The spinnaker is a sail which many sailors misunderstand, and few master. In this blog we show that it isn’t a black magic sail and you don’t need a doctorate to appreciate what it can do. The blog is written at what seems like a basic level. All we can say is that speed is basic, whether its advanced or beginning – the same rules apply.
We give you (the crew) some rough guides to setting up both major types of spins, and some top tips on how to sheet them, which are little different to any other sail. We also give you (the helm) some top tips on how to exploit the power that may be generated by your ace crew.
Symmetric and Asymmetric Sails Overview
Spinnakers come in many shapes and sizes. There are two main sorts, symmetric and asymmetric.
As a general rule symmetric spinnakers are used in more conventional, displacement boats, and asymmetric on faster boats that will plane easily downwind.
With a symmetric kite (spinnaker) you can drive the boat lower so gain a more direct route to the leeward mark. An asymmetrical kite means that you have to drive the boat higher, but it goes considerably faster than it would do with a symmetrical kite, and the VMG is better.
If we put an asymmetric kite onto a boat with a displacement (non-planing) hull such as a 470, the VMG it could achieve in most conditions would be inferior to that which can be achieved with a symmetric kite. Conversely if we put a symmetric kite onto a 49er, the VMG would decrease as you would not be able to sail the boat in most conditions in planing mode downwind, therefore negating the advantages the planing hull offers.
In both sail designs, as with other sails depth (the curve in the sail) gives more power. Sail depth will also slow the boat down as it produces more drag. Once again we reach a delicate balance between the need for power and the need for speed. If you design a kite that is flat, can we make it full by pulling ropes for the conditions we need power rather than speed? If we make it full, can we flatten it when we need speed? Obviously sailing waves and light wind means we need power. Sailing in flat water and small chop means we need speed – flatter sails and more flow.
How to set up and trim symmetrical kites
We are talking purely here about downwind sailing, not reaching, which is another mode we can adapt the kite to achieve and enhance.
The symmetric kite has a setup where it appears not symmetrical to the beginner. On the windward side we have the pole holding it out, and on the leeward side we have a barber hauler (the block which means that we can alter the sheeting angle) and the guy rope, or sheet. The first skill of keeping the kite flying once it is hoisted is a matter of practice, balancing the sheet with the position of the pole. In very light winds even good sailors can easily lose that balance and collapse the kite, so it appears as a creased rag hanging from the mast rather than a powered up sail.
Once the kite is flying, and the helm holding a steady angle, usually approximately 20 degrees from dead downwind, the crew can begin to trim the kite to the angle of the wind. If we want to go slowly, the principle is exactly the same as sailing a Laser or other single handed boat downwind – we go dead downwind and the sail acts as a barrier (or kite!!) which has wind hitting the windward side and gives us some power. If however we want real power, we cannot go dead downwind and have to encourage flow over both the windward and leeward surface of the kite. Kites have telltales so it is easy to see when we have flow.
Pole position (fore and aft plane) is decided by the optimum angle that the helm feels they can drive the boat at. The higher the boat is driven from dead downwind, the further forward (towards the forestry) the pole goes and the faster the speed becomes, encouraging flow over both sides of the kite.
The pole is always pulled as far back as it is possible to go without the kite collapsing, the kite is sheeted on the leeward side so the front edge (luff) always curls. If the crew over sheets the kite it will slow the boat down – the feel must always be that the kite is on the point of collapse, yet not collapsed, which produces the ultimate drive from the sail. The ability to set up and keep trimmed in this manner makes a massive difference to the speed a boat will go. More often than not it is the crew handling the kite who determines the speed of the boat downwind.
Pole height is determined again by what angle you are driving to the wind. As a general rule the pole needs to be at a height which means the windward side (height controlled by the pole) is at the same height relative to the boat deck as the leeward side (height controlled by the barber hauler and sheet). As the boat is driven higher, the pole height will go down and the kite will take on an appearance of being asymmetric.
Depth in the symmetric kite is controlled by how low the pole is pulled. If the pole is low it will stretch shape out of the luff of the sail, which will then enable the barber hauler to be eased and the kite sheeted harder, which again stretches the shape out of the sail. However, this produces an inefficient kite, as it goes against the rules of setting the kite symmetrically for depth.
For this reason it is easier to put shape into a flat kite rather than pull shape out of a full kite. If you need power to get through waves and you have a flat kite, you can raise the pole height (putting shape into the luff) and pull the barber hauler down meaning that the sheet will pull the leeward corner of the kite down putting more shape into the kite for less sheet pressure. Obviously it is a matter of practice to ensure that the corners (clews) of the kite are at the same height for sailing deep angles. The same rules apply – the kite luff must curl!!
How to set up and trim asymmetrical kites
Whilst apparently less complex than symmetrical kites, the critical parts of setting up an asymmetric are done on the beach rather than the water. The mechanics (hardware) of the kite become increasingly important. If the sail is not hoisted to exactly the same position up the mast every time, it will behave differently. If the pole doesn’t come out from the bow by exactly the same amount every time, the kite will feel very different to sheet and drive to.
Sailing an asymmetric kite is an exercise which is a very “narrow channel” driving feeling. Too low and you bleed too much speed. Too high and you place load on the boat, need corrective steering and create drag – as well as having to sail further than a driver in the groove!
So setting up the pole mechanism, hoist and stops become critical. Pole height is built into the boat construction, but the distance the pole comes out from the boat dictates luff tension. The kite is almost always pulled all the way up the mast, so the distance the pole goes out is critical to gaining the best vmg. As the crew hoists in a massive and explosive physical manner, the setup must be done on the beach as there is no time to do it on the water.
Generally the guide is this: In fast conditions (small chop and flat water, usually above 15 knots of breeze), you want to put more tension on the luff to flatten it off. This means the pole needs to come out a little further. If you need power, you do the opposite and the pole doesn’t come out quite as far.
You cannot usually control the sheeting angle of the kite as there are usually no barber haulers on an asymmetrical kite. This means that we see people testing pole stiffness (the poles DO bend when under load), and trying to limit any movement in the pole where it is supported before it clears the boat. We will also find, as the sailors gain competence, that small differences in seam shape can be crucial to speed and therefore VMG in different conditions, so equipment testing plays a very important part of sailing an asymmetric setup successfully at a high level.
As regards sheeting, the crew has to focus on keeping the luff curl – exactly like a symmetrical kite. The criticality of this curl is even more pronounced than when sheeting a symmetrical kite. Once again, the crew contributes massively to any success downwind, though with an asymmetric kite it is more down to the skills of the driver to keep in that narrow groove, and the crew has one job (luff curl) rather than several with symmetric pole heights, sheeting and barber hauler controls.
Many racers forget that a race consists of an upwind and a downwind. Too often conventional races are thought to be won and lost on the upwind. With the advances in symmetrical kite design this became less true. With the advances in asymmetrical kites there is now the ability to win and lose more distance and places downwind than upwind.
For these reasons spinnakers have become increasingly important. Whilst we have only covered to basics of downwind success, at Toplevel Sailing we pride ourselves in educating sailors to be fast downwind sailors too, and to recognize the opportunities for gains when they sail downwind.