Measuring Flex idea?

I read that measuring and quantifying flex is one of the “next big things” in surfboard design. I dont know if this is still true, but I have been thinking about it for a while now, and Univershuls post about drilling holes in stringers helped solidify my thoughts.

Would it be possible to drill a hole through a board and insert a load sensor, maybe even a whole bunch, across the width? As you use the board, it would record changes in pressure, im sure you could figure out the deflection of the foam/fiberglass knowing the stress and strain values for the foam. The sensors would have to be small, and lightweight. Im sure you could rig up a transmitter to it so you could collect data live from the beach. Has this been done? Do you guys think it would be feasible, or even worthwhile?

Im an engineering student at Cal Poly, San Luis Obispo and this would be the coolest senior project of ALL TIME! (all engineers must complete a design project to graduate.)

cheers

jd

I reckon strain gauges epoxied on the surface of the board top and bottom should do the job - they make waterproof ones - seen them in use on structures outdoors and out on the cliffs strapped across gaps in the rocks where the cliff is falling away. Could be very intersting research.

Cheers

Rich

www.thirdshade.com

Had the same idea myself, but I came to the conclusion that there are so many other things I need to fine tune first that it really isnt worth my time. I’d love to see some data though on the subject.

One of our members did a lot of research about this.  See these threads:

http://www.swaylocks.com/forums/hard-numbers-flex-demystify-flex-patterns

http://www.swaylocks.com/forums/swaylocks-fundraiser-to-measure-effects-flex-surfboard

The fun may be in logging it. Fortunately these days the loggers are getting much smaller.

 

http://www.loggershop.co.uk/madgetech/bridge120-strain-gauge-data-logger/prod_446.html

 

I’d recommend speaking to someone from Vishay or Omega for gauging glass fibre, as the ellongations are much higher than say aluminium, so make sure you get the right ones. Would be an awesome project and I’d love to hear what you learn. You could always go all out and use rossette strain gauges so you could build up a picture of how it flexes lengthwise, spanwise and its twist. 

 

I have often thought  that before you can measure and quantify flex you need to be able to measure the variable of  how a surfer swings their weight.

Therefore you need to measure how much pressure a surfer applies to sensors on the deck under each foot.

You hear descriptions that one surfer has a backfooted style, meaning that when they swing their weight when doing a bottom turn, they put 70% of their weight on their back foot.

At the opposite end you have front footed surfers who put only about 40% of their weight on their back foot when doing a bottom turn (notice their stiff front leg style).

Surely a board is going to flex differently if their is a 30% difference in back foot pressure.

Then there is the question of how a surfer transfers/swings their weight as they flow through the turn.

If sensors on the deck were capable of recording how weight is transfered in the 1 - 2 seconds it takes to do a bottom turn, this would be usefull information.

If I were to try and describe how I swing my weight as I flow through a turn, I would use as an example a wave I caught at the Superbank last thursday.

The wave was 5 ft and peeled from the middle of Rainbow Bay into Greenmount for 250 metres before closing out, the waves were  pumping courtesy of Cyclone Sandra.

If I were to describe my style it would be carving roller coaster rhythm, meaning I spend 50% of my time on a wave face surfing above the fall line and 50% below the fall line, riding a wide tailed board that sits high in the water and does not decellerate through a top turn as much as all other boards and therefore has a faster all round  planing speed.

I was riding a 7’ 4’’ by 22’’ by 3 1/4’’ wooden nugget (62 litres volume)(my weight 100kgs/220lbs), I paddled into the wave and dropped straight down the wave face, neither rail dragging in the wave face gives minimum drag and maximum accelleration, then as I start to do a bottom turn as late as possible, I apply about 80% of my weight onto my back foot, then as I rise up the face and bank off the very top of the wave which is at about 10 degrees before vertical, my weight is balanced on each foot at about 50/50, so between the start of my bottom turn and the top of the wave the weight on my back foot has changed from 80% to 50% as I flow through a bottom turn.

I tend to think that surfers who surf more vertical than me don’t put as much weight on their back foot (more like 70%) but transfer alot more of their weight onto their front foot as they flow through a bottom turn burying more of the rail.

Also I think that verticle surfers on low volume reactive boards (which therefore have a much slower planing speed than a high volume nugget), that you need to be a fast reacting surfer to surf, tend to surf more above the fall line (60%) than below the fall line(40%).

 

Kinda a different point, but Pinny hit on something that made me think. Windsurf masts have a stiffness measurement system called IMCS (if my memory serves). I think its a three point bending test to give it a stiffness number so riders can match certain masts to certain sails and certain conditions. I wonder if a similar universal system could be done for surfboards to indicate how a certain board may compare.