Tuning
The tuning of a boat involves gaining the optimum speed and height from a given rig on a given boat. If we change a hull, sail (main, jib, or kite) or mast, we have to tune the sail to the mast and the rig to the boat, and often change our technique to optimise speed and height.
Fundamentals of Tuning
Upwind tuning requires a set of anchor values that DO change under certain conditions.
We need the most power to allow the sailor to hike or trap as far out of the boat as they can under the prevailing conditions, and enough depowering so that the sailor can control the boat’s heel as the wind increases.
We need the tiller to be in the middle of the boat. Every degree that a sailor has to move the rudder away from straight creates drag in the water, which slows the boat down. A straight tiller is a pre-requisite to enable a sailor to tune a boat.
Nearly every dinghy is designed to be sailed flat, or almost flat. For the faster boats (especially skiffs) their need is critical for the mast to be at 90 degrees to the water. The foils only work correctly when they travel through the water perpendicular to the surface, and if the boat is slightly heeled it will try to steer away from the direction that it is heeled in. When that happens we need to use corrective steering, which slows the boat down.
Single handed unstayed boats such as a Laser, Finn etc. we can consider the mainsheet being pulled to the block to block position as being fundamental to our need for speed as soon as we are anywhere near hiking conditions. We will cover light wind sailing in another blog. If the boat steers in a straight line when it is flat and sheeted in, then we are in the zone and probably near to well tuned if we feel powered up, and not overpowered. The idea is to pull the centre of effort around (back/front, high/low) until we can achieve full controllable power and hiking/trapping, plus a straight tiller.
The outcome in terms of fine tuning producing speed rarely obeys theoretical logic, so once we are in the tuning “zone” we must explore illogical options as well as the logical ones to establish a setup that gives us that extra 0.1 knot of speed, which can make us look like a tactical genius. This process applies to all boats when tuning.
On single handed boats with a stayed mast, the hardware bends the mast, so it is important to understand your weight in relation to the boat prior to choosing a mast, spreader length and determining what settings to use for any given condition. The same principles apply to dialing in the mast on a double handed boat as described below.
Double handed boats with stayed masts and one set of shrouds such as the 470 can also be adjusted in the lower sector with mast chocks. Skiffs with lowers, shrouds and caps are a little more complex to set up, but follow exactly the same principles.
To set a mast up we need to tune with two boats, over a range of conditions. The manufacturers will inevitably produce tuning guides, usually based on a near straight bottom section with the middle and top bending to produce the correct power for the conditions. This means that we have a base from which to work, and then set the mast softer (more bend) or more powerful according to our height, weight, strength and talents. Boats with caps can control the twist of the head a lot better than the conventional dinghy, such as the 470, which relies on the stiffness of the mast above the hounds (where shrouds and forestay attach to the mast). That does not mean that at the highest levels the mast stiffness is not important, but the performance differences tend to be less if you have a stiffness of mast that is not ideal.
Once we have a main setup that is good, with the main sheeted to the middle of the boat and the power controlled, we can look at putting it all together with the jib.
Tuning the jib is a massive influence on speed. Wisdom states that mainsails are responsible for height and jibs for speed. Whilst this is definitely an oversimplification of roles, it is certainly a good starting point. Power and speed are related, insofar as a deep sail produces more power, but also produces more drag, which is slower than a flatter sail, which is also less powerful. The tradeoff is not just in the design of a sail, but in the way it is trimmed. Jibsheet angles are adjusted usually by job cars, but also are profoundly affected by rake and tensions. The main reasons to power and depower a jib are to move the centre of effort created by the mainsail forward or backward, so a more powered jib will create a forward movement of the centre of effort and produce less weather helm, or even lee helm, and a flatter jib will produce more weather helm.
As a result of this balancing act by the jib, it needs to go flatter as the mainsail depowers (the cunningham particularly pulls the centre of effort forward, or fuller when we are seeking power in the main and the leech drive pulls the mainsail centre of effort aft).
Tuning the kite is really a sensitive process. The forward drive varies hugely with minute seam changes on the kite. This means a sailor has to adapt before evaluating a kite, or buy a lot of kites (yes, even one design) to find the one that suits their height, weight, driving style. Do not discount the changes you need to make, both between designs of kite and between “one design” kites.
Manufacturing Variables
Despite claims of “one design” the seams of any sail are never precisely the same, mast stiffness varies quite a lot and the combination of sections varies, and even things like battens are usually 20% tolerances. All parts of the hull are subject to variations, and even the foils are different boat to boat, both in flex and section.
Whilst understanding tuning and evolving your system is a big contributor to success at the lower levels, at Olympic level top sailors will typically buy six rigs at a time and work through to see which ones they like. In a team the rejects get pushed down the food chain!
We mention this because we want to reinforce the fact that tuning is a skill needed to win, and time must be taken to make the most of what you can gain access to, whether you are sailing a Laser (relatively simple) or a 49er (relatively complex with more variables).
Tuning the package
Having established what we want to do we must think in terms of hardware tuning – that’s the part we cannot alter whilst sailing, which is the cut of the sail, the stiffness of the mast, and the tensions on the stays – against the software – parts we can alter during a race, which are traveller, mainsheet, cunningham and kicker, outhaul.
We are also able to play with the rake of the mast in most boats, which has a profound effect on whether we sail high or low, and on our speed. Tuning a boat is not a two dimensional task. We have to consider what the boat needs, what the mast wants, and where the sail is best adjusted. Once we do this, we need a setup to suit the style of sailor, which may be high mode or low mode, and will certainly be physically different from sailor to sailor.
One thing is for certain; boat tuning has no definitive answers. There are upwards of 200 combinations of factors to sort out. The majority of these are done with experience, the remainder need systematic analysis across a range of conditions. There are so many combinations available in terms of tensions, mast stiffness, sail cut, twist, jib setting, sheet tension, kicker requirements, cunningham use etc., that there are usually multiple answers to the same challenges.
At Toplevel Sailing we have our own prioritisation list of putting things together to go as fast as possible. Its not the only way to tune a boat, but it is a proven winner!