The J80 class has evolved greatly since the boats launch in 1993, therefore many tuning guides exist with different tuning numbers according to individual preference. What we have tried to achieve with this guide is to consolidate as much information and as many points of view as possible into a European North Sails guide. Please note that this guide is exactly that, a guide! Not a tuning Bible and we always suggest that teams experiment and find settings that suit their own sailing style and conditions but this guide should provide a good starting platform.

Basic Setup

This includes the mast butt position, the mast position at deck level and the forestay length. All the variables that remain fixed and can’t be changed whilst on the water. 

Mast Butt Position

Place one end of a ruler or measuring tape against the bulkhead, and along the metal beam. The back edge of the sliding metal plate should measure 215mm or to the back of the mast should measure 245mm.

Position at Deck Level 

The boat comes with a rubber mast collar and this is what we suggest is used. It provides even spacing within the partners at deck level.

Forestay Length

With the class rule change to allow an adjustable bottlescrew on the forestay it is now easier to set the forestay to the desired length. It is best to do this on the dock as it is easier than doing it once the boat is in the water. Our measurement is 10.020 metres. This measurement is taken from the centre of the pin at the stem head (bow) fitting and the centre of the pin that connects the forestay to the mast fitting.

Rigging Tension

1. Once the mast is in the boat and the forestay, backstay and shrouds are connected, the next step is to apply an even amount of turns (360 degree revolutions) to both vertical (cap) shrouds, 30 is a good starting point. Please be careful to start the turns from the same position on each bottlescrew rather than having the port bottlescrew half wound on and the starboard one fully wound off as this will produce an asymmetric result.
2. This will have the effect of stationing the mast safely. The next step is to apply an even amount of turns until the vertical shrouds measure 27 on the Loos PT-2 tension guage.
3. Next with the jib halyard, apply an even amount of pressure and measure side to side to check that the top of the mast is in the centre of the boat sideways. This can be done by pulling the main halyard to each chainplate or more accurately by tying a loop in it and standing over the side of the boat and marking the halyard where it crosses deck level on both sides. Adjust the turns on the verticles until the marks are even side to side.
4. Once you are happy with this, begin adding turns to the D1’s (Lowers) evenly until they read 18 on the PT-2 guage. Then add turns evenly to the D2’s (Uppers) until they read 15 on the PT2 guage.
5. At this point please re check the vertical tension as it will have increased and reduce turns until it reads 28 again.
6. Sight the mast up the mainsail track to check it is properly columned. If it seems to “s bend” or lean in one direction adjust the D1’s and D2’s accordingly.
7. The mast should set up with 40-50mm of pre bend (sighted from the gooseneck to the white band at the top of the mast) and this finalises the dock tune.
8. The final step is to check and sight the mast while sailing. On both tacks sailing upwind, look from the gooseneck to the mast tip along the mainsail track (forwards). In base sailing conditions (10-15 knots) the mast should be straight to the hounds with a slight bend on the tip. In lighter conditions a slight leeward bend is acceptable and conversely in more wind (20+ knots) a slight windward bend is OK.

Good luck on the water!

J/80 On the Water Tuning Guide


 Wind Speed      


Vertical Caps




0 - 5 knots




5 - 10 knots




10 - 15 knots (base)




15 - 20 knots




20 - 25 knots




25+ knots




Contact the J80 Experts:

Paul Heys
+44 (0) 2380 455669 Work


Hugo Rocha

+34 9865 48132 Work

Measurement Guide

J80 mast butt position
© North Sails