|Article 4 - Building the Hull Mould|
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With the boat being designed using a CAD package the first task that was required was to get the hull lines out of the computer and onto the 16mm chipboard to be used for the mould frames. The UNITEC Marine Technology Department has a high speed CNC (computer numerical control) router, which is used for their advanced boat building school. The machine is "programmed" to move the arm and cut out the frames exactly as specified in the CAD design files. We were generously offered time to use this machine by UNITEC which helped the project significantly.
The CNC machine's operation is impressive, sort of like a giant "terminator" as it cuts each frame out in less than 1 minute. Definitely a great improvement in accuracy and speed over the method used on the foredeck mould of transferring the lines of the frames onto chipboard and cutting them out with a jig saw.
A building frame was constructed out of 200 x 50 kiln-dried timber to make a solid base for the mould. This was set up level on the workshop floor, and fixed to the concrete with epoxy to minimise any movement. Frame positions were then marked on the building base. The frames were located so that stringers sat on the correct edge of the frames. This meant that on the back ½ of the boat, where the hull "size" is decreasing, the stringers will sit on the back edge of the frames, and conversely on the front ½ the stringers sit on the front edge of the frame. It is quite important to get this correct as it can make 3-4mm difference in stringer height and change the hull shape considerably.
Each frame had a vertical centre-line, and horizontal water-line datum scribed into it by the CNC machine when the frames were cut. These lines helped align the frames on the building base. The centre-line on the frame was aligned with a string line running down the length of the mould. The height of the frames was set with the aid of a builder's dumpy level, each frame is raised up using wedges until the water-line on each side is aligned with the dumpy level. As each frame location was determined it was screwed in place. This process effectively eliminates any inherent twist and distortion in the mould base at the time that the frames were attached.
Once the frames were standing upright, the stringers were attached. The first stringer runs straight up the keel line, with the chine stringers attached next. A problem we encountered with the foredeck was that screwing the stringers to the frames distorted the natural bend in the timber and thus affecting the shape. To minimise this problem in the hull mould we used lightweight panel pins to ensure the stringer only touched the correct edge of the frame and gap between the frame and the stringer was filled with epoxy glue. This resulted in a much fairer hull shape, and definitely saved a lot of work later on.
The stringers were attached about every 80 - 100mm across the hull. The mould was then sheaved in a lightweight 3mm plywood. On the back half of the boat the flat planing sections allowed quite large panels to be used. As we moved to the front sections we needed to diagonally plank the mould using plywood strips down to about 40mm wide to bend around the tight bow curves. The plywood was glued to the stringers using epoxy and held in place while curing with heavy-duty 12mm staples. An electric stapler was used to insert the staples, however after removing 4500 staples by hand I think we may have been a little trigger happy.
After a quick long boarding of the plywood, the hull was sheaved in chopped strand matt to give a working surface for filling and final fairing. We used Resamax epoxy resin, supplied with generous support from CRC Marine Industries. Resamax epoxy was used instead of the polyester resin (as used on the deck moulds) as the smell of the polyester is definitely a disadvantage when working at home, and not something we wanted to repeat.
As with the deck moulds, the hull surface was faired using an almost never ending process of long board sanding, filling and more long boarding. The final fairing coats consisted of a high build Duratec sanding primer. Strangely visitors are always scarce during the sanding phases.
After final sanding the mould was polished and a mould release wax was applied. A final coating of a special liquid mould release from Adhesive Technologies was then applied.
At this stage the mould is ready to be used, the next article will follow the vacuum bagging of the hull shell and foredeck. To see progress as it happens follow the "Virtual Javelin" links on the class web site www.javelins.org.
Around the yards
We now have three new hulls being built as part of our project in New Zealand, with another hull being modified (cut in ½) in Auckland to improve its downwind performance.
Across the ditch, our Australian cousins are also building new hulls. The current Australian champions have sold their winning boat and are building to their own new design, and another hull is being built out of the "winner" mould for one of the younger crews in the class.
This is all shaping up for a very impressive South Pacific Championship. This competition is being held in Wellington over the New Year break after the inter-provincial Sanders Cup competition. The organisers are currently expecting over 40 boats with some very high calibre competition, and a large Australian contingent.
Crews and Skippers wanted
Along with offering a number of good 2nd hand boats for sale in the $2000-$4,500 range, we also have a number of boats looking for keen skippers and crews.
If you are moving out of Starlings, or other single handers and want the challenge of fast affordable skiff racing the Javelin could be the boat for you. You can learn a lot more about sailing racing a Javelin than you ever will sitting on a keelboat rail.
For more information ring Rob (09) 444 6874, or email email@example.com