TECHNICAL FIELD OF THE INVENTION

The invention relates generally to seafaring and more specifically to a method, system and system element for determining seafaring conditions in a navigable passage and also to be able to safely transport more cargo on ships.

BACKGROUND OF THE INVENTION

Many important commercial ports, for example ports on the coast of the Baltic Sea, are surrounded by shallow water and archipelago. Deeper areas which are suitable for larger freighters and passenger ships are marked with navigation marks which represent the navigable passage. Even these navigable passages may have parts of relatively shallow water which limits ships draft so that large freighters having heavy cargo onboard may not be able to enter or leave a certain port.

On the other hand, the depth of the navigable passage fluctuates substantially due to changes in e.g. water level which might allow ships to take more cargo from time to time. The allowed maximum draft for a navigable passage must be based on water depth during very low water level in order to keep the passage in a promised condition virtually all the time. For example, typical water level fluctuation within one year near Finland's coastline is roughly one meter. The fluctuation of the water level can not be taken into consideration with prior art systems. The existing systems that provide information about e.g. wave height and water level are based on a few measuring points outside the navigable passages. Information about the whole coastal area is interpolated and extrapolated from these few measurement points. This means that the information is just a rough estimate and it can not be provided in real-time. US patent 6,317,079 discloses a system for an almost continuous monitoring of the clearance under a ship's keel. The monitoring is based on water depth data, two GPS receivers and tidal information. The system uses GPS to provide actual water level data while the ship moves through a channel and uses this water level data as a new reference to known water depth data. The problem is that cargo is usually loaded onboard on harbors and docks so the keel clearance information should be available to the ship already before it enters the channel in order to maximize the cargo onboard. OBJECT OF THE INVENTION

The object of the present invention is to provide a method, system and device for determining conditions in a navigable passage in order to be able to safely pass through the navigable passage with the maximum amount of cargo onboard.

SUMMARY OF THE INVENTION

The main characteristics of the method according to the invention are defined in the characterizing portion of claim 1 .

The main characteristics of the system according to the invention are defined in the characterizing portion of claim 7. The main characteristics of the element according to the invention are defined in the characterizing portion of claim 8. The method for providing information about a navigable passage is mainly characterized by the steps of: measuring characteristics of the water and/or the air surrounding an at least partially submerged system element, preparing the measurement results for transmitting, transmitting the measurement results from the at least partially submerged system element, receiving said measurement results at a receiving system element, and determining an acceptable draft for a ship for safe navigation through said navigable passage based on the measurement results and ship specific properties.

The ship specific properties that could be taken into account are e.g. the maximum speed, the sensitivity to wind and the squat i.e. the depression of the ship due to speed. When a big ship travels with high speed in a shallow passage the ship will be sucked towards the bottom of the shallow passage due to the flow of water in a direction opposite to the travel direction of the ship, which lowers the water level around the ship. This squat phenomenon is depending on the form of the hull of the ship and on the circumstances in the passage. A person skilled in the art knows several methods to estimate the squat in different circumstances for a specific ship. Ship specific diagrams are available. Also other movements of the ship such as e.g. jittering, acceleration, rising, beating, twisting and rolling have an influence on the draft of the ship. The way of loading the ship i.e. prow or stern low will also have an influence on the draft of the ship. Different ships must be loaded in a different way in order to optimize the draft. The ship must be loaded differently during the winter when there is ice and during the summer when the water is open. The frequency and the size of the curves in the passage will also have an influence on the draft of the ship. The measurement information can be sent either directly from the at least partly submerged system element or via a maritime information and/or navigation center to the ship. It is then up to the shipping company or the captain to make decisions based on this measurement information. Determining of an acceptable draft for a ship for safe navigation through said navigable passage can be done on the ship by the captain of the ship. An experienced captain can estimate an acceptable draft for the ship based on the measurement results and the ship specific properties. It is naturally also possible that the acceptable draft is calculated on the ship instead of estimated by the captain. This means that a program module for the calculation of the acceptable draft is then needed on the ship. The program takes into account the measurement results and the ship specific properties and calculates automatically the acceptable draft for the ship. It is also possible that an acceptable draft for a ship for safe navigation through said navigable passage is determined already in the at least partially submerged system element or in a maritime information and/or navigation center. This means that the acceptable draft is calculated by a program module, which is situated in the at least partially submerged system element or in a maritime information and/or navigation center based on the measurement results and ship specific properties. The ship has to be indentified and the ship specific properties must be available to the program module in order for the program module to be able to perform the calculation. At least some information relating to ships is already available in the AIS system. The ship specific properties might e.g. be stored in a database in the maritime information center or the maritime information center might get the information based on a request directed to the ship. The results of the calculation are then sent either directly or through a maritime information and/or navigation center to the ship. The measurement results measured at the at least partially submerged system element in the passage are important information to the captain of a ship in order for him to decide on how much cargo he could take on the ship and still pass safely with the sip through the passage.

Some embodiments of the invention will be described by reference to the drawings, but the invention is not intended to be limited only to these embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described in greater detail with reference to the accompanying drawings in which: Figure 1 illustrates a navigable passage to a harbor.

Figure 2 illustrates a system element i.e. a spar buoy according to the invention. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a navigable passage to a harbor. In the method according to the invention the effective depth of a navigable passage 400 is determined and that information is provided to ships that will go through the navigable passage 400 to the harbor 300 or from the harbor 300 out to sea. The navigable passage 400 is marked with sea marks, navigation marks, spar buoys and/or other indicative elements i.e. system elements 100a1 -100a3 and 100b1 -100b3. Terms buoy and spar buoy are used to refer to these system elements and especially to their floating parts in the following description. Typically these system elements are partly below the water surface and partly above it, i.e. they are partially submerged. A receiving system element 200 is positioned on the shore, said receiving system element 200 being connection with a maritime information and/or navigation service center. Figure 2 illustrates a system element i.e. a spar buoy according to the invention. The spar buoy has a submerged part which may be formed of a weight, foundation or anchor 180 on the seafloor, which is connected with a cable or chain 170 to the partially submerged floating part 100 of the spar buoy. The portion of the floating part 100 which is above the water surface is visible to ships and/or radars. The anchoring device 180 and the connecting chain 170 can also be seen as separate devices which are only means for keeping the floating part i.e. the buoy itself in place.

The first step of the method according to the invention is to determine the prevailing conditions of the navigable passage 400. These conditions can be determined by measuring certain characteristics of the water and/or the air surrounding the buoy. The passage is marked with buoys 100 and the measurements are performed with measuring instruments 1 10, 130, 140, 150 which are in connection with the buoy or inside it. The measuring instruments that are outside the body of the floating part 100 of the buoy may be connected to it with electric cords 160 or wires or by a wireless connection. The submerged part of the buoy comprises instruments 130, 140, 150 which measure characteristics of water and the part of the buoy being above the water surface comprises instruments 1 10 which measure characteristics of the air. The characteristics to be measured may include salinity of water, density of water, depth of water, velocity of water flow, height of waves, temperature of water and/or wind velocity. Also other characteristics which affect the draft of a ship may be measured. Draft (draught) means in this application the vertical distance between the waterline and the bottom of the ship's hull. It is further possible to use also other measurements in order to make sure that the buoy 100 is in working order and located accordingly. These measurements could include positioning with GPS or some other positioning system, checking the condition of the measuring instruments and the communication means, checking the state of the power source, etc. Checking the positioning of the buoy 100 can be an important feature in cold climates where the surface of the sea or lake freezes in winter and the ice may move the buoy from its intended location. These unwanted movements can be easily detected with occasional positioning measurements of the buoys 100. These additional measurements can be done either periodically automatically or they can be done in response to a request submitted by a receiving system element 200 being in connection with a maritime information and/or navigation service center. This means that the buoy 100 must have a receiver and a transmitter in order to be able to receive the request and to submit the measurement results.

The next step after the first measuring step is to prepare the measurement results for transmitting. This preparation step may include interpreting the outputs of the measuring instruments, analog-to-digital or digital-to-analog (AD/DA) conversions, applying correction factors, combining measurement data from a number of instruments, forming suitable packages for communications protocol and/or other actions which are performed to the measured data before transmitting it further. When the measurement data is prepared it will be transmitted. Preferably, the data is transmitted via an antenna 120 fastened to the buoy wirelessly on radio frequency using conventional data transmission means. The data can be transmitted using for example a mobile phone network, a mobile data network, a satellite phone network or some application-specific data transmission means. In cases where other infrastructure is relatively near e.g. the buoy is near the coast, a wired connection or wireless local area network (WLAN) may also be used. Preferably, the data is transmitted either directly or indirectly to at least one maritime information and/or navigation service center or using the systems provided by them, such as, for example AIS (Automated Identification System), ECDIS (Electronic Chart Display and Information System) or VTS (Vessel Traffic Service). Preferably, the buoy 100 is visible in the ECDIS system and the buoy is an AIS object which provides measurement data through the AIS system.

The data that is transmitted from the buoy 100 is received in harbors and/or ships and/or maritime information centers and/or navigation service centers. The measurement data can be transmitted either directly from buoys to ships and harbors or to at least one maritime information and/or navigation service center which then forwards the data to ships and harbors via existing systems, such as for example AIS, ECDIS or VTS. These maritime information and or navigation centers may be information centers dedicated for this purpose and/or existing information centers for different purposes, such as for example the AIS, the ECDIS, the VTS, weather stations, meteorological stations and/or a Meteorological Institute. The measurement data is preferably received through a navigation system element in these locations. The navigation system element can be a part of an existing system, such as the AIS, the ECDIS or the VTS. The navigation system element can on the other hand be a dedicated element which may be in connection with another navigation system. Next, the effective depth of the navigable passage is calculated for a ship based on received measurement data of ongoing conditions of a navigable passage. The effective depth means in this application the depth of the navigable passage when the ship in question and the ship's velocity, water currents, wind speed and other factors that affect either ship's draft or depth of the water have been taken into account. The basis for the calculation is the known depth of the navigable passage at a known water level and the measured condition defines a more accurate depth data. Preferably, the effective depth is calculated individually for each ship in order to apply also the ship's properties, such as maximum speed, sensitivity to wind, etc, to the calculation. The effective depth is then the ship's maximum allowable draft taken also into account a suitable safety margin.

It is also possible to calculate the maximum amount of cargo for a ship based on the calculated effective depth and the ship's properties. The maximum allowable draft is the effective depth with a safety margin subtracted from it. The ship's properties define the correlation between draft and cargo so the calculation of the maximum allowable cargo is a straightforward process when the necessary data is available. The calculated maximum available cargo is communicated to the ship and/or the harbor. This calculation is advantageously done in the maritime information and/or navigation center with access to a database containing ship specific information, but the calculation can naturally also be done in the ship or on the harbor or in the buoy. When the information is available, cargo can be loaded onboard until the maximum allowable amount is reached and the ship can still safely sail out of the harbor through the navigable passage from which the measurement data was obtained.

The system according to the invention for providing information about a navigable passage comprises means 1 10, 130, 140, 150 for measuring characteristics of the water and/or air surrounding an at least partially in water submerged system element 100, means for preparing the measurement results for transmitting, means for transmitting 120 the measurement results from the at least partially submerged system element 100, means for receiving said measurement results at a receiving system element 200 at a maritime information and/or navigation service center, and means for calculating an acceptable draft for a ship for safe navigation through said navigable passage 400 based on the measurement results.

The system element according to the invention for providing information about a navigable passage comprises means 1 10, 130, 140, 150 for measuring characteristics of the water and/or the air surrounding an at least partially submerged system element 100, means for preparing the measurement results for transmitting, and means for transmitting 120 the measurement results from the at least partially submerged system element 100.

The system element 100 could also comprise means 160 for calculating at least a coarse draft and/or an acceptable draft for a ship for safe navigation through said navigable passage 400 based on the measurement results at least partly before establishing the connection to a receiving system element 200 to report measurement results and/or said draft. This means that the calculation of the acceptable draft could be done in the system element 100 instead of in the maritime information and/or navigation service center or on the ship or on the harbor. The means 160 for calculation in the system element 100 might in such case receive specific information relating to the ship from the maritime information and/or navigation service center.

The system element i.e. the buoy 100 may in addition to means for sending measurement information also comprise means for receiving information from the maritime information and/or navigation service center or a second system element. This information can be in the form of e.g. signaling, update messages and/or commands to control the operation of said system element 100. The system element i.e. the buoy 100 may be configured into operation as a sea mark, navigation mark, spar buoy, indicative element of passage, or another indicator sign to indicate an object meaningful to navigation. The means 1 10, 130, 140, 150 for measuring characteristics of the water and/or the air surrounding the system element can comprise normal sensors suitable for said measuring tasks. Said sensors are commercially available and as such known to a person skilled in the art. Also the means for preparing the measurement results and for transmitting the measurement results are as such known to a person skilled in the art. The communication from the system element to the navigation system element AIS, the ECDIS or the VTS can be based on normal as such known communication methods in said systems. All of the sea marks, navigation marks, spar buoys and/or other indicative elements i.e. system elements 100a1 , 100a2, 100a3, 100b1 , 100b2, 100b3 in the navigable passage 400 may be system elements according to the invention comprising measurement means etc. It is, however, also possible that just some of the system elements in the navigable passage 400 are system elements according to the invention. The system elements according to the invention would in such case be positioned in the most critical positions in the navigable passage 400. When the ship is able to pass through the most critical positions in the navigable passage 400 the ship will be able to pass through the whole navigable passage 400.

The receiving system element 200 is in figure 1 shown on the shore, but a corresponding receiving system element 200 can also be positioned on the ship in order for the ship to receive information directly from the system elements 100a1 -100a3 and 100b1 -100b3. It is naturally possible to make several alternations to the embodiments of the invention described in the detailed description within the scope of protection defined by the claims.