Jones and Saunders bounced back with a 10th place in the final race of the day, but with an overall placing of 26th, they have a lot of work to do over the coming days if they are to force their way into the medal races.
The pair, who joined forces in the new Olympic multihull class in 2013, have regularly finished in the top 10 in the key regattas, placing fifth at the 2015 Rio test event, and fourth at last year's Nacra world championships in Denmark.
Olivia Mackay and Micah Wilkinson, New Zealand's younger combination in the Nacra class fared slightly better today with a 28, 27, 13 scorecard to sit at 22nd overall in the 43 strong fleet.
Standings after day two of sailing in Florida:
49er world championship
1 Peter Burling & Blair Tuke (1)
21 Isaac McHardie & Trent Rippey (11)
43 Logan Dunning Beck & Jack Simpson (22)
54 Markus Somerville & Josh Porebski (35)
49erFX world championship
7 Erica Dawson & Ellie Copeland (4)
11 Alexandra Maloney & Molly Meech (6)
Nacra world championship
22 Olivia Mackay & Micah Wilkinson (12, 28, 27, 13, 24)
26 Gemma Jones & Jason Saunders (27, 23, DNF, 24, 10)