Building a Jarcat 6 - Making the mast
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November 2005, and I thought I should look at obtaining a mast - even though it would be months before the boat was finished. The plans specified an aluminium wingmast so I duly telephoned local sail makers (who were not interested at all) and then a catamaran centre in Brisbane. Their reply was that the boat I was building was just a floating caravan and would only need a standard section mast which they would supply for about $1300. Somewhat taken aback but willing to accept their appraisal I sent an email requesting a firm quote - to which I received no reply.
 
What to do?
 
Well having read in the plans that apparently no one had yet made a woodwing mast for a J6 I decided to give it a go. I ordered cedar for the spar and trailing edge and 3 sheets of 1.2mm aircraft ply. The ply is in 1.2m square sheets and these would be cut in half to make up the required 7 odd metres.
 
Whilst waiting for the timber and in between working on the boat itself I started cutting out the formers for the front half of the mast. I found the sheet showing the mast section was not to scale and drew up the section in a CAD program and printed it out. This was used to mark a template on a piece of 6mm ply and this template used to mark out the formers.
Note I had to read the instructions about building the jig several times before it finally clicked. (Must be getting slow in my old age).
 
I set a base on the shed floor using some seasoned hardwood glued to the concrete. A former was set at each end and a fishing line stretched tightly between the formers on the mast centreline.
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Formers were then added (making sure not to put a former where the plywood sheets would overlap) one at a time and aligned with the fishing line. This should ensure a straight mast. I used more formers than recommended with spaces around 300mm between each.
 
This picture shows the formers on the base with the fishing line
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The cedar had arrived so I set about joining the sections to make the 7.2m central spar.
 
Having set the router to half the timber thickness, and after marking the end of the half lap joint with a saw cut, grooves were routed in the joint area to aid in accurate cutting
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The "blocks" left after routing were then removed with a chisel and the surface cleaned up with a rasp. When all joints had been cut the spar was glued together - ensuring that the spar was straight.
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The ply was marked on one side with the front centreline and the positions of the internal timber spar and trailing edge. Small holes were then drilled along the line marking the front edges of the timber spar and trailing edge. These holes would allow bamboo skewers to be inserted to support the timber at the correct position when gluing later.
 
The ply was then carefully bent and slipped into the formers on the base. I started at the top of the mast and placed the sheets in one at a time. Glue was applied to the overlap area prior to placing the next sheet and the centreline on the face of the ply was carefully aligned and checked with a fishing line stretched from end to end of the mould.
 
Note the use of clothes pegs and masking tape to provide pressure on the glue joint. The central spar with a strengthening block glued on is next to the mould.
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Once the ply joins had set and been cleaned up the leading edge timber was glued in position from the hounds to the base end of ply.
 
All the stiffeners on the spar were glued in place, the trailing edge was shaped on the saw bench (I joined the trailing edge pieces with a 300mm half lap join similar to the joins in the central spar) and all internal surfaces were given two coats of epoxy resin. The first coat was treated with reaction dilution agent.
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Before adding the central spar I took the opportunity to glue a coax cable and two twin power cables inside the ply. This would allow for connection of masthead lights and radio antenna later.
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The pulley was inserted into the central spar as shown in the plan and a shaped cedar block made holding the front pulley. This block fits between the front of the spar and the ply. When gluing in I was careful not to get any glue on the pulley or in the rope holes
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Bamboo skewers were placed in the holes to support the central spar and with Marg's help we glued the central spar into position. We used lots of glue to ensure that a good bond was achieved. I cut "special clamp X" :) from 6mm ply and used these to hold the trailing edge together while the glue on the spar set. These clamps would be recut and used later.
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The trailing edge was glued in place next. This was supported on more skewers placed in the previously drilled holes. Note that the "special clamp X" has been converted to "special clamp Y". : )
 
I didn't forget to run strings from the base of the mast to the top and through the pulleys and out the face of the mast at the hounds. This will allow easy insertion of the halyards later.
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Moment of truth!!
 
The back edge was planed flat and then the mast lifted from the moulds. Looked OK!!
 
Filler was used to fair the joins in the ply, the skewer ends cut off and any imperfections in the face filled.
 
The mast was then sanded smooth.
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We supported the mast on its trailing edge on a series of saw horses and with Marg's help applied a layer of 84gm/m² fibreglass cloth and epoxy resin.
 
Once the resin had set the mast was placed back in the moulds ready for routing of the sail track.
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I made a jig for the router guide that allowed me to keep the routed groove along the trailing edge central. I actually had to have two runs. One with the timber guides set for where there was only 1 layer of ply (i.e. between joins in the ply) and then another with the timber guides set slightly wider where the ply joins were.
( Hope that made sense)
 
It seemed to work. The routed groove looked straight.

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With the groove routed a 19mm aluminium tube was glued into the trailing edge. The outside of the tube roughened with 80 grit sandpaper to provide a key for the glue.
 
When the glue was set any gaps were filled and sanded and the aluminium sanded with a fine grade of sandpaper.
 
At this point I weighed the mast - just over 17kg. Given that the aluminium section specified was 2.2kg/m giving weight at about 16kg I reckoned we were going alright. Just hope that the strength is comparable. The section is certainly bigger with a depth of about 210mm. Maybe I will be able to sail on the mast alone. : )