Nautical charts in Finland

Sailing in Finland, particularly in the Bottenviken, requires a detailed preparation of the route to be followed. With very shallow waters, it is necessary to follow documented pathways indicating the minimum depth toà expect along the fairway. Yet, using different electronic nautical charts provide different informations and therefore, in those areas, it is useful to cross-relate information from different sources. Below is the different versions of the map showing the approach to Rönnskär (63.0616, 20.80613333).

On C-map (below), the approach is not very inviting with the pathway line on north-east going through a 1.5 m area. There seems to be a possibility from the north, but not clearly indicated. The East and West cardinal buoys on the north are in the 0-3 metres area without additional depth information.

Rönnskär on C-Map

On Navionics, the north-east pathway is indicated similarly, and the north pathway is drawn on the chart, but without clear indications about water clearance on either pathways. Clicking on the + marks attached on the north and south cardinal buoys indicates "Recommended track (1 m). However, clicking on the north dotted line between the east andwest cardinal buoys indicates "Recommended track", but without indication of depth.

Rönnskär on Navionics

Using the Navionics SonarCharts provides additional information as the shallowest part on the pathway to Fäliskäret pier. The area right of the Marina icon is in the 1.5 to 2.0 metre depth. The pathway to the north-east ends-up in the 0.5 to 1.0 metre depth while clicking on the dotted line indicates a "Recommended track (1 m)".

Rönnskär on Navionics, using SonarCharts

On Eniro ("På Sjön" app), the north-east pathway is indicated with a clearance of 1 metre using <1> on the dotted line. However, the north pathway does not appear. The east and west cardinal buoys on the north are inviting, but without clear information on depth in the 0 to 3 metre area is not inviting.

Rönnskär on Eniro sea charts

On Sailmate, the pathways are very well indicated. A black line is a pathway, and the value indicated along the line in the brackets applies to the line until a new depth is indicated. A dotted line is a shallow pathway or a pathway without indications of the depth. On the east part of the north-east pathway, the line is dotted, with indication of one metre depth <1,0>. The north pathway is indicated with a solid line indicating 2,4 metres in brackets (<2,4>). It means that this depth is ensured all way long to the harbour. Note the angle used to draw the cardinal marks, clearly stating on which side to pass.

Rönnskär on Sailmate

In conclusion, sailing in Finland, particularly in the Bottenviken, requires careful preparation and cross-checking information available on the various versions of the nautical charts. The Sailmate nautical charts seem to indicate the most precise information on both pathways, but the resolution is not very detailed. The basic Sailmate app is free but does not display precisely the position of the user. It can be downloaded on Android or iTunes. The premium version (19.99€ per year) allows displaying precisely the location of the user, allowing being used as a complement for navigation.