In addition to the wearable personal flotation device (PFD) requirement for all vessels, what type of PFD must be kept on board any vessel 16 feet or longer?

For any vessel that is 16 feet or longer, it is mandated to have a Type IV: Throwable Device on board in addition to the required wearable personal flotation devices (PFDs). This requirement ensures that there is an additional layer of safety for individuals on the vessel, particularly in emergency situations where someone may need immediate assistance in the water.

Type IV devices are specifically designed to be thrown to someone in distress, allowing for a quick and effective way to provide flotation support without requiring the rescuer to enter the water themselves. This is especially useful in emergency situations, where getting a person a buoyant object quickly can be crucial for their safety.

Other types of PFDs, such as Type I, Type II, and Type III, are all wearable devices tailored for different environments and uses. However, the unique function of the throwable device complements the safety measures provided by the wearable PFDs, making it a vital addition to vessels of this size. Thus, having a Type IV device on board is a critical requirement for enhancing safety and ensuring that all necessary precautions are taken for the protection of everyone on the water.