What type of ladder can usually be rigged to the side of a ship and is portable?

The portable ladder typically rigged to the side of a ship is known as a pilot's ladder. A pilot's ladder is specifically designed for safe boarding and disembarking from ships, often in situations where the ship is moored and access is required from a smaller vessel or the pier. This ladder is constructed in a way that allows it to be easily attached to the vessel’s side and provides a secure means for personnel, particularly pilots, to climb safely on and off.

In maritime operations, it's necessary to ensure the right type of ladder is used for safety and efficiency. The characteristics of a pilot's ladder, including its robust construction and ease of deployment, make it ideal for this purpose. This ladder usually consists of wooden or metal rungs and sturdy side ropes, enabling effective and safe transfer between vessels, especially in rough weather conditions.

By contrast, names like seafarer's ladder or emergency ladder may refer to other types of equipment but do not denote the specific and fully functional design intended for use in pilot boarding situations.