Jump to content


MYA Member
  • Posts

  • Joined

  • Last visited

  • Days Won


Everything posted by John949

  1. Yes well done Royal Mail, it arrived first thing this morning. By all means contact me. If I can help I will. Same goes for anyone else. If you want to send me non-working kit, I'll take a look. No promises, no guarantees, but no charge either. If I fix it and you are happy then make a donation to your favourite charity. Forgot to mention that these servos are definitely not waterproof. Keith's showed some water deposits, so don't leave your boat sealed up between outings.
  2. Eric (and anyone else who is interested), here's what I found when I took your winch apart. First picture is a comparison of the two winches. Left is one a club member gave me (just stopped working), right is Eric''s (suspected burn out) No prizes for spotting the problem with Eric's - a clear case of allowing the magic smoke to escape! The two chips visible are MOSFETs - basically electronic switches that control the motor current. The sharp eyed may notice that the circuit boards are slightly different - extra capacitors on the left hand one. Don't know which is the newer model. Digging a little deeper showed that Eric's motor had seized and was also open circuit (I was expecting it to be short circuit). Can't be sure of the exact sequence of events but I think the motor overheated first and melted the commutator, which then shorted and took out the FET. The commutator then melted further and went open circuit. I think this shows that the motor cannot take the full stall current for long - rather poor design but definitely worth knowing. Here is a picture of what's inside a coreless motor. Apparently the wire cage rotates and the central magnet stays still. I was expecting the windings to be melted but they look fine. The commutator was however a melted mess. Sorry Eric but when the FET went phut it damaged the PCB quite badly so I used your potentiometer to repair Keith's. It even seems to be working! There are still a few bits that are OK e.g. the case and the geartrain, so if anyone needs them let me know. I also took some pictures and can provide guidance on how to take it apart and put it back together (you need to de-solder the pot)
  3. I took an SW6119MD apart the other day and managed to read the chip numbers. To cut to the chase, the MOSFETS are rated at 20V @ 7Amps so the electronics should be fine on LiPo / LiFe batteries. The motor might be the weak spot but should be OK as long as you don't stall it. Presumably they will operate faster and give more torque at higher voltages too. My guess is that the 'HV' version has a more powerful motor but the same electronics / gearing- hence the weight increase.
  4. Trying to repair a friend's sailwinch and the feedback pot has gone open circuit and it appears to be a custom part. Has anybody got a non-working Kingmax (or Turnigy) servo that they would let go for a nominal sum? The servo I'm trying to fix is an SW6114MD but the pot appears to be common to all their sailwinches. I know they don't cost much but it seems a shame to chuck it away for such a simple fault. Thanks
  5. There is no max length of course but the sail area penalty starts to bite once you go over about 1350. The problem with a long boat is how to make it competitive in light airs. I generally leave the Bentley at home in the light stuff and have recently made a '10R' swing rig for my Starkers Marblehead. I now have two very competitive boats; as long as I sail the right one for the conditions. To make a long boat fast in light airs then you obviously need a low drag hull form, so something with round sections to keep the wetted area low and perhaps a light displacement? You also need to make the most of the sail area you are allowed, so an efficient rig is called for. Tempting to go for max luff, narrow foot and wide head, (to get the area high (where the wind is stronger) but this compromises the lower rigs thanks to the silly 10R rules. I've been toying with ideas for wing masts / fully battened sail but haven't yet found a good solution to 'popping' the camber when you tack in light winds. I made a Gothic Marblehead and wasn't too impressed with it's light airs performance. It was however my first attempt at CF moulding and came out quite heavy so probably more my fault than the designer's. I used to sail Contenders (a long time ago now) and many new owners were dismayed when the measurers insisted on drilling a hole through their pristine wooden foredecks to check the thickness of the ply used!
  6. I wasn't asking for advice. I have read the rules and formed my own opinion about them. I am interested to know whether other people have interpreted them in the same way I have. Given the response to my comments on the measurement forms, I felt there was little point in me raising a lone voice in comment on the rules. On the other hand, if a significant number of people felt changes were needed then just maybe something would change. I picked the multiple fin case as it is a fairly accessible example. I actually think the clearest indication of the current state of rules are given by G.1.4 i) & j) and the accompanying figure L.2.0. but I suspect that few people have studied these rules enough to form an opinion as to what they are trying say and what they actually say. If you want to know what I think the rules say about using multiple fins on a single certificate then: Limitation C.4.4 b) states that you can use any appendage that complies with the limitations on the certificate USED FOR THE EVENT i.e. this limitation allows appendages to be changed during an event. Limitation C.6.1 contradicts C.4.4.b) by stating that only one appendage is allowed to be used per event. Unfortunately 'event' is not defined in the rules, but we'll avoid that rabbit hole. Limitation C 4.4. c) is also relevant. This states that the boat must comply with the dimensions on the certificate used for the event. Now any Physicist / Engineer will tell you that mass is a dimension. (They will also tell you that when the certificate states the weight in Kilograms this is actually the mass not the weight) so I don't see how you can even switch to a lighter fin / bulb between events and still comply with this limitation (unless you add ballast to bring the 'weight' up to the value on the certificate - but see the following point). Even if the replacement fin happens to 'weigh' the same as the original there is still a risk that it won't comply with the rules - this where Archimedes principle comes in. If you have a short fin/bulb and a long fin/bulb that weigh the same, then the bulb on the long fin must weigh less than the bulb on the short fin (because the short fin must weigh less than the long fin). As lead has a higher density than carbon, the volume displaced by the short fin/bulb will be less and hence the hull must displace more water to compensate. The upshot of this is that the actual waterline length will be slightly longer with the short/fin bulb. and this could put you over the marks. A similar effect occurs if you use a lighter fin/bulb and then add ballast inside the hull, but the increase in waterline length is bigger. Limitation C.4.4. c) also affects the sails. Since the certificate contains the measurements of the A rig, can someone explain how you can use a smaller rig and comply with this limitation?
  7. I'm sure a read a definition that said port & starboard were defined by the wind direction alone, but I can't remember where now. The one you quote is from the RRS so that's the one we have to use. I don't actually like it because it can encourage deliberately running by the lee, which can be dangerous in some types of boats.
  8. If you are asking why this rule exists: The purpose of Rule 18 is to promote the orderly rounding of marks and giving port gybe boats mark room is considered to be the best way to achieve this. Imagine two boats overlapped on port gybe heading for a mark to be left to port. The inner boat has mark room and continues to sail towards the mark. if the outer boat now sails further away from the mark then gybes early and heads to the mark on starboard, if the starboard gybe boat has ROW, then where is the port tack boat supposed to go? I seem to remember that years ago starboard did have ROW but it was changed to avoid situations like this and because of the difficulty in deciding which gybe the other boat is on - don't forget that the gybe is decided by where the wind is coming from not which side the boom is on. I remember a few cases of people running by the lee on port whilst yelling starboard.
  9. To demonstrate how clear and simple the 10R Rules are; a little quiz to test your knowledge. Suppose you have a 10R that has been measured with a full length fin and you have set the waterline marks precisely for this fin. You now want to visit a 'shallow' venue and hence you have obtained a shorter fin. Questions: When (if ever) can you swop between the fins? Does it make any difference if the short fin is lighter, heavier or exactly the same weight as the long fin. (Clue - you need to think about Archimedes Principle for the last case). I will give my answers later.
  10. This appears to be a new 'High Voltage' version of the previous 6114 winch (of which I have two). It has presumably been produced to cope with the fact that most people are using LiFe / Lipo 2-cells these days. If you stall a 6V servo (rudder or winch) with a fully charged LiPo / LiFe, then it will probably burn out: as Eric has found out. I am currently using a 6114 in a 10R without any problems but there are a couple of things worth knowing. If you use LiPo /Life then I would recommend you install an external BEC (or uBEC) to protect your servos. It's not as fast as an RMG but fitting the bigger metal drum helps. Personally I think RMGs are pretty crude and overpriced as well as being very noisy (plastic gears on a brass shaft?), but there aren't many alternatives.
  11. Perhaps I confused you! On a Mode 2 transmitter (which is the most common these days): left stick U/D is throttle, left stick L/R is rudder, right stick U/D is elevator, right tick L/R is aileron. These definitions obviously come from model aircraft flying. For model yachts 99% of people use the throttle channel for the sailwinch and the aileron channel for the rudder. If you want L/R movement of the left stick to mimic the U/D movement of the left stick then you need to tell the transmitter to mix rudder into throttle. If you set the mix ratio to 10% then full left or right stick will move the winch by 5%. Changing the mixing sense from + to - changes whether the winch moves in or out when you move the stick left (and vice versa). You need to think about the set-up as you don't want to over-travel the winch and have it stalled for any length of time. Modern winches can draw quite high currents so leaving it stalled for any length of time will, at best, flatten the battery quite quickly. Depending on the type of winch and how you have it wired, it might even overheat things and do damage.
  12. You could do this by using one of the mixers to mix the rudder channel into the throttle channel (Assuming you use Mode 2 = throttle on left). However I don't think this would work well because it's too easy to move the stick sideways slightly without really realising that you are doing it. A better way might be to use the exponential function on the throttle to make the winch movement less sensitive at the fully sheeted in position i.e. the winch moves less distance for a given stick movement giving you finer control at the sheeted in end of the travel. You need to select 'Lo Base' in the throttle exponential settings to get less sensitivity at the end of the travel rather than the middle. This is one case where modern transmitters with electronic trims aren't as useful as old fashioned ones with mechanical trims. With my transmitter I can see if I've moved the trims off-centre (and put them back to the middle if I want to). I think you would be better off reading the manual rather than me trying to tell you exactly how to do it.
  13. The 1967 Rules consisted of 2 A4 sheets. The 2002 rules were 21 pages. The 2020 rules are 29 pages.
  14. A wise man once said that no information was of more use than wrong information. The first image is the graph produced by the current spreadsheet from my mainsail data. The second shows what I believe is a correct representation of the same data. I have already offered any help I can give in confirming / correcting the anomalies I have found, but so far I have only met with explanations as to why they either don't matter or are not worth fixing. Of course I accept that changing the spreadsheet comes with a cost but the publication of a bug / workaround list would seem to be no more effort than replying to my posting. It was the seeming lack of enthusiasm to do even this that led me to post the list on this forum. (Ideally I would have posted it on the IRSA or ITCA website so that measurers in other countries can comment but I have not found a suitable forum.) P.S. I might be forgiven for expecting a little appreciation for the time I have put into trying to resolve the issues that several people seem to be having with the spreadsheet, instead I seem to be being accused of 'hacking' and copyright infringement (both of which I strongly refute BTW). It doesn't encourage people to give their time in an effort to benefit the class does it?
  15. As part of my attempts to upgrade and improve my aging Bentley (longer fin, lighter bulb, revised sail plan), I have been entering its new data into the IRSA 10R Measurement Forms in order to check its legality before having it officially measured. The sail 1 / sail 2 pages of the spreadsheet produced many errors / warnings that I didn’t understand so I have spent a some time reviewing the underlying formulae in an attempt to understand why. I have reached the conclusion that nearly all the errors & warnings generated by my sails are erroneous i.e. they are due to errors in the spreadsheet. Also I have produced a private version of the spreadsheet that fixes all the issues bar the leech hollow problem, so I’m fairly confident that I’m correct in blaming the spreadsheet not my sail data. Fixing the problems took far less time than finding them as the spreadsheet uses some very (over?) elaborate methods to do some fairly simple things. I have listed the errors I have found to date below in case anyone else is having the same issues. I have also included the responses to my observations that I received from the MYA Technical Officer. I leave you to make up your own mind about the adequacy of the responses. If I’m right then this raises obvious questions about the process used to review and test the forms before they are released for use. A more interesting question perhaps is “why has no one else found them yet?” I have now spoken to four 10R measurers and it is clear that none of them fully understand how the checks and warnings work and hence the possibility that the checks themselves could be wrong has not occurred to them. Their attitude to the spreadsheet seems to fall into one of two camps. Either they just accept that the spreadsheet produces warnings for reasons that they don’t understand or they become frustrated and annoyed because they have to do additional checks that are clearly unnecessary. Either attitude severely reduces their confidence that the spreadsheet is providing them with useful support when carrying out measurements. In extreme cases it is seen as more of a hindrance than a help. Please do not think that I am against the use of the spreadsheet. In principle it is an excellent tool and the checking should help to catch many accidental errors in both data entry and calculation, however it is self-evident that it needs to be as error free as possible. One might even suggest that there ought to be some sort of formal bug / query reporting mechanism so that errors, which will enevitably creep in, can be flagged up quickly and experience in its use shared. Clearly a great deal of time (and cost?) has gone into producing this spreadsheet but if measurers don’t understand what it does and/or don’t trust the results it gives then much of the effort has arguably been wasted. List of Anomalies found to Date. John Millward report 18 February 2022 – GB replies 1 Number of Foot Heights The spreadsheet attempts to count the number of foot heights entered and compare this with the length of the foot to ensure the right number of heights have been entered. Unfortunately the code tests for a valid entry by comparing it to zero, so if one of the entered foot height values is 0 (as would happen if the tack and clew heights were the same height or the length is an exact multiple of 50mm) then it doesn't count this as a valid foot height and gives a warning when the correct number of foot heights have been entered i.e. it ignores the zero height and thinks there should be one more height. As replied to the Class Registrar some weeks ago - Any entry of zero in the legitimate spaces for measurements will give an ‘error?’ message. The calculations do not fail and there is no error in the calculations. The ‘error?’ message is to alert the measurer that something may be amiss and that he should check. Zero will be entered in ho in a very rare case i.e. the clew point lies on the perpendicular to the straight line between head point and tack point. Zero values in other legitimate spaces would normally indicate a hollow in the foot has not been bridged. The ITCA Technical Officer is aware of this and it is not regarded as something that is a priority to address. 2 Foot Hollows Check There are 3 separate errors in the table. 1) The first two columns in the yellow table and the legend (S25 – S36 to U25 – U36) List the heights from clew to tack (hn -> h0) whereas the result column (V25 – 36), is based upon data in the “ Data for Foot Graphs “ table which lists the heights from tack to clew (i.e. in the reverse order). The result is that “Check / OK” warning appears against the incorrect h value. The labelling of the heights hn to h0 in column S is reversed and will be corrected at some stage. (JM Note – I have informed GB that the fault is not just column S. Columns T & U are also reversed and the check / OK messages are therefore meaningless.) 2) The hollows check algorithm compares each height to the average of the two adjacent heights and issues a warning if it is less than the average. Obviously for this to work, there must be valid heights either side of the height being tested. Unfortunately the spreadsheet attempts to test the last h value (hn) and therefore this test is invalid and nearly always generates an error. Not knowing how many heights will be measured and recorded it is not possible to know which will the last h value. Hence this will happen. The note to ‘check’ is an advisory message to alert the measurer that something may be amiss and that he should check. (JM Note – The form already detects the last and the penultimate cross-widths in order to calculate A2 so the same method can be used for the heights.) 3) The foot hollows check is arguably too aggressive because it does not take account of rounding errors. The rules require that all measurements are rounded up (e.g. 35.1 becomes 36) but the check does not allow any tolerance in the check criteria. The result is that a perfectly straight line can produce hollows check warnings. It is anticipated that there will be false negatives because of this. However setting a value below which the ‘check’ message does not appear would permit some real positives to be un-checked. Again, the note to ‘check’ is an advisory message to alert the measurer that something may be amiss and that he should check. 3 Leech Hollows Check In contrast to the foot hollows check, the leech hollows check is arguably not aggressive enough as the cross widths include the luff curve so any difference in cross widths due to the luff curve could mask a hollow. Agreed. However, without measuring the offset of the luff itself from the vertical (or the offset of the leech) I do not see a simple way to address this. Please let me know if you do. (JM Note – Shouldn’t we at least be consistent? If the checks allow minor hollows in the leech to go undetected shouldn’t the same be true for the foot? False warnings will undermine confidence in the tool and potentially lead to real hollows being ignored) 4 Cross Widths Graph Although this is only used for information it does contain a number of errors / anomalies 1) The leech profile graph draws a point which represents the head of the sail Unfortunately it makes the assumption that the cross width is zero at this point, so if your sail has a reasonable width at the head (as most do) the graph looks quite strange at this point. As the area calculation for A2 calculates a notional head cross width, it seems rather strange not to use this for the graph. There were limits to the degree of realism that was sought in the diagrammatic representation of the sail. A notional head width could be estimated and used at some future stage. 2) The cross width differences have a similar problem to the foot widths problem 2) in that it calculates the last value as the difference between the last valid cross width (Cn) and zero. Thus the Cn cross width difference equals Cn, which is of course incorrect. See comment above. 3) A minor issue is that the cross width differences are plotted at the cross widths and so it is not clear which cross width difference they refer to e.g. does the cross width plotted at C5 give the cross-width difference between C6 & C5 or C5 & C4. It would be clearer if the cross width differences were plotted between the cross width points i.e at 100, 300, 500 etc. Most users are probably not aware of what the cross width differences demonstrate. The class registrars will be more aware of what they indicate. The adjustment you mention would be ‘more correct’ but I doubt it would make a great deal of difference in reality. 4) The foot height differences graph looks very odd at the clew and seems to have an extra point but I haven’t fully investigated this. By all means let me know what you find.
  16. John949

    6 Metre setup

    Shouldn't that be forward a bit? Weather helm is caused by the sail plan's centre of effort being behind the hydrodynamic centre so you need to move the sails forward to reduce the tendency to luff up. Or have it got it wrong? My own boat (not a 6 metre BTW) is driving me mad because it balances nicely when close hauled but develops vast amounts of weather helm on a reach and broaches at the drop of a hat. Any suggestions for a cure gratefully received.
  17. Thanks John, I had forgotten about Rule 43. Any comments on the other two questions? Is yellow allowed to sail green past the mark? Does yellow lose her Rule 11 rights once green enters the zone?
  18. There is an error that I found in the on-line forms in this area (which I have reported). The spreadsheet counts the number of heights you enter and checks that this matches the length of the foot. So, for example, if your foot length was 425mm there should be 9 entries - h0 to h8 at 0, 50,100 .... 350, 400. Unfortunately there is a bug in the spreadsheet that if one of the entered values is zero, then it ignores this value and counts one less height than you have entered. I don't know if this is your problem but try adding / removing entries until the error goes away and see whether it wants too many or too few entries. Or if you post your data I can check it for you. You may also notice that the graphs it draws of the sail profile look odd at the head. This is because it assumes that the head width is zero (why I don't know) so if your sail has a reasonable head width (my mainsail is 90mm) then the graph is not very helpful. I to have been entering my own data into the on-line forms and have many comments on the layout of the forms, the fact that huge parts of the final certificate are just guidance (and may be totally irrelevant to your particular sails), and the lack of any instructions / explanation on how to fill them in (even to the extent of which fields you have to enter and which are automatically generated). The fact that all the formulae are hidden doesn't help you understand what they do and hence resolve issues like this. If you want to see the formulae then is is pretty simple to unlock a sheet - you just take a copy of the spreadsheet and each sheet will then unlock without a password. Unlocking the whole workbook is a bit more complex but Google is your friend.
  19. Is rule 18 actually relevant here? Isn't the situation covered by Rule 11 W/L and Rule 13 Tacking? How fast yellow is allowed to luff is governed by Rule 17. Even if she were the overtaking boat, Yellow's proper course is to round the mark if she can so green would still have to keep clear under Rule 11. Rule 18 would be relevant if they were leaving the mark to starboard, in which case yellow would have to give green mark room. I think we all agree green has to give yellow room, but if it's under Rule 18 then yellow has to bear away and round the mark "in a seamanlike fashion", if it's under rule 11 then yellow can sail on past the mark if he/she wanted to. I also struggle with what happens if yellow establishes the overlap inside the zone. Rule 18 says that yellow must give green mark room, but how do you give mark room to a boat on your outside? I'm pretty sure that the intention is that yellow loses her Rule 11 rights if she doesn't establish an overlap before green enters the zone - I just don't think the rule is very well written to convey that.
  20. My personal view is that our whole measurement process could be simplified. At the moment every boat and its rigs are subject to quite a detailed measurement procedure which takes time and effort even before you add in the current hiatus concerning measurer's qualifications. All that tells you is that that boat and that rig measured on that day, it does not tell you that they will remain within the class rules for ever more. For example, boats tend to gain weight as they age and for a 10R this can easily put it over its original waterline length. There is also the issue of deliberate cheating - it's pretty easy to put new panel(s) in a sail while retaining the panel with the stamp and the signature. I'm not saying that such practices occur, I'm just trying to point out that, for a major championship, you can't rely on the original measurement and you have to conduct sample tests at least or possibly even completely re-measure the first few boats (like post race scrutineering in motor racing). Given that you need do this testing anyway, then do we need to measure every boat and every sail to the same degree if it is only going to be used for club racing? An alternative way forward might be to conduct a few simple checks on the hull and allow sails to be self certified by the maker (including home made sails) and then issue a certificate on this basis. If we kept the basic tests simple enough (e.g. use templates rather than rulers) then the training requirements for 'basic measurers' would be pretty low and a few more people might be willing to undergo it. Spot checks and sample measurements would then be carried out at major events by 'fully certified' measurers. Hopefully it would be self-policing as anyone getting repeatedly disqualified from major events would have some explaining to do to their customers and/or be obvious candidates for 'random' testing. This idea would need a bit of tweaking for each class e.g. classes with variable sail dimensions would probably need the sail maker to provides a 'certificate' with the actual dimensions and area on it to allow easy spot checking. 10R waterline measurement is always going to be tricky but I don't think anyone could claim that you need to go on an RYA sail measuring course to do it!
  21. Brad, Ah I think I understand what you are saying at last. I've just emptied the tank otherwise I'd have a try. Richard, sorry for the thread hijack, I promise to stop now, except.... how have you put the WL marks on your boat if you haven't made the A rig yet? Setting up a 10R is a bit iterative as you have to sort of guess a waterline, make an oversize rig, weight it, re-do the WL, trim down the rig and so on. In practice one iteration is usually enough but you do need to know the weight of the heaviest rig (almost always the A) before you can finally set the marks. I shall be interested to hear how it goes against other 10Rs. I suspect it might go well until you have to change down to the B rig i.e. give up your sail area advantage but suffer with a shorter WL. The Bentley's party piece is to be able to carry more sail area than most in a given wind strength, of course the wind has to be strong enough for everyone else to need to reduce sail area below the Bentley's maximum. It's on these days that I remember why I like sailing it so much. Makes up for all the drifting match days when I get embarrassed by well sailed IOMs!
  22. Unfortunately this picture doesn't show the meniscus as well as I'd hoped. It does show how bad my paint job is though! The blue line marks where the meniscus ends (if you look closely you can see the reflection of the bushes behind ends at this point because the water surface is no longer horizontal). What I was trying to show is just how far apart the waterline mark and the meniscus are - it's around 25mm! Brad, I don't understand your comment about 'ignoring the meniscus'. If you look under the boat with a mirror, all you can see is the edge of the meniscus. The sketch below reflects my understanding of the physics of surface tension. I agree you can see where the meniscus attaches to the hull and where it stops distorting the water surface, but neither of these is where the hull intersects the waterplane. In other words, you can see Point A and Point B but you can't see Point C
  23. Brad, I assume you've seen this: https://www.sailsetc2.com/downloads/waterline end checking device 10R.pdf It shows that Mr Bantock thinks the waterline is measured where the waterplane intersects the hull, not where the meniscus touches the hull. When Roger Stollery checked my Bentley for me he also used a device that used the same principle. If you measure by sighting the meniscus you will get a value some 5-25mm longer than if you use the Bantock / Stollery method (depending on the hull shape) so it is significant. Unfortunately the rules don't help because they use the term ''waterline ending" without defining what this means. One of the difficulties with the Bantock / Stollery method is that you can't set the 'gauge' by sight, you have to 'feel' when the boat touches it - hence my original comment about it being difficult and error prone. One of the reasons swing rigs aren't as universal on 10Rs as they are on Marbleheads is because the 10R rules require the B rig sails to fit within the profile of the A rig sails. As swing rigs need to use a tall narrow jib, this severely compromises you if you want to use a conventional B rig, as ideally you would want to use a much bigger jib for the B rig (as Marbleheads do). Some 10Rs use a B swing rig but I'm not convinced this is a great idea. In my view this rule is unnecessarily restrictive and is one of many I would change if I ruled the world. The current rules require you to re-measure the boat and get a new certificate if you want to change the profile of the sails but keep the area the same, surely it is only necessary to measure the new sails and confirm that they do not exceed the area quoted on the original certificate?
  24. Of course a well sailed boat can beat a badly sailed boat but hydrodynamics still applies. If you accept the well known maximum hull speed formula (for displacement mode) then the Bentley should be just over 5% faster at it's ultimate hull speed (when upright of course). If we assume equal displacements, one would expect the drag curves for the two boats to cross over at some point towards their maximum speed. The POE would be expected to have a lower drag at low speed, because of it's smaller wetted area but it's wave making drag will rise faster due to the shorter waterline. The overhangs on 10Rs are intended to increase the waterline length when heeled so it gets a bit more complicated but having a longer waterline to start with is generally beneficial. My comment about measurement accuracy is to do with the waterline length. The overhangs of a 10R (particularly at the stern) make a very small angle to the water surface so that if you are 1mm out in height you will be about 5mm out in length. Now add in the meniscus problem and I estimate you could easily be 10-15mm out. Incidentally I haven't found a definitive statement on how to handle the meniscus effect in the rules. I just know the Messrs Bantock and Stollery both say that you should try to eliminate the meniscus effect when measuring the waterline. I believe there is a more accurate way for boats that have been designed using a CAD modelling system and that is to produce a graph of waterline length v displacement from the model. One then only needs to weigh the boat to determine its waterline (and verify that the hull is built to the model.) I found it very difficult to get repeatable results when checking my Bentley so in the end I took a range of measurements at different displacements and then curve fitted a graph to the results so I can determine the waterline length from the weight. My worst point was indeed about 15mm off a fair curve between the other points.
  25. For comparison, a picture of the same sails on my Bentley. I think this highlights the major problem with the 10R class. Those sails are the maximum allowed for the Bentley's 1344mm waterline whereas the Pieces of Eight can have a significantly larger area. In winds under about 7kts I don't fancy the Bentley's chances but over 10kts there is only likely to be one winner. 10R's are lovely boats to sail and very fast but you sort of need a different one for every wind strength if you want to race seriously. Also probably best not to get me started on how hard it is to measure the damn things accurately.
  • Create New...