The aim of this tuning guide is to provide a solid base for you in regards to getting your boat ready, and trimming your new sails quickly and efficiently. Depending on your skills at the helm, or how you sail your boat, as well as its specifications and deck layout, you might have to slightly change the way your rig is tuned. Do not hesitate to jot down any question that might come up as you read on. We would be pleased to discuss those further with you, should you submit them to us. Our goal is to set appropriate trimming references for the sails we make; for them to be fast in any wind condition, whether upwind, reaching or downwind. Versatility is therefore a key concept; both in this tuning guide and in the design of your North sails.

Getting your boat ready

Hull skin smoothness is a prime factor, you should never make your way to the starting line without a perfectly clean hull. Even a couple of days is long enough for a greasy film to settle and therefore decrease your performance. You won’t actually feel slower than the rest of the fleet, given the fact that you won’t be the only one in this situation. However, your ability to accelerate will be seriously impaired. Competitors have sometimes won despite a lack of training, but never with a dirty hull.

Mast Preparation

Ensure that the spreaders are symmetrical.

There are three factors to keep in mind:

Length - class rules allow a margin of 2 cm. You can therefore adjust your spreaders’ length according to the genoa you choose. The genoa will overlay the spreader. For that reason, the latter will have to be cut as short as authorized (840 mm) so as to take the leech in as much as possible when sailing on flat water. Should you wish to put less strain on your mast, you will have to keep maximum spreader length (860 mm). However, this will keep the leech out by 2 cm.

The angle itself is given by the manufacturer, but it’s still necessary to check the actual symmetry. A slight difference, it sometimes occurs, will make proper tuning a lot more difficult.

The height of the spreaders’ tip has to be set permanently on the shroud, in order to prevent it from changing during transportation or sailing in rough seas; which in turn would affect mast tuning. The tips should be a little higher than the horizontal.

Pre- Tuning 

The mast butt should be positioned as far forward as the mast step deck fitting will allow it.  Surprise typically having weather helm, this will make your boat more balanced and softer to steer.

Mast rake plays an important part in both helm balance and genoa leech tension. The tuning we suggest is designed to give you good performance in a wide range of conditions; saving you the trouble of constantly adjusting the mast rake. You can of course refine the tuning by releasing forestay tension in strong winds; in which case you will have to remember to put tension back into the capshrouds and lower shrouds. Rake is strongly related to the length of the genoa leech. In order to keep the shape of the genoa as steady as possible, tack and clew points have to be as close as possible to the deck. This can be achieved by getting rid of useless shackles and shortening them as needed. The best would be to make a spliced eye on your sheets; this way the clew point itself acts as a stop against the genoa car.

When sailing in « hard mode », that is with the entire crew to windward and the sails hard trimmed – the point where you cannot take more pressure without easing sheet – the clew point should be about 2 cm away from the front end of your genoa car. If it is higher than that, you may want to add more aft rake. If you can’t take it in that much, more forward rake is required.

You will only get this precise tuning after several sailing sessions. So here is a basic tuning that received a lot of positive feedback:  take the genoa halyard and straighten it at deck level, on the mast step fitting. Make it then straight along the forestay. You should measure 92cm between this halyard and where the forestay meets the deck.

Forestay tension is a constant key number to have on all of our genoas. Tension is measured with a standard tension gauge (double blade, light grey aluminium). We should read a tension of 21. If strong winds are forecasted, tension may be increased up to 24; which will keep the mast more stable when reaching, or during certain manoeuvres. However, it won’t make you faster than if you had standard tension (21) with added backstay.

The shrouds must be tightened according to hull stiffness so as to reach the desired forestay tension. The stiffer the boat, the lesser the tension. You should read between 26 and 32 on the tension gauge. Also check that your mast is not slightly off to one side by taking the jib halyard to the shroud chainplates.

The lower shrouds’ purpose is to control mast camber and forestay tension. The tighter the lower shrouds, the less camber you will get; therefore the more tension on the forestay. North sails are designed to give you a very straight mast. You should only get a 2 cm camber to give the right fore-and-aft bend direction to your mast. Positioning yourself at the mainsail mast groove and looking up will enable you to make sure that there is no transversal S-shape. It is important to check your mast regularly because of aluminium shrinkage over time, often causing your tuning to be off after sailing in a strong breeze.

Tuning Principles

General comments on sail trimming and control.

Mainsail Trimming

Sheeting – Constant mainsheet trim is very important. Small adjustments can make a big difference in power or in your boat’s ability to point, as well as helm balance.   Sheeting in puts tension on the leech, resulting in more power and a better ability to point. On the other hand, the mainsail will be more prone to stalling. Looking at the upper batten tell tail is the quickest and most reliable way to trim your mainsail. You have obtained a good average trim when the sail is just about to stall. As you sail into an area of increased pressure, you can sheet in and make it stall all the way to help you point even more. However, as soon as the pressure fades, you will have to ease, so that the leech won’t be too tight – which would slow you down considerably. You should of course try to get a feel for the best trimming possible, as long as you pay attention to your boat speed. Know when you are about to slow down and how to prevent that by letting your boat build up speed! In choppy conditions, opening the leech (twisting it) will enable the sail to adjust to a larger apparent wind angle: the focus is now more on boat speed and less on pointing ability. When you find yourself overpowered, you will once again want to twist the leech, so as to reduce power until you reach a better helm balance. With the entire crew to windward and maximum boat power, you will have to sheet in extremely hard (with both hands). Tension on the mainsail leech will therefore have more effect on forestay tension than tightening the shrouds would. It is important to get a good understanding of how rig stiffness is controlled by mainsail leech tension. With a further increase in wind strength, leaving your boat overpowered, the backstay will take the lead role in holding the mast. You can therefore start easing a bit.

The mainsail traveller is trimmed according to the position of the boom. The aim is to have your boom in line with the boat’s centreline, which means that the traveller will always be positioned slightly to windward. This will compensate the boom’s fall-off due to the distance between traveller and boom. In stronger winds, it is recommended to ease it back to the centre in order to release some of the flow towards the back of the sails, resulting in less weather helm on your Surprise. This being said, the traveller should never be eased more than 15 cm to leeward which would impair your ability to point. The leech is kept in tension with the boom vang.

The boom vang acts as a pressure valve for the lower mainsail area. You should make your system easy to operate for a crew member to windward, and this on both tacks. It will enable you to flatten the lower mainsail area “on demand”, while keeping leech tension even when easing sheet. As you enter a puff, you will take in more vang. This will make the profile finer, the leech tighter, enabling you to sail higher. Make sure that you don’t forget to ease it out when the pressure decreases so as to create deeper volumes again, and get more power. A very high tension is likely in strong breeze. It is thus very important to remember to release it all the way before bearing away at the top mark to avoid fatal strains on your mast. For these reasons, good tuning of the lower shrouds is key to avoid too much mast camber which would lead to an overly flat mainsail along with too loose of a leech.

Foot adjustment allows you to fine-tune all the volume in the lower part of the sail. Since your North mainsail is rather flat, don’t hesitate to make it deeper by loosening the foot. In light conditions, and especially in chop, the gap between mainsail foot and boom can be as large as 20 cm. Whenever the wind necessitates having the entire crew to the windward side, the foot will have to be taken back in progressively; otherwise you might skid in the puffs. Keep in mind that if you find that you cannot accelerate well enough, the foot is probably too tight. 

Cunningham - Do not over-tighten the luff, especially in light wind conditions. Tighten the halyard first, always making sure that the mainsail headboard is as high as possible and that the halyard itself doesn’t stretch. Cunningham will only be used in order to make your sail finer, and twist the leech in strong winds. Horizontal wrinkles will not affect your boat speed at all. Your tack point has to be vertically free. It is held by a slide in the groove but needs to be able to move up freely.

The backstay's primary purpose is to pull the mast aft ; thus tightening the forestay. You want to start taking it in when the wind becomes too strong to keep the mainsail sheeted in. With a further increase in wind strength, you will have to put even more tension in the backstay, which will in turn twist the leech more. It is not uncommon to get a kink in the sail between clew and top batten with such tension on the backstay. However, in this case, make sure to release it all before bearing away in order to avoid buckling the top of your mast. We advise you to install a batten going from mast crane to backstay, to keep the latter away from the leech when not in use.

Trimming the jib and genoa

The halyard sets the tension on the front of your sail. It is not advisable to put too much tension on it. Just like for the mainsail, horizontal wrinkles are not as big deal as they will actually help in seeing the shape of your sail. However, if you want to tune even better, do not hesitate to increase the tension on the halyard in the puffs to make the leading edge narrower, as well as tightening the leech, two key factors increasing your ability to point. This type of tuning may necessitate a tackle system so as to avoid using the winch every single time.

The jib car is used in setting leech tension. The more forward the car, the more tension on the leech, and the deeper the lower headsail area. Conversely, the more aft position will release leech tension and flatten the base. Medium wind conditions will call for the hardest trim. The leech will come to touch the spreader, and the base of the jib will have to come close to the bottom of the shroud. As soon as the wind dies a bit, you will have to ease the sheet to regain volume, since the fabric shrinks due to its elasticity. On the other hand, whenever the wind increases in strength, you will have to depower the boat by moving the car aft which in turn twists the leech.


Concerning the upwind beat, your goal is to get the best efficiency out of your sails and mast in any wind condition. If you happen to be racing against other boats, you will have a very clear idea of what your speed is like… otherwise, your boat’s performance becomes more a “feeling”. The energy produced by the sails shouldn’t be wasted with an improper helm balance, meaning, for example, a constantly neutral helm with a slight weather helm tendency. With an overpowered boat, the helm will quickly reach a big angle and you will need to flatten the mainsail. If your boat seems to have lee helm, as well as a lack of power, small adjustments on the mainsail give it more power; which is usually enough to make the boat feel more lively again.

If some of our proposed settings still seem too vague or lacking precision, please feel free to contact our Surprise specialists, Pierre Ratajski and Arnaud Gavairon,  either at the sail loft or on-site during championships. We even come directly to your boat to help you with rig tuning, should you need it.

Contact the Surprise Experts:

Julien Monnier

+41 22 782 32 22 Work
+41 22 785 24 31 Fax
+41 79 574 11 15 Mobile

Rig Tuning

Surprise - Tuning Guide