Sail Measurement Diagram and Measurement matrix

Tony Edwards · Post by **Tony Edwards** » 16 Dec 2008, 13:55

As a matter of interest why did the current rules ditch the measurement diagram and matrix of key sail/rig measurements included in the early version of the rules?

In essence whilst the IOM hull and appendiges are development class the rig and sails are one design within strict dimensions. On that basis the sail diagram is unlikely to lead to interpretation issues and having all the key dimensions in a matrix was very usefull to those making sails and undertaking measurement. As they say a diagram is worth 1000 words. In the case of the IOM rules that's probably 2000 words! The way the current rules are written you are forced to read the whole lot to ensure that you have not missed a vital bit and that ensures a good knowledge. But a new person to the class probably then sits down and draws their own sail diagram which is potential for misinterpretation.

Could we not re-introduce the diagram and matrix - they don't take up much room and I suspect would be the most used part of the rules.

Andy Stevenson · Post by **Andy Stevenson** » 16 Dec 2008, 18:00

Hi Tony

The oldest version of the rules that Iâ€™ve got is 2003 and I canâ€™t find a sail measurement diagram. Do you have a copy of the version youâ€™re referring to that you could email to me?

Cheers

Tony Edwards · Post by **Tony Edwards** » 16 Dec 2008, 22:47

Andy,
A copy of the section of the old rules which, including the diagram and matrix, extended to only 7 pages is on its way by email. These rules were effective from 1.6.1995.

Andy Stevenson · Post by **Andy Stevenson** » 12 Jan 2009, 05:08

I've uploaded a .pdf version to the IOMICA website:
http://www.iomclass.org/measurement/Sail_Matrix.pdf

There's also a link from the measurement page
http://www.iomclass.org/7-measurement/

Cheers

Tony Edwards · Post by **Tony Edwards** » 12 Jan 2009, 12:19

Yes, thanks Andy that's the useful sail measurement matrix and diagram I was referring to.

Now hands up all those people who have kept this from the old rules so they can use it for sailmaking and measurement. Come on now don't be shy. And, why have these useful bits been ditched?

Andy Stevenson · Post by **Andy Stevenson** » 12 Jan 2009, 15:00

Hi Tony

why have these useful bits been ditched?

As I understand it the diagram wasnâ€™t included in the re-write of the class rules because the leech points could have been misleading. The diagram shows them at even intervals along the leech measurement(C in the matrix) where, of course, theyâ€™re not.

Cheers

Andy

Bruce Andersen · Post by **Bruce Andersen** » 12 Jan 2009, 22:28

I am in the final stages of producing a full scale sail measurement template on mylar. Having a bit of trouble with the printing output but should see some results this week. If it turns out OK, I could probably mass produce them for a reasonable price if there is interest.

Ken Dobbie · Post by **Ken Dobbie** » 13 Jan 2009, 00:24

Tony Edwards wrote:Yes, thanks Andy that's the useful sail measurement matrix and diagram I was referring to.

Now hands up all those people who have kept this from the old rules so they can use it for sailmaking and measurement. Come on now don't be shy. And, why have these useful bits been ditched?

I have a copy on the wall in my workshop and I know others that do the same (but enlarged)

Unfortunately the old rule did not follow the ISAF required format so an easily followed rule became the, to my mind, less readable one we have now.
The mass of pages discourage many from reading and understanding, the price of progress

valpro · Post by **valpro** » 13 Jan 2009, 10:17

I'll have one Bruce.

Tony Edwards · Post by **Tony Edwards** » 14 Jan 2009, 13:17

Ken
Well I am pleased that there is at least one person out there that finds this sail measurement information all in one place very useful. I suspect there are a few others too! I realise that the sail diagram has its faults but it would not be too difficult to make it bullet proof - it would make the one design section of the rules easier and less capable of misinterpretation and save several trees into the bargain.

Bruce,
Will your template be able to accommodate the effect of different luff curves and those that choose to use, for whatever reason, the minimum leech length which puts the leech points higher up the sail?

Tony Edwards · Post by **Tony Edwards** » 22 Jan 2009, 23:10

Whilst on the topic of sail making and measurement I would like to raise the difficulty, to a newcomer of identifying the "sail measurement points" on the sail plan. These are essentially one design sails so this should be reasonably easy. However I don't believe it is not possible to identify these points from reading the copious IOM rules. In fact to the best of my knowledge the only mention of "leech point" in the IOM rules is on page 22 as a relationship with "batten pocket point". They can be the same point or up to 20mm apart (and by inference the batten pocket point has to be exactly on the change of angle of the leech). And, being printed in bold it is reasonable to assume that there will be a definition of "leech point" in the Equipment Rules of Sailing but I don't think you will find a definition of "leech point" there either. There are words that by inference will take you close but not a precise definition. So, whilst those in the know carry on assuming the newcomer has to search for guidance from outside the rules like the useful measurement guidance to be found on the IOMICA site. There is quite a lot of scope for mistake here!
If I may be so bold, and I am really not trying to criticise, it should be possible for anybody to easily create the mainsail plan simply by reference to the IOM rules, ERS and RRS. Essentially the sailplan is simple but very difficult to describe in words. So, why don't we adopt a new anotated sailplan sketch or if necessary sketches together with the matrix of dimensions that were attached to the original rules. Those of us that have grown up with the IOM rules need to re-read them from the viewpoint of a new recruit.

Bruce Andersen · Post by **Bruce Andersen** » 23 Jan 2009, 07:06

The sail measurement template I am working on will be a line drawing of all 3 suits of sails printed on heavy drafting mylar to be portable and waterproof. To avoid it being too complicated looking to be easy to use, I only am plotting the maximum sail dimensions with all important measurements noted on the diagram, specifically luff/leach/foot/head dimensions as well as the fractional leech widths. Also included are mast band locations.

I decided not to include minimum dimensions as I don't see that as an option that many choose to use.

Hopefully, it will be able to be rolled out on a table upon which the rigs are placed to simply and rapidly see if the sails and spar bands exceed maximum allowable size. If the sail is significantly undersize, a tape measure will be needed.

I am proofing the final template in the next few days to check the dimensions again before having them printed. Will keep you apprised of my progress.

ps. the leach points are defined in the ISAF sail measurement rules, but basically say that to find the 1/2 leach point, fold the head to the clew and find the 1/2 way point, then measure the maximum dimension from that point on the leach to the luff of the sail. Similarly, the 1/4 and 3/4 leach points are also measured. Not too many folks want their sails folded, so the sail measurement template has those points printed on it. They are accurate assuming the leach is maximum dimension.

Lester · Post by **Lester** » 24 Jan 2009, 10:35

Hi Bruce

My experience of such measurement devices is that they struggle when the sail has any significant amount of luff curve. They also struggle when the sail is bent to the mast (since the sail may be measured while bent in accordance with the class rules). In both cases, the measurer must 'slightly rotate' the sail while moving up the luff to see if the leech falls within the envelope of its permitted profile, and this tends to make the process rather more subjective than it should be.

Worse, though, is that such devices also struggle if the batten is positioned at any distance away from any leech point. In this case the leech profile is quite visibly different from that which might be permitted if the batten was at the other end of the allowed range (which is effectively some 40 mm), and not even a subjective judgement can give a satisfactory answer as to whether the sail measures.

Because of these problems, I have usually advised clubs who wish to be serious about setting up IOM measurement systems (ie their measured rigs might be used at national or international events) not to attempt to use sail envelope diagrams.

valpro · Post by **valpro** » 26 Jan 2009, 18:30

Quite right Lester, that's why us Measurers use measurement sticks.

Bruce Andersen · Post by **Bruce Andersen** » 27 Jan 2009, 03:28

The leach points are defined not by batten position, but by the actual length of the straight line connecting the head point to the clew point divided into quarters (by measurement or folding). Those points (1/4, 1/2, and 3/4 leach for the main, 1/2 leach for the jib) define the min/max width measurements.

Although the leach has to describe straight lines between each of the battens and the aft head point, the entire sail has to fit within a maximum allowable envelope. Irrespective of the contour of the leach, lying a sail on the outline of the maximum sized sail allowed should pretty clearly show if the sail is oversize.

Sails that are illegally undersized are another issue, albeit a less prevalent one.

I understand your issue with measuring sails bent onto pre-bent spars and agree.

Tony Edwards · Post by **Tony Edwards** » 29 Jan 2009, 23:36

Like Lester I feel that there are too many variables to the luff round and to the profile of the leech for a template to be of more than limited use for check measuring sails at an event. It is unlikely that professional sail makers will use the max leech and luff lengths for a start because an allowance needs to be made on the luff for the downhaul and very minor errors, material stretch etc would easily render a sail out of class.

Its interesting for me to see who is responding to this thread. Are there any amateur sail makers out there who have recently tried to put an IOM mainsail plan onto paper? If so, how easy did you find it? Would you have found it easier with a sketch diagram attached to the rules? Would you like to see the rules in this area made simpler, more obvious and with less words!

Antonio Espada · Post by **Antonio Espada** » 15 Mar 2009, 20:47

A template, as is raising here is impossible, due to be measured between the maximum and minimum, and be measured from the leech.

However, we have created a system which makes it easy to mark points 1/2, 1/4 and 3/4 in the leech, with a simple movement, the dimensions are checked easily on a map printed on a plotter DIN A0, and then by transparency, controlling all other parameters of the sail (reinforcements, battens -position & dimension-etc).

Measuring a set of sails for this procedure is for children. In 5 minutes, controlling each of the 83 checks to be made for each rig. Â¡Â¡Â¡It is more complete the form!!!!.

Bands are also drawn from the edge of the mast and Stay, to be able to control immediately.

Same for the jib,In this case only to the midpoint ...

I'm trying the same plane that I printed in the Quantum Toni-TiÃ³ sailmaker(who made the template for measuring the sails of the Optimist class) on Polyester and it seems it will be possible at a reasonable price.

If you are interested, I can inform you when you're ready.

Roy Thompson · Post by **Roy Thompson** » 28 Apr 2009, 23:57

They are accurate assuming the leach is maximum dimension.

This is no good I am afraid. I have measured quite a lot of sails over the last few years and can gaurantee you that minimums are used for a significant number of sails.

The leach points are defined not by batten position, but by the actual length of the straight line connecting the head point to the clew point divided into quarters (by measurement or folding).

Bruce - you are wrong here and misleading people. I suggest you talk to a measurer or reread the ERS especially. This is the mistake many of us were making for a long time and is understandable and this has been discussed in various posts over the years
To find the 1/4 and 3/4 points you would need to refold/measure the sail from the 1/2 leech point to the head or foot point, not simply divide the line joining head and foot into quarters.

Roy Thompson

ESP IOM NCA Measurements Officer
Ex IOMICA Vice President Measurements

Bruce Andersen · Post by **Bruce Andersen** » 29 Apr 2009, 07:51

I understand the issues concerning the 1/4 1/2 and 3/4 leach measurements. To do it on a real sail, folding is necessary to determine these points. Assuming that the leach is a straight line between the head and clew, this could be done with a ruler. Folding the sail will give the same locations.

If the leach has a roach, you must measure along a straight line from the head to the clew and divide that into the appropriate lengths then extend them perpendicular to that line out to the leach to get the maximum sail width measurement points.

A template can be accurately used for maximum measurement sails and can alert the measurers whether or not a more traditional (and lengthy) manual measurement is required if the sail is less than max dimensions.

Since there is significant variability allowed in our sails, a template cannot be accurate in all cases, but could be used as a starting point. It can also easily check the position of the mast bands.

Roy Thompson · Post by **Roy Thompson** » 29 Apr 2009, 08:09

I understand the issues concerning the 1/4 1/2 and 3/4 leach measurements. To do it on a real sail, folding is necessary to determine these points. Assuming that the leach is a straight line between the head and clew, this could be done with a ruler. Folding the sail will give the same locations.

If the leach has a roach, you must measure along a straight line from the head to the clew and divide that into the appropriate lengths then extend them perpendicular to that line out to the leach to get the maximum sail width measurement points.

I feel that you are still confusing many people Bruce- It is not true that you ''measure along a straight line.........divide into appropriate lengths'.
When you have found the half measurement point on thre leach you must then draw new lines from this to the head point and foot point and divide these new lines in half and project out to the leach to find the 1/4 and 3/4 points. This is different and is an accurate, simple and effective way to find the correct measurement points required by ERS.
May I suggest that you rectify your comments.
All of this is well documented in this forum and in various other sites, and like I said, it is a common mistake which many of us have made in the past. We have now realised the error and I think it would be good for the current IOM Exec to reiterate the correction.[/quote]

Bruce Andersen · Post by **Bruce Andersen** » 30 Apr 2009, 07:22

Unfortunately there is no emoticon that reflects the "AH HA" moment I had when I finally got what you and Marko are saying. I am occasionally wrong but never in doubt! Sorry for the argument.

I just folded up an old IOM A rig mainsail to measure the difference between the ERS multiple fold method of locating the leech points and my (erroneous) method, and found the points only differ by 1 mm at the 1/4 point and 3 mm at the 3/4 point.

Is it worth trying to simplify sail measurement for our class? I like to think that I'm reasonably bright, and this fooled me up to now.

valpro · Post by **valpro** » 30 Apr 2009, 10:39

Bruce, interesting that you too applied the Sail Measurement method to an IOM sail, as I did some long time ago. I wanted to know just how much difference there might be between on-spar and off-spar measurement. Like you I found very minor variations. I also applied the vertical 'flaking' of the sail to get the leech to lie in the correct and undistorted position, something that makes an alarming amount of difference when you do it on any full size sail and was relieved to find that in both cases measuring the sail on-spar was acceptably close to measuring off-spar so I have no qualms about what we do with IOM sails.

Roy Thompson · Post by **Roy Thompson** » 30 Apr 2009, 13:10

Glad you got it, it took me very a long time too when they tried to explain it to me, (and sometimes I still forget and make the same mistake!)

The 1 to 3mm difference sounds about right, and I think it's probably important, along the length of the whole leach it would be a few square centimetres extra sail area so it's worth chasing. Finding the correct points isn't that difficult and for that reason, knowing how to do it 'correctly' (according to ISAF ERS) doesn't need simplifying in my books.
More of a problem is measuring accurately when there is a lot of pre-bend in the mast (rotating it normally sorts it out most of the time)and 'too many' or 'too tight' luff ties just where you want to measure at the luff... not as easy to sort out without removing them ... but that's another story.
A change I wouldn't mind seeing is sail measurement off-spar. Now that would be quick and easy (for the measurer at least), no?
The template that Antonio Espada (a highly experienced ESP multi class measurer) has developed allows an IOM measurer to find the correct points relatively quickly, accurately and easily.
Of course, as with any measurement, when the result is very very close to the limit, we tend to recheck and would resort to more traditional methods and a metric rule etc.

Have fun measuring out there!

Antonio Espada · Post by **Antonio Espada** » 30 Apr 2009, 22:28

Of course, as with any measurement, when the result is very very close to the limit, we tend to recheck and would resort to more traditional methods and a metric rule etc.

Only remark that if the template that comment, tall sail without attaching to the mast, the precision you get (the plotter that draws) is one tenth of a millimeter. In any case a precision much higher than you get with a normal one meters (1 mm) or if you do it with a ruler precision of 5 tenths.
The only problem we have is that I made on paper, so the subject to a board, they become difficult to transport.
Was by putting it to me printed on vinyl at QUANTUM sailmaker(which can be rolled), but I decided to wait and see whether the new leaders (which I hope will be different from other existing) clarify each of the points now under discussion, and have no semblance to reach a port.

How Roy L. can say that we must use a tank, and when you ask how to build it, and how to use it, do not know what to answer?
Andy can talk about how to dispense with the mistakes that were made (between 1 and 3 mm) in order to simplify the measurement of sails?

The regulation of any kind is not a soap opera on television, where writers do surveys for them in the public hearing which will give them more.
Regulations, write the experts who know what they are talking about and what it focuses more different attempts to find no advantages between the correct wording of the articles at rulebook.
Then as ISAF is responsible for implementing new rules and exceptions when someone is "victim" of a rule has a certain status.

Sincerely

Bruce Andersen · Post by **Bruce Andersen** » 01 May 2009, 02:28

I'm not quite clear on what you mean Antonio (other than you hope new leaders are elected) in your post. Are you saying that you want to measure sail dimensions to 0.1 mm tolerances? That's pretty thin, certainly thinner than any drafting/plotting pen/pencil.

I'm not trying to be argumentative, but I just can't understand what you are trying to say.

Antonio Espada · Post by **Antonio Espada** » 01 May 2009, 09:21

What I am saying is that with a template that has been drawn with a plotter that has a precision of 0.1 mm, gives a higher accuracy than using a meter with house brands each 1mm or each 0.5 mm.
Simply replace the "metro" for a more accurate template.
At no time did he speak of tolerance.
The dimensions must be between the maximum and minimum, and there, NO TOLERANCE.
In the first lesson of any course of measurement, which is NO TOLERANCE FOR TOLERANCE.

Someone has stopped looking at the templates used in the World Cup Marseilles by Mr Brun?.
You may also be a solution to get a quick control key measurement.

valpro · Post by **valpro** » 01 May 2009, 11:03

Using a template is fine and in 99% of the cases the sails will pass without comment. Where the sail appears to be on or over the limit than it MUST be hand measured using steel rules of the correct standard. Then, not only do you have a definitive answer but the means of arriving at it are clearly visible. The old tenet of 'When in doubt, get the tape measure out' still applies.

jeffbyerley · Post by **jeffbyerley** » 01 May 2009, 11:45

Gee Val, You managed, in less than 2 lines, to sum up what was preceded by a whole page of comments and opinions. Ten out of ten!

Antonio Espada · Post by **Antonio Espada** » 01 May 2009, 12:15

The old tenet of 'When in doubt, get the tape measure out' still applies.

Val:
With template, never have doubt, and if you see clearly "does not pass or passes."
The tape will only confirm what the plan has clearly shown.
Fortunately, technology is our best allied, and we must not despise those who have the task of compliance with the dimensions set by the rules.
AutoCad and plotter seem predestined to facilitate the measurement of the sails of an IOM.
... and you avoid having to read / re-read measure / re-measured 83 controls in each jig!!!!
And make sure that what you mark on the sheet is really what we want to mark (Who had the idea of the brilliant idea to include the double negative ... etc.?).

83 control points * 30 seconds per control point * 3 jigs (a high yield for a measurer that actually read, interpret, measure and enter on the form) = 7470 seconds = 2,075 hours (without stopping to take a sip of water).
Too long for something that template, it is in gear for 10 minutes. (It costs more to fill the form).
You really are using at least this time to measure each boat in its fundamental measurement?
If at this time, we add in addition to filling in the measurement form of the hull, weighing to be sure that it is over 4000 grams, and we get into the tank to check the draft of the hull (60mm) and draft total (proposed by RoyL)...
... and we started at 9 in the morning ... have just enough time to go eat ... and of course to celebrate with a good glass of red wine.

That indeed I have already taken me in memory of Ted and Tony.

Regards

valpro · Post by **valpro** » 02 May 2009, 10:32

Yes, Antonio, absolutely right but people do get stressed during the measurement process and I found that it defused a lot of argument when a sail was possibly out of measurement to simply put the tape over it. People generally calm down at that point. Same with weighing. Get the checkweights out and once they can see that the scales are accurate or that the error is known and the weight compensated for, all the argument go away.