn't even on the radar come and get a medal.

"It's one of the good things about rowing; it takes a long time to get to the top, and when you're there you generally see people coming."

Drysdale has had plenty time to survey the opposition this year, with an enforced three-month injury break curtailing training and competition until mid-June.

The only cure for his back injury, a torn disc, was rest: initial inflammation and irritation cleared up earlier in the year but reappeared a couple of weeks after the hard-working oarsman returned to the water.

"I had to have a couple of months off, and that got it right. Rest is really all you can do for a disc injury, which is pretty frustrating.

"All I could do was walk - it was pretty hard.'

But discipline and patience paid off, and Drysdale managed two weeks' fulltime training before lining up for the prestigious Henley regatta in England in June.

A win there, followed by bronze at the final World Cup regatta in Lucerne a month later, gave Drysdale a real boost as he prepared for the run into the world championships.

"It gave me a lot of confidence that the injury hadn't really put a dent in my preparation," he said.

"It felt good, that was the really good thing. I was really excited to be out there again. Racing at Henley and in Lucerne, it was just awesome to feel lucky to be racing, rather than just take it for granted."

Back in New Zealand and now with three months' solid training under his belt, Drysdale is quietly impatient for the championships racing to begin.

"I've made a lot of improvements since Lucerne, and I wasn't that far off the pace then. I'm still feeling pretty good going into the world championships."