Use the ISO variant’s power arrangement
NGW-1-ISO converts supported NMEA 0183 sentences and NMEA 2000 PGNs. This is the ISO cable version, not NGW-1-USB: its operating supply comes from a powered NMEA 2000 backbone. The manual specifies 35 mA at 12 V, maximum 50 mA and LEN 1. Add that demand to the network power budget. The gateway’s internal 9.5–35 V tolerance does not authorize running other NMEA 2000 equipment from a 24 V boat bank.