420 Tuning Guide

  • Last Updated: February 26, 2021
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Less Pre-bend More Pre-bend
Heavy Crew Weight Light
Softer Mast Stiffness Stiffer


You can see the above chart to search for proper pre-bend by checking your weight and mast stiffness. If you can’t find it, you can test to sail with every 5mm different pre-bend in the range provided in the tuning table to evaluate how the boat performs and you feel the boat.You may try pre-bend out of this range, if necessary.
*In case it is difficult to bring enough pre-bend, you may move the mast step position back by 1-3cm.

Spreader Deflection

Due to the base helm characteristics of 420, you need to put the mast step almost max forward in the rule which is 2830mm. From this position, you then adjust the deflection (D) to create the desired pre-bend.

Spreader Length

480mm is the standard length.
The length affects sideways bend. That makes a difference in stability of the mainsail leech and its response when a puff hits the boat. One suggestion is set longer spreader lengths for heavy crews and shorter for light weight crews. This can cover the weak area of each team’s weight. You can control it in range of 465-495mm, which is effective.


In the breeze you need to chock quite hard as you need to use a lot of vang tension in the wind.


Cunningham  – Do not use any until you are overpowered, then start to use gradually, you have to take it very hard on when strong wind.To archieve it,it is good to have a bowline tied at the end of the rope so crew could get their foot in the loop to get more cunningham tension on.

Windward Sheet – Windward sheeting is important to hold the jib leech position at the proper inside position to create the best performance, even though it is not easy to use it properly. Use to put mark on the jib sheet at the cleat. performance, even though it is not easy to use it properly.

Jib Height– The peak rope fixed at the head of jib controls the jib height.Normally it must be fixed by having a proper deck sweeping effect. However, for the 420 class it is important to know the height should be adjusted to provide the optimum jib lead angle. As the sheeting point is fixed, you should adjust the peak rope to move the jib clew up or down to achieve the desired sheeting angle. So you can use it for this sake.Clear understanding about the relationship between jib lead angle, jib height and mast rake will let you set up
the jib to suit the conditions.

Spinnaker Pole Height

When using the spinnaker in choppy waves on a flat run, it is best to set up the spinnaker pole height so the tack (corner of spinnaker the pole is closet to) is slightly lower than the clew.


You needed to have a good action to play the centerboard as it is hard to adjust the other controls readily. The centreboard slot needs to be packed well with the centreboard to allow the centreboard to be changed easily.

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