The programme, in which celebrities such as Richard Madeley and Dawn Porter sail around the south coast of Britain, pulled in 3.55m (15.6%) for ITV1 from 9pm.
However, the show was soundly beaten by BBC One in the 9pm hour, with Have I Got News For You attracting an impressive 5.76m (24.9%) and sitcom Outnumbered appealing to 5.7m (24.9%).
Earlier on BBC One, Watchdog averaged 3.79m (17.1%) from 8pm.
On Channel 4, Location, Location, Location pulled in 2.47m (11.2%) from 8pm and 291k (1.3%) on timeshift, followed by the return of How The Other Half Live, with 1.65m (7.3%) and 206k (1.6%) on timeshift.
In the 10pm hour, Charlie Brooker's You Have Been Watching attracted 760k (4.2%) for Channel 4 and 81k (0.8%) on timeshift.
Monty Halls's Great Hebridean Escape appealed to 1.2m (6.1%) for BBC Two from 7pm, followed by Bill Oddie's Top Ten Aliens with 1.43m (6.5%).
The second episode of new series History Cold Case attracted 1.63m (7.1%) for BBC Two in the 9pm hour, down 200k week-on-week.
Britain's Greatest Machines with Chris Barrie gained 539k (2.4%) for Five in the 8pm hour. A screening of Pistol Whipped followed with 1.6m (6.2%).
Overall, BBC One comfortably controlled primetime with a share of 24.2% to ITV1's 20.6%. Channel 4 came in third with 6.9% (+1: 0.8%), followed by BBC Two with 6.1% and Five with 4%.
Elsewhere, American Idol appealed to 371k (1.6%) for ITV2 from 9pm and 66k (0.4%) on timeshift, while a repeat of EastEnders pulled in 942k (4.7%) for BBC Three from 10pm.
BARB ratings data supplied by Attentional