7           Laminating the deck High Density (HD) foam

This step in the process is certainly the most complex, and requires meticulous preparation.  I always secure help from Rex for this stage as there is a lot going on and it is good to have someone around to mix small batches of epoxy and help get the board in the bag.

 As with the hull lamination, we’ll start with a list of preparatory tasks

1. Use high quality drafting tape to mask off the edge of the high density foam on the bottom of the board.  Mask off about 3” from the edge.  This tape stops the deck layer of high density foam bond to the bottom of the board.

2. In order to wrap high density foam around the rails of the board and use a bottom mould. we have to manufacture a lift of medium density foam for the board.  This lift sits between the board and the mould.   For the speed board I have used 28kg/m3 Blue Styrofoam (sourced from Solent Insulation Supplies).  I like the Styrofoam as you can cut sheets of it with your hot wire cutter, and it is relatively cheap.  This particular lift has been reused from a previous project, and has three sections that are screwed into the bottom of the board using 2” wood screws.  Don’t worry about the holes left by the screws, as they are easily filled later.  The lift has been scored with cuts from a Stanley knife about ¾” deep down the centreline at the tail (to allow the lift to accommodate the ‘V’ of the board), and also across the nose section (to allow the lift to take the curve of the nose rocker).  The lift sits about 1” in from the edge of the hull of the board.  Note also that I’ve taken the hard corner of the lift off, to allow the top HD foam to fully wrap around the rail.

3. The mast box on a windsurfer is one of the areas of high stress.  For this reason, we are going to reinforce this area.  One way to do this is to put a 16” stringer into the centreline of the board, centred on the mast box.  The stringer that I’ve used in the speed board is made from two pieces of 16”x1.5” 3mm high density foam.  I built a wave board in 2001 whose mast box failed.  Actually it wasn’t the mast box, so much as the reinforcement around the mast box.  In future, I’ll heed a top tip from Bill C and use a cassette of high density foam (something like Core Cell would do the job). The cassette Bill uses is 40mmx60mmx200mm, and provides more structural integrity than the stringer here. That said, I'm after minimum weight on the speed board and so am happy to use a stringer as it is significantly lighter   Mark out the mast box position on the EPS foam, and then mark out the position of the stringer/cassette.  In this case, the stringer is 16” by 6mm.  Then, use the router to cut a box that accommodates the stringer/cassette.   When the stringer/cassette is glassed into the board, there needs to be enough room under the stringer/cassette to accommodate 2 layers of fibreglass and some thickened epoxy, hence the box is cut 1/8” deeper than the depth of the stringer cassette.

4. We are going to put multiple patches under the high density foam to reinforce areas of stress, namely around the mast box, under the feet and on top of the fin box.  For the mast box, first cut two pieces of S-type glass that will be wrapped around the stringer/cassette.  So for the speed board these pieces were 16” by 11.5” (11.5” as I wanted 4” of glass each side  of the stringer).  Then cut two patches of 20”x10” carbon to cap the mast box stringer, two patches of 8”x6” carbon to sit under the front foot position, two patches of 12”x8” carbon to sir under the back foot, and two patches of 12”x6” carbon to cap the fin box position.  Mark out on the board where these patches will be positioned.  

5. We now need to fabricate a piece of high density foam to fit the deck of the board.  Using a soft tailors tape measure, measure the board at each 15cm station to determine the width of HD foam that is required at that station.  Add 1.5” to your measurement to allow for a ¾” overlap below on the rail on each side of the board.   Cut sections of HD foam according to these measurements, and if you have to use multiple sections (as I have done here) join them with your highest quality drafting tape.  The curves of the deck of the board are far more complex than the hull, so relief darts have to be cut into the foam, especially at the nose and tail, and along the nose rocker.  Test the fit of the foam to the board, and increase the size of the relief darts as necessary, so that you can be sure that the HD foam will conform to the curves of the board when put under vacuum pressure.  I am always amazed by the size of the relief darts that are required.   Make sure that the high density foam has a clearly marked centreline, as this will need to be aligned to the centreline marked on the board.

6. Roll out your 4oz S-type glass (or 6oz if strength is of more concern than weight), and use the high density foam as a template to cut a piece of glass to the same size.  I also cut a piece of carbon to further reinforce the section of the deck from the tail to 1m, as shown in the picture.

7. Cut two pieces of polythene that are at least 12” wider than maximum width of the high density foam, and 12” longer than the board.  Also prepare a piece of double thickness vacuum breather fabric that is 4’ by 18”.

8. Prepare the mixing table as per the hull lamination, but this time include 4 or 5 mixing pots, and a tub of glass bubbles.  Glass bubbles are used to thicken epoxy into filler.  For this stage, I use an epoxy that has a slow hardener (SP106 Slow) so that I have more time before it gels.  Familiarise your helper of choice with the mixing table, as this is where their time will be spent.  Make sure they understand the hazards involved and give them safety equipment.  

9. Be sure to have plenty of cheap drafting tape, 3x2” wood screws and a screwdriver to hand.

10. Prepare the vacuum pump and bag, as per the hull lamination.

11. Heat the workshop to at least 15 degrees, but not above 20 degrees.

Excellent, preparation is complete, sit down and chill with a cup of tea and read the rest of the process through before embarking.

• The first step is to wet out the fibreglass that wraps around the mast box stringer/cassette.  Mix some epoxy (50ml or so), and wet out the S-type fibreglass.  This will take maybe 20ml, leaving 30ml of mixed epoxy.  Thicken this epoxy using glass bubbles, until it is the consistency of mayonnaise.  If you get to peanut butter, you have gone too far!  Now, cover the high density foam that forms the stringer/cassette in thickened epoxy.  Also, use a mixing stick to cover the walls of the stringer/cassette cavity in thickened epoxy.  Place wet out pieces of S-type glass on top of the stringer/cassette cavity, and then push the high density foam stringer/cassette into its cavity, taking the glass with it.  The glass now forms a ‘T’ section, which is very strong.
• Place the other reinforcement patches on their pre-marked positions on the board for the top of the fin box, the foot positions and the cap of the mast box stringer.  Mix another small batch of epoxy and wet out these patches onto the board.  Now put the board to one side and move on to prepare the high density foam and 4oz fibreglass.
• Lay one of the sheets of polythene on the vacuum table, and fix it in place using a couple of pieces of drafting tape.  Place the deck high-density foam on top of the table, drafting tape side down.  Place the 4oz glass on top of the foam.

Mix enough resin to wet out the 4oz glass.  Pour 2/3 of the epoxy down the centre of the fibreglass and use a squeegee to wet out the cloth.  You may find that you end up with dry patches around the edge of the fibreglass.  If this is the case, use a 1” cheap paintbrush to wet out in these areas – it’s easier than the squeegee.  Once the 4oz glass is wet out, place the 6oz carbon patch over the tail of the foam and use more epoxy to wet it out.  In the picture here, I’ve wet out the cloth on a piece of polythene rather than the high density foam.  This saves a little bit of weight, as it avoids the open cell high density foam sucking up epoxy.  It’s a real bugger transferring the wet out cloth to the high density foam – if you are doing this for the first time, I suggest accepting a slight weight penalty and take the easier option of wetting the cloth out on the foam, after filling the grain of the foam with thickened epoxy.

• Put the high density foam and fibreglass to one side, take the vacuum table off the board stand, and place the board on the stand, deck side up.
• With your able helper, pick the high density foam up using the polystyrene sheet, and flip it over onto the board.  Remove the polythene sheet and discard it, as it is probably covered in epoxy.  Carefully align the centreline of the high density foam with the centreline of the board.  Now fix the high density foam to the board using 3x2” wood screws on the centreline.  Try and position the screws so they are not going through any carbon (or anywhere near the stringer), as they will be a bugger to get out once the epoxy has cured!
• Place the second sheet of polythene over the board.  Trim this sheet so that it overhangs the bottom of the board by about 6”.  Use a couple of pieces of cheap drafting tape to secure the polythene to the Styrofoam lift.

Now, turn the whole assembly over, so that the board is hull up.

Pull the polythene tight across the bottom of the board, and use long strips of cheap drafting tape to secure it in place.  Do this at 4” intervals for the length of the board.  The intention here is use the polythene to pull the high density foam as close as possible to the deck of the board.  Special attention needs to be given to the nose and tail – as you can see from the photo, they require a fan of tape to keep the deck foam in place.  Note that the tape pulls the deck foam and fibreglass right around the full curve of the rail.  This is good, as it means that the deck will bond all around the rail.  Don’t worry too much if the fibreglass comes into contact with the Styrofoam lift.  But do get concerned if you see that there is no fibreglass protruding past the rail – this means that there is nothing to bond the deck foam to the deck.  Corrective action is required if this is the case.

When you have finished tensioning the polythene, the top of the board should look something like this.   Don’t be too concerned if you have a few wrinkles in the polythene (as on the nose section here).  But do be worried if the polythene is not holding the deck foam to the rail of the board.

• Now, take the vacuum breather fabric and tape it to the top of the board.
• Put the board to one side, get the vacuum table in place, and put the bottom mould on the vacuum table.  Put the board to the bottom mould, and hold it in place with a couple of small pieces of drafting tape.

• Put all of this into the vacuum bag.  You may feel the temptation here to dispense with the vacuum table and bottom mould, and just put the board in the vacuum bag.  Do this at your peril – the forces introduced by the vacuum pump are enough to permanently crush the board when it is this fragile state.  Before you seal the bag, put the bottom of the through-connects into the bag on top of the breather fabric. Seal the end of the bag and attached the through connects, using the holes that were made when doing the hull lamination.
• Switch on the vacuum pump, and watch as the pump removes excess air from the bag. When the pump is close to removing all the air, disconnect it and make sure that the bag is getting into all the nooks and corners of the assembly, especially around the Styrofoam lift.  Switch the pump back on, and adjust the release valve so that the pump is pulling 4-6” Mercury

This is what the final assembly should look like.  Keep the vacuum pump running for 12-16 hours, and keep the workshop temperature at 20 degrees or so (or stick the whole lot in your oven if you have built one).

If you have successfully completed this step, then you can bask in the knowledge that you have finished the most technically challenging part of the build process.  It downhill from here in, and the process is a lot less stressful as it is not so constrained by time.  Once the board has been in the bag for 12-16 hours, switch off the pump, remove the bag, and place the board on the stand.  Remove all the polythene and drafting tape.  Remove the wood screws that are holding the Styrofoam lift in place, and carefully remove it.  You may have to take a knife to any fibreglass that has bonded to the Styrofoam.  You now have a full composite board with the deck foam overhanging the hull by 1” or so. The next stage is to trim away the excess foam and fibreglass/carbon.  Fit a new blade to your Stanley knife and dip it in Acetone.  Run the blade parallel as close to the bottom of the board as you can, and trim away the excess.  Remove the drafting tape from the hull of the board as you go.

It is likely that the edge of the deck foam is slightly proud of the hull in some places.  Fit 60 grit paper to your 10” sanding board, and very gently sand down the edge of the deck foam so it is flush with the hull.  With care, you can get a very smooth finish (see pic).  If you see any voids where the deck foam hasn’t bonded all the way round the rail, don’t worry, but do mark them out with a pen – you’ll need to fill these voids with thickened epoxy at a later date.

Now you have a composite board.  It is very easy to find high- and low-spots in the high density foam, compared to the EPS.  Run your hands over all the curves on the board and pick out the areas that need attention.  Use 60 grit paper on the 10” sanding board.  One useful tip is to draw several lines 1” apart across the high- or low-spot before your sand.  As you sand, these lines will tell you how close you are to achieving a perfect surface.  Pay special attention to the mast box stringer area, the edge of the carbon patches, and the fin box area.

The speed board at this point weighs in at a respectable 1.6kg!