HULL CONSTRUCTION

Contents

  1. Laminating Moulds
  2. Laminate
    1. Base Laminate
    2. Stiffeners
    3. Weight

Laminating Moulds

The shape of the hull is fixed by the class rules. The class rules formerly required that all laminating moulds be taken from one and the same plug (mother), in order to guarantee the uniformity of the hulls. This paragraph, however, was struck out because after the handover to Gruben the plug could no longer be found.

How many laminating moulds were used by Klepper over the course of time is not known. The plug used at Klepper was modified in the seventies to increase the clear width of the centreboard case from 24 mm to 30 mm. At present there are two laminating moulds in the possession of the Gruben boatyard that still date from Klepper. Both have the wide centreboard case. One mould is on loan to the Robert Franz yacht and boat yard. It was modified for the modern jib fairlead and the new cockpit layout. The outer shape, however, remained unchanged.

The lower shell is externally exactly the same on all boats. The upper shells of the hulls built by Klepper and Gruben are also identical apart from the width of the centreboard case. This also applies to the Berlin series, with one exception: the bases worked into the mould on the side deck for the windward jib cleats, and the recesses for the jib fairlead tracks, which are no longer needed for the modern fairleads, are absent. The new cockpit layout of the regatta JETON required a number of mould changes in the cockpit area; some additional moulded parts (centreboard case collar, thwart beam, side panels) are fitted in addition. The internal structure of the shells, however, has changed several times over the years.

Laminate

The JETON hull consists of an upper and a lower shell. Both parts consist of a base laminate of chopped-strand mat and glass cloth. In places, above all on flat surfaces, reinforcements are used in the form of sandwich construction or stringers for stabilization. The overall stiffness of the hull is increased by a half-bulkhead in the area of the shroud chainplates and a second in the helmsman’s seating area. Under the mast and in the double bottom there are longitudinal and transverse bulkheads. Apart from the glue joint at the rubbing strake and at the centreboard case, the upper and lower shells are also bonded together by the mast support and by bulkheads in the double bottom.

Base Laminate

  • On the Klepper and Gruben boats the base laminate consists of several layers of mat with one layer of roving cloth as the finishing layer.
  • The boats of the Berlin series and those from Fröschke and from Robert Franz are built with a higher proportion of cloth. Different material thicknesses serve for optimum load distribution and weight concentration.

Stiffeners

  • Support of the mast: On Klepper JETONs this was sometimes a foam block. Gruben, the Berlin boats and also Fröschke fit a transverse bulkhead made of wood. Robert Franz uses a cross member made purely of GRP.
  • Half-bulkhead: This lies on the line connecting the two shroud chainplates. On the Klepper JETONs it consists of two triangles that lie only in the side tanks. In the helmsman’s seating area there is a further pair of triangles. The half-bulkheads are absent on the Gruben boats. On the Berlin and Fröschke JETONs the forward half-bulkhead runs across the entire width of the boat and also projects into the centreboard case.
  • Sandwich / Stringer: Klepper used various methods of stiffening the deck over time. Older boats have stringers under the foredeck and in the seating area, laminated over foam formers. On the newer Klepper JETONs the foredeck was covered over its entire surface with a sandwich of PVC foam, the seating area with broad strips. Gruben uses Coremat to stiffen surfaces. On the Berlin, Fröschke and Franz JETONs a system of stringers is used, on the one hand to favourably influence the overall stiffness of the hull and on the other to stabilize surfaces.
  • Centreboard case stiffness: The stiffness of the centreboard case was always a problem on the Klepper and Gruben boats, since it contains no reinforcements or supports whatsoever. On the Berlin, Fröschke and Robert Franz JETONs the half-bulkhead is carried into the centreboard case to make it stiff in the forward area. The Berlin JETONs have a further bulkhead in the centreboard case at the pressure point of the centreboard. On the Fröschke JETONs the centreboard case is supported further aft by the thwart beam and stiffened over its entire length by the centreboard case collar. In Chapter 6 you will find a construction guide for stiffening the centreboard case.
  • Foam-filling of the double bottom: Some boats had the double bottom foam-filled. As long as the boats were new, this was good. Later the foam soaked full of water or crumbled away.

Weight

The hull weight used to be limited to 125 kg by the class rules. The Klepper JETONs had a standard weight of about 136 kg. There are said, however, to have been “outliers” whose identification plaque showed a weight of 165 kg. The Gruben boats lie in weight between 128 and 145 kg. The boats of the Berlin series weigh 125–127 kg. Robert Franz, like Fröschke, builds boats of under 115 kg in accordance with the now-changed class rules.

While the “normal” Klepper weight of 136 kg is reasonably acceptable for the JETON, heavier shells are clearly at a disadvantage, since the JETON then sinks noticeably below the design waterline. Reducing the weight to 115 kg has done the JETON good. The boat has become more sensitive and livelier.