Reposting a message uploaded to the Itchenor RS200 FB Page, I guess some may have received this as a mail from Paul Lewis? Firstly Happy New year to you all and please accept my apologies for not providing an update to yourselves sooner. I have received multiple emails from the fleet and I hope the following response will provide satisfactory answers to all the questions that I have been asked to date. If you have any further questions, then please do not hesitate to contact me and I’ll endeavour to answer. I would like to provide you an update on two key areas of development within the class. Firstly, the vote for hull improvements closed on the 1st January 2015, with a total of 64 votes received. 54 votes were in favour and 4 against. Based on this overwhelming majority the Class Association has instructed RS to proceed. At this time the moulds for the hulls are being commissioned with production test and proven boats due to be available at the beginning of April. Throughout this process the technical committee will be working closely with RS and providing regular updates to the community. Secondly, the sails. Since my last communication it really has been a very busy and intense period of development sail testing. We have undertaken more than 400 hours of testing and consultancy and developed more than 27 sails which have been individually tested against our published success criteria since my last communication in the summer. What is the current situation with sails? We are now very close to being able to recommend a set of sails that the Class association members will be able to vote upon that meet the published success criteria. This includes a square top main option. We aim to be in this position by the end January with sails being available to purchase in April. The process has taken longer than the published plan due to lack of suitable test conditions in 2014 and the conscious decision that we wanted to extend the testing period to ensure the sails are fit for purpose and serve the fleet as the predecessors have done for the 20 years. In order to maximise in week testing Frances Peters has been independently supporting us; using the sails under the watchful eye of the sail designer, Mike Lennon, to refine development. This has not only added additional testing feedback but with an experienced RS200 sailor(s); light-weight helm and crew ensures accurately that the sail plan to weight ratio is maintained. Most of the conversations I have witnessed to date have centre around the mainsail. I have been privileged to have witnessed all the sail testing and sailor feedback with Mike Lennon. What have we learnt to date? • It is hard to replicate the same performance and characteristics of the old main sail with either the square top or the standard main configuration due to the use of modern sail cloth and radial cut (necessary for the sail cloth being used). For example the standard sail configuration requires use of Cunningham earlier than it’s original to keep the draft of the sail forwards. This is simply due to the different loading on the cloth fibres stretching differently. Without question there will be a transition of learning for us all whether it is the original sail plan or the square top sail. Interestingly at this stage of testing, there are more similarities with sail controls of the square top and the old standard • Although in the testing conducted to date we have not witnessed any conclusive performance (speed) differences with the standard or the square top sails compared to the original; due to the modern cloth change it is likely within a year we will be able to get more performance from either of the standard or square top sails. However, due to the lack of availability of original cloth we have no choice but to accept this. • Based on the testing conducted to date we appear to have been able to achieve the sail plan to performance success criteria for both the square top and the standard main configuration. Most conversations I have witnessed centre around the assumption that the sail will have more power and will be harder to sail with the light weight crews. Within the testing that I have seen I have seen no evidence to this at all. If anything the square top is very responsive to the sail controls and has been easily managed but the lighter female crews testing the boat to date. • We have been able to develop a jib and spinnaker that has been tested and raced by the community that the technical committee feel meets our success criteria. The picture below left shows the new radial spinnaker and new standard sail configuration. The Square top in the background is being sailed with an old style spinnaker Picture right: new spinnaker with old standard main • The UK technical committee is currently working through the commercials of the sails. We are close to finalising the position but at this juncture I can confirm a complete set of sails will be cheaper than the originals; there will be an introductory discount for association sailors for a period of three years for the first set of sails. More details will be provided as part of the briefing pack. Answers to the most common questions I have been asked: How will the square top design to deliver the same performance as a standard? Technical Response: It can’t deliver the exact same performance in the same way - as having some span width at the head can change the downwash angle (depending on applied depth and twist). They can be made to perform in similar manner depending on set up. A narrow headed main sail will have little or no attached flow near the head (the span width is too narrow) so this part of the sail is nearly always form drag with little or no lift. I imagine the vortex rollup is at the head but can’t say for sure. I would estimate the roll up will only move down if the head produces up-wash (negative lift). A square top should be able to get a more efficient L/D ratio. As both sails area are similar and the luff length is the same the form drag on both will be the same (perhaps a little worse on the square head as the head sits in faster moving are stream compared to the bottom and form drag goes up with wind speed squared). Simple Response: All this tells us is what we already know - it’s likely the square top will be better in underpowered conditions and the narrow head in over powered conditions. But as the total sail area is the same and the span height is the same there should be little difference overall as we have witnessed to date. How will we ensure that the current crew weight to performance ratio is maintained? Sail area is the same - span height is the same - equates to same weight to sail performance. Why do we not need a new rig for the RS200 such as lowers with the Square top configuration? Sail area is the same. Span height is the same so the load on the mast will be the same. OK so the top 10% of the rig has a little more area and the mid span is a little narrower so we change the load distribution a little We only need a new rig if the head won’t stand (top mast is too soft to take the load) but there is no evidence of this in testing. In fact the early iteration sails stand up too much (won’t washout) indicating either the sail is too full or the mast too stiff. Isnt a square top just the current fashion accessory? Does it have longevity? See question 1 - They are closer to producing an elliptical load distribution and constant downwash angle = most efficient L/D. (Although sails rarely operate with an elliptical span due to too much wash out (twist)). When over powered we are probably getting a small up-wash at the head so span load is defiantly not elliptical. A tip with little more than zero span width (girth) will never have attached flow. So narrow head sails like jibs and older design restricted sails carry the top part of the sail only to support what’s underneath. So if you can support what underneath without carrying the bit above you would have much improved L/D. Is there likely to be more loading on the rig with a Square top? We are confident that this will not be an issue - when it’s washed out completely little or no difference - when its carrying a full aero load yes but as the mid sail will be carrying a little less load so based on the span load distribution calculation we are within tolerance. As a female helm will I not find it harder to play the main? Technical Response: Same area / same span length - the head of the sail is carrying more load; the middle less. However once we have zero AOA at the head the aero load drops away but form drag is higher — but you can argue the square top is closer zero L/D max more of the time ……. Simple Response: Based on the testing conducted to date we have not encountered any increased loading with the square top from female helms. I do apologise for the length of the communication but want to provide as much transparency and feedback into this process as possible. If you have any additional questions then please contact me and I’ll ensure that you get the answer to your questions and publish to ensure all association members are well informed to be able to make a decision. Over the coming weeks we are planning to continue to test another set of sails with small tweaks based on the feedback from the testing sailors. Much of the focus in the final weeks will be really ensuring performance against each of the old and new sails. Many Thanks Paul Lewis UK Class Chairman
Posted on: Thu, 15 Jan 2015 08:53:46 +0000
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