Technical manual - how to measure a DN

[Paul Goodwin - US 46]

I have been tossing an idea around the Technical Committee that would make it easier for IDNIYRA members (and particularly builders) to understand how the DN Specifications apply to the design of parts, and how to measure DN hardware to make sure it is legal.

My idea is to create a "Measurement Handbook" under the ownership of the Technical Committee.  This handbook would be a supplement to the Specifications and Interpretations, and would carry the same level of authority.  The handbook would illustrate the correct methods for measuring hardware as it relates to the Specifications (through pictures, drawings, written description, or other means).

Measuring Committees at regattas would be required to follow the procedures in the Handbook, provided there is a relevant measurement technique illustrated..  This would help eliminate confusion over the Specs, and bring uniformity to measuring.  This way builders could measure their hardware, and not worry that someone at a regatta would have a different interpretation on what a particular Specification intended.

The idea of a Measurement Handbook was brought up at the Europeans Secretaries meeting this past Spring (2007) and was well received.

Obviously this is a big task, monumental perhaps.  I would welcome opinions on the idea, plus volunteers to help flesh out details.  Of particular help would be people that could write technical descriptions and/or produce drawings showing measurements techniques for each Specification.   The Tech Committee could then edit the information and compile it into the Handbook.

To get an idea of what I envision, check out the "recommended practice" from the Technical Committee for measuring a couple of Specifications: Spec Measurement

These recommendations were made after a request last year prior to the European Championship.

What do people think???

Paul Goodwin
Chairman - IDNIYRA Technical Committee

[Ken Smith]

Paul:

If you compile a list of desired measurement items, I am sure we could find well qualified folk, divide the list up and work on smaller pieces.  This way, we can eat the elephant a bite at a time.  Then the drafts would need to go to the technical committee for concurrence.

Tech committee --> Defines items to be recorded
                          --> Provides list

Tech support writers --> Assigned items
                             --> Drafts measurement methods
                             --> provides to Tech committee

Tech committee -->  Circulates among members for review and approval.

Authority of technical committee is as the “official measurers” so vote not required.

Ken

[Paul Goodwin - US 46]

As the normal day-to-day discussions proceed within the Technical Committee, the usefulness of a "Measurement Handbook" becomes more and more evident.  Indeed, this manual would be more than useful, it is becoming clear that it is almost mandatory due to the complex Specifications of the DN class, and the trend of builders to construct hardware (hulls, planks, runners, sails, etc) that is very close to either the maximum or minimum dimension allowed.

In the normal context of doing business, tolerances are put in place to allow for the expected range of building error.  As building techniques get more sophisticated, allowing greater control over building errors, it is normal for builders to adjust their average towards one end or the other of the tolerance range to provide some competitive benefit.  However, it is expected that builders will always understand their errors and make sure that the final product remains within the tolerance.

In the DN class, there are builders that will attempt to build at the extreme allowance of the tolerance range.  This practice is fraught with danger.  Some of the Specs are difficult to measure, some have inherent variation, and some are subject to varying interpretations on how to measure. 

The DN Specs generally have a large tolerance on allowable dimensions.  It is expected that a builder will make sure hardware measures within the allowed tolerance range even in the event of difficult measurement techniques, and varying dimensions.

Where the Measurement Handbook will come into play is when there are differing opinions on how to measure a DN, and in difficult measurement situations.  By defining how to measure a Spec, everyone (builder and measurer) will be on common ground.  This is VERY important in order to have fairness in measurement and enforceable Specifications.  I'm stepping up my request for volunteers to help generate measurement techniques for this Handbook.  If you have a good solid understanding of one or more of the Specs and think you can help with this undertaking, please contact me.

Paul Goodwin
IDNIYRA Technical Committee Chairman
email:  webmaster@idniyra.org

[John Davenport]

Paul,

You are correct that anytime you attempt to measure near a spec limit, care must be taken.  This is where a great gage is critical.  It is also imperative that a GR&R, (gage repeatability and reproducibility) study is conducted to access the capability of the gage and how it is used.  Simple Go/No-Go gages are typically a poor gage near a spec limit.  Good gages are a matter of good fixturing, good measurement devices and simple SOP, (standard operating procedure).  Also, it is imperative that some form of calibration is done on the gage and repeated with a schedule based on risk of the gages robustness.  I can help with all these things.  With a little careful planning we can put together a “kit” for measurement that we can with “good confidence” use to measure boats.  Good confidence being the operative part.  When a trophy is on the line, accuracy is essential.  Sign me up…

Regards,

John Davenport US-4961

[Geoff Sobering]

...  It is also imperative that a GR&R, (gage repeatability and reproducibility) study is conducted ...

Spoken like a good 6σ graduate!   

(sorry, I couldn't resist...   all good points for sure)

[Ken Smith]

Having been there a few times, and having built parts and boats, errors can and do creep in.  And no one wants to protest a friend and fellow competitor.  So nothing is consistently fixed at a race.


What are the most often found errors?  In my humble opinion:

1.   The race instructions require stickers on boat components and runners at continental and world championships.  Last few years, no one was checking in the US.

2.  Masts with sticks inside fail to meet the mast balance requirements.  C.3.g and h

"g.When supported at one point in an approximate horizontal position, the mast,
without stays but complete with hardware and halyard in sailing position, must
balance at a point a minimum of 84 inches (2133.6 mm) from the mast base."

"h.A removable internal reinforcement of allowable materials is allowed. This
reinforcement may not be altered, turned or removed during a regatta."

Kentski's masts meet the balance criteria, but do NOT with sticks.  I added two pounds at the tip to make the balance spec.

3.  Carbon in the hull and plank.  Both are prohibited.  Carbon is such an easy reinforcing material, it is natural to try to use some beneath the deck or on corners.  First-time builders beware.  However, carbon used as fittings are specifically allowed by interpretations.  This means a riser on the aft deck, mast ball devices, steering hardware and tubes, etc, all can be of (or reinforced with) carbon fiber.

Interpretations:
"3/18/89: Specification A.25. specifies wood in the fuselage with fiberglass added for
reinforcement only. Carbon fibers and other materials are not allowed. Specification
B.7. specifies wood in the runner plank and fiberglass may be added . Carbon fibers
and other materials are not allowed. Specification D.8. specifies the boom will be of
wood or aluminum. Carbon fibers and other materials are not allowed."

4.  Boom reinforcement in non-aluminum booms.  Tubes in the bolt-rope tunnel and fibers other than fiberglass are not allowed.

"D.8.Boom shall be constructed of wood or aluminum. Fiberglass may be added for
reinforcement only." 

5.  Boom stripe is required.
"D.7.  A 1/2" (12. mm) wide stripe shall be painted around the boom in contrasting color.
Stripe shall be perpendicular to sail tunnel. Forward edge of the stripe shall be 8' 10"
(2692 mm) or less from forward inner surface of mast sail slot projected fairly."

6.  Fastening the ratchet block to the tiller, not correctly.  It must be fastened to the tiller post higher than the tiller.
"H.17.One sheet block shall be installed on the tiller post. This block may incorporate a
one-way feature."
"Interpretations 3/18/89: The tiller post must be located forward of the bulkhead at the front of the
cockpit. The tiller must be attached to the post at a point above the level of the deck.
The sheet block that is installed on the tiller post (Specification H.17) must be
attached to the tiller post at a point higher than the point of attachment of the tiller."

7.  Some dimension of the boat is off just past min or max.  Cockpit length, location of plank.  Location of overhang forward.  Mast step and plank location, mast fore-aft measurement, mast below minimum side-to-side, 

8.  Maximum width, maximum length of cockpit tail. 

A. Fuselage

                               English            Metric
                                 Max Min          Max Min
1.Length overall:        147 141       3733.0 3582.0
2.Beam:               21-1/2 17-1/2     546.0 445.0
11.Stern width at stern: 4     1-1/4     101.0     31.0

[Bob Gray]

Ken,
  I disagree with your interpretation concerning the bolt rope tunnel in a non-aluminum boom. There is nothing wrong with a aluminum bolt rope tube in a wooden boom ( spec. D.4.).
                                                       BOB

[Ken Smith]

Bob: 

I agree, and was sloppy in my writing.

Bolt rope tunnel in a wood boom can be aluminum.  Not plastic.  (I'd like Paul's view on glass tunnel, as glass reinforcement is allowed.)

"B.4.Only one boltrope tunnel is permitted. The boltrope tunnel shall be substantially
straight with boom relaxed. An aluminum boltrope tube is allowed. It must weigh
less than three ounces per foot (280 grams/meter). The internal diameter must be at
least 3/8" (9.5mm). The cross section of the tube is optional."

I know many figure, what-the-heck, a plastic tunnel isn't going to affect my speed (true), works well (true) and it is easy to make (also true).  No one has made an issue of it.  However, one is on thin ice, so to speak, when rules are selectively ignored.  The boom spec could easily read:  "The primary materials shall be wood or aluminum.  Fiberglass reinforcement is allowed.  The boom may be hollow.  A single boltrope tunnel shall be installed.  The boltrope tunnel on a wood boom may be of wood, plastic, aluminum or glass fiber reinforced plastic.

The point of the discussion is not a complaint about booms.  The point is that there are practices on the boats that are not fully consistent with the "letter of the law" and discussions about detailed technical inspection open the door to tightening of the rules and practices on the ice.  Also the sticker-marking of runners and components is lax. 

If you gather data or inspect, you affect the outcome.

My first North American regatta was in Muskegon.  Hull weight was a new rule at the time, and scales were present.  Lots of people were weighing boats.  If there were a technical inspection site at the North Americans, or a pre-race mandatory or voluntary technical inspection  as well as the post-race inspection for gold and silver fleet top finishers, lots of folks, especially newer racers, would likely bring their boats to be inspected.  In the worlds at Estonia, a technical inspector walked the starting line each race, looking for stickers and two-piece masts that were matched and marked.  We don't do that. 

Should we?

[Paul Goodwin - US 46]

My plan is to perform a more comprehensive measurement at this years North Americans.  I also plan to bring my scale to weigh equipment.  It's very accurate, but has a 50lb limit - fine for checking compliance to the specs, but it won't tell people how heavy their overweight hull is.

I would like to allow people to check equipment before the regatta, however this will require some help from other volunteers.  Some volunteer help would be needed from people that know the rules and how to measure.  One thing I'm contemplating is to provide a time for sailors to have their equipment checked, but require a donation of time to help with the measurements for the privilege of having your boat checked.  Seems reasonable to me - if you get your boat checked, you help check the next one...

Any potential volunteers who would donate some time on practice day for this effort please let me know.  This would also be a great time for any volunteers for the post-racing Measurement Committee to get together and coordinate (split up the tasks and do some trial runs).

Paul Goodwin
email: webmaster@idniyra.org

[sailorman]

Hello Gentlemen,

The reason I joined your fine chat group was exactly what Paul Goodwin is trying to create, to find a rule book on how to build a DN ice sailor.

To my person, I am from southern Alberta, far and away from any ice sailing group, the closest would by the Ghost Lake group around Cochrane (about 4 hrs, one way) or the fellows in Montana.

We have a nice lake close by, only 5 minutes by truck and my son and I have done lots of wind surfing. Then came my idea (crazy, so my wife) to build two identical ice sailors for me and my son, because it only is fun if you compete against someone else, even better if it is your own son.

I have had no exposure to ice sailors in any way, but have a good shop and could build one if I had some drawings or spec's.

My first thought was to build this from aluminum tubing but then I read somewhere, that the hull need to be able to float, so i guess alu is out and wood back in?

So, any info or links are welcome,

All the best and cheers,

Joerg Klempnauer, alias sailorman

[Ken Smith]

Sailorman:

Contact Paul Goodwin, and get a great set of plans and instructions.  Add wood and epoxy.  If its your first project, make the bottom more flat, its a little easier.

Or join teh DN association and get a free set of plans with the yearbook.

Also read the archives!  dnamerica.org front page, Follow the link.

Good luck.  Good plan!

Check Jane Pagel for information on sails, or search the web.  Some low durability very low cost sails of tyvek have been done, to get you started.


Ken

[sailorman]

Hello Ken,

Thank you for your reply and I will see what I can dig out. My plans are for building two until next winter, this winter will be to late anyway, unless I go the cheap and fast way, where I did see the 'skimmer' type sailors, what intrigues me a little, specially, where I will not race competition (at least for now).

I have a large stock of sails from 3.2 - 10m/2 with mast and booms, but they are for wind surf boards and with a flexible mast food, one would need to do some fiddling with a mast head suport for the rigging etc., but to sail and to look pretty are two different issues.

Kind regards,

sailorman 

[Ken Smith]

Sailorman:

Whatever moves you.  Check the iceboating.net site, too.  A used DN is the best sailing bargain about, but everyone has to scratch their own itch. 

There is a blocart that uses metal frame and sail.  Others have front seating and windsurf rigs, and other designs about. 

http://www.youtube.com/watch?v=RNfvJEb9foo

I do not know where you are, but after zipping around a lake a while, the urge follows to race.  The number of DNs around holds the market up for resale, as well as making it likely another DN is nearby on whatever lake is frozen. 

Post an ice report and others being there is more certain!

Ken