Hull of a tugboat and tugboat comprising said improved hull

A tunnel-hull of a tugboat for towing/assisting a vessel, said tunnel-hull having a water plane, a base line, a main section, as well as a longitudinal axis dividing said tunnel-hull in a first lateral part and a second lateral part, said tunnel-hull comprising a bottom, a bow, a stern, and further comprising:

• an underbody, said underbody comprising a first keel and a second keel, wherein said first keel is parallel to and faces said second keel,
• first thruster means and second thruster means,
• wherein each keel is arranged on a respective side of said underbody, in a substantially central position, and is connected to said underbody respectively in correspondence of the bow and the stern of said tunnel-hull, said two keels extending in depth perpendicularly or in a substantially perpendicular manner so as to have a draft equal to or greater than that of said first and second thruster means, and wherein said first thruster means and said second thruster means are positioned respectively at the bow and stern of the tunnel-hull, and are substantially aligned along said longitudinal axis of said tunnel-hull;
• wherein
• said two keels are integral with said tunnel-hull and are configured in such a way that they form a tunnel with at least a portion of said bottom of said tunnel-hull,
• and
• said tunnel-hull has a longitudinal section having a concave bow portion, a concave stern portion and a convex intermediate portion, positioned between said bow portion and said stern portion, and has a first concave bottom portion which extends from said first thruster means to said main section, and a second concave bottom portion which extends from said second thruster means to said main section;
• said two concave bottom portions being substantially symmetrical with respect to said main section;
• each concave bottom portion comprising a respective first portion, externally to said tunnel, which extends from the respective thruster means to the keels, and a second portion, internal to said tunnel, which extends from the keels to the main section, said first and second thruster means being arranged in said first portion, externally to said tunnel, of a respective concave bottom portion, so that, when a water flow is generated by said first thruster means or by said second thruster means, said water flow is channeled within said tunnel, following a respective concave bottom portion, and only a minimal amount of water of said water flow reaches respectively said second thruster means or said first thruster means.