The vessel drop-down allows you to selected the vessel from the unit that was involved in the incident.

When the form is first created it assums these will be vessels from your unit. If you have changed the unit - you must update the form to get a list of vessels from the unit you have specified in the SAR Unit drop-down.

If more then one vessel was involved (even if they are from the same unit) a seperate form must be submitted for each vessel/crew involved.