Correct Tension Allows for Best Sail Shape and Improved Boat Speed

The North 470 mainsail comes standard with a black flex plastic rope for the bolt rope (luffrope). Due to its great flexibility, the cunningham works efficiently to make the sail shape control easier, compared to the fiber bolt rope used before. Please read the instructions below carefully to set up the mainsail properly for the best shape and performance.

The bolt rope is fixed into the lufftape of the mainsail with some pre-tension applied during manufacture. Because of the elasticity of the bolt rope, you need to have some cunningham tension at all times to keep the main tack position where you will have the correct amount of wrinkles along the luff. The amount of wrinkles makes a significant difference in sail shape.

Control the cunningham tension according to the examples showed below. In conditions above 11-12 knots of wind, you can use cunningham as usual.

Important:

The bolt rope stretch is affected by heat, sometimes significantly when sun exposure is strong. For this reason, it is important to check and adjust the initial setup of the bolt rope tension.

If the bolt rope is elongated by UV exposure, the tack corner will fall down and sometimes the luff is stuck above the boom. In this case, you need to take a few stitches off to pull the rope out of the luff to allow more tension, so that the tack corner is lifted up roughly 10-12 cm above the lower band on the mast.

 

Cunningham On

When the cunningham is on, you will get a crease between cunningham grommet and tack corner (like image below on left). Pull the tack down to flatten it. If the area between the cunningham grommet and the tack is not flattened, you cannot measure the proper height of the tack corner, thus you cannotfind the proper position for your settings.

We also recommend placing a thickplastic tape at the bottom edge of the opening groove to avoid the bolt rope getting stuck when cunningham is pulled on. With the tape in place, the edge of the bolt rope will slide out without friction as soon as controls are eased anad pressure is in the sail.

Tack Down – Proper Setup

The tack corner is set at 2-3 cm distance from the upper side of the color band. Keep 2 cm offset from the back face of the mast.

Pull the tack rope down so that the area between the cunningham grommet and tack is smoothly flattened. If wind is light, you may need to help it down manually.