Ship motion limits are often defined in terms of maximum ship pitch and roll attitude, as well as wind speed and direction.
Ship motion limit analysis is conducted to establish safe operating limits and provide operational guidance for helicopter operations including start up, shut down, flight deck traversing and the use of a particular lashing scheme or restraint system to secure the helicopter.
Significant savings in cost and time as well as improvements in safety can be obtained by computationally predicting operating limits prior to conducting First of Class Flight trials (FOCFT).
Using the Ondeck code, operating limits can be rapidly assessed for a range of helicopter configurations, lashing schemes, restraint systems, ship motion and wind conditions. The effect of spinning rotors and ship manoeuvring can also be accounted for. Sinusoidal ship motion, simulated ship motion data as well as experimental data covering a range of ship speeds, relative wave headings and significant wave heights can be used as input.
The high speed of the Ondeck code enables many thousands of conditions to be analysed rapidly.
Unrestrained limit conditions can be defined for wheel lift off, tyre sliding, airframe clearance or structural limitations. Restrained limit conditions include lashing load limits, restraint system (RAST, Decklock / Harpoon) limits and airframe structural limitations.
Top: Typical Wave Amplitude vs Relative Wave Heading "Limit" Plot for Different Ship Speeds
Centre: Typical Sinusoidal Roll and Pitch Limit Plot
Bottom: Simulation of ARH Tiger
Left: Seahawk aboard a Royal Australian Navy ship