Frequently asked questions
The N2000 is the vertical coordinate reference system that is used to report ground and sea levels. It is the Finnish implementation of the common European Vertical Reference System, and it uses the Amsterdam zero level, or NAP (Normaal Amsterdams Peil), as its base level.
The N2000 vertical coordinate reference system is based on the third Finnish high-precision levelling process (1978–2006). The systems that were used previously include the NN, N43, N60 and theoretical mean sea level.
The Baltic Sea states have adopted a common moniker for the system, BSCD2000 (Baltic Sea Chart Datum 2000). For example, Sweden uses the abbreviation RH2000 and Estonia the abbreviation EH2000.
When a nautical chart product is based on the N2000 vertical coordinate reference system, its depth and fairway information are linked to the Earth’s crust. Previously, these figures were based on the theoretical mean sea levels in sea areas and on the NN vertical coordinate reference system for inland waterways. The use of N2000 system-compliant nautical chart products requires the utilisation of water level information that is based on the N2000 system.
In practice, sea-area water level figures that are based on the N2000 system will be larger than previous figures, i.e. there will be more so-called plus water than before. Correspondingly, the depth and fairway information on N2000 charts will indicate this same difference between reference levels. In sea areas, this difference can vary between 10 and 20 cm, depending on the area in question.In the future, those navigating in sea areas must pay closer attention to the real-time water level observations provided by the Finnish Meteorological Institute and the vertical coordinate reference system used in these observations.
In the N2000 system, the zero level is fixed, whereas the zero level of a system based on the theoretical mean sea level shifts by a few millimetres every year. As such, the theoretical mean sea level is not actually a single, clearly defined reference level, but rather an annually changing reference level. What this means is that depth values based on the mean sea levels of different years are not directly comparable with each other. Due to practical reasons, mean sea level charts always contain information from different years, and this error inherent in mean sea level charts is entirely hidden from the end user. The annually shifting reference level also causes problems in regard to maintaining information. Over long periods of time, the error can become significant. In the N2000 system, measurements made in different years are directly comparable to each other, meaning that the depth information will not expire.
Nautical charts tied to the mean sea level do not account for land uplift, which means that depth information goes out of date quickly. In the N2000 system, the zero level is tied to the earth’s crust. Therefore, the system also accounts for land uplift.
This change will help harmonise and clarify the information used in nautical charts and fairways, and it will also allow us to take land uplift into account in this information. The water depth information in N2000 nautical charts will always remain up-to-date when you use water level information that is tied to the N2000 vertical coordinate reference system. This way, chart users will only have to follow a simple process to know the current water depth of any given area on a chart. In the future, the reform will also enable the introduction of new types of navigational products.
The nautical chart and fairway reform is based on both practical necessities and new regulations. Public administration recommendation 163 states that the N2000 vertical coordinate reference system is the national vertical coordinate reference system of Finland. The hydrographic authorities of the Baltic Sea states have also agreed on the adoption of a common N2000-based vertical coordinate reference system (the Baltic Sea Chart Datum 2000, BSCD2000). This system is compatible with the European Vertical Reference System (EVRS), which will make it easier to utilise the information presented in the system both nationally and internationally.
The publication of N2000 nautical charts will change the symbols used on charts. N2000 charts will no longer include authorised draughts for merchant shipping lanes. Going forward, channel information will be presented in separate Sailing Directions.
However, the instructions published in 2021 regarding the use of fairways must already be followed throughout Finland, regardless of whether you are using MSL or N2000 nautical charts. The authorised draughts presented on current MSL charts must also be interpreted as design draughts as per the instructions.
The publication of N2000 nautical charts began with the Bay of Bothnia in late 2021. The reform will proceed from the Bay of Bothnia via the Sea of Bothnia and Archipelago Sea to the Gulf of Finland. For inland waters, the reform is planned to start in 2023. The reform is estimated to take approximately 5–6 years to complete. An up-to-date chart product index detailing the progress of the reform is maintained on Traficom’s website.
Useful links:
Channel depth instructions:https://www.traficom.fi/sites/default/files/media/file/SYVYYSOHJE_EN_2021_11_01.pdf (PDF)Sailing Directions for Finnish waters:https://www.traficom.fi/en/services/sailing-directions-finnish-waters
Publication status of N2000 charts:https://www.traficom.fi/en/transport/maritime/publication-status-n2000-charts
Finnish Meteorological Institute’s sea level data, also according to N2000: https://en.ilmatieteenlaitos.fi/sea-level
N2000 nautical charts no longer present authorised draughts for merchant shipping lanes. From a global perspective, presenting authorised draughts on nautical charts is unique to Finland. Nautical charts are internationally standardised to an extensive degree. In other words, the symbols used on nautical charts and their meanings cannot be freely decided in Finland. Based on standards, the symbol used for authorised draught on Finnish charts (INT M6) means maximum authorised draught. However, this is inconsistent with the Finnish definition for authorised draught (‘kulkusyvyys’ in Finnish), which is a measurement value used in channel design. Since the presentation of authorised draught values is inconsistent with national guidelines, they are being removed from merchant shipping lanes. From now on, the term design draught will be used to refer to the authorised draught of fairways.
Sailing Directions are official SOLAS-compliant nautical publications aimed at supporting nautical charts that present a variety of information related to navigation. Traficom began publishing Sailing Directions in late 2021. Sailing Directions include channel information, for example. According to the Finnish Maritime Code, before starting a voyage, the master of the vessel must make sure that the intended route has been planned using appropriate nautical charts and nautical publications for the area.
Safe clearance depth refers to the depth to which it has been secured that the channel is clear. Minimum depth refers to the actual minimum water depth in a given area. On nautical charts, the safe clearance depth of an area is indicated with the minimum depth symbol, even if this is not necessarily the actual minimum depth of the area.
Having a design draught of 9.5 m means that the channel has been designed to be used at a draught of 9.5 m under normal conditions when the water level is at the zero point of the reference level. In other words, design draught is dependent on the reference level. The actual design draught at any given time depends on the current water level. If the design draught according to the N2000 system is 9.5 m and the water level according to the N2000 system is +20 cm, the channel can be navigated at a draught of 9.7 m.
It should be noted, however, that the aforementioned design draught is neither a guarantee of safe passage nor an absolute limit. In certain situations, a vessel meeting certain conditions can navigate a channel at a higher draught than the channel’s design draught corrected with the water level. The master of the vessel is always responsible for assessing the required gross underkeel clearance, the vessel’s draught and safe passage.
The depth information and safe clearance depths of merchant shipping port basins will be converted to match the N2000 system. New design draughts and safe clearance depths will be defined for each port entrance, which, depending on each case, will be 0–20 cm less than current figures. However, the actual water depth will not change. As part of the reform, the Finnish Transport Infrastructure Agency will also make sure that the depth information needed in port areas is converted to the N2000 system.
It is important for port information to be up to date, of high quality and accurate to ensure that the N2000 fairway and nautical chart reform brings the expected benefits for safety and transport efficiency. Up-to-date and accurate port information is crucial when making decisions about the loading opportunities of vessels and the safe and efficient utilisation of fairway space.
Traficom has launched a port cooperation model that enables the production of nautical chart products with expanded information content and next generation official nautical chart products that provide more precise information all the way up to the quay. The purpose of this cooperation is to harmonise measurements, information maintenance and the distribution of the nautical charts and nautical publications based on them in both state fairways and port areas.
The change in reference level will reduce depth values on nautical charts by approximately 10–20 cm, depending on the area. In some cases, the design draughts of fairways have not been correspondingly decreased, however, meaning that the design draught is the same for both the MSL and N2000 levels. In addition to the water level, design draught is affected by the speed of the vessel used in the channel design, among other factors. Decreasing the speed of the vessel decreases the vessel’s squat, reducing the required gross underkeel clearance. In some cases, gross underkeel clearances may have been higher than normal due to land uplift so that the channel would remain safe for years to come. In the N2000 system, land uplift is reflected in the lower water level, so these types of ‘buffers’ are no longer needed, making it possible to transfer the additional clearance to the design draught. In most cases, the design draught of a fairway staying the same means that design speeds have been lowered (0.5–1.0 knots on average). These considerations are fairway-specific, and if the design speed of the vessels has been too low, the design draught of the fairway has been lowered. Going forward, design speeds will be presented on both fairway information cards and in Sailing Directions.
The N2000 fairway and nautical chart reform will also affect recreational boating. Since the zero level of the N2000 system is below the current mean sea level (MSL), the reform will reduce the depth values presented on nautical charts by an average of 10–20 cm while correspondingly increasing the N2000 sea level values presented by the Finnish Meteorological Institute by the same amount. In other words, the available water depth will not change when the sea level data used in the N2000 vertical coordinate reference system is taken into account.
As a rule, the design draughts (previously authorised draughts) of shallow channels will decrease when fairway data is converted to the N2000 system. However, the available water depth will remain the same even on small craft tracks when using N2000 water level data.
On the other hand, the depth information concerning the sea areas outside these fairways will decrease by a larger figure than just the difference between the zero points used in the vertical coordinate reference systems. The reason for this larger reduction in depth information is that, as part of the reform process, all older depth information figures will be updated to take into account any long-term changes in land uplift. It should also be noted that the depth information used in the nautical charts for areas outside Finnish fairways are still partially based on old and incomplete hydrography figures.
The publication of N2000 nautical charts began with the Bay of Bothnia in late 2021. The transition period and the completion of the reform is estimated to take approximately 5–6 years. The reform will proceed from the Bay of Bothnia via the Sea of Bothnia and Archipelago Sea to the Gulf of Finland. The publication of inland chart products is planned to begin in 2023. https://www.traficom.fi/en/transport/maritime/publication-status-n2000-charts
The reference level used in a chart is indicated on the upper left corner of the chart. In addition, to help facilitate the transfer to the new vertical coordinate reference system, the lower left corner of each chart will include the abbreviation of the system that is used. If a chart’s depth information is based on the Mean Sea Level, it will use the abbreviation MSL, and the charts whose depth information is based on the N2000 system will use the abbreviation BSCD (N2000). Each nautical chart series will feature this mark on the inside of its front cover.
The easiest way to check the most up-to-date information on the reference levels used in your products is through the Nautical Chart Catalogue.
The easiest way to check the most up-to-date information on the reference levels used in your products is through the Finnish nautical charts portfolio.
In addition to this, the cells will feature a target that is titled M_NPUB, the INFORM field will contain information on the reference level that has been used. Future Notices to Mariners publications will include information that will help chart users find the information they need.
The same concepts have been referred to in different contexts using different abbreviations. The Baltic Sea states jointly agreed to call the new vertical coordinate reference system the Baltic Sea Chart Datum 2000, which is abbreviated to BSCD2000, or, on Finnish navigational charts, to BSCD (N2000).
The Baltic Sea Chart Datum 2000, or BSCD2000, is compatible with the national vertical coordinate reference systems of different countries, which include N2000 in Finland, RH2000 in Sweden and EH2000 in Estonia.
The abbreviations MW (Mean Water) and MSL (Mean Sea Level) both refer to the theoretical mean sea level and mean the same thing. MSL is an established term in seafaring. In channel design and engineering, the abbreviation MW is more common. Learn more: Get to know the new terms.
The Finnish Meteorological Institute will publish its water level observations and forecasts for the N2000 system as well. These will be available on e.g. its website (https://en.ilmatieteenlaitos.fi/sea-level). The publication of N2000-compliant water level information will be initiated at the same time as the publication of the N2000 nautical charts is set to begin at the end of 2021.
The differences between the zero levels used in the theoretical mean sea level and the N2000 system are presented in a chart published by the Finnish Meteorological Institute (https://en.ilmatieteenlaitos.fi/theoretical-mean-sea-level).
The N2000 system makes it easier to follow long-term changes in water levels. Since the reference level remains the same from year to year, only the water level needs to be monitored. However, average water levels vary by area, so variations in the water levels of different areas cannot be directly compared.
