Revolutionary changes in shipping, navigation, and offshore monitoring activities are being witnessed with the implementation of Internet of Things (IoT) technologies in maritime environments. Nonetheless, the IoT wireless networks in maritime environments are dynamic and open, which increases critical security issues at several levels of the network stack. This work provides an in-depth review of IoT maritime applications with a focus on multilayer security mechanisms considering the problems of low moisture and temperature extremes, limited connections, and diverse class of devices. The author looks into security problems and potential solutions for the physical, data link, network, transport, and application layers, emphasizing cross-layer security approaches, and lightweight cryptographic mechanisms. Real-world maritime IoT deployments are presented in case studies demonstrating the strength of integrated security solutions. The results of this study expose the weakness in existing solutions, which do not employ appropriate techniques to protect sensitive information while maintaining operational effectiveness in maritime IoT systems.