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To cover such situation & avoid cutting one of sea-service activities - we recommend you to use using Vessel Transfer functionality.
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If there is only one port, selection is not active, and you can just click Link to Port.
Click Apply.
Step 5 (if applicable for your system setup):
Confirm Sign On/Off
Person is added to the shift, now you need to confirm sign on/off, so he to appear on corresponding crew changes for vessel 2.
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Locate shift, select Confirm > Sign On then Sign Off:
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Yes
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Yes
Click Apply.
Step 6 (if 1 day of overlap is needed):
Change activity Estimated End Date.
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