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John949

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Posts posted by John949

  1. Your method sounds right but it is easy to check if you have got them right.  The straight line distances from the half height point to the head and clew should be the same similarly the distances between the 1/4 point and the head and 1/2 point. Ditto 3/4 point and 1/2 height / clew.  The 1992 version of the rules had a useful diagram.

  2. 2 hours ago, Darin Ballington said:

    Hi John,

     

    This covered in Appendix E, E 3.5 and is a requirement of the race team.

    I was thinking of full size racing where ther is no requirement to call out sail numbers but it is often done but perhaps shouldn't be.

  3. Nearest common occurence would be the RO calling out numbers of any boats over the line at the start.  This is often covered in local sailing instructions but could be considered outside assistance according to the letter of the law.  

  4. APPROXIMATELY 660, you have to make the gauge if you want to be sure.  My 10R and M fins are about the same length.  I thought about making them interchangeable as the 10R is 400g heavier but don't want to start an arms race for club level racing.  It may work for you but most people would suggest that a dual rated boat would suffer against a real 10R when the wind gets up.  The overhangs increase the waterline length as the boat heels / starts making a significant bow wave and the forward one helps with nosediving allowing a bigger rig to be carried in a given wind strength.

  5. Quote

    I have managed to gain a nice pre-bend

    Years ago (when I sailed high performance dinghies) there was a politically incorrect joke about someone froma certain part of Great Britain sending his mast back to Proctor's to have some pre-bend put in it.  The joke being that pre-bend wasn't about putting a static bend in the mast but using the ring tension and standing rig set-uo to bend it according to the wind strength - under no load the mast is still straight. This is not the first time I've heard of IOMs using masts that have a static bend.  I really don't see the point in this.  If you need to bend the mast that much to get a good sail shape then I would think that the sail has been made with too much luff round.

  6. On the subject of soft sails:

    Quote

    A sail where the body of the sail is capable of being folded flat in any direction without damaging any ply other than by creasing.

    This is a terrible definition.  What does flat mean in this context?  One can fold something over so that the top surfaces are parallel (into a U shape) but still leave quite a big gap between the two surfaces, is this flat?  Surely creasing is damage (local yeilding for any metallugists). How is a measurer supposed to determine if the material has been damaged if visible changes to the material are allowed but invisible ones (e.g. microscopic cracks) aren't.  Just to put the tin hat on it, what does 'ply' mean in the contect of a hetrogenous material like mylar film or a plastic batten material? If the material doesn't have ply's then, as written, the material can break and still pass the letter of this test.

    Sorry I'll shut up now.

  7. Sorry to bang on about this but a sail thickness rule will not stop fully battened rigs or indeed other areas of local stiffening.  If you didn't like my appeal to the science of measuring the wrong parameter, here's a guide on how to make a fully battened rig with a sail thickness rule in place.

    The most simple rule would be ' The sail thickness shall not be greater than X'.  Fair enough, but does this apply to seams?  

    If it doesn't, then one simply creates seams wherever one wants to create stiffening and 'hides' a piece of stiffening material in the seam.

    If it does, then what is the value of X? If it is an actual value then it has to be large enough for two layers of the thickest sail material that will be allowed plus a layer of double sided tape or whatever to join the sail.  So if I use relatively thin material thin material then I have plenty of spare width to include some stiffening material as well.  I can see a market opportunity in really thick stiff double sided tape.

    Something like 'The seams shall be no thicker than twice the thickness of the thinest material plus X' where X is a reasonable width for double sided tape.  This is better. but what about stitched seams? The minimum thickness now has to allow for two thicknesses of material, plus the double sided tape, plus two thicknesses of the thread.  Sails are normally sown with a swing stitch so there must be an allowable width of stitching; so instead of using a swing stitch, sew two parallel lines of straight stitch and fill the gap with the batten material.

    And so it goes on.  There are also issues with scrim sails and sails made of two different thicknesses of material (perfectly legal at present) which give yet more scope for producing local stiffening and still meeting any thickness rule.  A scrim sail made with 'stripes' of wider, stiffer 'thread' material looks interesting.

    Now you may be thinking that some of my suggestions break other rules that already exist, but that is the whole point of the argument.  If we already have rules that prevent local stiffening then we don't need an additional rule.  If we don't have such rules then a sail thickness rule doesn't prevent local stiffening.  My contention is therefore that a sail thickness rule is either redundant or ineffective and therefore should not be considered.

    P.S. I made a jib this afternoon and used 'finger style patches to reinforce the tack and the clew.  Quite by chance, as the jib was quite narrow, the patches actually overlapped slightly (on opposite sides of the sail) so I accidentally created a sail with full width additional stiffening across the foot.  Is this legal?  If you think it shouldn't be then how could you write a sail thickness rule that prvented it?

  8. Brad makes an interesting statement which is worth considering in more detail:

    Quote

    Surely the first priority of any governing body is to protect any class from change, more so change that is entirely unnecessary with an outcome more likely to increase cost and disenfranchise current owners and supporters. Sadly such changes are becoming all too common with those that control and steer our classes.

    Marbleheads (and As) are not one designs so change is supposed to happen slowly over time.  Marblehead design has changed beyond recognition over the years with the result that (most) boats over 15? years old are totally uncompetitive against modern designs.  Allowing change lets the class evolve and remain viable in performance terms against current designs.  The price you pay for this is that older designs are not competitive, so older (and cheap) 'beginner boats' are not really worthwhile and attracting new sailors to the class becomes difficult i.e. expensive.  

    What is needed is evolution not revolution so that existing boats / designs are not suddenly put at a disadvantage.  As an example, suppose the rule on battens was removed and someone developed a fully battened sail that was significantly faster in high winds, say.  Then every serious Marblehead racer would have to go a buy a new fully battened sail.  This is not what we want to happen.

    In a development class the rules are used to prevent development in an unwanted direction such as cost (e.g. banning gold keels) and practicality (e.g. mast height). If the above premise is accepted then the rules (concerning the design of boats) should change for one of two (and only two) reasons:

    1) To ban a development that has been shown to be a significant advantage, but is unwarranted for reasons of cost, practicability, safety or accessability.

    2) To allow a previously banned development that would now reduce cost or increase practicability, safety or accessability.

    An example of the latter might be 'First Person Video' which could become so cheap as to not be a cost factor and may encourage more people to take up the sport.

    Applying these rules suggest that the batten rule should not be changed unless and until someone demonstrates that there is a significant advantage to be gained by 'bending' it AND we, as a class, decide that there are good reasons for NOT allowing it.

     

     

  9. I don't think it's the thickness of a sail that's the issue, it's the flexibility of the material that matters.  Of course thickness is much easier to measure but it's hard to come up with a good rule that is based on measuring the wrong parameter.  If rule changes are being considered then we should also look at the term 'soft sail'.  From an engineering standpoint, softness (cf hardness) is the resistance of the material to compression, not how easily it bends.  For example, sponge rubber is soft, diamond is hard.  If we do want to limit the stiffness of sails then the rule should state what the maximum bending stiffness should be.  

    Many years ago (40 odd?) a read an article on the development of padded sails i.e. two sails with a thin layer of shaped foam between them.  I don't think the idea worked but it is interesting to consider whether such a sail could be described as soft, it would certainly be described as thick.  It's also intersting to note tht the idea has re-surfaced (in a slightly different form) on the current AC75s.

  10. I watch it with the sound off and FF to about two minutes before the start because I find the commentary so banal, but each to his own.  If you have Sky or Virgin then it's worth recording both the live and the replay versions as they frequently get delays and the live version can finish before the race does.  The boat designs are interesting from a safety point of view as half the crew would be underwater in the normal capsized position.  Let's hope there isn't anything for their clothing or safety lines to snag on.

  11. Thought I'd have a go at sailmaking but I'm a bit confused by a couple of points in the rules.

    1) Width Measurement. The sail measurement diagrams show that the 'widths' are measured  between the 1/4, 1/2 & 3/4 points on the leech and the nearest point on the luff.  Simple enough but how do you find the 1/4, 1/2 & 3/4 points on the leech?  Since the leech has a significant curve, do you have to measure round this curve, as that is a difficult to do in advance.

    2) Leech Radius.  The wording of J.6 is confusing to me.  I think it's saying that you can have angles (or radii less than 900mm) in the leech, as long as they occur at either the leech points or at batten points.  Or put anther way, one could have a sail with the 1/4, 1/2, 3/4 widths all the same.  The sail would effectively be a quadrilateral with a right angled triangle on top.  Obviously not a great idea but there is clearly a temptation to increase the width of the upper part of the sail for light airs.

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