Sail-World – 2018 – Racing Editorial 148
A distinct pleasure
Being at the 2019 Etchells Australian Championship most certainly was enjoyable. It kind of came as a good and necessary fix, after the short hiatus following on from the 2018 Worlds late last year. The Brisbane Etchells Fleet, together with the Royal Queensland Yacht Squadron turned on yet another fantastic event, and the weather seemed to go Groundhog Day after Groundhog Day. Awesome.
That a new Australian mould boat, with an Australian crew par excellence on board won it was also really fitting. Phil Smidmore can be proud of his boat. The highly talented and credentialed Iain Murray, Colin Beashel, and Richie Allanson can be more than chuffed with their overall win, on the back of a come through the fleet to take out the last race and get the gun result.
Dragging Beashel out of retirement, as it were, certainly seemed to pay off! I could not also help but notice that in spite of their incredible sailing CVs, Murray and Beashel just got their Maiden Championship, whereas Allanson now has three to his name.
Obviously with no competitors there is no regatta, and during the course of the event we also highlighted the amazing work that all the volunteers do to make it happen. Yet whilst they sometimes get a picture taken when out on the track, and a mention in a report or broadcast too, the great David Healey pointed out a very special group of volunteers that could be forgotten.
They are all the team who do the myriad of admin tasks, from hull and sail certificates, to weigh-ins, next of kin details, and so forth. Invariably, they are the partners of some of the Flag Officers or office bearers, and so to all of you, and from anyone who ever did a race, thank you!
Tacking now. Big time. So we’re kind of already at half, when you consider that Idec Sport hold the Jules Verne record presently at 40 days, 23 hours, 30 minutes, and 30 seconds. So it does make you wonder where the maxi tri Spindrift 2, which at 40m is a whole 8.5m longer than the Ultime tris, can take it all. The crew of 12 have been waiting for a tilt at it since early in November.
The magic point to break on the space/time continuum is on February 26 @ 11h 16m 57s UTC. Before that they are attempting to get to the equator from the Brittany/Cornwall start line in under five days, and the Cape of Good Hope in less than 12. At the time of writing they were just three days into it, belting out an average of 27 knots, having already amassed just under 3000nm of sailing, and are an impressive 225nm ahead of Idec Sport’s relative position. Nice one, team.
Off on another board completely now… Last week in, It’s all about wings (again…) https://www.sail-world.com/news/213757, we looked at the Semi Rigid Wing from Advanced Wing Systems, who have been contracted by American Magic to assist them in the dark arts. As stated, the SRW is available now, so below is a bit more detail on how to make it all work with the five main controls, with many, many thanks to AWS for providing the material.
One - Mainsheet
The SRW is ideally set up with a mid-boom main sheet, and a full width traveller to provide good twist control through a wide range of angles. The mainsheet on the SRW is used much like a vang. Its primary function is to control the leech layoff, or twist in the wing. Once set, it is not frequently adjusted. The control of power in the wing is angle of attack, which is adjusted by the traveller. A conventional vang/mainsheet arrangement will work, as long as the system is adequately engineered for the vang loads.
Two - Outhaul
Outhaul is set up as per a conventional mainsail, and is the primary way of controlling camber. Easing the outhaul allows both the windward and leeward battens to bend more under wind load, thus increasing the camber of the section.
Not surprisingly, increasing camber has a positive impact on the lift co-efficient of the foil. The additional lift does come with a drag penalty. Initially, increasing camber by only a small amount has quite a pronounced impact on lift (below about 10% camber). Whereas, an increase from around 10% to 12.5% camber has minimal impact on lift below about 20 degrees angle of attack. However, that same increase in camber causes a marked increase in drag. Above 20 degrees angle of attack, the lift is increased, and the stall angle is increased with increasing camber.
Three - Traveller
The SRW works better if a reasonable amount of leech tension is maintained. Although this can be achieved with a conventional vang and mainsheet, it does require heavier engineering of the mast and boom. A full width, mid boom traveller negates the need for a vang, as the main sheet provides the leech tension, whilst the traveller is used to adjust the angle of attack.
Below 10-12 degrees angle of attack, the coefficient of lift varies almost linearly with angle of attack. Unlike a conventional sail, the SRW does not stall or collapse when the wind angles get very low. Consequently, sheeting the traveller can provide good power control, without the need to change the setup of other controls.
The traveller has separate port and starboard sheets. This is necessary, as in light airs it is desirable to sheet the boom above centre.
Four - Leech Slip
Designing for variable twist is a challenge for the designers of three-dimensional wings. Unlike conventional sails, where twist is essentially a two-dimensional phenomenon, in a three-dimensional structure, the designer must deal with difference in behaviour of the leeward and windward sides of the foil. When a wing twists, it must either distort the materials making up the faces of the wing, or these must be able to react somewhat independently from one another.
If distortion is allowed to occur in the faces of the wing, then they have to be elastic, or local areas of high distortion, and creases or wrinkles will appear. Excessive elasticity in the membranes will mean they will distort under aerodynamic load, and affect the characteristics of the foil.
Furthermore, creating a mast section (or structural member), which is capable of supporting the required rig loads and still able to twist, is a very complicated endeavour.
The leech slip system on the SRW allows the two membranes to move independently, to a small degree at the leech of the wing, but still maintains the connection between the windward and leeward membranes that provides the rigidity to the system.
The practical implication of this aspect of the design is that it allows the upper section of the wing to be controlled to give the desired aerodynamic section. In light airs, it can be increased in thickness to increase the lift. In very strong winds it can be made flat and, with adequate twist, can essentially produce very little lift and drag. This is effective when sailing upwind.
For a racing yacht, it means that a full sail plan can be carried upwind into stronger winds. The decision to reef is then governed more by the ability to carry the area downwind, where rigging restrictions prevent the top of the sail from reaching very low angles of attack.
Five - Rotation
Rotation is fixed relative to the boom and is adjusted from tack to tack. The method of controlling the rotation is somewhat flexible. On the K8 for example, the control is via a rotation quadrant, which is fixed to the mast via a pin. This quadrant is attached from each side to the boom such that the leeward side of the quadrant can be pulled towards the boom, thus rotating the mast so that the leeward side moves aft and the windward side moves forward.
There is an interaction between rotation and outhaul. When there is no rotation and outhaul is fully on, the thickest part of the section is widest towards the mast. As rotation is applied, the thickness increases rapidly and the position of maximum thickness moves back towards the position of maximum camber. As outhaul is eased, the thickness reduces, and moves forward again.
The main purpose of rotation is to induce asymmetry into the section. One of the big benefits of the SRW system is its stability. The section shape is not subject to luffing, or distortions like a conventional sail. This is particularly evident when going to windward in waves, or if pinching upwind. This stability is largely due to the rotation of the mast applying a compressive force to the leeward battens, and a tension force to the windward battens.
So it is important that some rotation is carried in the mast setting. Adjusting rotation does have an effect on the characteristics of the aerofoil. From modelling, it can be seen that at low angles of attack, there is a marginal improvement in lift with little change in drag, as rotation increases. However, between about 7 degrees angle of attack and 18-19 degrees angle of attack, the lift reduces and drag increases with increasing mast rotation. Above 19 degrees angle of attack, mast rotation has less impact on lift but increasing mast rotation reduces drag.
When sailing off the wind, a point is reached where it is not possible to sheet out further. As the apparent wind moves further aft, the angle of attack will consequently increase. Outhaul to control camber then has a greater impact on the lift and drag of the section.
Right oh – here today there are some gems for you to review. We have information about racing on the River Derwent, Musto skiffs, Farr 40s, intel from North Sails, J/80 Worlds, all things AC, having a crack at an Olympic offshore event, IMOCAs and the Vendée, gear from Musto, Etchells, Golden Globe Race, Heaven Can Wait, Caribbean 600, youth sailing, Moths, Taipans, Mark Jardine gets a bit Harry Potter on the water, and certainly there is much, much more.
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