There's that "one-design" phrase being misused again.

Well you comment immediately proofs that Radius of Gyration is bad measure then.

One can reduce the radius of gyration by the way you decrease and end up with worse performance. One can increase radius of gyration adn also end up with worse performance. This makes this measure a bad to optimize upon. Better to use the real thing : the total moment of enertia.

>>Something like this could happen if the new rules maintained the minimum mast weight unchanged but eliminated the mast tip minimum weight.

It sure could but why would you want to rule against that ? You end up with a worse performaning bad so this will selfregulated itself into oblivion. No class rule needed for that.

Wouter

I still see some misunderstanding in the posts and since engineering jargon confuses people and is not appropriate for the forum I feel obligated to do a better job explaining in terms of concept (no fancy words). This can be done by comparing two imaginary boats that are identical in their shape, volumes and rig geometry. Boat A is the stock Marstrom Tornado built of S-glass and aluminum spars. Boat B is a tornado made out of imaginary stuff that is infinately strong and stiff so it dosen't weigh anything. Say we want to correct boat B so it can race fairly with boat A. One approach might be to fit a single large weight correction on the centerline just aft the beam of boat B and a few inches above the designed waterline. So now boat A and B float on the same waterline and if we pull them through still water they have the same resistance. But are they fairly handicapped? Next boat A is sailed against boat B in a seaway and boat B beats the crap out of boat A. Why? What's the difference? Boat B has smaller radius of gyration with respect to it's three rotational axes: pitch, roll, and yaw (this is the technically correct term in continuum mechanics in this country). The concept here is fundamental to boat design. It is expressed by the sailors intuition to keep weight out of the ends and as low as possible.

Kevin

Mark,
I agree with the points you make. Another thing to consider is that the variability between carbon tubes in terms of weight and stiffness can be quite a bit less than the current alumunum hardware. This is assuming you standardize on one builder using identical prepreg material and layup schedule. Variation in the weights of the Marstrom prepreg platsorms run in the neighboorhood of several ounces for a 284 pound weight. So, we are talking in the nieghborhood of .1% weight variation. This is also the type of results obtained with aerospace composite parts. I suspect this is less than the current tolerance on the aluminum sticks. The goal is to to make sticks with enough similarity that no one has an incentive to shop for multiple masts optimized for crew or wearhet conditions. To do this with composite tubes you almost have to commit to a single builder because even if material an tooling are specified the layup (individual ply orientations) can be manipulated to produce tubes with a wide range pf properties even though they weigh and look the same. Thus, you would also have to specify and control layup schedule. Not a hard thing with one builder but becomes more difficult with multiple builders.

Kevin

Kevin: In the ballot proposal, they do mention some stringent stiffness measurement procedures to make sure the mast has the proper one-design virtues. I guess masts not buildt to the spec. will not be accepted at measurement before competitions.

Kevin,

The best parameter to compare a normal boat and one with less weigth in the extremities is the moment of inertia (around each axis).

Equal boats or masts have the same weight, the same moments of inertia and the same "stiffness". It is simpler then using radius of gyration as a parameter, which only confuses things.

If I understood correctly, the idea is to have a one design mast in order to reduce its price and the work done to tune the rigging. The downside is that it will create an optimum crew weight in the Tornado (for each wind force) and the sails will be more complicated to customize for each crew.

Cheers,

Problem with radius of gyration is as follows :

Lets take your Boat A = the stock Marstrom Tornado built of S-glass and aluminum spars.

Keep your boat B is a tornado made out of imaginary stuff that is infinately strong and stiff so it dosen't weigh anything. This one has a reduced radius of gyration and performs better.

Then we introduce boat C this one is the same as boat B but has a given weight strapped to it dolphin striker pin. As the radius of gyration is defined as "Moment enertia / totall mass" we can say that this boat has a reduced radius of gyration as well ! But we all know this boat to be a worse performer. So the net result is one where the radius of gyration is reduced and the boat performs worse.

In the imginairy case we could strap an very large weight (infinite even) to the pin and arrive at the same radius of gyration as boat B. Naturrally this boat C will have far war performance than boat B because it will be on the bottom of the lake ar form a black hole (different topic)

Point of this example is that a similar reduction in radius of gyration can be had by both increasing and decreasing weight; both leading to better performing and worse performing boats. Radius of Gyration, although technical useable, is therefor a traiterius principle to use.

Moment of enertia calculations don't have this problem and will assign a higher value to boat C no matter what the added weight.

Wouter

Hi Jake,
You bring up an interesting question, "what is one design"?
Is it exactly identical equipment for all sailors within a given class? If so, how do we handle the fact that "people are not one design"? Heavier people make the boat have more drag going through the water; lighter weight people have an advantage with less hull drag. When the wind blows hard, say 15 knots and up, the heavier people have an advantage because they can generate more righting moment and therefore have more sail thrust. Even enough more sail thrust to more than offset their greater hull drag. We all know from experience that lighter weight teams have a speed advantage in light winds and heavy weight teams have a speed advantage in strong winds. Putting non one design people on our class boats has shot a big hole in our one design class objective of having all competitors having the same max boat speed potential on all points of sail in all wind conditions. How do we fix this? What is the best way, the most fair way, to compensate for this inequality?
Let the ideas flow....
Bill

Bill,

In response to the argument that the Tornado class should allow other manufacturers to produce Tornado parts, I was actually trying to point out the difference in the phrases "one design" as defined in the spirit of the Tornado rules and "one manufacturer" that everyone now seems to consider the Tornado. The very context of the phrases indicates that while a "one manufacturer" class can also be a "one design" class, a "one design" class doesn't neccessarily have to be "one manufacturer". I don't interpret any intention for the Tornado to be a "one manufacturer" in the class rules.

However, I agree with you (did I say that?)

Louis, Wouter,
I follow what you are saying. We are trying to describe the same effect but are tangled up in terminology. You have raised enough question for me to go back and check. I have always been under the impression thet RG is defined as mass X moment arm. But from the point of view of the forum, probably nobody else is interested in this and next time I will avoid using any technical words - we all should.

Jake,
What about this "one design problem". How do we compensate for the fact that sailors, people, are not one design and this by itself has a large affect on the outcome of sailboat races???
There seems to be two schemes in place today.
1. One is the factory class where only factory parts are legal. All other parts are illegal. This is a money driven idea and does not inhance one design sailboat racing but is used as an excuse/example of "one design sailboat racing".
2. Another plan is to have all identical boats, masts, etc except for the sails. In this plan all sails are the same size/area but the camber distribution, the shape in the sail, differs. There are full cut sails and medium draft sails and flatter cut sails. The heavier weight teams use the full cut sails because with their greater weight, they are going to bend the one design mast more and therefore their sail must have more luff round. The medium/average weight teams use the medium cut sails and the light weight teams use the flatter cut sails. This plan has shown in many different one design classes over several years that it leads to tighter competition than giving all sailors the same cut of sail.
Let's look at Olympic class sailing and see how "the best", the ultimate sailing classes/contests, do it. If there is a more correct way to handle this problem, surely it is done most correctly in the Olympic sailing contest. When I check on the Star and Soling and Yingling and Tornado and Finn and other Olympic classes, I find that the Laser is the only class requires all sailors to use the same cut of sail. All other classes allow variations in sail cut within some max limits for that class. Who is right? Other large one design classes in the US such as Snipe, Thistle, Lightning, J24, etc all allow variations in sail cut within max sail measurements for that class.
Both of these schemes cannot be more correct. One of them has to be more fair and the other less fair, less correct, in compensating for variations in sailors weight.
We can require the light weight teams to add weight up to the average teams weight and this fixes the light weight teams advantage in light winds. How do we help the light weight team out in heavy weather sailing? To take away their light wind advantage and not fix their heavy weather disadvantage is not fair.
What do we do to get it right???
Bill

Kevin,
The radius of gyration squared equals the moment of inertia divided by the mass. RG**2 = I/m. Therefore I = RG**2 x m. RG is a radius at which if all the mass was concentrated there, it would have the same inertia as arrived at by integrating (r**2dm)of the body over its entier length.
Bill

Kevin,
Now you are really confusing me. You are saying that the variation in Tornado platform weight is several ounces out of 284 pounds or about 0.1%, one tenth of one percent. That platform is made up of two composite hulls, some fixed rigging and two aluminum beams 10ft long each. These aluminum beams are extrusions. They seem to be very consistent in weight and therefore other properties. Why is it that the extruded beams can be so consistent and yet the extruded masts are out of control??? The company that manufacturers the carbon mast also manufacturers the aluminum mast. The only company that manufacturers the carbon Tornado mast is the company that is partitioning the class officials to change to the carbon mast. Is the fox in the chicken coop??? Other classes have no problem extruding aluminum masts by the hundreds that are identical. If the Tornado class has a problem doing this, maybe they need a new aluminum extruder with better quality control.
There is one other important point relative to the carbon mast. Carbon sands very very easy, cuts fast. Sandpaper cuts carbon like crazy. What is to keep a carbon mast owner from sanding his mast to make it bend to fit his weight? If he does is this legal or illegal???
Bill

mastrom quality control allows him to make

285 lbs = 129.105 kg platform within a margin of no more than 0.1% = 0.129 kg = 129 gram or the equivalent of 1 and a halve ronston smart ratchet blocks (the small kind) ? The pre carbo ratchmatic Harken ratchets were 142 grams per single block.

I think this to be a really strong claim. Halve of a plastic coffee cup with resin weights the same 120 grams if not more.

If you spread that out of two hulls of about 15 - 17 sq.mtr. overall surface you would add a film of only 42 micrometers = 1/600 of an inch.

And the funny part is that people can easily differ by some 5-10 kg's per person or 50 - 100 times the margin that Mastrom gives his boats. What is the use ? That is a whole lot of accuracy for nothing.

Better still is one of the sailors decided to take a cup of coffee for the race, as Mitch did at the 2004 F18 worlds, than that crew would allready by 2 times the marstrom margin overweight. No wonder Mitch finished 15th in that race. (joke). A pair of sunglasses weight 100 grams or more

Wouter

Bill: I dont know about the quality control on the Marstrøm masts, but generally Marstrøm has _very_ good quality control. As I know Gøran, he has done his best to get mast extrusions with identical physical properties. Gøran seems to be doing quite good business supplying alu. masts. 500K EUR is real money spent on masts since the new rig.

Regarding sanding the proposed carbon mast: There are a whole new regime of measurements to be taken with regards to stiffness. These rules are designed to weed out masts with differen properties than the one design mast.

As Mr. Granfield wrote, the RYA has developed a propetiary alu mast that measures in under the current rule. This mast is used by the very succesful british team. He wrote quite a lot about why he was not happy to spend money buying a new alu. mast.

Interresting times...

Hi Rolf,
I know Marstrom tries to do his very best and his very best is very good. That is why there is only one Tornado manufacturer now. He is not in the extrusion business. Some company extrudes masts for him. Marstrom is not in control of the mast extrusion quality although he can reject masts upon inspection.
Aluminum shapes, tubes,angles,flat bar,T bar, all kinds of special shapes are extruded all around the world and done so very consistently. The aluminum Tornado mast should be no exception.
I remember from my SC days, initially we had a problem breaking the mast extrusion die at the part that formed the sailtrack. A diemaker advised a slight change in the internal shape of the track and no more breakage of dies. There is a little art in the die making and extrusion business/process.
I remember reading not too long ago about a new aluminum alloy that is superior to the 6061T-6 aluminum alloy commonly used for sailboat masts. It is both stronger and lighter in weight. It is used in the commercial aircraft business, airliners, and is making a significant increase in aircraft range. If the Tornado class is going to make a change, this new alloy should be investigated for all their extrusions.
The situation of the Finn class carbon masts is scary. I'm sure before they started building carbon masts, the situation was thoroughly investigated and the conclusion was that the carbon mast was the best answer. Now the class has a big mess on its hands. I'm sorry to learn this. It hurts the Finn class and Olympic sailing.
Bill

Well, I dusted off the textbooks and the right term for what I have been trying to express is "polar moment of inertia". In my case I confused the term with RG. The polar moment is a different mathematical expression from what is commonly called "moment of inertia". So, we are all guilty of using less than accurate terminology.
The assertion that Tornado hulls have very little weight variation came from a 1996 article in Cat Sailor magazine that was describing preparation for the Olympics in Savannah. The measurer stated he was surprised that weights of the Marstrom boats only varied a few ounces. But, if the measurer's claim is still suspect, there is data from many other composites applications. For instance, carbon helicopter blades completely out perform aluminum and have better tolerances on both weight and stiffness.
It would not be practical to alter a carbon stick by sanding it. You could not remove material with enough uniformity to achieve any desired end result. Whatever you ended up with would be sheer luck. If someone really wanted to cheat, it would be much more feasible to chemically mill an aluminum tube than sand a carbon one.
There is a potential problem with measuring stiffness as a way to ensure consistency. This is because even if stiffness of both the major and minor dimensions were measured, games can be played by altering ply lay up alter stiffnesses in other orientations. What makes the unidirectional fiber such a flexible material to design with becomes a liability when trying to assure exact properties from one builder to another. To remove variation in composite sticks it drives you towards a single builder. I reserve judgement whether this is good or bad. It's certainly not in the spirit of the original Tornado rules but then the current aims of the class are different.

Well,

It is also known.

I(polar) = I(axis 1) + I(axis 2)

So I(polar) is nothing more than the sum of I(axis 1) + I(axis 2) where the two axis are perpendicular.

Of course with a mast the I(y-axis) is very small compared to I(x-axis) ; a ratio of 1 to 30,000. So it is very convenient approximate masts (the thing we wre initially talking about) by calculating only I-(x-axis). In short Ipolar of the mast is very closely approximated by I(x-axis) alone.

In basis you are right however. I(polar) is the thing you need to do math on rotations dealing with the whole platform. However for dive decelleration calculations you'll need I(x-axis) again and not I(polar).

Things are getting easier by the post aren't they.

As Radius of Gyration was not incorrect in the strickt sense but a it is a confusing expression to use.

may point was however than reducing mast weight by a factor of 2 reduces the polar moment of the mast by 2.0000333 when looking at rotational oscillations. For decelleration dives only one of the normal moment of enertias is involved and this is reduced by 2. This is only for the mast and the total of I(polar) is determined by many components INCLUDING for example the crew itself especially when far away from the main beam. The overall net effect of reducing the weight of the mast by a factor of 2 can have a net result of about 5-15 % overall depending on several factors

I think ths wraps it up nicely for all of us.

Wouter

It seems the construction/manufacturing tolerance is why the sailors have found masts with different stiffnesses. Skiffness of the mast is a function of dimensional properties and physical properties.

Aluminum dimensional properties will vary http://www.almag.com/tolerances.htm
Yes, you can reject masts, but at what cost?
In the manufacturing world no one likes their product to be rejected.
What dimensional tolerance are the sailors willing to pay for?

For aluminum physical properties, to my expensive/suprise I have found the Modulus of Elasticity (Young's Modulus) for one sample of aluminum alloy 6063-T6 to be 9 msi, when it is supposed to be 10 msi (10 percent difference) How is this possible?

For carbon dimension properties what if someone misses a layup?
How are dimensional properties of carbon mast going to be checked?

For carbon YM I have found it can vary from 30 msi to 100 msi.
Someone could accidentally ship 40 msi carbon fibre.
How is carbon YM going to be monitored?


Rather than the TRADITIONAL quality control of the dimensional and physical properties of each mast to decide weather to accept or reject it; use the RESULTS OF the above properties AND field measure the deflection/stiffness by placing a weight. (I don't think to many extuders would be happy doing this, but you get what you pay for)
Some type of mast rating system could be used; ie, this could be based upon tip or midspan deflection in both major and minor axis.
Again, measuring the RESULTS OF the manufacturing process, after all the sailors are interested in the results/stiffness not the thickness or YM. (provided of course is it properly designed for bending and shear)
The resulting measure of mast stiffness could then be catalogued to crew weight (but how many catagories is another thread)

The most important thing is to have a sail and mast that make a good combo.

Most differences between masts, I'm told, can be taken out of the equation by measuring your mast bend characteristics and order a mainsail to fit your mast.

Ordering custom sails for a given mast flexing is standard stuff with many sailmakers. The testing itself takes two saw horse a bucket able to hold 20 litres of water and about 2-3 hours of your time.

Also I would like to add that an oddset need not be the same over the full length of the mast. Meaning inconsistancies can wave over the full length of the mast and average themselfs out a bit as a result.

I personnally think it to be cheaper if the class collects the batch of produced mast and puts in a day of measuring each mast and marking each mast with the basic characteristic. The sailors can then request their perferred mast section and only pay for one mast. This is always inmensely cheaper than everybody getting carbon and due to the normal distribuation of crew weigths and sailing style all masts will be sold. Remember that the off sets of the mast themselfs , as a result of a natural proces, has a normal distribution as well. I think people familiar with Random variables ar familiar with the term "normal distribution"

At least it is this approach that I think I will propose in my class when the differences between mast proof to be to great to be acceptable. We are already sharing mast stocks between builders.

I think it would be a small feature for either the Tornado class or the marstrom yard to perform this trick as well.

Would leave everybody happy and keep cost down. That is unless other reason lead to the decision to go for carbon.

Wouter