Caterpillar Marine is supplying complete propulsion packages including main engines, thrusters and hybrid systems to a growing number of tug newbuilding projects
It has seen growing interest from tug owners and shipyards for its integrated solutions for green and economic propulsion. The first two tugs with full Caterpillar suites – Dr Hank Kaplan and Rich Padden – entered service in 2017. The first tug with a complete hybrid Caterpillar package is scheduled to enter service in Q1 2019.
Caterpillar Marine tug and salvage segment manager Jörgen Karlsson told Tug Technology & Business that tugs with a complete Caterpillar propulsion package are more efficient than those with main engines and thrusters supplied by separate manufacturers.
Owners can achieve even more efficiencies by including hybrid propulsion technology, he said. “Hybrid systems use less fuel, are more economic and have lower maintenance than conventional propulsion systems,” said Mr Karlsson.
“Hybrid systems use less fuel, are more economic and have lower maintenance than conventional propulsion systems”
He explained that Caterpillar can identify the most efficient system and recommend if it should be hybrid or conventional propulsion using a Cat Select program to review anticipated tug operating profiles, fuel maps and thruster propulsion curves.
“It depends on owner requirements and on price, but we expect there will be more hybrid tugs ordered in the future,” said Mr Karlsson. Hybrid tugs can meet the stringent emissions regulations of the US Environmental Protection Agency’s Tier 3 or Tier 4, and IMO Tier III, requirements. They minimise NOx and SOx gases and reduce CO2 emissions.
“There is demand for hybrid solutions, as they make a lot of sense,” said Mr Karlsson. Hybrid propulsion prices remain higher than conventional propulsion, but there are operational efficiency advantages, depending on the operating profile of the tug.
“Harbour tugs operate on a lower engine profile 80% of the time,” said Mr Karlsson. They only operate with significant engine loads 10-20% of their operating time and “almost never on maximum bollard pull.”
This means tugs can operate on a hybrid mode most of their operating life, for example during downtime or during transits and even during some ship manoeuvring. To achieve this, power take in (PTI) motors are fitted to the thrusters. “When running in transit with PTI motors tugs can achieve 8-9 knots without the need for the main engines,” said Mr Karlsson.
Caterpillar’s hybrid propulsion system includes main engines, fixed pitch thrusters, gensets, switchboards, frequency drives, PTI motors, booster drives and controls. A harbour tug could have a pair of 3512E main engines generating up to 1,900 kW at 1,800 rpm, with selective catalytic reduction (SCR) units for EPA Tier 4 and IMO Tier III compliance.
A hybrid tug could also have two MTA 628 fixed pitch thrusters with two 560-kW booster motors. Its gensets would include two C18 units that generate 565 kW of electricity, plus one Cat C7.1, genset rated at 200 ekW.
In the wheelhouse there would be propulsion controls and a panel with pre-installed operating modes including one for economic operations, another for transit and one for power required for higher bollard pull requirements.
US shipyard Washburn & Doughty Associates is building two tugs – to be named Tug Ralph and Capt Robb – with full Caterpillar hybrid propulsion packages for owner Harbor Docking & Towing. These are under construction at the shipyard in East Boothbay, Maine, for operations in Lake Charles, Louisiana.
Caterpillar is providing a stem-to-stern hybrid propulsion system that includes 3512E main engines, C18 generator sets, a C7.1 generator set, shaft lines, MTA 628 fixed pitch azimuth drives, booster motors, variable frequency drives, switchgear, and controls. Both vessels will be built according to ABS-class and with FiFi 1 fire-fighting systems.
A decision to invest in a hybrid system was taken after a Cat Select study that compared propulsion system options against actual engine load history data from Harbor Docking and Towing’s existing vessels. Smaller engines were selected, 3512E’s instead of 3516E’s, and slightly larger gensets.
Caterpillar tested the azimuth thrusters and hybrid system and sent them to the shipyard in August. There are booster motor inputs on the aft side of the Z drives to enable the thrusters to take in power from the main engines and/or the electric motors.
Mr Karlsson said this hybrid propulsion system would yield substantial maintenance cost savings, reduce fuel consumption and lower emissions.
Harbor Docking and Towing expects Tug Ralph to be delivered in March 2019 and Capt Robb to enter service in June 2019.
Caterpillar’s conventional and integrated propulsion system may not have the same low fuel consumption as the hybrid system, but is still cost efficient and has the benefit of all the equipment being supplied by one manufacturer, said Mr Karlsson.
“We already have a high market share in supplying tug engines, so we developed azimuthing thrusters for a fully integrated propulsion system,” he said.
There are options across the stem-to-stern MTA system including the choice of main engine. Owners can install Cat high-speed, MAK medium-speed diesel or dual-fuel, or Electro-Motive Diesel medium-speed two-stroke engines with SCRs for EPA Tier 4 and IMO Tier III compliance if required.
Main engines can power MTA azimuthing thrusters of various sizes for harbour and terminal tugs. These are fixed pitch or controllable pitch versions with nozzles optimised for bollard pull operations.
Also included in this MTA package are generator sets, fire pump and C32 engine, Cat Connect for monitoring condition and performance of engineroom machinery and a control system that interfaces with an autopilot and dynamic positioning, with a panel for controlling the clutch and thruster. The shaft arrangement can either include a solid rod or tube shaft in steel or composite materials.
Mr Karlsson said Caterpillar made some innovative adjustments during the design of this system. “We took some of the features from the thruster and installed it on the engine, such as the bow-mounted clutch that was then mounted on the engine and not on the thruster drive.”
“Our target for the whole concept was to reduce installation time for the shipyard”
There is built-in power on the azimuthing thruster and a power take-off device unique to this package. Apart from the maintenance and fuel efficiency benefits, there are also advantages to the tug builder. “Our target for the whole concept was to reduce installation time for the shipyard,” said Mr Karlsson.
The first two tugs with Caterpillar’s MTA propulsion package were built for Harley Marine by Diversified Marine in Portland, Oregon. They were built to a Robert Allan RAmparts 2400 design as 24-m tractor tugs with 70 tonnes of bollard pull.
They are equipped with two 3516C marine propulsion engines, which each deliver 1,920 kW of power at 1,600 rpm, and a pair of MTA 524-T azimuthing thrusters, each with a 240-cm diameter propeller.
Mr Karlsson said there would be more tugs built with a full suite of Caterpillar propulsion as Diversified Marine shipyard is building a tug with this package for Brusco Tug & Barge and there is interest from Turkish shipbuilder Sanmar for tugs with these solutions.
|Conventional vs hybrid|
|Tug bollard pull||Prop type||conventional power||hybrid power||booster motor|
|80 tonne||MTA 628||3516 at 2,525 kW||3512 with 1,901 kW||600 kW|
|60 tonne||MTA 524||3516 at 1,920 kW||3512 with 1,500 kW||400 kW|
|Tug package with high-speed engines|
|Type prop/engine||diameter (m)||prop type||power (kW)||thrust (tonne)|