On departing Town Quay at Southampton, the Jets would normmaly accelerate to thier normal service speed unless there is a "reduction" in place as notified by Southampton Vessel Traffic Services (VTS).
On their return from Cowes, permission from Southampton VTS is needed (on aproach to the North West Netly bouy) if they wish approach the dock "at speed", they would normally continue "near the reds" up to abreast of the Town Quay pier, reduce speed and cut accross to thier berth.