3. Board Design

There are two ways to go about board design.  The adventurous could start from scratch and produce a unique design.  There are a number of software products around to help with this approach such as Shape3D.

An easier way to progress is to modify an existing design.  This involves two steps – first copy a existing board (the donor board) and then make modifications to the plans.  The advantage with this approach is that outcome is likely to be an improvement (or at worse, a slight regress) in a board that you already know you like.  I’ve never worked in the windsurfing industry, but I’d be amazed if they don’t use last year’s designs as a baseline for next year’s improvements (I guess the exception here are certain Starboard ranges that really break the mould, such as the Hypersonic).

The approach that we will use here involves modification of an existing design.

For this particular example, I’m going to have to tell you about a wedding last September in Wales.  I met up with my friend Windy John who has opened a windsurfing shop in West Kirby.  West Kirby used to be one of the principle speed venues in the UK, and Windy has it in his head that he wants to get speed back on the map.  So, he introduces me to ‘Turbo Shandys’, and before you know it, I’ve agreed to build a speed board.  Never built one before, so where to start?

A couple of phone calls and emails and I find out that the UK speed record is a shade over 42 knots, and held by Dave White.  Apparently that record was made on a 270 F2 Sputnik, which by today’s standards is still considered a fast dedicated slalom board.   The stats on the board are interesting – 270 length, 52 wide, 88 litres.  I manage to get hold of one and it weighs an impressive 7.4kgs.

Windy and I discuss the new design, and conclude that we want something that’s 250cm in length (I insist on that, building boards longer than 250 involves gluing blocks of EPS together which is a real pain in the arse), 35 cms wide and about 70 ltrs.  We want to use a modified version of the rocker line of the Sputnik, which is a proven quantity.  Windy also puts several other requirements in;

• He must be able to get his heel wrapped around the rail without catching the water.
• He wants a power box fin.
• He wants the option of a central back footstrap.
• And I want to build a board that weighs less than 5kg!

3.1         Board Design - The End Game

It is easier to understand what is required from the design process if we look at the final outputs.  There are three; profile templates, the plan-shape template, and the design sheet.

The picture shows a pair of profile templates.  These eventually are screwed into the side of a block of EPS foam and guide the hot wire cutter around the rocker line and deck.  In order to produce these templates, we need the rocker line (the curve of the bottom of the board), and the depth of the board at 15cm intervals.

Any defects in these templates cause problems later in the process, so it is worth spending the time to get them right.  Any low or high spots have potential to cause real issues.

3.1.2        Plan-shape Template

The plan-shape template (sometimes called a spin template) gives the curves around the outer edge of the board.  In the picture, the left hand side of template gives the curve at the front of the board.  The right hand side of the template gives the curve at the back of the board. 

The quality of this template is not as critical as the profile templates, but it’s still worth the effort to get this as perfect as possible.

The design sheet becomes the holy grail of measurements throughout the board building process.  The details on this sheet are;

1. The width of the bottom of the board every 15cm.
2. The width of the board (including the curvature of the rails) every 15cms
3. The ‘V’ of the board every 15cms (more on this later)
4. The depth of the board every 15cms
5. The rail profile every 15 cms
6. The position of the front and back of the fin box
7. The position of each footstrap hole
8. The position of the mast track

The design sheet is becomes the board builder’s bible for measurements.  Here are the steps to a perfect design sheet.

1. You need a big piece of paper that is at least the length and width of the donor board.  My mate Adrian (not seen him for ages) worked in a newspaper print factory, and could get hold of rolls of newspaper.  This was ideal for the job, as its slightly see through.  A close second is grease-proof paper especially if you can get hold of a roll with a good width (Mrs ECB is sick of this disappearing from her kitchen).
2. Mark a centre line down the middle of your paper.  Why?  Because you can’t rely on your donor board being completely symmetric.
3. Cut a couple of small holes in the paper near the centreline, and attached the paper to the underside of the board using drafting tape, such that the centreline of the paper is central on the board.  If the drafting tape won’t stick, you have salt on the board.
4. Take a Stanley knife and shave down the tip of a pencil so that you have a length of lead about 1cm long.
5. Pressing the paper around the rail of the board, run the pencil lead around the outline of the bottom of the board.
6. Make a mark on the centre line every 15cms from the tail and every 15cms from the nose until they cross in the middle.  Draw a line across the board on each of the 15cm stations, using a large set square.
7. Measure the width of the board at each 15cm station.
8. Measure the ‘V’ of the board at each 15cm station.  The easiest way to do this is to place a rule across the width of the board, and press down on one side.  The height of the rule at the other side is 2V.  If you have a concave board, you may want to consider whether this is a good donor board, as the methods here can not copy this design (goodness knows how AHD do it).
9. Using a profile gauge, take the profile of the rail at each 15cm station and transfer this to the design sheet.
10. Measure the distance of the front and back of the fin box and write these measurements on the sheet.
11. Do the same for the footstrap holes and mast track.  When taking measurements on the deck, use a soft tailors tape that can measure around curves more easily than a rule.
    You now have a design sheet for the donor board.  If you want modify your board, you can now scale the measurements up or down depending on what you want to achieve.  You can see that in the picture here, you can just about make out that I have scaled down the length of the board by 11%, and the width of the board by 20%.  The scaling takes some time, as I decrease the station interval from 15cm to 5cm to improve accuracy.  Once it is scaled down, new 15cm stations are marked out on the design sheet.

3.2.2        Making the Plan-Shape Template

The plan shape template uses the design sheet and a piece of 3mm plywood.  It has to be at least half the length of the board + 10cms.  My board is to be 240cm long, so I need a 130cm length of ply.  Once you have that, its simply a question of transferring the curves of the design sheet onto the ply.  If you wish to be absolutely accurate in your template, you should redraw the curve to account for the depth of the high density foam, in the case of the speed board this meant taking off 3mm inside the curve of the plan shape. Instead of using a jigsaw to cut exactly to shape, I’d suggested using the jigsaw to cut out around the template leaving about 5mm of ply all around.  Then use a small block plane to take the template down to size.  This means you are more likely to avoid high spot and low spots on the edge of the template.

Once you have finished with the block plane, rock a 30cm rule round the edge of the template to highlight any high or low spots.  If you do find any, use 60 grit paper on a small sanding block to correct to smooth flowing curves.

3.2.3        Making the Profile Templates

These templates deserve a quality job, and lots of time.  Cock these up, and the whole board is jeopardised!  A little bit of care and you avoid so many problems later on.

First of all, we need to get the rocker profile from the donor board transferred onto a piece of newspaper or grease-proof paper.  This is a painful process.  In my experience, the best way to do this is to use a piece of 3mm ply to copy the curve.

The piece of ply needs to be the length of the board and at least 40cm wide.  Once you have made up this piece (ply only comes in 244cm lengths round here, so I have to use more than one piece for a 270 board), turn the donor board through 90 degrees and set it on top of the ply on its rail.  Then, using a long pencil, transfer the rocker curve to the ply.  Using this technique, you’ll only get a rough approximation to the rocker curve, but that is all we need at this point.  Be sure to mark the tail and nose.  Then, use a jigsaw to cut the curve.

Next, put the donor board on the board stand, bottom side up.  Sit your ply on top of the board, aligning the tail and nose marks that you made.  You’ll notice that at some points the ply touches the board, in others there is a disappointing gap.  Here is the clever bit.  Take a pencil and place it flush to the bottom of the board, perpendicular to the ply.  Now, run the pencil along the ply.  This allows you to mark off those parts of the ply that are touching the board, or within half a pencil width of it.  Use a small block plane or spoke shave to remove the areas that are marked off.

Now offer the ply to the board again.  You should notice that the ply is a better fit to the board this time.  Use the pencil to mark off the high points, and use the block plane and spoke shave to shave off the high points.  A couple of iterations, and you should have a piece of ply that fits snugly to the central rocker line of your donor board.

The next bit is optional.  If you want to modify your rocker line, you should transfer it to a length of newpaper and scale as appropriate as shown here.  I scaled down the Sputnik 270 rocker down from 270 to 240 in length, and also took 10% off the nose rocker.

Now, we prepare some 8mm ply for the profile templates.  We need two identical templates, so its best to fix two pieces of ply together with wood screws and cut both at once.  Transfer the rocker profile from the newspaper onto the top sheet of ply, and mark off 15cm intervals long the rocker line.  Now, from your design sheet, take the depth of the board at each 15cm interval and mark onto the ply. The high density foam that gets laminated to the top and bottom of the board will add to the depth of the board. For the speed board I'm using 2mm Airex foam, so I take 6mm off the depth measurement at each station - 4mm for the foam and 2mm for fibreglass and paint (thanks to Bill at BC Boards for this tip!).  Now you can join the dots of the modified depth measurements to give the deck profile of the board.

To recap, we now have the rocker and deck profile of the board drawn on the top sheet of ply.  Wood screws are holding a second sheet of ply in place along the full length of the profile template.  You may now use a jigsaw to cut both templates out, leaving a 3mm margin of error – the templates will be finished in the same way as the plan shape template, using a block plane, spoke shave and sandpaper.  By the way, its worth using a decent jigsaw with pendulum action to cut out the templates.  The tip of the blade on a jigsaw that doesn’t have pendulum action tends to wander as it cuts, leaving you with two differing templates.  My friend John has a workshop over the hedge from mine, and I always ask for a borrow of his Makita to cut templates.

Now we have two roughly cut templates that are screwed together and so can be planed down to a final shape together.  I use a large hand plane for the flat sections at the back of the rocker line.  These sections tend to be flat and a large plane helps avoid making low spots.  For the curves at the front, use a small block plane for the convex curves on the hull, and your spoke shave for the concave curves on the deck.  As you get to within 0.5mm of the line, use a 30cm rule to find high and low spots on the curves at the front of the board, and a long 1m rule to find high and low spots on the critical planning surface at the back of the hull.  It is really worth spending time here to get the curves on the profile template absolutely perfect.  As a guide, I spend 4-5 hours at least producing the profile templates.  The way I look at it is that an hour invested at this point saves multiple hours of correction later.

Before you separate the templates and admire your work, drill a pair of 3.5mm holes (1.5cm apart) at every 15cm station, through both templates, and countersink opposing sides.  Now unscrew the templates, and use sanding paper to take off any hard edges and splinters.  Run 10mm drafting tape around each template – this helps the hot wire run smoothly.

On a final note, I always extend the templates slightly beyond each end of the board, to give the hot wire time to bed in before cutting into the foam of the board.  The theoretical depth of the profile template at the nose and tail is zero, but its worth making it 1” – shaping this back to zero later is no problem.