V. De AngelisMay 2009
CCCG, MCPD
COMPARISON STUDY OF ELECTRIC, ELECTRO-HYDRAULIC, AND HYDRAULIC DRIVE SYSTEMS FOR SCIENCE WINCHES
Slides 2 and 3:
The Canadian Coast Guard (CCG) Fleet Renewal Plan is a multi-year plan with the goal of replacing aging vessels with new vessels. In 2007 – 2008, the CCG fleet comprised 114 vessels with varying years of service (Table 1). Many of these vessels are equipped to support two or more simultaneous operations (i.e., multitasked). Other vessels have many specialized capabilities (e.g., marine research requirements of DFO's Science Program).
Table 1 – Age of CCG Vessels
TotalNumber / Vessels Over
25 Years Old / Vessels 15 to
24 Years Old / Vessels Under
14 Years Old
114 / 37 / 34 / 43
Slides 4, 5 and 6:
Traditionally CCG ships have used hydraulic or electro-hydraulic drives to operate various science winches. These winches are primarily used during fishing and science missions to deploy, tow and retrieve various payloads.
A study comparing the advantages and disadvantages of electric, electro-hydraulic, and hydraulic drive winches was conducted by SNC-Lavalin for the CCG in the Winter of 2009. The intent of the winch drive study was to update the technical knowledge base of the CCG Major Crown Projects Directorate (MCPD) with regards to current winch drive technology.
The study was conducted for the fisheries science and oceanographic science winches listed in Slide 5. The study compared the advantages and disadvantages of each winch drive with regards to the evaluation criteria specified in Slide 6. Various winch manufacturers, commercial fishing vessel operators, oceanographic research organizations, and research vessel operators were contacted in order to obtain information regarding the drive systems.
Slides 7, 8 and 9:
The studyonly considered electric drive winches using variable frequency, alternating current (AC) induction motors. Direct current (DC) motors were not considered.
The study defined an electro-hydraulic drive winch as being powered with hydraulic fluid supplied from a dedicated hydraulic power unit (HPU). The study defined a hydraulic drive winch as being powered with hydraulic fluid from a hydraulic ring-main. The ring-main supplies various winches with hydraulic fluid from a common HPU.
Slide 10:
Electric drive systems offer the advantage of eliminating the need for hydraulic pumps, hydraulic reservoirs, and hydraulic piping and fittings. The hydraulic piping and fittings are replaced by electrical cables which occupy less space (especially versus low pressure hydraulic piping) and have a lower mass. The hydraulic pumps and reservoirs are replaced by VFDs and controls which have a lower mass. The disadvantage of electric drive winches is that the electric motor and gearbox assembly occupies more volume and has a greater mass than a hydraulic motor.
Due to limited feedback received from electro-hydraulic and hydraulic drive winch manufacturers, the HPU sizes and masses were obtained from commercial-off-the-shelf models provided by HPU manufacturers. It was assumed that two separate hydraulic ring mains, supplied from three HPUs, would be provided for the hydraulic drive winches as follows:
- two HPUs for the Trawling Winches; and
- one HPU for the remaining winches.
The results of the survey indicated that for the winches evaluated, the electric drive winches and control cabinets occupy a smaller total volume and have a lower mass than the hydraulic drive winches and hydraulic winches including their respective HPUs. The hydraulic drive winches and HPUs occupy approximately 23% more volume and are approximately 23% heavier than the electric drive winches and control cabinets[1]. The electro-hydraulic drive winches and HPUs occupy approximately 43% more volume and are approximately 43% heavier than the electric drive winches and control cabinets.
These results do not include the volume and mass of the electrical cabling, cooling water system piping, or hydraulic piping and fittings as they are dependant on the size of the vessel and the locations of the winches, drive controls and HPUs.
Slides 11, 12, and 13:
The design values used to estimate the efficiencies for electric, electro-hydraulic and hydraulic drive winches vary from manufacturer to manufacturer. The efficiency of an electric drive winch is estimated to vary from a minimum of 70% to a maximum of 85%. These values are based on an estimated loss of 5% to 10% in efficiency due to the electric drive system (i.e., electric motor, and reduction gearbox) and 10% to 20% due to the winch mechanical systems (i.e., winch bearings, and level wind)[2]. An efficiency of 80% was used for determining the power requirements for electric drive winches for the winch study.
The efficiency of an electro-hydraulic winch drive is estimated to vary between 45% to 70%. These values are estimated based on an estimated loss of 20% to 35% in efficiency due to the electro-hydraulic drive system (i.e., hydraulic motor, electric motor, hydraulic pump, and piping losses) and 10% to 20% due to the winch mechanical systems (i.e., winch bearings, and level wind)[3]. An efficiency of 70% was used for determining the power requirements for electro-hydraulic drive winches for the winch study.
The efficiency of a hydraulic winch drive is estimated to vary between 35% to 60%. These values are estimated based on an estimated loss of 30% to 45% in efficiency due to the electro-hydraulic drive system (i.e., hydraulic motor, electric motor, hydraulic pump, and piping losses) and 10% to 20% due to the winch mechanical systems (i.e., winch bearings, and level wind)[4]. An efficiency of 55% was used for determining the power requirements for hydraulic drive winches for the winch study.
A comparison study was conducted between the Atlantic Enterprise (fitted with AC electric drive trawling winches) and the Ocean Tiger (fitted with hydraulic drive trawling winches) by the operator of the two vessels (i.e., Ocean Prawns). The study compared the power consumed by the winches during identical trawling operations. The results of the study indicated that the electric drive winches installed on board the Atlantic enterprise consumed approximately 70% less power during trawling than the hydraulic drive winches installed on board the Ocean Tiger.
The study also demonstrated that the Atlantic enterprise was able to generate approximately 200 kW of power during lowering (i.e., shooting) of the trawl net. Conversely, the hydraulic drive winches consumed 300 kW during lowering (i.e., shooting) of the trawl net. Ocean Prawns estimates that approximately 400 kW of power per winch per 24 hours is returned to the main switch board during regenerative braking on board the Atlantic enterprise. The vessel specifics are presented inTable 2.
Table 2 – Atlantic Enterprise and Ocean Tiger Data[5]
Vessel / ConstructionDate / Length
(m) / Breadth
(m) / Gross
Tonnage
(Ton) / Fuel
Capacity
(m3) / Fresh
Water
(m3) / Main Engines
Ocean
Tiger / 1997 / 60.0 / 14.0 / 2,223 / 570 / 60 / Wârtsilâ 12V32E
(4920/3970 KW)
Atlantic Enterprise / 2002 / 70.5 / 16.0 / 3,454 / 1,000 / 50 / Wärtsilâ W12V32
(4990KW)
Slides 14 and 15:
Information received from various commercial fishing vessel operators emphasized the fact that modern electric drive winches have proven to be very reliable under extreme operating conditions. Proponents of electric drive systems claim that AC electric drive winches are much more reliable over time than hydraulic driven winches because electric drive systems consists of fewer rotating and moving parts.
Despite the positive feedback received regarding the use of electric-drive winches, failures of the electric drive, power supplies and controls have been reported. A common cause of failure appears to be VFD circuit boards due to corrosion from moisture and salt in the air.
Slide 16:
The level of sophisticated electronics and controls incorporated into modern AC electric drive systems requires a fairly high level of specialized electrical training to troubleshoot and identify issues with the electric drive systems. Many commercial fishing vessel operators identified the requirement to have a qualified electrician on board as the main disadvantage of electric drive winches (in the past, the ship’s maintainers and engineers could all equally maintain the electro-hydraulic and hydraulic drive systems). In addition, the availability and cost for the support of field service representatives (FSRs) is a large disadvantage for most commercial vessel operators and research vessel operators.
An additional disadvantage of electric drive winches is that the many of the electrical components are “repair by replacement” items. This requires that various electrical components be carried on board as spare parts. In addition, unlike hydraulic components and fittings which can be purchased at various locations around the world, machined on board, and/or taken from other hydraulic systems fitted on board the vessel, many of the electric drive winch spare parts can only be obtained from specific suppliers, cannot be machined or fabricated on board, and are unique to the winches and cannot be taken from other electrical systems fitted on board.
One of the advantages of electric drives systems is that they require significantly less preventive maintenance and routine maintenance activities to be conducted than electro-hydraulic and hydraulic drive winches. Preventive maintenance activities include inspecting the electrical cabling and motors to ensure that they are free from water and salt corrosion, greasing the motors, and ensuring that there are no issues with sealing mechanisms (especially for machinery that is exposed to the elements).
In contrast, preventive maintenance activities for electro-hydraulic and hydraulic drive systems include verifying hydraulic fluid levels, and conducting leak checks. Routine maintenance activities include replacing filters, flushing hydraulic fluid coolers, sampling and inspecting the quality of the hydraulic fluid, replacing the hydraulic fluid, and flushing hydraulic lines.
Slide 17:
Due to the fact that science winches are custom designed, there was a lack of pricing information received from winch manufacturers. Comparison costs were only provided for the oceanographic science winches. A summary of the costs are provided in Table 3. Feedback from one electric drive winch manufacturer indicated that the cost of electric drive winches is approximately 20%-30% greater than hydraulic drive winches. However, the costing data provided by a hydraulic drive winch manufacturer indicates that the difference in pricing can be greater than 95%.
Table 3 – Winch Costs
Equipment / Electric Drive Winch Cost($CAD) / Hydraulic Drive Winch Cost
($CAD) / Electro-Hydraulic Drive Winch Cost
($CAD)
Fisheries Science Winches / 7,200,000 / 2,140,000* / 3,400,000*
Oceanographic Science Winches / 3,800,000 / 1,490,000 / 1,940,000
*Estimated cost based on Oceanographic Science Winch pricing. Hydraulic drive winch costs do not include the cost of the HPU(s).
Pricing for the hydraulic and electro-hydraulic drive winches shows that the cost of the winches is directly related to the bare drum line pull of the winch and not to the horsepower of the winch (i.e., horsepower = line pull (kg) x line speed (m/s)/76.2).
Slide 18:
AC variable frequency electric drive winches can provide better control of cable tension, speed and payout in comparison to hydraulic drive winches. Electric drives permit variable speed operation from 2% to 100% of the maximum rated RPM while providing full torque at any RPM including zero. This feature allows full rated cable tension control at zero speed. The control systems can be programmed for automated casts, tension and speed control including pre-programmed speed and tension profiles.
Modern electro-hydraulic drives, equipped with PLC control and software using a variable displacement pump, complete with solenoid valves and proportional control valves, can provide comparable control of cable tension, speed and payout to an AC variable frequency electric drive winch.
Slide19:
One of the most common causes of electric drive motor failures is attributed to a lack of adequate motor cooling, resulting in overheating and eventual burnout of the motor stator windings. Air cooled motors are not recommended for electric drive winches that are installed on the working deck. The primary reason is that the motor will be exposed to salt water and moisture in the air and large variations in ambient air temperature throughout the year (ranging from -35˚C to +40˚C) as well as throughout the day. The temperature variations can result in over-heating of the windings due to warm temperatures during the day or condensation in the windings due to cold temperatures at night that can deteriorate the insulation on the windings. To prevent these issues, totally enclosed water cooled motors are typically used. The advantages of water cooled motors are that they prevent overheating of the motor and protect the windings from salt water and moisture. The disadvantages are that they increase the cost of the electric drive, and they require cooling water piping to be connected from the ship’s cooling system to the motor
Hydraulic drive winches offer the advantage of being able to locate the HPU in a controlled environment within the ship. This offers the advantages of protecting the HPU from the elements and being able to use less costly methods such as cooling fans and space heaters to control the temperature of the hydraulic fluid. The disadvantage is the large amount of piping required to distribute the hydraulic fluid from the HPU to the winches located throughout the ship.
Similar to electric-drive motors, the electro-hydraulic drive winch HPU is typically exposed to the elements for deck mounted machinery and is subjected to salt water and salt air corrosion. Deck mounted HPUs require oil heaters to protect the hydraulic fluid from cold temperatures. The electric motor and the system components and controls will need to be provided with protection from the elements as well, resulting in increased costs. Alternatively, the HPU for each winch can be located in a controlled environment in the vessel (e.g., a hydraulic pump room). The disadvantage associated with this solution is that a greater amount of piping will be required to distribute the hydraulic fluid from the HPUs to the winches.
Slide 20:
One of the appealing features of electric drive winches is that they eliminate the possibility of hydraulic fluid spills and leaks. Hydraulic fluid leaks also pose a safety issue to the crew. Injuries can be caused by hot hydraulic fluid spraying from leaking fittings, flailing hydraulic lines under high pressure, and fire resulting from atomized hydraulic fluid contacting a heat source. In addition, old or dirty hydraulic fluid, hydraulic filters and cleaning rags must be disposed of through proper channels which can be costly and time consuming if numerous HPUs are used.
In addition to eliminating environmental issues with regards to hydrocarbon spills, electric drive winches offer the advantage of emitting less noise than electro-hydraulic and hydraulic drive winches. Hydraulic pumps transmit structure-borne and fluid-borne noise into the system and radiates air-borne noise. This is due to the constant motion of the pumping chambers which result in a pulsating delivery, which causes a corresponding sequence of pressure pulsations. These pulsations create fluid-borne noise, which causes all downstream components to vibrate. One means of reducing the noise produced by the hydraulic pumps is to locate the HPU within an area in the vessel that can be designed to reduce noise. This option lends itself more easily to hydraulic drive systems as the HPU(s) will be located in a space(s) within the vessel.
1/5
[1] Two control cabinets are required for the electric drive science winches and oceanographic winches. Each cabinet measures approximately 2.1 m H x 5.0 m L x 1.2 m W and has a mass of 4,600 kg. Three HPUs are required for the hydraulic drive science winches and oceanographic winches. Two HPUs measures 3.4 m H x 3.6 m L x 1.9 m W with a mass of 8,600 kg each, and the third HPU measures 3.0 m H x 3.1m L x 1.25 m W and has a mass of 5,500 kg.
[2]Winch Technology - Past Present and Future, A Summary of Winch Design Principles and Developments, Pearlman, Michael et al., InterOcean Systems Inc.
[3] Ibid
[4] Ibid.
[5]