Goofs

In the movie Freya states there is no way to contact the coastguard as the radio is broken. However on the bulkhead behind her there is an bright yellow EPIRB, an emergency beacon that can be activated and works via satellite.

If his hand was caught in the winch, it would not be merely bloodied but badly mangled, if not completely torn off.

When they boarded the boat, they would have heard the music that was playing, even before they reached the dead sailors.

When discussing how to neutralise the creature in the water tank, Siobhán suggests electricity. Omid replies that this only works with salt water. This is wrong in the context of the scene, since Omid refers to sea water in contrast to fresh water. It is correct that chemically pure water is not electroconductive, as such characteristic needs the presents of ions. Drinkable fresh water contains ions, and it is specifically mentioned that the water filtration system aboard the ship is fitted with an ioniser (although details remain unshared).

Siobhan hasn't never seen the sea creature before, doesn't know whether it's a cnidaria or squid, yet she knows it is hadopelagic. Hadopelagic organisms live in the hadal zone which is the deepest part of the ocean between 6000 and 11000 m. The hadal zone represents less than 0.25% of the sea floor and there is no hadal zone anywhere near Ireland.

Around 15 minutes in the crew are told there are Whales on the starboard side of the boat. But they're not Whales - they're Dolphins.

Dolphins in fact belong in the cetacean family, so are a type of whale, making it correct to refer to them as such.

Freya terminates a radio conversation with the coastguard with "Over and out". This is very commonly heard in moves and TV but is in fact incorrect. "Over" means "I am finished speaking and I expect a reply from you", while "Out" means "I am ending the conversation". Thus you would never use these words together. The coastguard correctly replies "Coastguard out".

When Siobhan and Omid are talking before heating the tank, in the shot from her back, Siobhan's head and face does not move as she is speaking.

Internal shots show the vessel has a wooden hull. The premise of the movie is the sea creature attaches to the vessels by appendages which eats through the wood to inject eggs. All external views of the "Niamh Cinn Oir" clearly show it has a steel hull construction.

The parasites could not go into the fresh water supply when Johnny's parasites break out in the sink . Waste water would go into a storage tank or be dumped directly into the ocean, not cycled back into the fresh water to then infect Sudi.

Siobhan refers to the creature's appendages as tendrils. Tendril is strictly a botanical term to describe a modified stem or part of a stem, usually spiral, that helps a plant climb. The correct term for an animal is tentacle, appendage is also correct. A marine biologist at the PhD should know that.