JOSM is a powerful tool to edit all elements of the chart with high precision. 

A SeaMapEditor is available to help you add nautical information. Seamark objects are chosen from drop-down menus and specifications can be entered manually. Only characteristics which are relevant for a particular object will be editable. A validity check is performed before saving.

For Windows, an installer that installs a fully configured JOSM can be downloaded. The installed JOSM can be used for both OpenStreetMap and OpenSeaMap. 

Video-Tutorial 01, 02, 03



You will need an account (which gives you access to OpenSeaMap as well) to upload changes to the map.

Create new account

Detailled description of JOSM in the Wiki

JOSM for Windows Download

JOSM for Mac OS X Download

Linux users should install JOSM from their package manager.

Once you have started JOSM:

Click the Preferences button in the toolbar,
in the Preferences dialogue panel, click the 4th Icon from the top ("Plugins"),
scroll all the way down to "SeaMapEditor",
click the check box and then click OK.

Click the Preferences button in the toolbar,
in the Preferences dialogue panel, click the 9th Icon from the top ("Remote"), click the check box "enable remote" and then click OK.

In the menu "Edit" click to "Preferences",
click there on the left to the 3rd icon "Settings for the map projection and data interpretation"
click there on the 3rd tab "Tagging Presets",
select the presets "Hafen", "Seamarks", "Watersports" and "Gerätetauchen",
and move thems to the right column "Active Presets".
Finally click OK

Now exit and restart JOSM.

You will then find the SeaMapEditor icon in the "Tools" menu.
You will then find the Seamark, Harbour, Watersports and ScubaDiving preset in the "Presets" menu.

Seamarks correspond to IHO norms S-57, S-100 and INT-1.
Details about objects, attributes and values.

Aerial photos you can apply via menu "Background" point "Bing satellite photos" as background. So you can edit also areas without local knowledges. You can draw harbours and harbour facilities, exact coastlines and also buildings and roads very exact. So the chart will be approved.