Flying Moths And A Look At High Tech Boat Building

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Our May toolbox visit was to  Fastacraft” in Yangebup, owned and operated by shipwright, John Ilett, to see the latest incarnations of the new high speed moths.  John does his own design and development work and had a completed boat to his latest design on show for us to inspect.  John also gave us a detailed informal presentation on the background to the moth design, his state-of-the art approach to design and the construction methods he deploys using 21st century procedures, materials and technology.

John Ilett is a shipwright trained in the 1980s and he worked for a number of firms including Thomas Craft and OceanFast. He went overseas for a period of time and amongst other high tech things, worked on Formula 1 racing car construction involving similar technology to the current Moth build. On his return, he established his current business substantially using the skills and techniques he had learnt overseas but he also does repairs to carbon fibre bikes and fiberglass boats. In his own time, he has always been a Moth sailor.

The Moth in Australia developed from a hard chine scow called an Inverlock 11 foot class which was established in 1928 in Victoria. In 1933, its name was changed to the Moth class and as the saying goes ‘the rest is history’. See  for further information.

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The Moth is an unrestricted development class 11 feet long. The class has very general rules which cover length, width and sail area. Historically Moths were scows until the mid 1980s when the skiffs began to emerge as better performers. By the late 1980s skiff type Moths had won the world championships in strong wind conditions in which they had traditionally been outclassed by the scows. At that time, their hulls were about 2 feet wide. By 1990 they were 14 inches wide and they are now 12 – 13 inches wide.

Moths remain a fairly popular class internationally and John pointed out that half the people currently involved in the America’s Cup sail moths on the side. In WA, Moths are mainly sailed at South of Perth Yacht Club.

The latest Moths weigh in at 11 kg for the bare painted hull. The full sized boat weighs 35kg all up and is carried to the water on its side due to the center board with its hydrofoil being fitted from the bottom. Fully assembled a moth requires a trailer 2.2 metres wide but the entire boat can be fitted into a 400 mm wide box for transport when disassembled.

The original foil design for moths was developed from a foil cat in 2002 and had foils on each side of the hull. This was outlawed on Moths as this was deemed to be a multihull.

The current hydrofoil Moths have two single central foils – one on the bottom of the centerboard and one on the rudder. The centerboard foil is controlled by a wand hanging from the bow which skims the water and adjusts this forward main hydrofoil. The aft foil on the rudder is adjustable by rotating the joy stick. These Moths can reach a speed of up to 30 knots down or cross wind and can do up to 17 knots upwind.

The cost of a complete new Moth is $23,000.

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 John has worked on the development of this new all carbon fibre design for several years and has now completed the build of the first boat which we were able to see at his factory. The main features of the new design are a fuller bow, more rounded hull and more rocker in the fore and aft direction.

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The construction of this Moth is substantially carbon fibre ‘pre preg’. This is a carbon fibre cloth supplied with the resin already (pre) impregnated in the cloth. This cloth is only slightly sticky to touch but its big upside is that it contains the minimum resin required and has no smell. In fact John’s premises are the first that I have visited that have been doing this sort of work that had no lingering smell at all. The other big advantage of ‘pre preg’ is that it can be cut to almost Exact shape and placed in the mould together with other components of the build up without the operator handling any liquid resins or other ‘messy’ materials. Curing of the resin on completion of the layup is achieved by applying heat – generally by placing the component in a temperature and time controlled oven environment.

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 John ran us through a ‘dry run’ of this layup process which went roughly as follows;

  • cut the piece of pre preg to the required shape to suit the mould.
  • on the pre preg, peel the paper from the mould side and the release plastic film from the outer side.
  • place the pre preg in the mould with the carbon (noted as about 0.2 mm thick) on the mould side. Here John showed us that there is a thin layer of relatively soft foam in the layup which can dent easily through the thin but very strong carbon layer.
  • The type of carbon to be used needs to be selected. Both woven carbon cloth and unidirectional carbon (which tears in one direction) are available. Analysis and targeting of particular load areas allows the correct form of carbon material to be used.
  • If there is a possibility that the pre preg may not contain enough resin for the job, additional pre preg resin can be added by using ‘film glue’ which is resin in a light fabric carrier. There is also no problem mixing resin brands if need be – all resins are epoxy.
  • When the dry layup is complete, the breather for the vacuum bag is attached.
  • The vacuum bag is then installed across the whole mould using double sided vacuum bag tape around the edge.
  • The vacuum valve is then attached and connected to the vacuum pump. A vacuum gauge is usually used to check for leaks but John also had an ultrasonic leak detector at hand.

The whole mould is then placed in the oven to cure at 90-100 degrees C for varying times depending on the design and size of the moulding. A two pack polyurethane varnish is then applied to provide the finish to the completed carbon fibre moulding. All this technology is similar to F1 racing cars and aerospace technology.

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In closing, John showed us a small scale model of his new design Moth which he had built as a tool to prove some aspects of the development as his design developed. He also used this model to develop the maximum transport dimensions of the new boat. The model de-rigs and dismantles exactly as the full size version now does and even came with its own scaled trolley.

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This completed a most interesting visit which opened all of our eyes to the future materials and methods of boat building which whilst they may not all be available to the amateur at this stage, are clearly the direction that professional building of competition boats will be heading in the immediate future.

We thank John Ilett for making his premises available on Saturday morning and for sharing so much of his specialist and high tech knowledge so freely with us.