These chart house vent locating jigs are designed to be used with my chart house vents (available separately).
They are created based on measurements given in Elco drawings and are used to accurately place vents using distance up from deck and distance aft of chart house front (except for the port aft vent on PT 103-196). Make sure you buy the set applicable to the PT you are modeling. They are available for PT 103-196, PT 314 on except PT 565-624, or PT 565-624. PT 589-624 had different vent horns / cowls.