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Abstract
The cost of ship operation is dominated by the cost of fuel. The efficiency of ship propulsion depends on number of
parameters. After selection of the most important we can further analyze them for taking relevant action to increase
the ship propulsion efficiency. Biofouling of underwater part of ship’s hull has direct influence on vessel resistance
and engines power required to maintain the speed or keep optimal fuel consumption. HISMAR is a name of the
project directed on development of robotic system that can be used to introduce new approach to keep ship hull
clean and almost free of bio-fouling. Frequent cleaning using HISMAR robotic system could be a new tool to
increase ship performance as well as conduct specific types of ship hull surveys underwater. New approach for
inspection and cleaning needs field research to validate the financial and technical benefits.
The HISMAR Project no 012585 was founded by EU-FP6 Framework Program.
Keywords : underwater cleaning, robotic system, underwater inspection, ship propulsion, efficiency
1. Introduction
We observe continuous growth both the global and EU shipping fleet. When speaking about
the measures that can be taken to improve the shipping efficiency one of major issues is hull
performance increase by the reduction of the wave and frictional resistance and increase of
propulsion system efficiency. Whilst shipping is one of the cleanest forms of transportation, the
fouling of ships reduces efficiency, increases fuel consumption and in extreme cases - corrosion.
To minimize wave drag, special attention is given the smooth ship hull design and construction
quality. The numerous efforts focus on frictional drag reduction using not only computational
techniques. Modern anti-fouling paints and special low friction coatings are another large area
of investment into research and achieved spectacular performance. When speaking about the
increasing efficiency of the propulsor system there is a number of another opportunities like
new highly efficient diesel engines, advanced propeller designs as well as promoted by some
companies propeller coating techniques that prevent biofouling. Some guidelines and draft data
regardding potential savings due to lowering of fuel consumption can be found in technicalliterature. An example taken from data collected by Wartsila is presented in Table 1. The
important comment to that table is that, there is very limited amount of data available that could
be referenced as being confirmed by measurements at real sea conditions. Bearing that in mind,
when using such data for calculation of potential savings we have to treat that figures as
guidance. More detailed data can be collected during research on ship performance using real
object data gathered during ship operation. This is quite complex task and will need certain
financial resources and positive approach from ship operators to collect and validate the data
with assistance of ship crew.
Table 1. Estimated savings due to selected measures applied to various types of ships
Ship Type Tanker Container Ro-Ro Ferry
Efficiency measures
Hull clearing < 3% < 2% < 2% < 2%
Propeller clearing and polishing <10% <10% <10% <10%
Modern hull coatings < 9% < 9% < 5% < 3%
Propeller efficiency measurement < 2% < 2% < 2% < 2%
Constant versus variable speed operation < 5% < 5% < 5% < 5%
Source: Wartsila [1]
It is obvious, that machinery that operates for longer time and at higher power and loading is
more susceptible to failures. Lower engine loading in general means lower wearing of certain
components of ship drive system that could lead to longer operational life of the ship propulsion.
Furthermore, it results in better reliability of the main propulsion and resulting ship safety
improvement - particularly important for tankers, bulkcarriers, ro-ro and passenger ships.
Monitoring of the ship hull condition for estimation of fouling or coating roughness
measurements when coupled with means for cost effective ship hull cleaning (an example could
be HISMAR system), could be valuable operational tool that could be used for ships in
operation. Such procedure could be a part of more complex propulsion efficiency audits being
a part of modern ship hull survey procedures.
2. Environmental and legal aspects
There is ongoing discussion at International Marine Organisation (IMO) with regard to Marpol
Annex V (Regulations for the Prevention of Pollution by Garbage from Ships). IMO has already
defined the residue from hull scrubbing as ships waste and it is therefore covered by the
convention. As a consequence of this, it is likely that restrictions will be introduced as to where
and how ship hulls may be scrubbed. The scrubbing of hulls by divers is forbidden within many
European harbours. Fouling on a hull increases a ship’s drag through the water, thus increasing
the amount of power required to maintain the same speed or reducing the speed of the vessel for
a given power. Fundamental data on that subject can be found in reference [2]. It is estimated
that serious fouling can increase the drag on a ship by up to 40%, reducing the speed by up to 2
knots and increasing the fuel consumption by 10÷20% [3]. For the shipping industry, this
means increased costs and time delays. The extra fuel consumption also increases greenhouse
gas emissions, being composed of NOx, SOx and CO2 from ships by up to 20 million tonnes
per annum. Although shipping produces the least amount of greenhouse gases annually when
compared to other modes of transportation, under the Kyoto agreement the EU is committed to a
5% reduction in emissions by 2012.3. Underwater ship hull cleaning -- advantages and tools
For over 130 years people have thought about machines or robots for cleaning ship hulls.
Various devices and technology has been developed and tested. Only few developments have
found wider application, an example could be hydraulic brush system operated by diver
(BrushCart). In recent years, we are observing growing interest in robotic system that are
developed to cope with the bigger ships and eliminate diver’s presence underwater. Important
issue is stress on marine ecology requirements. Robots are able to cope with that case using
suitable tools. However, the investment in robotic system may be substantially high, such
system will be able to work continuously underwater and possibly above the water where divers
do not have access. Plug in sensor modules could allow to conduct detailed inspection of the
almost whole hull during the same mission.
3.1 Brush technology
Brushes are used in cleaning carts, handheld polishers and some robotic systems and are
able to cope with almost all types of fouling. Most systems consist of one or more rotating
brushes pneumatically, or hydraulically driven. This requires the minimum of equipment
beyond the cleaning device itself thus reducing the cost of the system. Before the ban on
tributyltin (TBT) came in, brush technology was preferred to underwater jetting systems, as it
was easier and more economical to use. However, the increase in use of environmentally
friendly low friction coatings can cause a problem, as these coatings are less durable and more
easily damaged by the abrasive action of the brushes. Research has shown that bristle density,
angle and gauge have a greater effect on shear and normal forces produced by brushes, while the
brush speed and stand-off distance has little or no effect. The main point demonstrated by the
research was the selection of the brush cleaning system and forces involved is dependant on a
number of factors and their relationship is very complex. The major problems in cleaning using
heavy duty brushes could have place when dealing with calcerous forms of fouling.
3.2 Water jetting technology
The use of high pressure water jets has become an accepted alternative to brush cleaning
systems. Unlike the brush-based systems, water jets can be easily controlled by reducing or
increasing the pressure from the pump. A water jet's effectiveness is dependant on the surface,
pressure of water, jetting angle and distance from the cleaning surface. Jet nozzles, such as
CaviJet or SwirlJet have been developed to enable effective cleaning of the hull underwater.
Tests using cavitating water jet nozzles showed that the cleaning process can remove various
types of fouling from hull coatings, while at the same time, minimizing the damage to the
coating. Although jet washing provides increased control of the cleaning process, the perceived
increase in the cost of the equipment is still thought to be prohibitive. In hase of the HISMAR
system low pressure jetting will be sufficient to remove effectively and safely the layer of slime
from the hull surface.
4. Cleaning problems
Diver(s) presence enhances the risk of diving accidents at work. Some data revealed by HSE
show that probability of diver accidents during professional diving operation is higher than in
farming or civil engineering. The number of accidents in offshore and inshore diving is in a
range 20-40 for 100000 dives while fatal accidents occur in number of 6-7 for 100000 dives.
Additionally to the risky job, diver has limited time to be able to work underwater so a team of
divers is required to perform cleaning task. An open issue is the cost of diver safety measuresand environment protection requirements that must be taken into consideration discussing the
cost benefits. Remotely controlled machines are not able to clean the whole wetted ship surface
due to some hull features that restrict the robot operation. Ship bow and stern, due to hull shape
are very difficult for automatic cleaning and that area will probably be cleaned by divers.
Generally it is assumed that cleaning of 80% of the ship underwater area from slimes could
provide suitable effect of drag reduction.
5. HISMAR idea
The abbreviation HISMAR stands for Hull Identification System for Maritime Autonomous
Robotics. HISMAR is intended to be a multifunctional robotic platform which will be able to
perform specific inspection or maintenance tasks such as structural integrity monitoring of the
ship’s hull or cleaning operations. Apart from Project leader - Newcastle University, the other
partners in the project were Graal Tech of Genoa; the UK's Shipbuilders and Shiprepairers
Association; TecnoVeritas of Portugal; Polski Rejestr Statków; Robosoft of France; Carnival;
Moscow State Technological University; Royal Thai Navy and TEPAC Technology & PatentConsulting of Germany.
Robotic platform is to be deployed for the board of the ship, harbour service craft or from
the pier using simple care or special launching and retrieval device. The control over the vehicle
is provided via the special umbilical with power, control lines and hoses used for removal of
cleaning wastes to the surface. Intervention with the use of HISMAR robot needs some
preparation before the vehicle is placed on the surface of the ship hull. The desired situation is
the case when digital data of the ship hull construction are provided to the robot control
computer. On the other hand, at start of the job a map of the hull is automatically charted,
recording the location of every weld, thickness change, rivet and indentation on the ship’s
surface. Adjustable jets of pressurised sea water blast the marine growth off the surface of the
ship which is then sucked up into the main chamber. Here, ca 150 litres of water a minute is
filtered and the bio-fouling removed and rendered harmless to the local environment. In this
way, the ship’s robotic ‘vacuum’ can continuously roam the ship’s hull, preventing the build up
the layer of slime.
Hull surveying is an important part of any vessel's life span and a number of periodic
inspections of the hull are required during the vessel's life. Currently, the minimum requirement
is for a visual inspection of the hull and with some thickness measurements being taken in
specific areas of the hull, or where a probable defect might have occurred. These are usually
performed using an ultrasonic sensory system that is placed on the plate's surface. Due to the
size of the detection head and the skill required to operate the equipment, only a small
proportion of a vessel's hull can be accurately measured. A full hull inspection is required to be
performed in dry dock every five years, but up to 20% of the hull may not be inspected due to
the vessel's dock supports. Between these class renewal inspections, intermediate hull
inspections are required. These are general visual underwater inspections performed by divers.
However, in recent years a number of robots have been developed to improve the accuracy,
coverage and reliability, while reducing the time and cost of the inspection. The current robotic
systems available are limited to visual inspection and ultrasonic plate thickness measurements.
6. The critical components of the HISMAR Robotic Platform
The HISMAR robot design is presented in Fig 1 and 2. The key systems of the robot
include:
Drive Systems & Central Robotic Platform
Key to the HISMAR robotic platform is the versatile central drive module. This incorporates the
robot’s drive systems, navigational sensor systems and control electronics. Robot is linked withthe surface by a mean of specialised umbilical that contain power and data conductors and
possibly hydraulic hoses for removal of cleaning debris.
Cleaning & Debris Extraction Systems
The cleaning system will utilize a water jetting to clean the hull. The jet spray system is
intended to provide the customer with sufficient control for their cleaning needs while
preventing damage to the hull coatings. A complete extraction and waste handling system is to
be developed to comply with current and future marine environmental legislation.
Mapping & Navigation Systems
HISMAR’s unique mapping and navigation system will allow for full autonomy of the robot
after the initial process of mapping the hull. This will allow for complete or partial cleaning of a
ship’s hull, the latter being complete at the crew’s convenience with no loss of operating time.
The map will be a permanent record of the condition of the ship’s hull, being updated by the
navigational system whenever a cleaning operation is performed.
7. HISMAR robotic system advantages
Marine growth on ships is a huge environmental and financial problem for the marine
industry and HISMAR offers a unique solution to both of these — and more. Created is a
system that works totally independently — in or out of the water — and not only keeps the ship
clean but also feeds back vital information about the hull’s condition. Because the map it
follows is so detailed, if there is a change to its path caused by corrosion or a crack in the steel
then it feeds this information back. This means it can be used as an additional check the
condition of ship’s hull and provide important reference data for classification society
surveyors. All other developed cleaning or inspection systems currently available are remotely
controlled during their operation, requiring highly skilled and experienced operators to
effectively clean the hull, while the ship is out of operation and usually in dry dock. The
advantage of the HISMAR robot is that it is an autonomous system so it can continue cleaning
with the ship remaining in service.
The platform can be launched whenever the vessel is in port or at anchor. The device will be
able to complete its tasks partially whilst in one port and be re-launched at successive points to
complete the task. The generic platform will offer the option of using targeted plug-in modules
to perform specific inspection or maintenance tasks such as structural integrity monitoring of the
ships hull or carrying out cleaning and waste recovery operations. This project offers a means to
effectively and efficiently undertake hull inspection and maintenance thereby extending the safe
working life of the vessel. Cleaning of the hull ensures the vessel maintains the lowest possible
hydrodynamic resistance and consequently reduces amount of fuel oil consumed. Therefore
ensuring a clean and smooth vessel underwater hull surface reduces vessel emissions and
reduces operating costs.
8. Validation of fuel consumption data and effectiveness of cleaning
There is noticeable amount of published data providing general information about cleaning
benefits but only few data available that provide reliable figures of possible savings due to
periodical cleaning of the ship hulls. A very optimistic diagram that presents possible
advantages from cleaning ship hull is given in Fig. 3. Some companies are offering advisory
optimization services of vessel performance and in some cases also hull cleaning underwater
using hydraulic tools. Up to our knowledge, only one company is using specialized ROV system
and no reliable commercial or scientific data regarding its performance are available.Taking decision about cleaning requires certain data to be analyzed. US Navy underwater
husbandry practice requires the decision to be taken after underwater inspection and precise
estimation of the area covered by fouling after comparison with reference data. Other
commercial practice requires analysis of periodically collected voyage data as well as basic data
about the prime mover operation like – rpm, specific heating value of fuel oil, fuel oil
consumption, power measured by special device or torsiometer, turbocharger revolutions,
exhaust gas temperature – just as example. In that case, the collected data are subject of
evaluation using dedicated software by commercial company on a subscription basis. In case of
some ships and sea routs potential savings are big enough to pay for kind of ship services..
9. Conclusions
The use of remotely controlled technology for underwater cleaning is subject of numerous
R&D activities. Commercially available devices are not cheap and the cleaning in dry dock is
much more popular and usually coupled with class surveys. Prime target for robotic tool is to
achieve performance and cost of operation at the competitive level. Hull cleaning by costeffective robotic devices that are able to cope with slime will limit fouling and lower the fuel
consumption. The use of intelligent crawling underwater robots will expand as there will be
more comparable data available describing ship propulsion performance increase as a result of
more frequent robotic cleaning. Collection of reliable data about the financial and technical
benefits of the robotic cleaning technology will be important for independent assessment of
ship propulsion system performance. Plate thickness measurements and other data describing
ship hull condition that will be collected by robot during cleaning missions could be further
used by classification societies for class renewal surveys. The hull surveying using innovative
robotic technology is in development phase and needs additional founds to be recognized as
mature technique recommended for wider use |
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发表于 2017-5-3 13:35
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