The flow under bow bottom of ships was calculated using CFD methods and characteristics of flow-speed distribution were analysed. In the study, it was confirmed that flow speed under the bow bottom of a ship changes according to water depth by disturbance of the sailing ship and a range of the field where the disturbance effects depends on types of ships, draft and ship speed. In this report, a developed measuring system named "multi-layered relative velocity meter" is introduced to measure distributions of relative flow speed along water depth. After testing a function of the measuring system on a test boat, the measuring system was installed on a PCC and the relative flow speed at each layer was measured during a voyage. The obtained data were evaluated by comparing with the result of CFD analysis and it was confirmed that relative flow speed measured on the PCC had a similar distribution with the result of CFD analysis. Considering both the CFD analysis result and the onboard measured data, finally a new method to improve measurement accuracy of ship's speed through water is proposed.
