2007 Johnson 2 HP 4-Stroke Service Manual, Page 29Get this manual
INSTALLATION AND PREDELIVERY TRANSOM MEASURING AND DRILLING
TRANSOM MEASURING AND DRILLING
Hull Centerline
Locate the centerline of the boat transom as it relates to the hull (bottom) of the boatUse straightedge to draw line connecting the port and starboard chinesThe chines should be used as reference points for determining the centerline of the hullUse framing square to accurately place line on the transomThe centerline of the hull should be in line with the keel of the hull and perpendicular to the midpoint of the line connecting the port and starboard chines
Transom Heights
Make sure the transom height is consistent with the height of the outboard to be installed 19 to 21 in(48.3 to 53.3 cm) transom height uses 20 in(50.8 cm) shaft outboard The shaft length of the outboard being installed should come close to matching the transom height of the boatDetermine transom height by measuring from the top edge of the transom, along the centerlineUse straightedge as reference to extend the bottom of the boatPosition the straightedge along centerlineThe distance from the top edge of the straightedge to the top edge of the transom is the actual transom height1