older mast vs. newer mast
- Thread starter emilebr
- Start date
Rob B
Well-Known Member
Some people at the highest levels of our sport believe that some top/bottom sections are stiffer than others and use them in different wind conditions. As for the rest of us, if you have straight mast sections old or new those are the ones you should use.
Mullet Time!
Member
The only reason i use a new top section is because i broke my older one. I have heard tho that the old sections are better
GeoffS
Member
I'm in the "100 kilo club" and like to sail in high wind, so I'm living in deathly fear of breaking my older top section and having to replace it with one of the newer (and apparently much more fragile) ones - again, and again, and again... 
Cheers,
Geoff S.
Cheers,
Geoff S.
David
New Member
I bought an old laser (1975) for $300CAN just for the spars...I definetly like the older spars much better because of their strength.
Hi,
Older seems to be better, strength wise. My experience includes 148469, a '94 boat. I've had many boats, from 1041 on, and race 66451 now. I never yet (knock on wood) had a bent/broken spar. That's gotta be very slow! And I would hate to rip a nice sail, due to the spar, or trash it by sailing home with a "gaff rig" (did that in a J24, ugh).
I just bought a spar set from a '93 whose hull was destroyed, and will keep them as spares. Judging from what we hear on hear and on the race course, any spar from 168xxx on is pretty suspect.
I'm sure the super techies will prefer newer (presumably softer) spars for a lightweight, as it will bend "off" in a blow/puff. See the Olympic pics of Ben Ainsley(CF mast on a Finn) in heavy air to see what I mean. I wonder how many Laser spars bent in Greece?
Al Russell 66451
Older seems to be better, strength wise. My experience includes 148469, a '94 boat. I've had many boats, from 1041 on, and race 66451 now. I never yet (knock on wood) had a bent/broken spar. That's gotta be very slow! And I would hate to rip a nice sail, due to the spar, or trash it by sailing home with a "gaff rig" (did that in a J24, ugh).
I just bought a spar set from a '93 whose hull was destroyed, and will keep them as spares. Judging from what we hear on hear and on the race course, any spar from 168xxx on is pretty suspect.
I'm sure the super techies will prefer newer (presumably softer) spars for a lightweight, as it will bend "off" in a blow/puff. See the Olympic pics of Ben Ainsley(CF mast on a Finn) in heavy air to see what I mean. I wonder how many Laser spars bent in Greece?
Al Russell 66451
Around here we break masts like match sticks, so almost everyone uses newer masts. i find the harder our team sailed the more we broke so eventualy you wont be able to find old ones any more.
A little advice i got from wickid sailor was to always tape the coller of your top section, because the tighter it fits into the bottom then the more evenly the weight is spred out onto all the aluminum......... this is especially important for older spars and new north american ones
A little advice i got from wickid sailor was to always tape the coller of your top section, because the tighter it fits into the bottom then the more evenly the weight is spred out onto all the aluminum......... this is especially important for older spars and new north american ones
LooserLu
LooserLu
Hi, just came back from a short vacation from the Netherlands (lots of rain, lots of wind, lots of waves this year I had there). I use an old Laser(-hull) that is from 1977. The Spars (I use both: old-fashioned Radial and Standard) are from 1981-1989 "mixed".
I don´t had any problem with the quality of this Spares concerned the bending. The old boom has no sleeve and works fine (I use Shevy´s Outhaul/Cunningham-systems). Only the length of the old-fashioned (-halyard-) Radial-lowermast is not correct, compared to the measurement diagram from now. It is longer, maybe in reason of that old haleyard-design, but in strong winds this mast-part also holds good (I use a selfmade 15:1 Vang etc.).
Ciao
LooserLu
I don´t had any problem with the quality of this Spares concerned the bending. The old boom has no sleeve and works fine (I use Shevy´s Outhaul/Cunningham-systems). Only the length of the old-fashioned (-halyard-) Radial-lowermast is not correct, compared to the measurement diagram from now. It is longer, maybe in reason of that old haleyard-design, but in strong winds this mast-part also holds good (I use a selfmade 15:1 Vang etc.).
Ciao
LooserLu
I discovered some differences between spars too. I've an older boom from a 150-number laser and a newer boom, the same for the upper mast. And I noticed that there was much difference in the weight of the spars. Does anyone know if that's normal? Did they change something to the spars, not only the weight but also the length of a lower mast of a radial rig? And what is better? Heavier or lighter? Or does it depends to the weather?
Emile and Teeftie,
Good info, almost. We need to be more specific to figure this one out.
For instance Emile's 150-number is 150xxx we assume, vs. 150xx. I had 148469, and I believe that the boom had a sleeve added later, as standard equipment, which could explain the weight gain? if it's a gain you are talking about? Or is it lighter? we can't tell from what we have here. A lighter/newer boom? I never heard that one before...
A lighter top section, though suspected, is news to this thread. Did you weigh it? Or are you just pretty sure? I have sold very old stuff in the barn, that we can compare, if we had specifics.
Teeftie? do you break tops?, bend tops, bottoms, radial bottoms, "like match sticks"? I agree with your point, however, that oldies get comsumed. I scrounge all over, thanks to the internet.
Let's try to get some useful info on here, if you don't mind (s'il vous plait)? Otherwise, this is just another "rant" board, that Vanguard and PS will ignore, I believe. So, please be specific, and supply known facts.
Al Russell 66451
Good info, almost. We need to be more specific to figure this one out.
For instance Emile's 150-number is 150xxx we assume, vs. 150xx. I had 148469, and I believe that the boom had a sleeve added later, as standard equipment, which could explain the weight gain? if it's a gain you are talking about? Or is it lighter? we can't tell from what we have here. A lighter/newer boom? I never heard that one before...
A lighter top section, though suspected, is news to this thread. Did you weigh it? Or are you just pretty sure? I have sold very old stuff in the barn, that we can compare, if we had specifics.
Teeftie? do you break tops?, bend tops, bottoms, radial bottoms, "like match sticks"? I agree with your point, however, that oldies get comsumed. I scrounge all over, thanks to the internet.
Let's try to get some useful info on here, if you don't mind (s'il vous plait)? Otherwise, this is just another "rant" board, that Vanguard and PS will ignore, I believe. So, please be specific, and supply known facts.
Al Russell 66451
The old uppermast (from laser 152448) was heavier than the newer upper mast (from laser 160784, not much used). I'm very sure, because I could really feel it, and my father too (a second opinion). I'm not sure about the differences from the boom. The old upper mast has a little bend. The 160784 is a Performance Sailcraft laser, but I'm not sure about the 152448 (was a laser from the previous owner of my masts), but I suppose it was a performance sailcraft laser, because the owner was from Belgium (and lives in Belgium). I can't imagine that after much use the weight of a mast will increase.....
LooserLu
LooserLu
”....Let's try to get some useful info on here, if you don't mind (s'il vous plait)? Otherwise, this is just another "rant" board, that Vanguard and PS will ignore, I believe. So, please be specific, and supply known facts.
Al Russell 66451”
Hi Al,
since several days I think about your words. How we can get a basis to talk in a more objective, scientific way.
Of course, engineers have methods for this to offer.
For the upper mast we can use the deflection (in reason of the total load from weight plus a definite point load) in the meddle of that bar. For this, we have to decide about an arrangement of the test (keeping the ends ot the bar “hold free”(not: “clamp fix”) like an element of a bridge, the bar lies horizontal):
.......|
.......v
_________
^...........^
From the measured deflection we can calculate back to the so called “modulus of section” (“Young´s modulus” “E” multiplied with “the moment of inertia” “J” -> “1/(EJ)” like engineers say). “EJ” could be a measure for the productional-quality of that tested bar, if this solution is analysed in relationship to other, same, tests with other upper masts.
To minder the influence of temperature (-elongation of the bar), we have to define a test-temperature (in the air / of the bar) that must be there.
We have to take in consideration, that there is not only bending in reason of normal bending-moments, we have also moments from the prestressing-force “Cunningham”. Both, the stress in reason of bending and prestressing, make the uppermast to get the form of a banana. But to include the cunnigham will be 2 difficult - our test-modell should be easyer
Of course the point-load and the test have to be described exact (equal for every test) to get the solutions comparable. We can not measure the influence of the fatigue of the aluminium-tube in reason of the swings it got in the time before the test is done (trivial solution: the mast is new). And we can not measure the influence of the not-equalness of the cross-sectional-area of the tested bar (inside: in reason of production and outside: damaged surface of the bar). Also the influence of different earth-acceleration is not practical measurable.
The same we can do with the boom, but we must decide how 2 handle the influence of the (probably different fittings of the vang and the blocks, the camcleat). A problem will be the influence of the maybe existing inner sleeve in the boom.
The under-mast we can fix like a mast for a banner (f.e.: the Laserhull-maststep). Then we put a define shear-force to the upper end of this mast-bar and measure the deflection of the bar compared to the unload shape. From this we can calculate back also to the modulus of section. Problem is the influence of the gooseneck- and vang-fitting and the influence of the inner sleeve, if a Radial under-mast is tested.
What I´m talking about, you need not to be an engineer, the calculation can be done online + the mathematics for “calculation back” is an “old hat” and stands in every good book for technical architecture.
With such tests (if we have enough tries/numbers at least), we can get objective numbers about the lower/better quality of the spars. But I think the out-of-the-box-boat-builders find 1 mio reasons to not accept this tests…
Have I forgotten something Al?
Ciao
Ludwig/LooserLu
Al Russell 66451”
Hi Al,
since several days I think about your words. How we can get a basis to talk in a more objective, scientific way.
Of course, engineers have methods for this to offer.
For the upper mast we can use the deflection (in reason of the total load from weight plus a definite point load) in the meddle of that bar. For this, we have to decide about an arrangement of the test (keeping the ends ot the bar “hold free”(not: “clamp fix”) like an element of a bridge, the bar lies horizontal):
.......|
.......v
_________
^...........^
From the measured deflection we can calculate back to the so called “modulus of section” (“Young´s modulus” “E” multiplied with “the moment of inertia” “J” -> “1/(EJ)” like engineers say). “EJ” could be a measure for the productional-quality of that tested bar, if this solution is analysed in relationship to other, same, tests with other upper masts.
To minder the influence of temperature (-elongation of the bar), we have to define a test-temperature (in the air / of the bar) that must be there.
We have to take in consideration, that there is not only bending in reason of normal bending-moments, we have also moments from the prestressing-force “Cunningham”. Both, the stress in reason of bending and prestressing, make the uppermast to get the form of a banana. But to include the cunnigham will be 2 difficult - our test-modell should be easyer
Of course the point-load and the test have to be described exact (equal for every test) to get the solutions comparable. We can not measure the influence of the fatigue of the aluminium-tube in reason of the swings it got in the time before the test is done (trivial solution: the mast is new). And we can not measure the influence of the not-equalness of the cross-sectional-area of the tested bar (inside: in reason of production and outside: damaged surface of the bar). Also the influence of different earth-acceleration is not practical measurable.
The same we can do with the boom, but we must decide how 2 handle the influence of the (probably different fittings of the vang and the blocks, the camcleat). A problem will be the influence of the maybe existing inner sleeve in the boom.
The under-mast we can fix like a mast for a banner (f.e.: the Laserhull-maststep). Then we put a define shear-force to the upper end of this mast-bar and measure the deflection of the bar compared to the unload shape. From this we can calculate back also to the modulus of section. Problem is the influence of the gooseneck- and vang-fitting and the influence of the inner sleeve, if a Radial under-mast is tested.
What I´m talking about, you need not to be an engineer, the calculation can be done online + the mathematics for “calculation back” is an “old hat” and stands in every good book for technical architecture.
With such tests (if we have enough tries/numbers at least), we can get objective numbers about the lower/better quality of the spars. But I think the out-of-the-box-boat-builders find 1 mio reasons to not accept this tests…
Have I forgotten something Al?
Ciao
Ludwig/LooserLu
GeoffS
Member
Ah, a topic close to my heart! In the DN iceboat class the bend of the mast and runner-plank are the primary component of boatspeed:LooserLu said:
Measuring mast-flexibility is a critical part of tuning a DN. There is a great article on the procedure I like on the IDNIYRA.org web-stite (under "Articles"), but for some reason the site is down right now, so I can't find the link. The basic procedure is to hang a series of increasing weights and measure the deflection caused by each one. Then you plot the data-points and fit a line through them. The slope of the line is the spring constant of the object (lbs/inch or kg/cm), which it really the stiffness.
As Lu points out, measuring a uniform tube is pretty easy (i.e. the upper mast section). Setup two saw-horses, support the mast at each end and hang some weight in the middle (I use bags of water-softener salt, but anything will do). You can either measure the deflection to the ground, or pull a string taught between above the spar and measure from there.
Measuring the lower mast will be tougher. I believe the full-rig is a uniform tube (ignoring the vang & gooseneck), so a pretty good measurement could probably be made using the above technique. For the Radial and 4.7 rigs somethig like Lu's suggestion of supporting the mast like it is in the hull, and hanging weights off the end would probably be necessary.
I'll try and take some measurements of my (older) top section and post the data and some photos in the next few days to see if it will work.
Cheers,
Geoff S.
Today I've been to the sailing club, and I compared the booms. The newer boom feels much more massive than the older one. So I think I made a little mistake: there is difference between the booms and maybe not between the uppermasts. So maybe I have mistaken those. Wednesday I will go to the club again, and then I will compare the uppermasts (one is at home, the other is there). Maybe there's no difference between the uppermasts......
LooserLu
LooserLu
Emile,
don´t think only about the wight alone. Geoff is absolutely right.
Take the upper masts and try to fix them like Geoff told. put a point load to the middle (not too much, just only that the tube bends a bit / some 1 to 2 cm deflection is enough, we want to test the "homogen-elastic" bending-area ["Hooke-area", for the expert]); measure the outer and the inner diameter of the tube of the mast (for that you have to put one of the plugs of the mastube away and take a micrometer-instrument) measure the exact distance between the saw-horses (better try to put them nearly exact to the ends if you can and then you can take the length of the tube as distance), where the tube lies on in the bending test; wight the ballast you load on the meddle of the tube and before wight the tube, of course.
I do the same at the next weekend with my uppermast.
The mathematics for calculation I can get from my technical-dictionary. I only need some time, please
,thanks.
We make the test easier and define: the temperature (of the tube) has no influence, scratches etc. have no influence.
We are not at the MIT/Berkley/Stanfort-university with its top equipement
We just make a first try, to get a first answer about the question, is there any "significant" difference or not. Can we do smething like AL adviced - only with our on-the-boat-equipement.
I think, we should try to get easy tests, so that everyone, who can screw a screw, should be able to do this test. I also think, we should (first) forget about fittings of the undermast and we should take the standard undermast, because it is much easier to calculate.
Is someone here an expert in statistics ( "Zero-Hypothesis / Alternatives" Tests etc. f.e.)? - We will need this stuff to make a correct answer very later on.
If I forgot something, please add it, thanks!
Ciao
Ludwig
don´t think only about the wight alone. Geoff is absolutely right.
Take the upper masts and try to fix them like Geoff told. put a point load to the middle (not too much, just only that the tube bends a bit / some 1 to 2 cm deflection is enough, we want to test the "homogen-elastic" bending-area ["Hooke-area", for the expert]); measure the outer and the inner diameter of the tube of the mast (for that you have to put one of the plugs of the mastube away and take a micrometer-instrument) measure the exact distance between the saw-horses (better try to put them nearly exact to the ends if you can and then you can take the length of the tube as distance), where the tube lies on in the bending test; wight the ballast you load on the meddle of the tube and before wight the tube, of course.
I do the same at the next weekend with my uppermast.
The mathematics for calculation I can get from my technical-dictionary. I only need some time, please
,thanks.We make the test easier and define: the temperature (of the tube) has no influence, scratches etc. have no influence.
We are not at the MIT/Berkley/Stanfort-university with its top equipement
We just make a first try, to get a first answer about the question, is there any "significant" difference or not. Can we do smething like AL adviced - only with our on-the-boat-equipement.
I think, we should try to get easy tests, so that everyone, who can screw a screw, should be able to do this test. I also think, we should (first) forget about fittings of the undermast and we should take the standard undermast, because it is much easier to calculate.
Is someone here an expert in statistics ( "Zero-Hypothesis / Alternatives" Tests etc. f.e.)? - We will need this stuff to make a correct answer very later on.
If I forgot something, please add it, thanks!
Ciao
Ludwig
LooserLu
LooserLu
Hi all,
here is the description of the stiffness-test I have promised you last week.
http://www.laserforum.org/attachment.php?attachmentid=41&stc=1
In figure 1 of the picture (please go to the link) above are sketches, that describe all that what is to difficult for me to tell in words.
We search for the “Young´s Modulus” “E” in the unit “Mega-Newton per Square-meter [MN/m²]” that is the angle of the line in the graph of the tension/stretch-diagram (see figure 2).
We have (* =Symbol of multiplication):
- length = l (in Meter m) = distance between the saw-horses (not the full-length of the upper-mast)
- Test-Force = F (in kilopond=kilogram) including the weight for it´s fixing-stuff
- Wight of the upper-mast G= q*l (in Kilopond=Kilogram)
- Acceleration of the Earth “g” = 9,81 in the unit “Meter/Second/Second”, to keep the Forces G and F from the unit Kilogram to the unit Newton “N” [1N=kg*m/s/s]
- Outer diameter of the tube of the upper-mast measured with a micrometer-instrument = D (in Meter)
- Inner diameter of the tube of the upper-mast measured with a micrometer-instrument = d (in Meter)
- pi = 3,1415926…. (has no unit)
- measured deflections “f”, “f1”, “f2” (in Meter)
- Moment of Inertia “J” (in Meter*Meter*Meter*Meter) for the upper-mast
J= „pi“/64*((D*D*D*D)-(d*d*d*d))
We define:
E, J, g are constant (which are not constant in reality)
Temperature (of the mast and the air) has no influence and is about 20 degrees Celsius
The former swings of the mast-part has no influence to the stiffness of the tested bar (which has in reality).
The bar reacts full-elastic (which does not in reality reacts full-elastic), like a spring, and the deflection is low (-> Conditions like the “Sentence of Hooke”, for the Experts) and at least:
For all this conditions named above: the measured deflections at the mast can be added. “f=f1+f2”
Formulas of the bending of a bar:
f1= 5/384/E/J*G*g*l*l*l in reason of case "weight" and
f2= 1/48/E/J*F*g*l*l*l in reason of case point-load in the mit of a bar.
(This Formulas come from a book of technical Architecture and are known worldwide in civil-engineering)
Solution for getting the “E”
We know: f= f1+f2
This is the same like
f = f1+f2 = 5/384/E/J*G*g*l*l*l + 1/48/E/J*F*g*l*l*l
This is the same like
f = f1+f2 = g*l*l*l/E/J*((5/384*G) + (1/48*F))
This is the same like
E = g*l*l*l/J/(f1+f2)*((5/384*G) + (1/48*F))
This is the same like
E = g*l*l*l*64/pi/((D*D*D*D)-(d*d*d*d))/(f1+f2)*((5/384*G) + (1/48*F))
Now put all the other information’s in to that term
E = 9,81*64/pi*l*l*l/((D*D*D*D)-(d*d*d*d))/(f1+f2)*((5/384*G) + (1/48*F))
This Formula we use for calculation.
Put your measured D,d,f1,f2,G,F and pi (“pi” you normally have on your calculator somewhere, or say it is “3,1415926”) into that last term and do the calculation.
What you get is the sum of “E of the upper-mast” in the unit “Newton per Square-meter”. The engineers like to say this sum in “Mega-Newton per Square-meter” (MN/m²). So, you divide your sum with 1000000 (this is “10^6”). 1 “Newton” “N” has the unit “Kilogram*Meter/Second/Second”.
I got these following results from my test:
G = 2,52 Kilogram
F = 4,60 Kilogram
l = 3,55 Meter
D = 0,0505 Meter
d = 0,0471 Meter
f1= 0,004 Meter
f2 = 0,0115 Meter
I got for “E” the sum E = 46895 [NM/m²].
Like Geoff said already, it is better to let the test-force “F” increase by a step:
I put another 2,69 kg to the bar: F = 4,6 kg + 2,69 kg = 7,29 kg and got a new “f2” that I measured with f2 = 0,0185 Meter.
I did the calculation again and got an E= 46378 MN/m².
At least, I have done the calculation without any other additional loads (means: f2=0) than the weight of the bar and I got an E = 46349 [MN/m²]
The different sums of E come from the mistakes in the measurements. Especially not exact possible measuring D and d, but also f1 and f2 makes the sums to become different. For example: if I had measured, that the f2 would be 0,0117 Meter instead of 0,0115 Meter, I would become an E = 46297 NM/m². That would better fit to the other E´s. But it is impossible for me to measure such exact.
And it is not correct to analyse in such exact way to the solution, because many other factors, that we defined to be constant, for real are not constant and have more influence to the result and makes the real solution different to our measured sum. But I think I can say that the “E” (= “measure for the stiffness of my upper-mast” is about 45000 to 50000 MN/m².
And if you, out there, do in the same way, we could compare our sums and get a more specific answer to our problem with the stiffness of the Laser-spars is my opinion.
Of course the out-of-the-box-boat-builders laugh at this, but maybe some other Laserite (Student, Assistant or Professor, this makes no difference to me) that can use testing-instruments in a test-laboratory at their good technical-universities and makes some exacter studies about that
I bet, the laughing in the faces of the out-of-the-box-boat-builders will pass-through/wear-off in their faces.
And the least I mean not bad, but more constructive
If you do this test, try to get the measured numbers very exact. Take time for this and measure twice or more.
You can use this test also for the boom, but know, that a sleeve in the boom makes the solution incorrect. Also the fittings on the boom have influence to your results.
For the under-mast-section (standard we can do such test also. The deflection “f” (you have to measure) has the formula f = F*g/3/E/J*l*l*l (F in the unit “kp=kg”) with J= pi/64 ((D*D*D*D)-(d*d*d*d))
For this test put the mast into thee maststep and fix the mast, that it get exact vertical (then the weight of the mast has nearly no influence to the results of bending). Put a known test-force to the top of the under-mast. Measure l which is the distance between the point, where the Force F come to the mast and the beginning of the maststep. Measure D and d also. Transform the term for f in this way, that all you have measured stands right and E stands left side of the symbol for equal “=”. Do not forget to divide the result with 1000000 to get the unit MN/m² for the E.
Maybe someone is fit in programming and put the terms into a little program and make it online to the web – would be nice.
Cheers and happy testings
LooserLu
here is the description of the stiffness-test I have promised you last week.
http://www.laserforum.org/attachment.php?attachmentid=41&stc=1
In figure 1 of the picture (please go to the link) above are sketches, that describe all that what is to difficult for me to tell in words.
We search for the “Young´s Modulus” “E” in the unit “Mega-Newton per Square-meter [MN/m²]” that is the angle of the line in the graph of the tension/stretch-diagram (see figure 2).
We have (* =Symbol of multiplication):
- length = l (in Meter m) = distance between the saw-horses (not the full-length of the upper-mast)
- Test-Force = F (in kilopond=kilogram) including the weight for it´s fixing-stuff
- Wight of the upper-mast G= q*l (in Kilopond=Kilogram)
- Acceleration of the Earth “g” = 9,81 in the unit “Meter/Second/Second”, to keep the Forces G and F from the unit Kilogram to the unit Newton “N” [1N=kg*m/s/s]
- Outer diameter of the tube of the upper-mast measured with a micrometer-instrument = D (in Meter)
- Inner diameter of the tube of the upper-mast measured with a micrometer-instrument = d (in Meter)
- pi = 3,1415926…. (has no unit)
- measured deflections “f”, “f1”, “f2” (in Meter)
- Moment of Inertia “J” (in Meter*Meter*Meter*Meter) for the upper-mast
J= „pi“/64*((D*D*D*D)-(d*d*d*d))
We define:
E, J, g are constant (which are not constant in reality)
Temperature (of the mast and the air) has no influence and is about 20 degrees Celsius
The former swings of the mast-part has no influence to the stiffness of the tested bar (which has in reality).
The bar reacts full-elastic (which does not in reality reacts full-elastic), like a spring, and the deflection is low (-> Conditions like the “Sentence of Hooke”, for the Experts) and at least:
For all this conditions named above: the measured deflections at the mast can be added. “f=f1+f2”
Formulas of the bending of a bar:
f1= 5/384/E/J*G*g*l*l*l in reason of case "weight" and
f2= 1/48/E/J*F*g*l*l*l in reason of case point-load in the mit of a bar.
(This Formulas come from a book of technical Architecture and are known worldwide in civil-engineering)
Solution for getting the “E”
We know: f= f1+f2
This is the same like
f = f1+f2 = 5/384/E/J*G*g*l*l*l + 1/48/E/J*F*g*l*l*l
This is the same like
f = f1+f2 = g*l*l*l/E/J*((5/384*G) + (1/48*F))
This is the same like
E = g*l*l*l/J/(f1+f2)*((5/384*G) + (1/48*F))
This is the same like
E = g*l*l*l*64/pi/((D*D*D*D)-(d*d*d*d))/(f1+f2)*((5/384*G) + (1/48*F))
Now put all the other information’s in to that term
E = 9,81*64/pi*l*l*l/((D*D*D*D)-(d*d*d*d))/(f1+f2)*((5/384*G) + (1/48*F))
This Formula we use for calculation.
Put your measured D,d,f1,f2,G,F and pi (“pi” you normally have on your calculator somewhere, or say it is “3,1415926”) into that last term and do the calculation.
What you get is the sum of “E of the upper-mast” in the unit “Newton per Square-meter”. The engineers like to say this sum in “Mega-Newton per Square-meter” (MN/m²). So, you divide your sum with 1000000 (this is “10^6”). 1 “Newton” “N” has the unit “Kilogram*Meter/Second/Second”.
I got these following results from my test:
G = 2,52 Kilogram
F = 4,60 Kilogram
l = 3,55 Meter
D = 0,0505 Meter
d = 0,0471 Meter
f1= 0,004 Meter
f2 = 0,0115 Meter
I got for “E” the sum E = 46895 [NM/m²].
Like Geoff said already, it is better to let the test-force “F” increase by a step:
I put another 2,69 kg to the bar: F = 4,6 kg + 2,69 kg = 7,29 kg and got a new “f2” that I measured with f2 = 0,0185 Meter.
I did the calculation again and got an E= 46378 MN/m².
At least, I have done the calculation without any other additional loads (means: f2=0) than the weight of the bar and I got an E = 46349 [MN/m²]
The different sums of E come from the mistakes in the measurements. Especially not exact possible measuring D and d, but also f1 and f2 makes the sums to become different. For example: if I had measured, that the f2 would be 0,0117 Meter instead of 0,0115 Meter, I would become an E = 46297 NM/m². That would better fit to the other E´s. But it is impossible for me to measure such exact.
And it is not correct to analyse in such exact way to the solution, because many other factors, that we defined to be constant, for real are not constant and have more influence to the result and makes the real solution different to our measured sum. But I think I can say that the “E” (= “measure for the stiffness of my upper-mast” is about 45000 to 50000 MN/m².
And if you, out there, do in the same way, we could compare our sums and get a more specific answer to our problem with the stiffness of the Laser-spars is my opinion.
Of course the out-of-the-box-boat-builders laugh at this, but maybe some other Laserite (Student, Assistant or Professor, this makes no difference to me) that can use testing-instruments in a test-laboratory at their good technical-universities and makes some exacter studies about that
I bet, the laughing in the faces of the out-of-the-box-boat-builders will pass-through/wear-off in their faces.
And the least I mean not bad, but more constructive
If you do this test, try to get the measured numbers very exact. Take time for this and measure twice or more.
You can use this test also for the boom, but know, that a sleeve in the boom makes the solution incorrect. Also the fittings on the boom have influence to your results.
For the under-mast-section (standard we can do such test also. The deflection “f” (you have to measure) has the formula f = F*g/3/E/J*l*l*l (F in the unit “kp=kg”) with J= pi/64 ((D*D*D*D)-(d*d*d*d))
For this test put the mast into thee maststep and fix the mast, that it get exact vertical (then the weight of the mast has nearly no influence to the results of bending). Put a known test-force to the top of the under-mast. Measure l which is the distance between the point, where the Force F come to the mast and the beginning of the maststep. Measure D and d also. Transform the term for f in this way, that all you have measured stands right and E stands left side of the symbol for equal “=”. Do not forget to divide the result with 1000000 to get the unit MN/m² for the E.
Maybe someone is fit in programming and put the terms into a little program and make it online to the web – would be nice.
Cheers and happy testings
LooserLu
Attachments
GeoffS
Member
Here's the URL to the article I mentioned earlier: Measuring Mast Stiffness (DN)GeoffS said:
I haven't had a chance to read Ludwig's last post, but at first glance it looks interesting; I can't wait to take time and check it out in detail.
Cheers,
Geoff S.
49208
Tentmaker
A simpler method may be all that is needed. The method used for Finn masts is about as easy as it gets, and it was enough for us to exchange info and make decent decisions when it was time to buy masts or have new sails made.
There's a good explanation of it here:
https://www.northorder.com/class/finn/finn_mast.html
As far as the amount of weight to use for a Laser mast, it should be enough to put the average mast near max bend (I'll try and measure that in the next day or two). We don't need to worry about side bend numbers like Finn masts, as our section is round.
As far as where to support it, it would be at the butt and where the mast exits the deck.
There's a good explanation of it here:
https://www.northorder.com/class/finn/finn_mast.html
As far as the amount of weight to use for a Laser mast, it should be enough to put the average mast near max bend (I'll try and measure that in the next day or two). We don't need to worry about side bend numbers like Finn masts, as our section is round.
As far as where to support it, it would be at the butt and where the mast exits the deck.
LooserLu
LooserLu
49208 said:
I see some difficulties in the Finn-mast-test.
How do we fix the point-load to the Laser masttop in a way that all, which do the test, make it in the same way?
Measuring another two values means more numbers (advantage), but also more possibilities to measrue wrong.
How do you fix the mast-part in such way like shown on the picture in a way, we all can do it also (angle, fixing-arrangement)? My Laser-mast-part lied on two simple + equal metall-chairs from the garden (with higher back in the exact same hight-the last I made with sheaves, that I put under the legs of that chair, wich was a tiny bit lower first). Measuring of the deflection I´ve done by measuring the hight at the mid of the lenght of the bar at the underside of the bar to the ground (the ground was exact horizontal and very plan -> the hard-pvc-floor of my kitchen) and subtract this from the hight at the end of the bar.
We have to define the distance between point "A" and point "C"/"B" (if not, we all maybe take a bit different distances and got deflections that probably are not exact comparable to other test-results).
Geoff´s test is nearly the same like mine. The analysing is different to my way but it will work, I think.
Bye-bye
LooserLu
One of the guys who sailed for Royal Canadian Yacht Club actually had some notes on this for each year of mast, the thing is not old or new its when exactly it was made, as the dies that they use in the manufacturing get older, it changes the thickness of the wall of the section. eventually they are replaced and it starts over again, I forget what conclusin he came to about the best yearbut its a thought at least. A lot of it depends on your sailing style as well some people like a stiff mast, others like a softer top section with a stiff lower for more power through waves.
Mast flex--overall it's been found that within the (massive)variables in laser spar flex,,,that whatever your weight,,you generally want to find a bottom as flexible as possible and a topsection nearly as stiff as you can-thes balances/shapes the sail the best.
In terms of judging spar flex--it is usually only accurate to compare flex between spars in ONE session,,at ONE time,,,as too many variables come in otherwise--a way around this is to have a sample from one measuring session as a 'sample' to calibrate the next session-so whatever system you use,,it's just a 'comparitive' sample.
with laser spars,you get a reasonable test very accurately and simply,by >>weighing<< your spars,,another method is the 'chime' method ,which is VERY quick,,where you support the selection of spars in a 'like' manner,,and >tap< them,,listening for the sound of each---low tone=heavier,,,high tone=lighter.
a way to extend life of top/bottom spars,is to reverse ends/fittings.You can even do this with a bent spar that you have straightened,as the (potentially)weakened area is move to a lesser load area.--I recommend that the collar on the topsection be 'bonded' in place rather than riveting,,since the rivet weakens the mast substantially--this practice is very simple,but not legal as you would cheat the manufacturers out of many $ over the years!!
If you find one boom substantially heavier than another,,it is because the heavier boom will have a sleeve in it.
Hope this helps!,,and sorry ,no I don't remember examples of light/heavy spar weights.
In terms of judging spar flex--it is usually only accurate to compare flex between spars in ONE session,,at ONE time,,,as too many variables come in otherwise--a way around this is to have a sample from one measuring session as a 'sample' to calibrate the next session-so whatever system you use,,it's just a 'comparitive' sample.
with laser spars,you get a reasonable test very accurately and simply,by >>weighing<< your spars,,another method is the 'chime' method ,which is VERY quick,,where you support the selection of spars in a 'like' manner,,and >tap< them,,listening for the sound of each---low tone=heavier,,,high tone=lighter.
a way to extend life of top/bottom spars,is to reverse ends/fittings.You can even do this with a bent spar that you have straightened,as the (potentially)weakened area is move to a lesser load area.--I recommend that the collar on the topsection be 'bonded' in place rather than riveting,,since the rivet weakens the mast substantially--this practice is very simple,but not legal as you would cheat the manufacturers out of many $ over the years!!
If you find one boom substantially heavier than another,,it is because the heavier boom will have a sleeve in it.
Hope this helps!,,and sorry ,no I don't remember examples of light/heavy spar weights.