What equipment is used to keep a boat steady while being hoisted?

The equipment used to keep a boat steady while being hoisted is steadying lines. These lines are specifically designed to provide stability to a boat during the hoisting process, ensuring that it remains balanced and secure. When a boat is being lifted, it can be affected by various forces such as wind or uneven weight distribution, which can cause it to sway or tilt. By utilizing steadying lines, operators can control the position of the boat, minimizing the risk of capsizing or swinging during the hoisting operation.

Other options do not serve this particular function: sea painters are typically used to tow a boat; monkey lines are used as safety lines or for securing equipment; and lifejackets are personal flotation devices designed for the safety of individuals, not for stabilizing boats during lifts. Thus, steadying lines are the most appropriate choice for maintaining a boat's steadiness while it is being hoisted.