The device used to prevent raw water from siphoning into the boat is known as:

A vented loop is the correct device used to prevent raw water from siphoning into a boat’s systems, particularly in situations where there is a risk of back-siphoning due to changes in water level or orientation of the vessel. The vented loop is essentially a horizontal loop in the discharge line that is higher than the water level in the associated tank or bilge. By incorporating a vent, it allows for air to enter the system and breaks the siphon effect, which stops water from flowing back into the boat.

This mechanism is crucial for maintaining the integrity of the boat's systems, especially those that handle raw water, such as engine cooling systems or baitwells. When installed correctly, the vented loop ensures that raw water cannot enter the vessel and provides a safeguard against potential flooding and damage.

While check valves, manifolds, and gate valves serve important functions in marine plumbing and engine systems, they do not specifically address the siphoning issue as effectively as a vented loop does. Check valves permit flow in one direction but do not provide the necessary break in the system to prevent siphon back. Manifolds manage fluid distribution within a system, and gate valves control flow but are not designed for back-siphoning prevention. Therefore