Britain's challenge for the Admiral's Cup suffered a massive blow yesterday with a ruling by the competition's race jury which sent the host nation plummeting from second place to fifth.As the 21-yacht fleet battled on an inshore course in Christchurch Bay for the Mumm Trophy, Britain were heavily penalised for two errors of navigation during Monday's racing.Andy Beadsworth, helmsman on Britain's 40-footer `Easy Oars', and Olympic silver medallists John Merricks and Ian Walker on the Mumm 36 boat `Bradamante' were found guilty of breaching strict right of way rules.In Ireland, former class champion Roger Bannon has reverted to using the hull of his former boat Endeavour following substantial damage to his new boat Mydi at the Heineken Mermaid National championships at Wexford Harbour Boat club.Defending champion Derek Joyce sailing Zulieka - itself damaged in similar circumstances last year - has won both races so far in the 20-knot winds off the Wexford coast, but Jim Dempsey's Elizabeth has moved in to second place after Dempsey was awarded average points for a successful appeal for redress from a black flag start in the opening race.In a desperate bid to prepare his former boat - in which he has won the championship three times before - Bannon embarked on a 24-hour hull-swap to be ready in time for yesterday morning's second race in which he scoredfourth, enough to keep him in overall contention in the 39-boat fleet.Ireland's dominance in the first day of the Mirror World championships in Kingston, Ontario, was shattered yesterday by the British sailors who took both winning guns and hold first and second places overall. But Ireland hold six of the next seven places in the fleet of 100 boats representing eight countries with four of the 10 races completed.Howth YC's Brendan Foley and Spencer Mitton had a disappointing 16th in the morning race, but came back to take second place in the afternoon to hold third overall, while Ross Killian and Darren McCann, also Howth YC, who had a disappointing first day with places of 20th and eighth, posted two third places yesterday to move into fourth overall.A further blow to the Irish camp yesterday was the disqualification of Max Treacy and Nick Craig, of the Royal St George YC, for a starting line infringement in race two in which they finished second, and their placings yesterday were both in the mid 30s.Mirror World Championship (Kingston, Canada) - Subject to protest Race Three: 1 D and J Gebhard (Brit); 2, G Owens and Rebecca Killian (Howth YC); 3, Ross Killian and D McCann (Howth YC). Race Four: 1 D Balding and N Harper (Brit); 2, B Foley and S Mitton (Ire); 3, Ross Killian and D McCann (Ire).Overall: 1, Balding and Harper 23 pts. 2, Gebhard and Gebhard 29 pts. 3, Foley and Mitton 31 pts. 4, Killian and McCann 34 pts. 5, E Moloney and A Woodward (Ire) 46 pts. 6, I Capener and F Capener (Brit) 51 pts.Mermaid Week overall after two races at Wexford Harbour BC) - 1, Zuleika Derek Joyce Wexford Harbour BC; 2, Vee Jim Carthy rush SC; 3, Mydi/Endeavour R Bannon.