The original thread:
http://www2.swaylocks.com/forums/swaylocks-fundraiser-to-measure-effects-flex-surfboard
Problem#2:
Of two identical boards (stiffness and everything), but one weighs 4.75lb and the other 5.25lb, the 4.75lb rides better.
Evidence#2:
Riders say that the lighter board is “more responsive”.
Theory#2:
Prior to this experiment I also thought that weight was not critical. I thought that pros wanting 5lb boards was just an artifact of wanting a flexible board (lightly glassed).
This false notion is a misuse of Archimedes principle. If you add half pound to the surfboard, that's a fraction of a percent of the weight of the entire system (surfer + surfboard= 160 + 5), so it wouldn't affect the system. If you took two buoys, one that weighs 165lb and the other 165.5lb, no observer would be able to see the difference in buoyancy. But this is a static system, unlike surfing which is dynamic. In a dynamic system, it is important to account for inertial effects. My opinion now is that the weight of the surfboard IS NOT important, whereas the mass of the surfboard IS very important. Weight is simply the effect of mass in a gravitational field. Without gravity (think in outer space), you don't weigh anything. Whereas your mass is the same throughout the universe (Newtonian universe). (I think there needs to be a fundamental change in the way we view surfboards...that we need to see the board as an inertial object, not so much a weighing object).
So if we separate the masses of the surfer and surfboard, the importance of the mass of the surfboard becomes very apparent. The picture at the bottom is a spring-mass model that demonstrates this effect.
-the floor would be the water
-m1 is the mass of the surfboard
-k1 is the spring effect of water on the surfboard (buoyancy and lift)
-c1 is damping effect of water and surfboard
-m2 is the mass of the surfer (on which gravity works)
-k2 is the intelligent spring effect of the surfer's body
-c2 is the intelligent damping effect of the surfer's body
-m2 is 30 times more massive than m1
When you set this system into motion, you will see that m1 generally moves with m2 because m2(surfer) is much more massive. As you increase the mass of of m1(surfboard), it's motion becomes less dependent on m2(surfer). In other words, the less massive the surfboard, the more aligned the path of the surfboard will be with the surfer...the surfboard goes where the surfer goes. As the mass of the surfboard increases, so does it's inertia and the energy required to change the direction of it's path.
When the surfer's body changes direction, the surfboard follows, but there's a lag. The lag is related to the mass of the surfboard, not the weight. This lag is a fraction of a second of poor connectivity between the surfboard and the surfer. Connectivity is function of STATIC FRICTION and CONTACT SURFACE AREA(and distribution of surface area--footprint) between the feet and the surfboard. Static friction is a function of CONTACT FORCE--the more force placed on the surfboard by the feet (or vice versa) , the more friction there is. Contact force also increases contact surface area because the foot is soft and conforms to the shape of the surface it is touching.
During this lag time, there's less contact force, therefore less contact surface area and less static friction between the feet and the board, therefore poor connectivity. With poor connectivity the surfer cannot exact his will on the surfboard. So there's fractions of seconds in every second where the board responds poorly to the surfer. The more massive the surfboard, the greater are the fractions of seconds where the board is poorly connected and therefore not responsive. Therefore more massive surfboards will be less responsive than a less massive surfboard, assuming all other characteristics are the same (and neglecting the effects of wind).
Solution#2:
I have to get the boards down to 4.5lb, because the instruments weigh .5 lb. This is easy to achieve on a chip surfboard with a pro glass job, but my boards need about 20% more volume (see problem #3). My boards also can't dent or ding because then the stiffness and damping will change throughout the life of the test. The only way to do this is sandwich construction: I'm using 1lb Marko foam with 1/8” 5lb divinycell on the deck. I'll post the details somewhere else soon.
Second part of the solution is that I will need to add small weights to the boards that weigh less than others...similar to how they balance tires on cars. All boards need to have the exact same mass and same mass moment of inertia.
Status#2:
These boards kick ass. The last board I built is the best board I've ever ridden. I'll get the other riders on them soon, but I already know the response is going to be really good.
**hey ben rember this do i get an award**?
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** huie quote**
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**for me the importance of this blank become aparrent by page 3& i have never even seen it**
20 pages later no mention from the techies. haaa’’
**i would like to here from someone from marko do they in fact make 1lb moulded
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&tell them that i am sure they will be surprised
marko themselves say to glass the lighter blank more glass
i know its a theory of others respect in that tech
resin ratio to fabric is important
so lets find out what that blank density realy is?
for there is a real use for it which has not been looked at.
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( one prblm bro thats old tech look for another way to skin this cat?)
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A lot of this makes sense to me, but seems more directly related to high performance thruster shortboard surfing, and less related to recreational mid-length or longboard surfing. Still, Ben's explanation does seem to explain the alleged responsiveness of ultralight surfboards among pro's and more skilled shortboard riders.
I guess what I'm saying is that not all styles of surfing are dependent on split-second responsiveness, but I can see how reducing the mass of a board in motion would increase its responsiveness to the greater mass of the rider directing it. I just think that the standard for pro surfers' competition boards is not necessarily a valid standard for the guys just having fun in the lineup.
Here's a video to illustrate my point. I don't know the exact weight, but these are hollow wooden boards, so its a safe bet they're heavier than the hpsb's that Ben is working with. But they are plenty responsive enough to have fun with. ( tried to embed but couldnt' get it to work)
Ben, I’m struck by how well you have put into words what happens in the water. Light weight/low mass is good. For me.
I’ll be following this with interest.
However, don’t taint your results with your early bias: “…but I already know the response is going to be
really good.”
Those 3 last years i made the same egg wombat bear inspired surfboards for friends in many construction: sandwich, classic, stingerless, multiaxial etc. Intermediate to good surfer. We made comparison test in muchy to good waves, everyone like better the same board: light and still flexible (stringerless+veneer deck on 1,5 lb foam), the lightest (balsa sandwich on 1lb) feel too stiff. No one want to surf the heaviest, old PU/PE with water in.
Now i use multiaxial fiber with a bit of UD carbon on rails, all who test those boards say they are the best i do and work relly well so i start an egg test board with this technology to see.
Thanks Benjamin for your work ingineering is always the key of progress.
Sorry for my frenglish
“I have to get the boards down to 4.5lb,
because the instruments weigh .5 lb. This is easy to achieve on a
chip surfboard with a pro glass job, but my boards need about 20%
more volume (see problem #3). My boards also can’t dent or ding
because then the stiffness and damping will change throughout the
life of the test. The only way to do this is sandwich construction:
I’m using 1lb Marko foam with 1/8” 5lb divinycell on the deck.”
I find this interesting because the sandwhich construction was reached as a result of other limiting factors in the test outside of performance and ride quality, but in order to quantify those attributes a whole other construction method was needed.
It’s like attacking a problem from 2 totally different angles, one being purely empirical, trial-and-error based and the other being purely technical formulating the board based on equations and numerical targets. Both seem to meet in the middle at a common ground but for different reasons. Both land on a light core with the outer reinforcement providing most of the strength and flex characteristics.
My thinking is that the board and its fins is an energy transfer system, a transducer.
Mass thinking is ok, except when doing airs ;)
So Ben, are you saying that we should stop measuring our boards in pounds and use slugs instead? I guess we could use kilograms, but that's just un American.
Kidding aside... I think the issue is not about using mass vs. weight, since they are essentially proportional here on the surface of the Earth. I think a better way to put it is that the distribution of mass is just as (if not more) important than the actual weight of the board. For example, adding wood to the rails pushes the weight... I mean mass... to the sides, which impacts the way a board turns. Two boards of equal weight could surf completely different depending on their distribution of masses. I think that is the point you are trying to make -- right?
I know you understand what I am saying, Swied, but I’m going to going on a rant anyway…
Weighing the boards is still important. Measuring the boards in lbs just as good as finding the mass.
The important thing is to realize that the board’s response is more related to the inertial effects of the surfboard, than gravitational effects. Let’s not say, “the board isn’t responding because it’s weight sinks it (gravity pushes it into the water).” The more important factor is that the board is massive and has inertia. The correct statement would be “the board isn’t responding because it’s difficult to change the direction of a massive object.”
Think of a BMW sports car and a Cadillac town car. They have to navigate a course of cones on a flat open parking lot. Everyone knows that the BMW will navigate the cones with ease and the Cadillac will not. The reason is not because gravity is bearing on the Cadillac more than the BMW, it’s because it takes a lot more energy for a massive object to change directions.
You’re right, distribution of mass (mass moment of inertia) is also important…though I only mentioned it once. You’re opening a whole nother can of worms.
Now we’re talking about stability and responsiveness. As the mass moves toward the rail, the board should be more stable, but less responsive. This is why tight wire walkers have those huge poles. As mass is more distributed (mass moment of inertia increases) the system becomes more stable. Responsiveness is the inverse of stability…generally in the most simple scenarios. While the pole keeps the walker stable, they also can’t do any acrobatics.
I think this is the reason why jumbo jets have wide wingspans and fighter jets have narrow wingspans. Jumbo jets need to be ultra stable, while fighter jets need to be ultra responsive.
This is why the thruster is the most responsive setup (I’m sure this will upset quite a few!). The difference in toe angle between the side fin and the rear fin, causes instability in the flow…which means its much easier to break your path…much easier to change directions…much easier to transition from one turn to another. A very stable flow is hard to break…I think people call this tracking. (Disclaimer, while most things I say about solids are pretty much accepted as fact in the scientific community, I know very little about fluids. Everything I say about fluids should be assumed to be an uneducated opinion)
It suprised me to hear you just now talk about thinking in mass. As much as statics and dynamics make me puke, and Crafty would prolly know why, I think I’ve been stuck watching mass budgets for too long now. Momentum, intertia and fluid friction impacts are definitely key to all the non-linearities you are hovering around. Keep your measurements stable and variables bound!
It’s same concept for bumps or wing in outline and kick in rocker.
What i find for mass distribution is that all my best boards have more glass on bottom and less on top than others (same lam top and bottom). Better feeling on waves but quick denting. But now it’s not more a problem bcause dents are good LOL.
Sorry for my frenglish
That is completely wrong!
When considering calculations relating to surfing:
- The premise for your argument that weight & mass are different is completely untrue.
- They are totally equivalent & interchangeable, it does not matter which you choose, the results will be the same.
At the surface of the earth (where we surf) weight w & mass m are equivalent, because gravity is constant.
w=mg where g is acceleration due to gravity at the earths surface. As far as a surfer is concerned g is a CONSTANT.
The slight variation in g while surfing is TOTALLY insignificant.
Therefore Mass and weight are totally interchangeable. in all your equations, replace m by w/g & you will get the same result.
Mass & Weight are TOTALLY interchangeable when considering problems related surfing.
Well that’s true, but also totally irrelevant to the problem at hand.We dont surf in outer space.Newtonian or otherwise!
We surf in a place of constant gravity, so take your pick, mass or weight. It absolutely does not matter which you choose.
This subject was beaten to death just a few short years ago. Too bad the search function isn't so user friendly as it once was.
W.W.R.D?
(what would roy do?)
Its all important: weight, mass, inertia, energy transfer, from an analytical point of view. But what you can actually do with that information is relative to the skill of the designer/builder/rider.
Science is good. but there's a lot of synergistic art involved, and many many variables.
You engineering type guys are gonna follow this thead on a whole different level than someone like me. I'm not opposed to the idea of using science to push the envelope per se, but I'm really skeptical of the actual application, and this one seems to be going a familiar route. For starters, the one directing the experiment already has admitted to a preconcieved notion he is trying to push: "most surfboards today are not flexible enough".
Furthermore, he discusses responsiveness in terms of fractions of a second - while that may be noticeable and important to some people in some circumstances, I think it is irrelevant to a large percentage of the surfing population, and might even be a drawback under certain conditions and for certain styles of surfing. Plus, if less mass is so important to direction changes, then smaller surfers with less body mass should be able to do directional changes easier than larger, heavier surfers. But that really isn't a deciding factor, is it? If the real factor is how the surfer uses his body mass while surfing, then by extension it seems to me that how a surfer uses his surfboard's mass is gonna be a bigger factor in performance than how much mass it actually has.
I know followers of certain types of boards, and certain types of surfing, are rooting for him - Yay, you are proving our style boards, and our style surfing, is better. But if the results are being cheered before the testing is complete, something is wrong with the picture, IMO.
Nevertheless, as long as we remember surfing is just fun time, and surfboards are just water toys, then its all good, I guess. Just gotta keep things in perspective.
Good post.
Summing up: surfboard analysis will never be totally OBJECTIVE.
Not even close.
But the quest to analyze surfboards on a truly objective level will likely never die either.
Its like trying to completely conquer the game of golf...no one has ever shot an ideal score of 18...not even close...but some people will sacrifice their whole lives trying.
God, I wish Newton was here. I’d settle for Simmons though.
Somehow I’m crazy for stating what’s been know for 350 years.
good post huck good on you
**cheers huie
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Greeny, let it go. Not helpful.
Ben is offering up some research and opinions. Disagree, if you want to, but tone it down. Otherwise this turns into a shouting match, and that discourages discourse. It looks like you just want to be the smartest person in the room when you call someone out like that. If I am wrong, sorry.
If you followed Surfdings experiment on blanks and glassing you know what I mean. For the life of me, I cannot see how he managed to finish that with all the experts bearing down on him. It started out as a helpful experiment and almost got locked down for all the bickering.
all the best
Huck, I’ll add my thanks too. But can we say “important water toys” to distinguish them from floaties and other things you can’t ride down the face of large waves of energy on and get covered up in, and duck under and just revel in, and get spiritually recharged as God’s own little living water drops sitting on wood and plastic and fiberglass and …I’m having an Ambrose moment here. Ambrose, take over.
All the best