The name given to a tunnel structure which tends to run from the fore end of the engine room to the collision bulkhead. It is usually large enough to accommodate an upright walking man. Access is normally gained through a manhole cover situated at the bottom of the engine room near the fore and aft line and close to the forward engine room bulkhead. Its function is to carry pipelines through the forward length of the vessel. There is no need for an aft ‘duct keel’ because the same function is available with the shaft tunnel arrangement.