In offshore engineering, geotechnical investigation is an important step for structural analysis and design to ensure the integrity and serviceability of infrastructure. The Cone Penetration Test (CPT) stands as the prevailing technology for offshore soil characterisation. However, this test method requires a substantial allocation of resources for equipment transportation and operation personnel. This proves inefficient and costly for conducting comprehensive surveys over ocean beds. Alternatively, free-falling penetrometers (FFP) have attracted attention as a CPT replacement for soil characterisation. Nevertheless, these devices can penetrate only to shallow depths within sands, limiting their applicability for offshore site investigation purposes. An inventive prototype has been created to overcome this constraint, featuring a dynamic penetrometer launched by a speargun. Unlike conventional free-falling penetrometers, this apparatus can attain greater penetration values, with the potential for the penetration depth to diameter ratio to surpass 30. This value for the currently available penetrometers is ~5. The process of experimental testing yielded notable enhancements, particularly in effectively addressing challenges associated with tilting when attempting low-penetration depths. By implementing rate corrections into the methodology, promising results were obtained for static and dynamic penetration resistance. This approach not only represents the capacity of influencing future penetrometer designs but holds the promise of elevating the overall efficiency of in-situ soil characterisation procedures.