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Introduction
Towage at sea has developed over
the years. The towed vessels, barges and other floating objects are
increasingly large, expensive, complex and delicate.
Therefore the preparations for sea-going tows are thorough: engineering
studies (motion analysis) and sea fastening calculations result in
complex and expensive sea fastening constructions and ‘limiting sea
states’ during the voyage.
Scheduling, weather delays and potential damage can cause large
(financial) risks for Operators, Clients and Insurers.
Regulations
and Guidelines
Local and
International Maritime Laws and Regulations for safe transportation are
often supplemented by Industry Standards (‘LOC Guidelines for Barge
Transportation’, ‘Noble Denton Guidelines for Marine Transportation’,
Client Specific Guidelines, etc.) that specify the criteria for design,
sea fastening, vessel/barge motions and sea states.
The vessels and cargoes will often also have their own specific
limitations and restrictions on maximum allowable forces and
vessel/barge motions.
Reality
Again: Towage at
sea has developed over the years. As a result of thorough preparations,
the fast majority of tows arrive safely at their destination.
Sufficient safety margins in the engineering and preparations, improved
weather forecasting / weather routing capabilities ensure safe
transportation in most cases.
The calculations and preparations are verified by Warranty Surveyors and
other Third Party experts.
But
………………………………………….. !!!
Once the voyage
preparations are completed, the Master of a tug will be guided during
the tow by good seamanship and the limits that are defined in the
Transportation Manuals:
- Maximum
allowable sea states (Significant Wave Heights) during the voyage
- Maximum
allowable forces on the cargoes, usually expressed in Roll/Pitch
angles
At
sea the Master of the tug is on his own again.
He will receive
weather/wave height forecasts and routing advice for guidance.
It is however well known that on board it is virtually impossible to
observe the correct wave heights. 5 Captains and 10 Warranty Surveyors
on the bridge of a vessel will give you 15 different answers on what the
actual wave height is.
The actual Roll/Pitch angles of the tow are visually observed from the
tug, and then again only during daylight. At night the motions of the
tow are often ‘in the dark’.
Since the
start of seagoing tows nothing has really changed over the last decades!
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The Solution
MaxControl
and
Siri Marine have
developed a Tow Monitoring System that
really works!!
One or more
DimMax
motion sensors are placed on board of the towed object
The sensors
measure accelerations in 3D with accuracy of 1 mg
Roll/Pitch
angles with an accuracy of 0.05 degrees (static) or < 0.5 degrees
(dynamic) are computed and displayed
A continuous
signal from the
sensor(s)
is transmitted to the tug, where the measurements are displayed
‘real-time’ and continuously on a PC screen on the bridge
The Master (or
Client’s Representative) can monitor the ‘real-time’ accelerations,
forces and motions of the tow at all times.
The system also displays the history of the accelerations, forces and
motions and stores all data for future reporting and/or voyage
evaluation.
The system is very easy to install and can be operated by the tug’s
Master and crew.
Additional
features of the SafetyMax Motion Monitoring System are:
Heave
Monitoring
Hull Stress:
Deformation (Deflection and Torsion) of vessels and objects (minimal
2 sensors)
Fatigue Life
calculations (post processing of the data)
Calculation
of lashing forces
click for larger view
The system
will enable the Master to keep better control over his tow.
Alarms for maximum
allowable accelerations, forces and Roll/Pitch motions can be generated.
The system immediately displays the results of corrective actions.
The theoretical assumptions during the engineering and preparation phase
of a transport include large safety margins. This is required because
the actual motions and resulting forces (=accelerations) on vessel,
barge or cargo are not known and may differ from the theoretical
assumptions.
With a Tow
Monitoring System installed, the safety margins can be significantly
relaxed because the tow motions and forces are known and under control.
Increased knowledge on actual tow motions will assist in the (Risk)
evaluation and voyage preparations of future projects and transports.
This will
result in a significant reduction in cost, a significant increase in tow
performance and NO increase in risk!
Voyage
Reporting
There is an
increasing demand from Clients, Owners, Operators and Warranty Surveyors
for voyage reporting and evaluation. In the event that damage is
suspected, or has occurred, a reliable log of the voyage events is
essential.
SafetyMax
Motion Monitoring System already includes the possibility to generate
such reports.
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