The number of ferries providing access to the internet on board is gradually increasing. Some companies offer their Wi-Fi service for free, while others charge a fee. Usually, you can purchase Wi-Fi on board by opening your device’s web browser and providing your credit card details. For more information you can ask the crew members at the ferry reception.
Please note that the bandwidth of these networks is often limited. You will, therefore, be able to access your emails for example, but it may be difficult to engage in online activities that require a large bandwidth. It is also worth noting that for most of your journey, you will likely have internet access on your mobile through 3G or 4G networks.