JOSM Map Paint Styles:

• INT1_MapCSS.mapcss (rendering of nautical symbols according to IHO standard INT-1)
• CEVNI_MapCSS.mapcss (rendering of notice marks according to European standard CEVNI)
• BNIWR_MapCSS.mapcss (rendering of notice marks according to Brazilian BNIWR standard)
• PPWBC_MapCSS.mapcss (rendering of notice marks according to Brazilian/Paraguaian PPWBC standard)
• RIWR_MapCSS.mapcss (rendering of notice marks according to russian RIWR standard)
• seamark_styles.xml (obsolete)

JOSM Tagging Presets:

• INT-1-preset.xml
• Presets_Hafen.xml
• Presets_Sport.xml

JOSM Tagging Validator:

• Seamarks.validator.mapcss

To deploy these styles

• start JOSM
• Edit > Preferences > Map Settings > Map Paint Style
• Add a new style by entering URL
• eg. https://raw.githubusercontent.com/OpenSeaMap/josm/master/INT1_MapCSS.mapcss

To deploy these presets

• start JOSM
• Edit > Preferences > Map Settings > Tagging Presets
• Add a new preset by entering URL
• eg. https://raw.githubusercontent.com/OpenSeaMap/josm/master/INT-1-preset.xml

Just make sure, the URL points to the RAW file content!