Work to remove the 300-ton piece of equipment that failed to stop the massive BP oil spill could be delayed until the weekend or longer because of rough seas.
Retired coastguard admiral Thad Allen, the US government's point man on the Gulf of Mexico oil disaster, said that seas were 6ft or higher and had to be closer to 4ft for the work to be done safely.
The process of removing the blowout preventer involves taking off the cap that stopped oil from gushing in mid-July.
Removing the failed blowout preventer and replacing it with a new one would clear the way for completion of a relief well and the final, permanent plugging of the well with mud and cement from the bottom.
The BP-licensed Transocean drilling rig Deepwater Horizon exploded on April 20, killing 11 workers.