Factual error: Throughout the movie, the characters talk of "the" engine room. The Queen Mary (aka Poseidon) has four engine rooms: forward port, forward starboard, aft port, and aft starboard. There are also four shaft alleys (one for each propeller shaft), along with two generator rooms and five boiler rooms.
Other mistake: In the scene in the engine room, a steam pipe bursts and sprays hot steam (you can see the rising mist) on the handle of the door to the propeller shaft. After the steam has been off, Borgnine then grabs it with abandon. It should have burned his hand.
Other mistake: There was no way the dining room could have filled up with that much water in that amount of time.
Factual error: When they first encounter the sliding red fire door it is supposedly hot to the touch, when the fire door is slid open it leads to the kitchens, the "fires" are the gas burners from the stoves. First of all, the ovens and stove tops on ships are run on electricity, not natural gas. These burners would not produce sufficient heat to make the room extremely hot, not even with hot steam from burst pipes.
Visible crew/equipment: When Belle is swimming, you can see at one point, that she is swimming in a tank, with a crew member in front of it guiding her with a flashlight to turn right.
Continuity mistake: When Terry falls from the table into the skylight, you can see passengers standing around on the ceiling. A moment later, everybody is lying strewn around.
Other mistake: In the scenes bookending the underwater swim, there is no way to figure out how both pools of water are set up. Sometimes a cast member jumps in and appears to be standing in 3 feet of water and other times cast members dive in as though the water is 25 feet deep. In fact, the whole underwater scene makes no sense at all. Cast members swim up meaning they're going through a hatch in the ceiling or floor, there are railings attached willy-nilly and there appears to be no regular doors anywhere.
Revealing mistake: When the cast is assembled before jumping into the water, the scenery appears to be the same as in the scene where they leave the water, with just a few things moved about.
Continuity mistake: During the capsizing, the piano crushes two passengers against a wall. When the piano falls to the ceiling/floor, you can see the same two people fall, but are very much conscious/alive.
Continuity mistake: At the end of the capsizing, Terry falls from the table into the ceiling light, and there are people standing around, clutching each other, which shouldn't be because they wouldn't have had time to recover. When the emergency lights come on, everybody is strewn and about to recover, nobody is standing clutching each other.
Answer: Because he doesn't boil, there's no suggestion that the water is that hot. After Ackers falls in, and while Rogo tries to save him, there are two large explosions in the shaft; we can presume that, while Rogo was able to escape, Ackers was injured/trapped/otherwise incapacitated below the surface, and drowned.