Tugboats make fast at about anywhere between 10 knots for escort duties and 6-8 knots for your general harbor approach. Now imagine making fast in the turbulent wake of a big sea-going vessel sailing at 8 knots and what effect this has on for example tugboats with big lateral underwater areas.
A Rotortug® enables a tug master to make fast in between 5-7 minutes. Twin-drive tugboats with big lateral surface areas generally make fast in excess of 10 minutes. This doesn’t look like much, but the sea-going vessel moved some 750 meter ahead in the meantime.
Generally a ship calling at a port will enter the port under escort of tugboats before being turned in a turning basin and towed to its designated berth. Turning a ship before berthing generally enables simple un-berthing and sailing from a port after loading or discharging. By using the Full Pull method of connecting a Rotortug® center fore and one center aft increases the turning moment with 30% due to towing in the line instead of pushing on the designated tug area. This increased turning moment reduces turnaround time over 30% and is an effective way to increase number of ship movements within fixed timeframes (in case of tidal restrictions);
Berthing a ship means bringing the ship alongside its berth such that the line-handling crew and ship’s mooring system can safely connect the assisted vessel to its designated berth. In order to achieve this the tugboats bring the assisted vessel alongside and keep her stationary until a safe shore connection is established. By using the Rotortug®'s Full - Pull method and making use of the unique features, we limit repositioning time when changing vessel direction from/to berth with quick reaction times and we will suffer no thrust reduction from propeller wash in case of Rotortug® propulsion configuration, which you would have when you need to push in the side. By pushing against the wire the Rotortugs® can deliver ±70% bollard pull transverse force on the assisted vessel at zero risk to damage to assisted vessel and tugboat.
Three (3) 80 ton BP Rotortugs®, can deliver the same effective bollard pull compared to four (4) 80 ton BP conventional tugboats 99% of the time. More and high-power tugs do not necessarily improve safety levels, the safe method of Full Pull does bring this extra safety factor for tug and ship.
Due to the close proximity of the assisted ship and tug, hydrodynamic ship-to-ship interaction creates a yawing momentum on the tug. This is generally considered the most dangerous deployment of tugs during ship-handling operations. Rotortugs feature a double ended control ability (operating over both bow and stern subject to their deployment). The Rotortug® minimizes collision risk through the large momentum from fore- and aft thrusters (to overcome the ship-to-ship yawing momentum) and can also always get into a safe position .The double-ended control ability and the ability always sail astern (either in the bow – or stern tug position is especially beneficial when operating in waves