Tuesday, January 25, 2011

Kiteboard Design - Broad Parameters.


Kiteboard design remains a bit of a black art even though there is a lot of feed in from surfboard, windsurfer and boat design. There appear to be some accepted wisdoms about what does what on a board but it seems that in reality the different parameters have a highly non-linear relationship and board performance is dependant on the relative amounts of each so that ultimately design needs to be honed through prototyping and testing.

A blog/website by Derek Comancho http://www.dcboardz.com/kite.html sums it up nicely

"Kiteboard designing is not a defined equation, it is a combination of all the things I have mentioned above and more. It all has to work together in synergy. There is a lot of high tech 'know how' in terms of the materials used and construction technique used, but just like surfboard making, there is still a big part of personal feel by the shaper that has to go into the shaping and making of a great kiteboard . The shaper is still a big part of the process to get the 'great feel' of a custom board that has not been able to be reproduced by machines in a factory. This is where knowledge, creativity and skill meet to make art"

So what does this mean for the virgin kiteboard project? It means I'm going to get out my tape measure and start by copying the bejezez out of my favourite board ( also my only board) and tweaking it for what I think might improve its performance in our local conditions.

The terms

Here is good intro to the meanings of some of the key design terms and the authors view on how they affect the boards performance.


A website of Derek Comancho mentioned above has some really information about the relationship between pairs of features and the usual stuff - rocker, flex width/length with some interesting explanations involving the flow and release of water. http://www.dcboardz.com/kite.html

My design goals

I'm keeping the design goals of the board pretty humble given it the first one. Once it completed I'll start tweaking the parameters of the board and reference those back to this first board to see whether any insights emerge.

The board is going to be used mainly for freestyle riding but in the pretty choppy conditions we get locally.

My current board is a crazyfly raptor 132x41cm full carbon board. It has a progressive rocker meaning its relatively flat through the middle and the rocker kickers up at the ends. There is only about 2.5cm of rocker in it at each tip and about 5 mm single concave.

Things I like about it

  • big planing area so its good in lighter winds

  • Its very stiff and so when you can hold the edge down it pops really well

  • Despite having 50mm fins its tracking is skatey enough to not grab to hard when you're coming in fast after unhooking.

  • Wide stance - you can beat it for feeling stable

  • Tips are not too square so the board carves nicely in the waves without having to bear down too hard to get the rear toeside tip to get traction.

Things I'm not so fussed about with it

  • 41cm is a wide board for my weight. I find it quite remarkable what a difference there is between 40cm and 41 cm. As the wind picks up the 41cm wide board looses it edge a long time before the 4ocm. I guess this makes sense because if you think about the forces acting on the edge of the rail you have the force of the water trying to make your board rotate about your heal and lay flat. The distance from your heal to the edge of the board is typically just a few centimeters and so a 1cm in the width can corresponds to as much as 33% increase in the torque trying to rotate the board about your heal. With this in mind it make sense that a centimeter or so is a material amount when it comes to width.

  • The rocker profile does not deal with chop well. The progressive increase in the amount of rocker at the tips means the leading tip underside slams into the chop and goes straight into you knees and also throws up a lot of spray. This means that you need to lean back hard on you back foot to get the nose up which leads to aching legs in no time. The continous rocker boards with slightly more rocker are far superior in the chop.
    So the broad parameters for this board will be:
    i) 129x 39cm with the outline similar to the raptor pro except that the tips will be a bit more squared off. (For a really square board have a look at a slingshot lunacy and try to ride it in the surf).
    ii) continuous rocker with 3.5cm at each tip to help with handling the chop
    iii) 10mm concave together with small fins. My hope is that this will maintain the upwind ability (concave) but allow the board to skate a big more when coming in hot (the small fins)
    iv) Stiff through the mid section and increase the flex in the tips again to help smooth the way through chop a bit.
    v) 10mm abs plastic rails because that's what I had on hand. However, in the next board I'd like to try wrapped rails (reinforced with carbon) so that I can experiment with the rail shapes.
    vi) wide stance 18" instep to instep.
    vii) lots of 'duck' in the footpad angles because I'm part Chinese and walk like I have flippers on
      vii) No grab handle because it forces you to carry it like a hand bag and that's just not ok:)

    Monday, January 24, 2011

    Rocker Table Pt 3 - Construction

    So now to actually building the table.

    As I mentioned a few posts ago I wanted to make mine at least semi-adjustable as this seemed the best trade off between complexity (and sweat) and cost.

    So the first thing to do is cut out the rocker jigs. I printed out the continuous rocker line for the edges and the center. Then cut along the line, taped it 2 narrow chipboard doors that I found on council clean up day ( they were about 20cm wide which was about right to accommodate the amount of rocker plus some extra on the top and bottom for securing them to the frames of the table. Then traced it out with a marker and cut it very carefully with a jigsaw. This created the male and female versions that will be used to clamp the edges.

    Only the female version of the centre rocker line is necessary. I used a over sized mold factor of 2 in fixing the height of this piece ( see last post) which turned out to be a bit underdone given how much larger the able is than the board but this will be easy to increase by building up the centre jig.

    So here's what they look like.

    The round holes in the side are where I am going to insert the G-clamps to secure them to the frame.

    Next is the bottom frame. If you have been lucky enough to get hold of 2 single bed bases then 3/4 of the work is done. I had chopped bits out of mine so I needed to build the base. I used 3 x 20 mm angle iron pieces form Bunnings with each length about 1.5m.

    I screwed 2 x 1.5m length of angle iron to some chipboard pieces 1 m wide. I screwed another piece of angle iron so that the inside edge of the vertical part was exactly at the center point between the 2 bottom pieces. Done.

    The female jigs can now be secured in place.

    They are held in place with 2" G-clamps but you could just put it all together with bolts and wingnuts.

    The mold surface ( the surface that the board will ultimately be clamped to) is going sit between the female and male jigs. I used a piece of 4mm plywood with about 6 coats of acrylic paint from supercheap auto. I'm not sure this was the best choice because it may not be stiff enough to resist deforming when stiffer board core material is used but it will certainly do for PVC foam and probably balsa. Other options would be melamine coated MDF or maybe Laminex/Fomica which would probably be stiff enough to use for PVC and balsa and could be laminated onto 4mm or 6mm ply wood if you were going to use stiffer core material.

    The mold surface measures 1m x 1.5m - big enough to cover any board that I make. You need to make sure you have at least 10 cm between the edge of the board and the edge of the table to allow you to tape the vacuum film in place and put any other breather material around the edge.

    The acrylic paint is used to seal the pores of the wood. If you're using a melamine coated surface or perspex then no need to do any of this. In all cases you'll end up using release wax on the surface to help the resin lift away from the mold. The important thing is to make sure that the surface is smooth if you are going to use a single sheet of vacuum film taped down to the surface. (the alternative is to enclose the whole mold surface in a big vac bag, excavate it and then clamp it down.)

    The matching male jigs are then clamped to the single bed base that will serve as the top of the rocker table. This leaves a good open working area and the weight of the base means that I probably won't need to put any more clamping pressure on it to get the mold surface to bend into the exact line of the jigs.

    This photo shows you how the centre jig introduces the concave.

    This spirit level across the mid section shows the presence of the concave. Remember that I used an oversized mold factor of 2 and wanted to get 10mm of concave in there. However, as you can see from the picture below the net result was about 7 mm at the edges of the board. That is, 20 mm of concave as measure at the extremities of the mold (45cm away from the centre reduces to 7mm at the board edge which is about 15 cm from the center).

    There is also a noticeable flat spot the middle where the centre jig sits.

    Fortunately its a simple mater of just laying a strip of material about 6mm thick along the centre jig and all else being equal the desired 10mm should be introduced. Also, making this piece narrow will help remove the flat spot in the middle of the board.

    Out at the tips the concave vanishes like it was meant to.

    With the rocker table completed, the next step is to actually start making the board!!!!!!


    Sunday, January 23, 2011

    Rocker Table Pt2 - Designing the Jigs.

    Rocker Jig Design

    At this stage I already had in mind the type of rocker line that I wanted so I made the jigs as a first step. If you are making an adjustable table then this can naturally wait until later when you've decided on all the design parameters.

    I wanted to make a continuous rocker. That is, a rocker line that is a segment of the circumference of a circle - no flat spots or rapidly curving tips. I tried an M8 board that had a continuous, generous rocker and it handled really nicely in the choppy conditions we get locally. Also, after listening to Brokites video and seeing that they use a continuous rocker as well this seemed like a worthy first attempt.

    It was also very easy to create the exact line using MS Excel as continuous rockers are just part of a circle. What I like about the idea (and lets see if it actually works in practice) is that if the board has sufficient flex in it the curve between your feet will flatten out when you ride because of the pressure exerted by the water in this region. This should help up wind ability and popping. It all hinges on getting the right amount of flex - which at the moment is a bit of a black art for me....but trial error will reveal all.

    i) Work out the radius of the circle that traces out the rocker line you want.
    There is a bit of maths need but it straight forward even if this explaination is a bit long winded.

    It's based around the equation of a circle with centre at the origin (coordinates (0,0)).

    The general equation is x^2+y^2= R^2,

    where x - x coordinate, y- the y-coordinate and R is the radius ( '^2' denotes squared)

    The rocker line will be that part of the circumference of the circle the sits at the very bottom and lies symmetrically about the y-axis. We only need to work out the coordinates of a single point on that circle to work out the radius. Once we've got this we can then plug it in to excel and get it to spit our all the points along that curve.

    The point we know is on there has a x coordinate of half the board length L/2 and has a y coordinate that is equal to the y coordinate of the lowest point on the circle (0,-R) PLUS the amount of rocker you want to have in it, call this 'r').This point is at the tip of one end of the board. Put this in the formula for the circle and you get

    (L/2)^2 + (-R + r)^2 =R^2 - (1)

    where L = length of the board, R is the radius the circle on which the continuous rocker line will lie, r = amount of rocker at the tip of the board.

    A little rearranging of this and you get

    R = L^2/(8r) +r/2 - (2)

    Remember that r is going to be about 0.04 m ( 4 cm) and L=1.3m. This means that the L^2/8r is going to dominate.

    EXAMPLE: Using (2) for a 130cm board with 4 cm rocker then the radius is 5.3013 m.

    We now have everything we need to get excel to plot out the rocker line.

    ii) Generate the coordinates in excel. In excel create a column of x coordinates starting at about 5cm longer than the half board length L/2 you board. So for a 130 cm board start at 70. Reduce this buy 0.1 each row down so that you have the x-coordinate for each millimeter of the board. Take this down to -70

    In the column next to the first x-coordinate (say its cell A1) enter the following formula

    = R - SQRT(R^2-A1*A1)

    where 'R' is the radius in centimeters calculated above using (2). This will generate all the x, y coordinates you need to plot your rocker line so that the center of the board sits at the coordinate (0,0).

    iii) Chart it in Excel - Highlight all the data and generate a line graph and there you have your rocker line.

    iv) Rescale the chart in both x and y direction so that when you print the chart so that 1 interval on the y axis is exactly one centimeter when you measure it after printing. Same thing with the x- axis. The only way I could think to do this was to zoom way out (20%) so the graph shrinks on the page to a business card size. then just grab the corners of the chart and drag them out. Deselect the chart and in the page setup menu set it to print 1 page high and 6 pages wide. Print off the first page and measure. Resize, measure, resize, measure........until you get it exactly right. Then print off 2 copies the chart and tape them together.

    v) Do the radius calculation for the rocker line down the center of the board. For my board, I wanted to have about 10mm of concave in the middle of the board an then have it reduce down to nothing in the tips. If you were going to have the same amount of concave all the way through the board then this is dead easy. You just use the R you calculated above and subtract the amount of concave you want. You'll need to adjust this if your mold is more that about 5 cm wider than your board because part of this increased height of the center jig that pushes the concave in will be clawed back as the mold continues to slope down from the edge of your board to the edge of your jig. In my case the mold was about 30cm wider and the board on each side so even though I only wanted 10mm of concave I need to reduce the radius by 2.5 times that so the right amount of concave was introduced. This can be tweaked once the jigs are completed by placing additional height on the centre jig to increase the concave. Reducing the concave is not so easy unless you lob off a bit from the bottom of the centre jig.

    To get the concave that I wanted ( diminishing to 0 near the tips) there's one extra step because the circle that you want is not going to be centred at the origin (0,0). The centre will sit above the origin now otherwise the centre rocker line will end up being roughly parallel to the rocker line at the edge and you'll have the same concave at the tips as at the centre. Fortunately, you can use a trail and error method to find this new origin or use goal seek in excel if your familiar with it.

    The new origin will be on the y-axis so we know the equation for the new circle is

    x^2 + (y-c)^2 = Rc^2 - (3)

    where c is the y coordinate of the centre of the new circle and Rc is the radius on the circle for the centre jig.

    This equation has 2 unknown quantities in it c and Rc so we need 2 points on the circle to calculate these two unknowns. We can't you the coordinates of the other tip because putting them into (3) will give you the same equation so it won't be helpful in solving for 2 unknowns. You need to use one tip and then the lowest point in the centre rocker line. This is obviously going to still be on the negative y-axis (so x=0) but its y coordinate will be R minus the amount of concave you want with this figure adjusted for the reasons discussed above.

    So using the equation of a circle again but this time with the centre at (0,c) we get

    (L/2)^2 + (-R+r-c)^2 = Rc^2 - (3)


    0^2 + (-R+con-c)^2 = Rc^2 - (4) , where con, measured at the center of the board MUST the amount of concave adjusted for oversized mold. (i.e con = concave * oversized_factor)

    Putting (3) and (4) together you get

    (L/2)^2 +(R-r+c)^2 -(R-con+c)^2 = 0 - (5) where the only unknown quantity is c.

    You could keep going with the algebra but the easiest way is use Excel to solve this for you. Put the left hand side of this formula in a single cell with the values for L, R,r and conc in cells of there own. (make sure you use the same units for everything i.e. all centimeters or all metres..) and see what number it calculates. Then adjust c until the value is very very close to zero (e.g 0.001 is about right). You could also use the goal seek function if you're familiar with it.

    Example: For a 130cm board, with 4 cm rocker (r=4cm), concave = 1cm, oversized mold factor =2 (con = 2cm) and R (calculated in the example above) = 530cm we get from (5) that c= 529.15cm. That is, the radius of the circle that passed through the points we need it to is almost 2x as large as the one for the out jigs.

    This gives you the value for 'c' and so you can work out Rc above and like before you now have everything you need to plot out the coordinates, resize the graph, print it out and tape the sheets together.

    Next post will get into the actual construction of the rocker table


    Monday, January 17, 2011

    Kiteboard making videos


    This is post is going to be updated from time to time with links to videos of web pages about kite construction.

    Brokites - great detail of the whole construction process. They use 6mm divinycell but cut the core lengthwise into 4 ( and more recently 5 pieces). Each section has 11.5 oz carbon stripes glued to each long edge and then completely in the same. They say that this builds up carbon 'stringers' (22oz each side) rather than just laying up the carbon in complete sheets over the core which would cause teh board to be too stiff.

    The video shows there whole set up (rocker table and construction technique)


    The latest addition to the Brokites videos that does a bit of a wrap up of their technique and shows the boards in action.

    Slingshot SX
    Checkout this guy taking to a slingshot with a circular saw. Great insight into construction!!

    Vacuum Bagging Videos!!!


    The whole shebang


    Rocker Table

    The rocker table is the mold on which the board with be clamped (by the vacuum) while the resin is curing. This is how the rocker line (lengthwise curvature) and the concave (width wise curvature) are introduced into the board shape. In addition the surface material of the mold must be selected to help make sure the cured resin won't bond to it leave your work stuck to it.

    There are only a few things to consider before you make your rocker table:

    i) Do you want to be able to adjust the table for different rocker lines?
    ii) Do you want to be able introduce concave into the cross section of the board?
    iii) Will you (at some stage) want to use very stiff material in the board such as denser wood like paulonia or cedar?

    Adjustability: If you plan on making a few different boards you will very likely want to experiment with the rocker line and so making it adjustable is a good idea.

    The right rocker for the type of conditions and riding you want to accommodate involves a lot of proof by 'Trev Reckons' and so we owe a great debt to the big names who churn through tweaked prototypes until the board 'feels' right. We'll explore this more in the design section but for the moment the main decision is how easily adjustable you should make it.

    There are a couple of approaches here.

    At the more sophisticated end I've seen a metal plate (this the actual 'Mold') with holes drilled around the perimeter each 10cm. At each end there are solid pieces of wood about 10cm high. Holes are drilled through the base and long bolts (15cm) passed through the base up through the holes in the plate. With nuts under and above the plate the level can be adjusted so you get exactly the rocker line you want. This is the ultimate in adjustability.

    You could simplify this a bit by not suspending the mold (plate) on a bed of bolts but rather using different height blocks under the plate and using clamps to lock it in place. This example, http://www.youtube.com/watch?v=WoMySXm6heY&feature=related , takes this approach.

    I've gone for what seems to be a bit more robust approach and which borrows from the BroKite video http://www.youtube.com/watch?v=wPGhSevDs94&feature=related (brilliant video form the good ol' boys of kiteboard making). They cut out of marine ply 2 sets of both the female of the rocker and the male version of it (the 'Jigs') so that the mold surface can be clamped solidly along the edges between the two matching surfaces. I think that this will have the advantage of being able to use very stiff mold surface (1/4" ply for example) so that stiff core material (denser wood) can be bent over it without distorting the mold.

    The downside of this approach is that you need to cut the Jigs each time you want to change the rocker.


    Concave does a couple of important things to the board. Firstly, it causes the rails to dig into the water at a sharper angle and so you get better edging and hence upwind ability. Secondly it makes the board stiffer. The way to understand this increased stiffness is to image concave taken to the extreme where the last couple of centimeters of the board's long edges are perpendicular to the deck. These would form an I-beam along the length of the board which would stiffen it considerably. The effect of normal levels concave (5 -1 0 mm) is obviously not that pronounced but the same principle is at work. The FGI document on sandwich material gives a detailed treatment of the increased moment of inertia that results from introducing the concave.

    In terms of how to introduce concave into the mold, my approach has been to cut a female version of the boards centre rocker which will be higher than the Jigs that will be clamped along the side of the mold surface. The height difference is the concave height and the curvature of the concave profile will derive from the material properties of whatever you've used as the mold surface.

    The 'art' in designing this centre profile comes in when trying to calculate how much higher the centre jig should be. As the mold surface will be wider than the board you will need to estimate how much the mold will slope down between where the board edge will lay and the point where the mold is clamped. If there is 20cm from the board edge to the Jig then you may need to make the height of the center rocker jig relative to the rocker in the clamping parts 2x the required amount of concave. This will need to be tweaked in situ to make sure you have the right amount.

    Using stiff core material

    This has already been alluded to above. If you try to bend stiff core material over a softer mold surface then the mold will deform and you will get a board that is different from what you designed. As I'm interested in using wood cores at some point, I opted not to use the perspex (Plexiglass) mold material used in the video above.

    In the end I opted to use 4mm plywood as the mold material and just coated it in acrylic paint from Supercheap auto so that it sealed the pores in the wood. I'll still be using mold release to avoid the resin sticking to the mold. 4mm will be fine for the PVC foam and probably balsa core. However, I'm not so sure it will stand up to other types of wood cores. Only time will tell.

    Building the rocker table


    1. 2 x rectangular frames at least 70cm x 160cm - these will be used top and bottom to hold the male / female rocker line Jigs for clamping mold surface. I found that single metal bed bases were an easy solution for this as they had the weight needed to easily bend the mold surface over the center rocker jig. They are convenient because there's no construction needed and they are very stiff.

    2. Sheet of 4 mm ply wood ( 2.4m x 1.2 m sheet for $23 from Hardware and General in Brookvale). This is the mold surface. Alternatives to this include melamine coated MDF or perhaps with laminex applied.

    3. 1 litre tin of clear Acrylic paint (supercheap auto - $20)

    4. 3 pieces of chipboard or MDF 10cm longer than the target board and about 20cm wide. These are for the rockerline jigs. I found a load of cupboard doors on council cleanup day the were perfect. Once I decided on the rocker I cut along the line with a jigsaw and this produced the male and female Jigs.

    5. 10 G clamps - These are used to clamp the rocker jigs to the frames in (1) above. You could drill and bolt it together but we had a $2 shop having a closing down sale and so got 10 for $10.

    6. A piece of angle iron as long as the frames in (i) This will run down the center of the bottom frame (just off center so that the jig itself is perfectly central) and will be where the centre rockerline jig will be bolted. You can buy strips of this at Bunnings for about $15 but again a piece of metal bed base is perfect for this.

    ..... apologies for no photos in this post but I'll put some up in the next post to show the actual construction.



    Friday, January 14, 2011

    Vacuum pump Part 3 - constuction


    Here is the schematic for the pump showing the pneumatic lines in red and electrical in green.

    1. Mount the fridge compressor on the base board. I used a bit of chip board for the base and put pieces of rubber from a thong under each foot and then just loosely screwed it down. The rubber under each foot just reduces vibration.

    Remember that the compressor is full of oil so be careful not to turn it on its side or it will spill out everywhere. When the compressor is running it will spit some of this out the 'air out' line. This makes it necessary to have some sort of collector. I just used a long piece of tubing in put a few coils in it so that the oil will hit one of the walls at some point and drip back down. A rag over the end also helps to catch it and stop things crawling inside.

    2. Put the pneumatic circuit in place. Connect the vacuum gauge in line with the pvc tube coming off the vacuum connection on the compressor. I was using 8mm tube and the copper tubes on the compressor where more like 4mm. As luck would have it the piece of fuel line I had from the carby was perfect for covering the resizing. I places the fuel line over the copper tube and then put the pvc pipe in boiling water to soften it and this let me easily put the pvc tube over the fuel line and make a really tight fit.

    The vacuum gauge used the same tubing size as the fuel line so I could have used a piece of this as well. I did this to step up the diameter of the t-connector that came with the gauge so that the pvc tube would make a tight connection.

    I placed a second t-connector (this time it was the one from Bunnings) so the diameters were right for the 8mm tubing. This allowed a line to be connected that would be the line used to connect to the vacuum bag.

    Then finally I connected the t-pieces together and then connected a tube that will go to the vacuum advance when its in place.
    At this stage you should be able to plug the compressor in and by placing you finger over the open end of the last bit of tube watch the pressure drop. When it reaches about 25 inHg switch it off at the wall and watch it to how quickly the pressure drops. You should see next to no drop in pressure. My set up lost about 1 inHG in 1 hour. This means its largely leak free. If it is leaking, try putting ties around the t-connectors and the connections to the compressor as this is the most likely place to get leaks.



    3. The regulator is laid out exactly as in the diagram above. I built a wooden box with the front and bottom open. On the inside back wall I put a 1 inch block of wood. This is where the microswitch will be mounted. IMPORTANT. AT THIS STAGE DO NOT FIX THIS BLOCK OF WOOD IN PLACE. ITS POSITION NEEDS TO BE ADJUSTED SO THE SWITCH IS JUST CLOSED WHEN THERE IS NO VACUUM BEING APPLIED. THIS POSITION WILL DEPEND ON HOW LONG THE LINKAGE IS AND WHERE YOU PUT THE PART THAT PRESSES THE SWITCH.

    4. Drill a large hole in each end to let the vacuum advance armature and the adjusting bolt to pass through easily. In terms of location you want the center of it to be 1cm further off the back wall than the block of wood that you'll mount the microswitch on . This is because the wire that you pass between the vacuum advance and the tension bolt needs to pass close to the microswitch which will be about 5mm off the mounting block.

    Also, drill a hole on the back near one of the ends so that you can pass the electrical wire through it for the switch.

    5. Mount the vacuum advance on the left hand end. There will be a mounting bracket it already but you may need to bend it mount it on another wood block if the angle isn't right.

    6. Make the linkage that runs from the armature of the vacuum advance to the tension spring. When sizing it up remember that the spring will connect to the tension bolt and the bolt must protrude a couple of centimeters out of the other end so that there is still plenty of thread inside the box so that additional tension can be applied to adjust the cut off pressure.

    For the link from the armature to the tension spring I used some really stiff wire of the bed base. You could use piano wire or similar as well. Its important that it is stiff so that when it is holding the tension for a long period of time it should not stretch or loop (shown above) should squash down as this will change the cutoff pressure.

    I made a loop in the wire for the point that will press against the microswitch and squeezed this down with pliers.

    I made another wire link to connect this to the tension spring as the the orientation of the hook in the link and the natural way the spring sat didn't work and if I twisted the stiff wire it broke as it had already been worked a fair bit. This may not be necessary in your set up.

    7. Assemble all the regulator bits except the microswitch. Screw the wing nut on to the tensioning bolt and put and screw the wing nut down a few turns to make it secure. Now you are ready to place the microswtich.

    8. With the box assembled connect the pvc tube on the vacuum line to the vacuum advance.


    A- In my construction I used the normally open contacts on the switch so that the regulator is set up so that when the pressure drops to the desired level the switch will open and the compressor will switch off.

    B - The alternative way is to use the normal closed connections on the switch and place the switch so that when the desired pressure level is reach the switch is closed by the loop in the link pushing against it.

    On reflection I actually think that the second way is better. The reason being that in A you must turn the tension screw so that lots of force in pulling against the armature in the vacuum advance so that it moves off the switch once the required pressure is reached. However, when the vacuum is released and the spring relaxes, all this force will be exerted against the switch and so there is a chance that the switch could be pulled of the mount.
    With B this is not the case as its only when the desire pressure is achieved that the any force is applied against the switch. This is a much better situation and easier to adjust to the desire pressure.

    To avoid this issue with A, the best that can be done is to store the compressor with the tension bolt undone so that there is no force against the switch and make sure to use long screws to mount it.

    Continuing with A - with a little bit of tension in the spring, place the microswitch on the wooden mounting block so that the switch is closed and the loop in the link contacts the lever on the switch half way between the button and the fixed end. Mark the position of the block and the switch and then assemble the bits exactly this way.

    9. Solder the wires to the appropriate connections (Normally On - 'no' for A and Normally Closed 'nc') and run them up through the box to the wire connector block that can be screwed to the top of the box. The switch runs in series with either one of the live lines ( i.e not the green earth wire in AUST) so just cut and connect one of these lines into the connection block according to the diagram at the start of this. IT WOULD ALSO BE IDEAL TO PUT SOME SORT OF SHORT CIRCUIT PROTECTION IN CASE YOU ACCIDENTALLY MAKE CONTACT WITH THE LIVE WIRES. COVER THE CONNECTION BLOCK SO NO ONE CAN ACCIDENTALLY TOUCH IT. REMEMBER THIS 240V AND IF YOU TOUCH THIS AND YOU ARE CONNECTED TO THE GROUND VIA VIA ANY MEANS AT ALL THEN THIS CAN KILL YOU. WHEN YOUR DEALING WITH 240V YOU SHOULD ALWAYS GET SOMEONE WHO IS QUALIFIED AND KNOWS WHAT THEY ARE TALKING ABOUT TO CHECK IT OUT, OR BETTER STILL WIRE IT UP FOR YOU.

    10. Connect the earth wire to a point on the compress that has had the paint scraped back so there is a good connection. Connecting it to one of the screws that holds the compressor down might be a useful place to do this.


    Using the A method I used you need to crank in a few turns on the tension bolt wing nut and then just fire it up to see what pressure it is going to cut out at. To adjust it up or down FIRST TURN THE COMPRESSOR OFF AT THE MAINS. Then adjust the screw tension and then turn the compressor on again. LEAVE ABOUT 30 SECONDS BETWEEN SWITCHING IT OFF AND ON AGAIN AS RAPID SWITCHING ON AND OFF OF THE COMPRESSOR WILL TRIP THE OVERLOAD PROTECTION ON THE COMPRESSOR AND YOU'LL HAVE TO POWER DOWN AND WAIT ANYHOW.

    If you're using approach B then it dead easy. Put a lot of tension onto the screw and turn on the compressor and wait till the pressure drops to near the desired level and the quickly decrease the tension until the switch closes and turns off. Too easy!!!!!

    The final step is to high five yourself for a job well done!!!!!!

    ..... next up is the rocker table.......

    Vacuum Pump part 2 - Parts list discussion continued


    PART 5 - The microswitch that is used in the regulator. You can buy these from Jaycar Electronics, Dick Smith... Instead of having just the button they have a 3cm lever over the top.

    This worked out to be ideal for using in the regulator because by having the armature from the vacuum pump contact between the button and the fixed end of the lever on the mocroswitch you get very rapid actuation of the button and so a nice clean shut off and turn on. Originally I had the armature contacting at the other (free end) end but the vacuum advance armature had to travel twice as far to depress the button fully compared to having it directly on the button. As the movement is slow this meant that the button was partially depressed for a couple of seconds. The result was audible arcing inside the switch which in turn caused the compressors overload protection to kick in. When this happens you have to unplug the compressor and let it cool and reset - a big problem if you are leaving the job unsupervised while the resin cures.

    PART 6 - The Vacuum Gauge. This is optional as you could probably manage the clamping visually and by listening to the compressor labouring. However, this is a cheap addition that takes a lot of the guesswork out of it.

    Boost gauges for turbo chargers are ideal as they only measure less than 1 atmos pressures and so don't waste the scale on pressures greater than 1 atmos which we wont make use of. I found this one at crazysales.com.au 'RacerTech' for $14. In SuperCheap Auto they're about $80, I guess because they are higher precision and bling.

    This one came with the tubing and T piece needed to add it to the pneumatic circuit and so you need to take this into account when picking the size of the tube to use elsewhere in the circuit.

    Part 8 - the regulator spring. Don't underestimate how much force the vacuum advance will apply when you pick the spring to use. The vacuum advance I got had a diaphragm area of about 4 sq inches which at 14.7 psi ( 1 atmos) this is about 60 lbs or about 25kg of force it will exert against the spring. I salvaged a spring from an old metal bed base which turned out to perfect. In addition, the bed base turned out to be great for making the rocker table so if you can track one down , in fact 2 is even better, then it would be handy.

    ..... next instalment will cover the construction of the vacuum pump.

    Thursday, January 13, 2011

    Tooling up - Vacuum pump part 1

    Vacuum Pump

    Before I finalised the design of the board itself I thought it would be good to make the tools needed to make the board. In particular the vacuum pump and rocker table.

    The vacuum pump is obviously at the heart of vacuum bagging and of the pieces of equipment needed it is the one that for me had the most unknowns about it.

    I cruised the net and the general design that kept coming up involves using a compressor out of a fridge with an optional regulator so that its not running continuously. With a well sealed vac bag setup the compressor only needs to turn on about every 15 mins or so so having it run continuously is not necessary and probably shortens the life of the compressor.

    In one article I read of someone using a kite pump's deflate side and hand evacuating the bag. He had installed a pressure gauge and one way value and came back every 10 mins or so the check and repump it. Although this seems like a easy solution, having to hang around for the hours that it needs for epoxy resin to fully cure and come back each 10mins sound like a real pain in the arse. On top of that given the sand and crap that ends up in side the pump I wouldn't be that confident of being able to get it down to the sort of pressure needed without the pump itself needing to be in perfect condition. Maybe a brand new one and some quite viscous lubricant inside to seal over imperfections might work ok.

    The best resource I found for teh fridge compressor version is on seabreeze and the compressor I made follows this pretty closely. The only material variation on this design that I've seen is to add a reservoir (made from a big diameter piece PVC pipe with end caps). This would be a great addition as it would mean that it could cover compressor failure (they occasional need to be reset if the overload relay is tripped).

    and this one as well for a slightly different discussion (and no regulator)

    And so here is my finished vacuum pump. I've tested it and holds a vacuum of 28 inHg ( 1 atmosphere is 29.9 inHg - inHg stands for inches of mercury).

    To put this in context 1 atmosphere in pounds per square (psi) is 14.7 psi or 10,332 kg/sq m. A 130x39cm is about 0.5 sqm so the pressure that the vacuum pump can apply to the surface area of the board is about 5 tonnes!!!!

    PARTS LIST (see the photos below and in subsequent posts for pictures of the parts)

    1. Compressor from fridge with connection box and power cable (begged, borrowed or stolen is fine). Size of the compressor doesn't seem to be an issue other than perhaps how long it takes to suck the required volume of gas out. The small one I got from a 75 l bar fridge is 1/15 hp and sucks out all the air in under 30 seconds or so.
    2. 8mm and 10 mm pvc tubing (Bunnings)
    3. 8mm and 10mm hose connectors (Bunnings has 't' pieces and connectors for joining different size tube )
    4. A vacuum advance of a carburetor (local wreckers had one in a throw out bin that they sold me for $20. Most wreckers I spoke to wouldn't sell a vacuum advance on its own, just the whole carby so old ones from a mechanic might be easier/ cheaper.)
    5. 240v 10A microswitch (jaycar electronics)
    6. A vacuum gauge. These are commonly used on turbo charges and called 'boost' gauges. At repco / supercheap they cost around $80 but usually because they are very bling. I found one on an online retail site for $14 delivered and its perfect. http://www.crazysales.com.au/racetech-2-52mm-7-color-led-mechanical-vacuum-gauge-meter_p375.html . You need a fair bit of granularity in the pressure measurement so avoid ones where too much of the gauge is taken up with positive pressure measures (as opposed to pressure less than 1 atmosphere ie. vacuum).
    7. Electrical wiring and the 240v cable on the compressor.
    8. A strong spring for the pressure regulator. One from a metal bed base is perfect. At first I underestimated how much force there is associated with the pressures in the system and used a soft spring and the regulator kept cutting out at just a few inches of mercury (remember 1 atmosphere = 29.9 inHg).
    9. A bolt with a wing nut on it for adjusting the regulator setting
    10. Strong wire for the regulator linkage
    11. A rubber thong ( for mounting the compressor on to minimise )
    12. A handful of screws and cable ties
    13. Wood for base and for regulator housing


    1. The fridge compressor is mounted inside a sealed black metal container and has 3 or 4 copper tubes inserted into it.
    I was lucky enough to come across a 75 l bar fridge that had a working compressor but that the gas had leaked out of so wasn't keeping anything cold.

    I had tried a few different places to get one without luck: in our area there is a council program from collecting and degassing old (10 year old) fridges, I tried the local recycling centre but they would let me near the dumped stuff and so if not for lucking it on clean up day on the road side the next port of call would have been friends.

    If you get one out of an unwanted working fridge remember that it will most likely be full of ozone killing refrigerant which will escape if you cut the lines.

    On the compressor one line is the pressure line that's used to compress the refrigerant another is the vacuum side that helps pull it through the expansion valve in the fridge, one is a lubricant line ( the actual compressor is suspended in a lubricating oil in the metal housing) and the other is where the refrigerant is added. On the one I got from the 75 l bar fridge the last of these was permanently sealed off. Here's the inside view of the compressor http://www.youtube.com/watch?v=P7zYPj5nwQI

    The connection box (the black box on the side) is where the start relay for switching on/off is housed along with the overload protection that shuts the compressor down if its working too hard. Be sure to get all of this and the power lead when you salvage it. This compressor had a solid state start relay (PTCR) in it which looks like a simple disc of plastic with 3 connections on it.

    This link provides good discussion of how it works. http://www.e-refrigeration.com/index.php?page=ptc-relays.

    The PTCR provides increased current to required to get the compressor started and then opens to reduce the current to the lower level needed to maintain operation. The solid state start relays do this by letting the resistance of the device change rapidly as it lets the initial current through. In about a second the PTCR resistance has increased to 30kOhms because the current running through it has heated it up. This causes the relay to effectively be an open circuit.

    http://www.jimdow.com/jimdow/sales/diagrams/compressor12.jpg (PTCR is a solid state relay)

    The wiring diagrams are usually on a sticker on the compress. You'll also see that the earth wire in the 240v cable will be connected to the chassis of the fridge. This makes a path to earth if there should be a short circuit that send current through the metal chassis. Its a good idea to scrap of paint from the compressor at one of the feet and make sure you connect the earth wire there.

    PARTS 2 and 3. These are cheap as chips and the size means they won't collapse under a vacuum and pinch off the pneumatic circuit. The size was largely because that's what I came across at bunnings when I went looking for the brass connectors suggested in the seabreeze article. However, the plastic connector are perfect and even without the cable ties I put around them did not leak. The one thing to keep in mind when choosing the size is how big the tubes on the compressor and also the vacuum advance and the vacuum bag connector if you end up using one. You may end up (as I did) needing to have a couple of different sizes. The connector needed 10mm hose with the compressor was more like 5mm which I sized up to 8 mm using a piece of fuel line that was connected to the carby.

    PART 4. Vacuum advance

    UFO shaped thing off the carby. It is very basic. Inside the metal housing there is a rubber membrane that moves acording to the pressure in the space above it and so the armature out the bottom similarly moves. That's all there is to it. It converts pressure to displacement which in turn will press or release the button on the microswith to turn the compress on and off.

    ... to be continued

    Tuesday, January 11, 2011

    Construction and Materials


    As this is the first board making project I've had a go at I decided to keep the design 'mid tech' because even though a few people have created some great looking boards just wetting up a foam core by hand and hanging weights off it to pull the rocker and the concave into it, it seems natural that vaccuum bagging will produce lighter stronger boards which, even for a first attempt, is one of the goals.

    Some evidence of the weight issue (Trevor reckons) comes from some tips from the extremely helpful people at FGI (Fibre Glass International) in Brookvale here in Sydney who gave me a 'rule of thumb' estimate on the amount of resin needed:

    i) if you apply one layer of 6 oz e-glass at a time and let it dry between successive layers then you can expect to use about 800gms of epoxy resin per sq. meter on average across a few layer. The first uses more because it needs to bond to the core;

    ii) if you apply wet-on-wet, i.e put all the glass layers on at the same time without any drying time in between, then this comes down to about 500g/sq m. This apparently needs a bit more skill and speed as the resin will start to cure when its spread out and so if you have 6 layers to do then you will already have the early layers going off before you can clamp the work down;

    iii) If you then vaccuum bag it this can come down to around 300g/sq.m

    iv) if you use peel ply on top of the work (perforated plastic sheet the sits between the glass and then vaccuum bag itself) to allow the excess resin to flow away more easily then this could come down again to 230g/sqm.

    When you tally up the difference by vaccuum bagging then you can end up using 50% to 30% of the amount of resin that hand layups might achieve. On a average sized board with 3 layers of 6 oz cloth on top and bottom this adds up to 1.5 kg to 3.5 kg!!! This is a massive difference when it comes to kiteboards where a couple of hundred grams is very noticeable. Reading around various blogs 2kg before accessories seems to be the goal for most board makers. Less and strength appears to get compromised.

    On top of this, vaccuum bagging just seems like such a cool idea that I wanted to have a crack at it.
    There is a brilliant resource on vacuum bagging available on the West Systems webiste (providers of epoxy resin systems among other things).

    So, even though this first attempt may not be the greatest board on the market it is going to cost a couple of hundred bucks and so I wanted to give it the best chance of being half decent.


    On youtube I came across a guy who used this technique but also cured the board under heat lamps. With the standard epoxy resin that I bought at FGI the data sheet says that curing under temps up to 50 degrees c can dramatically improve the strength of the board. The video I saw certainly supported that as the guy put it between 2 stacks of books and bounced up and down on the middle (travelled about 10cm each bounce) without it snapping. In the video he just put the whole rocker table inside a 'tent' of insulating material and put a few heat lamps inside and let it cure away. I also came across a video from Brokites on their construction techniques and they similarly use heat to cure it and get similar strength (althought their boards seem to use a lot of carbon).

    I'll be keen to give this a go in the future and compare the results but at this stage its in the high-tech basket.

    Core material was the next thing I spent some time researching.

    The main options for core material are marine ply, other wood, PVC foam.

    i) marine ply wood - I've seen people laminate 2 layers of 3/16" or 1/4" marine ply, one layer of glass and few bolts and away they go.

    ii) other types of wood - balsa, western red cedar, poplar and paulownia. In general the stronger the core material the less glass that is needed and fasted you get out on the water. The choice between the different woods is largely about the strength/weight trade off ( look goes without saying).

    Balsa - 40 - 340 kg/cu m (huge range)
    Paulownia - 275 kg/cubic meter
    Poplar - 350 - 500 kg/ cu meter
    Western Red Cedar - 450 kg/ cu m


    Paulownia seems to be the board making wood of choice at the moment. Its touted as having superior strength to weight compared to the others - can't say. But it does seem that as the heavier density woods get introduced they are often used only as part of the structure.

    Check out this video of a crazy many with a circular saw showing the composite construction of a slingshot SX but cutting it open!!!! http://www.youtube.com/watch?v=EtI1AJiiC9o

    iii) PVC foam - PVC foam is used extensively in boat building and often goes by the name Divinycell or Klegecell. It light at, typically stocked stuff, at 80 kg/cu m. Its pluses are its very easy to work with - you can use a standard old hobby knife to cut it and it can be sanded and shaped just like a surfboard blank - it comes in large sheets ( 2.4 x 1.2 m ) which can be cut into 5 pieces for for various sized boards. The cons are that its obviously the weakest of the core materials mentioned and so needs the most glass. One blog I read said that you need about 30% more glass on a PVC core compared to balsa core.

    The other thing that was attractive about this as a first timer is that its lack of stiffness makes it easier to have the rocker and concave introduced without worrying whether the vaccuum set up I'm going to use has enough rigidity in it to bend the material.

    On pure aesthetics I was keen on using balsa. It is very available (though pieces need to be glued together as I could find pieces longer than 1 meter - hobby stores sell the stripes used to make models with and FGI sells sheets 1 m x 75 cm), easy to work with and looks brilliant. However, only big downside is that if the glass skin on a balsa board is ruptured then the standard balsa will absorb the water and it will become waterlogged. High density PVC foam repels it. So this made PVC foam a lower risk option for my first board.


    The choice between glass and carbon for me was a $$$ issue. The difference is $5 /m for e-glass vs $45+ /m for carbon. Carbon is a hell of a lot stronger than glass so you naturally use less of it (lighter, stronger and potentially stiffer boards) but I'm guesstimating that I'll use about 7m of glass mating in the board (3 layers top and bottom) so the initial outlay for carbon is too much until I know what I'm doing.

    S-glass is stronger than e-glass, the chemical structure is different and you can save weight by using s-glass. It is also a little more expensive ( as you'd expect) and so again that is in the 'next time' basket so that I at least have some benchmarks for how strong the standard stuff is.

    Laying the glass so that that weave runs at different angles seems to be a common method for improving strength of the board. You need to take this into account when working out the length of cloth to buy as the it can mean that you will end up with quite a bit of off cut cloth to accomodate the off-axis line of the weave.

    EPOXY vs Polyester Resin


    In a nutshell epoxy has stronger adhesion to the laminating material (4 times the strength in the kevlar example in the above link) and has lower moisture absorption and is more flexible than polyester resins. Epoxy is a bit more expensive but you'll end up with a stronger lighter board less prone to delamination - expect to pay around $75 for 2 kg of resin + hardener vs c. $55 for polyester resin + catalyst (MEKP)(note: the polyester resin hardening process catalyst as the resin apparently has the hardening process already underway when you buy it and the catalyst speeds the process up) http://www.dionchemicals.com/resin.html .

    Part of the price difference is the different ratio or resin to hardner that is used. In Epoxy resins the ratios of Resin to Hardner are in the order of 5:1 while with polyester resins you use around 100:1. Hardner accounts for a lot of the price difference.

    Having said that also depends on what quantities you are purchasing. The pricing on epoxy is set for the typical large quantities of resin used in boat building the price per Kg drops fair quickly.

    Although at 1.5% hardner the curing time for polyester resin is short (5 - 10 mins) it is possible to control cure rate by using less resin. However, 1.5% in the typical volumes being used in board making scales down to partial 'drops' so managing the cure time to allow you time to wet out all the layers and get into clamped/ sucked onto the mold might be tricky. According to the wikipedia page above of the resin comes with the hardening reaction already underway (albeit very slowly). The 'hardner' MEKP is actually a catalyst that speeds the process up.

    The resin I've got hold of is R180 Epoxy with H180 hardner. H180 is a slow hardner and give 40-50mins gel time which should be plenty to do the lay up.


    There seemed to be 3 main options here again: poured epoxy rails, abs plastic or wrapped.

    Poured epoxy rails are made by routing a 1o mm channel around the outside of the blank core and pouring in a mixture of epoxy resin, q-cell ( or microballoons) with chopped strands of glass. Q-cell thickens the epoxy and is a hell of a lot cheaper than epoxy so it saves money and the chopped strands are literally 5-8mm pieces of glass fibre that you put in to increase the strength of the material once it sets. You can then flip the blank over and sand it down till you expose the pour material and there you have your rails. Note that q-cell does weaken the epoxy a bit and 15% q-cell by volume seems to be about the proportions people have reported using.


    Q-cell is also useful as a filler to fill the gap between square edges on different layers of the board ( if you're laminating several layer of foam etc). Fibre glass can't conform to the sharp changes and will bridge over them which means it is not in contact with the core material. Q-cell can be used to thicken the resin up so that you can fill these 'steps' so that the glass has a bonding surface to attach to.

    ABS plastic seems to be the best choice. Unlike some other plastic material, epoxy will bond to abs plastic. Other plastics ( and #$#% there is a lot of them) may need to have the surfaces of them 'flamed' to get the right chemistry on the surface so that the epoxy will bond to it. Its very easy to work with and very flexible. I got an off cut sheet from a plastic supplier which was about 1.5 x 75cm and it cost $70. Ouch but I used it to repair the rails on another board that had been smashed when I ran over some rocks - it worked like a charm. I have heard of people going to sign makers and getting off-cuts for less.

    I've just become aware of another possible approach. I'm waiting for some more details but it involves using liquid ABS plastic rather than the sheet discussed previously. My initial thoughts are that you would lay the core material over wax paper and fix it in place, then squeeze out the liquid ABS and sculpt it (like you would putty) into the rails making sure to make the 5 mm or bigger than needed so that you can trim it back later and get a nice clean edge, let it cure and the sand if back to the thickness of the core. After having spent about 3 hours cutting the ABS sheet to the exact shape I needed this approach seems brilliant.

    A bit of searching on liquid ABS revealed that you can make your own by simply disolving ABS shavings in acetone and letting it disolve in a sealed container. If you end up with mixture that is too thin then you can just let the acetone evapourate off or add more shavings. One blogger said that he was able to get a bag of ABS plastic pellets from a local vacuum forming shop. Other just took ABS plastic offcuts or sheet and shaved it with a surform or an electric plane. One guy cut a sheet into 2cm x 2cm pieces and he said it took about 3 days to dissolve - so shavings seem like a better approach.

    From all reports, when the liquid ABS cures it is as hard as the original material. Lots of people have used this liquid ABS as a glue for ABS plastic pieces and claim that the glues material broke before the joint itself.

    The role of the acetone is to disolve not only the plastic to get the liquid material but also dissolves the material that the liquid ABS is subsequently applied to and hence forms an ABS-ABS bond (this is effectively solvant based plastic welding). A question yet to be answered is whether the acetone will destroy the PVC core material being used for the board. I'll update the blog once I find out more.

    One final comment on this approach is that I have seen one guy who mixed up epoxy and Q-cell and chopped fibres to 'peanut butter consistency' and used this same approach to as described for liquid ABS to sculpt the rails. This may be a slightly cheaper way to do it.

    WRAPPED RAILS as I understand is just where the glass is wrapped around the rail so that the board is completely encased in glass rather than relying on the rail material to form the waterproof barrier. The one, small, drawback of this approach is that you have to have the rail shape finalised before you do the layup. Not a big issue unless you want to experiment. This approach could be used in conjunction with other rail material as I suspect it would be important to have tougher material on the rails as they do take a real beating and reducing the risk of water logging if the rails are damaged through having a 10mm or so rail before the core would seem to serve this purpose.

    As I had the ABS plastic on hand I decided to use this.

    So that is all the basic construction and materials selected. The next installment will look at the design of the board itself.


    Monday, January 10, 2011

    Project Kiteboard

    I've started this blog to keep track of my first attempt to build a kiteboard.

    Along the way I'm hoping to turn up some online resources, tips from the pro's to help and learnings from mistakes to help anyone else who is a first time builder have a good go at it.

    I've spent a lot of time studying in at the University of Google (UoG) and it seems that there are loads of people who have had go at making their own boards. One of the encouraging thing is that the range of sophistication and cost is enormous. Boards made from a single sheet of plywood with seatbelt and carpet footstraps through to exotic wood and vacuum infused, full carbon boards. The great thing about this is that the range of techniques and ideas that you can cherry pick from is huge and even better that some of the sophisticated techniques have been 'backyarded' so that they are much more achievable with the basic and often primitive setups that most of us are likely to have access to when DIY'ing a board for the first time.

    One of the best resources I've come across is at http://www.kiteforum.com. There is a board builders forum that has a huge range of posts on all sorts of topics with graphics getting a lot of air time. Youtube is also invaluable to actually see how a technique is executed. There are a large number of videos (and a number of time lapse videos) showing the process from start to finish. This has been really useful for learning techniques such as vacuum bagging that was very new to me. I'll post some of the specific resources at the relevant step along the way.

    All though there is a lot of information spread around, there are a lot of questions I found myself asking along the way that were nebbie questions whose answers were often assumed by the people who already have experience. Things such as the pro's and cons of different techniques, materials, curing temperatures, how much rocker, to concave or not, do you need to earth your fridge vacuum pump, where to get the material you need and very importantly how much do the different options cost. Part of the purpose of this blog is to record the answers to those questions that occurred to me along the way as a first time builder.

    It seems that while there is a lot of science in building the boards (material selection, process and strength/flex - datasheets on fgi's website www.fgi.com.au/files/images/stories/pdfs/literature/sandwich_hd.pdf
    have the full suite of equations governing these properties and more for composite materials using PVC foam or balsa) there is a hell of a lot of art to it and proof along the lines of 'Trev reckons!'. Part of the fun on this project will be seeing how much of each is useful and coming up with my own rules of thumb.

    If you do happen to find any of the information useful along the way please let me know - It would be great to hear from other board builders and compare notes on what should be a fun project.


    Saturday, January 1, 2011

    BoardOff Design Tool Revision History

    This post contains a link to the latest version of the BoardOff Design spreadsheet (MS Excel 2007) that is available free for download.  Also, if you want to comment on any bugs, suggestions for new features, or ask how to's please use the comments on this post so all can see.

    BoardOff contains a new tab that tracks the changes.

    Click link below for latest version

     Latest Version

    ** Note as of 31 May 2017 this has been moved to a git hub site where you'll need to download it.

    Version 1.3.17

    Added smoothness conditions at the corner-mezz, mezz-mid section joins.Also, enforced smoothness conditions at the joins in the rocker and the concave profiles. Note: some of the stock outlines needed to be updated as the outlines were modified slightly under the continuity conditions (matched first derivatives and zero second derivatives at the ends)

    Version 1.3.16
    • Added function to composite different templates on the nose and tail side of the board. This allows mutants and surfboards.
    • fix the flex models to accomodate the longer maximum board length.
    • Few minor bug fixes.
    • NOTE: ACAD9 will not display boards longer than 140cm. Use Draftsight. It is a superior tool and has no problems with the longer boards (and still free)

    • Version 1.3.15 BETA

      There have been a couple of people asking about the possibility of using BoardOff for boards longer than 140cm which was the previous maximum length. It turned out to be a bit easier than I thought to extend the outline drawing part of the program. I haven't takled the flex model as I am not sure whether anyone is using that part of BoardOff and so I've left it as is.

      The maximum length is now 180cm.

      Updates in latest version of v1.3.12a

      Minor fixes 1. Fix error in location of fin inserts that resulted in fin inserted offset too far from rail 2. Add automatic function to force the rails to be added to the board dimensions prior to exporting the rocker table outline. 3. Add fin insert holes instead of just center cross hairs. This is needed for CNC cutting 4. Allow the fin inserts to be drawn as either channels or jus the insert holes. Again a refinement for CN cutting. 5. Added new board outline and rocker design for wake style board similar to the DarkSide.

      Updates in v1.3.11a

      1. Added footpad outlines to the dxf export function for outline template
      2. Added footpad corner markers to the Draft Outline chart to help size the decks to avoid the footpads overhanging
      3. Added .dxf merge function to  the rocker table templates so that they can be  merged into the board outline .dxf file for printing on large sized paper ( e.g. B0)

      Updates in v1.3.10
      1. Added an overlay grid option on dxf exports to help with manual compositing when sticking A4 tiles of the 1:1 scale plans.
      2. Added new tab 'RockerRibs' that generates lateral profiles of the boards rocker and concave profile.

      Updates in v1.3.8/9
      1. Add saveable laminate schedule templates
      2. Add gradient 'ants' to help make the outline continuous
      3. Seperate core design and Flex testing into seperate tabs

      Updates in v1.3.7
      Only minor revisions and bug fixes in this version
      1. Add DXF export for rocker jigs
      2. Add 'water line' - an attempt to determine the line that the surface of the water traces across the bottom of the board. This is an FYI and was an attempt to start understanding drag and board surface design.
      3. Minor bug fixes in the flags for the corner calculations in the outline template.
      4. Replace footstrap insert holes with cross hairs and similarly added cross hairs to the fin insert positions.
      5. Add text box in outlinetemplate to allow an annotation to be recorded on the baord template.

      Updates in v.1.3.4 (2 Aug 2011)
      1. Add function to export OutlineTemplate in DXF format. (Autodesk Autocad format)
      2. Add function to allow dxf files to be be merged together so that multiple deck templates can be merged into a single file.
      3. Add compositing tool to help with designing multideck boards or comparing different outlines. The tool works but take a snapshot of the existing chart and add it as the background of the chart object thus allowing a new outline to be superimposed on top of it.
      4. Add 'waist' or cut-away mid section like the 2011 North board designs.
      5. Add swicthes to toggle the display of the fin inserts,footpad inserts and control points.

      Updates in 1.3.2 version
      Added savable rocker and concave profile templates.
      Added switch to draw convex (cut-away) tips
      Added a 'none' option to the laminate schedule to allow layers of laminate to be be quickly removed.
      Improved FlexProfiler to allow stringers to be modelled in the flex profiling.
      Fixed a couple of formula errors in FlexProfiler
      Relabled the OutlineTemplate control points to clarify their function