Esse 850


The aim of this tuning guide is to provide a solid base for you to start 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 it's 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

Make sure that the spreaders have the same angle vertically and horizontally, as well as the same length. The angle itself is given by the manufacturer, but it is still necessary to check the actual symmetry. A slight difference, it sometimes occurs, will make proper tuning a lot more difficult.


The tuning values we recommend are for the most common circumstances. They should enable you to be fast in various conditions without having to change the mast rake or tensions. However, you will have to trim your sails accordingly. Before getting started, it is better to loosen the upper diagonals or D2 shrouds connecting the first spreader tip and the second spreader root. Adjusting the cap shrouds’ tension increases the load on the diagonals, which in turn might overstress the mast.

Mast rake plays an important role in the positioning of the jib’s clew point in relation to the sheet track on the deck. Mast rake should be set first. You should start with hoisting the mainsail halyard, to which you should carefully attach a tape measure, then hoist all the way up to the mast crane so as to measure the distance down to the hull–stern intersection. This distance should amount to 13m. You will actually read 13.05m, but these 5cm are used up by the knot or splice and the shackle on the sail’s headboard.

The forestay tension
should be a fixed measurement on all of our genoas. Tension is measured with a Loos & Co. tension gauge, model PT2. All of the readings have been taken roughly 1.50m above the forestay attachment. The forestay tension should reach 15. If you wish to get more power in a light breeze, you may loosen it down to 13. However it is not recommended to sail like this in winds stronger than 10 knots. This softer tuning makes it imperative to quickly tighten the backstay in order to increase the tension on the forestay.

The cap shrouds
must be tightened according to the hull stiffness so as to reach the desired forestay tension. The stiffer the boat, the lesser the tension. Also check that your mast is not slightly off to one side by taking the jib halyard to the shroud chainplates.

The lower diagonals
, or D1s, are used to control the fore and aft mast bend as well as the tension on the forestay. The more you tighten them, the straighter your mast will be, therefore making the forestay itself tighter. You should only get a 3cm camber to give the correct 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, often causing your tuning to be off after sailing in a strong breeze.

The diagonals counteract the side bend of your mast from the spreaders. For this reason they have to be slightly tightened, preventing transversal fall-off. Exercise caution as over tightening will weaken the top of the mast. If sailing with a gennaker, especially in strong winds, excessive tension on a diagonal can cause the mast to break below the second set of spreaders. Proper tuning is therefore absolutely necessary, even though climbing up the mast can be a bother.

Trimming Principles

General comments on sail trimming and control. We recommend hoisting the mainsail all the way up to the mast crane before tightening the halyard as much as possible. This way, the halyard will stretch less as you trim on, and the sail will stay high.

Mainsail trimming

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 a large headed mainsail, there is a tendency to not put enough tension on the leech. In order to prevent sailing with too much twist, we encourage you to step back now and then and check the actual leech tension. Mark your sheet once you are satisfied, usually with a harder trim than you originally thought adequate.

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 sail, resulting in less weather helm on your Esse. This being said, the traveller should never be eased more than 10cm to leeward which would impair your ability to point. The leech is kept in tension with the boom vang. If you encounter a situation where you need to point alot, to get clear air, for example, after starting or rounding a mark, the Esse 850 is very forgiving in regards to taking the boom in higher than the boat’s centreline. This will slow you down, but enable you to point better than ever

Tuning the cunningham
helps alot when you find yourself overpowered. It is used to generally flatten the volume of the sail, but more importantly, it dramatically twists the upper part of mainsail. The cunningham then acts as a release when twisting the leech.

The boom vang
is primarily used to control the leech tension as you ease the mainsail sheet. A vang that is too loose will make you lose power by over-twisting, likewise too much tension on the vang won’t allow the boat to build up speed upon entering an area of higher pressure. It is also very useful in absorbing the volume in the lower part of the sail. Don’t forget to release it with a gennaker to obtain a smooth curve on the mainsail’s leech.

Foot adjustment
allows you to fine-tune all the volume of the lower part of the sail. To make your sail deeper than usual, it is possible to loosen the foot aggressively. 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 can’t accelerate well enough, the foot is probably too tight.

The backstay
is used a lot in sail trimming. Since the Esse 850 has a 9/10 fractional rig and a very stiff mast, the backstay will directly affect forestay tension. Therefore, the helmsman or a crew member will constantly have to adjust the backstay according to wind pressure. It also affects the mainsail leech, the latter having to be sheeted in to compensate for the twist caused by the backstay. This will make for a narrower entry and enable the boat to point better in a puff. This tuner affects both the genoa and the mainsail, it is therefore key in making you gain, or lose, up to half a knot in medium conditions.

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. Horizontal wrinkles are not a 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. 

The jib car is used in setting the leech tension. The more forward the car, the more tension on the leech, and the deeper the lower headsail area. Conversely, a more aft position will release leech tension and flatten the base. Medium wind conditions will call for the hardest trim. 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 of 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 Esse 850 specialist, Daniel Schroff, either at the sail loft or on-site during championships.

Copyright: North Sails

Contact the Esse 850 Experts:

Julien Monnier

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

Daniel Shroff

+ 41 71 686 85 25 Work
Tuning Diagram

Esse 850 diagram