J120 front copy

J/120 Mast Bend Guide


Right: Fatal Attraction is sailing in 9 knots true wind with 10 deg. heel - a little too much for maximum VMG. Take a look at the headstay "sag." Headstay sag is the deflection of the headstay to leeward of the yacht’s centerline relative to the spar. Headstay sag shortens the chord length between luff and leech and makes the sail fuller. Controling headstay sag is an important tool to widen the range of your All Purpose genoa. The easiest way to control headstay sag is with the hydraulic backstay.

J120 tune 007

Right: Here is a an example of a 3DL mainsail perfectly matched to mast bend. The headstay length, mast butt position, backstay and runner tension all combine to create an even bend from masthead to deck and also matching the sail luff curve. Notice that the mainsail draft is perfectly located at the top, middle and bottom girths (stripes).

J120 tune 008

Right: Same boat, same wind, same backstay tension as above ... but no runner load. The mast bend can double if the runner is eased off for a given backstay tension.

J120 tune 009