How to build the Pantanal 25

A strip planking HOWTO

The Pantanal 25 is specified for strip-planking sandwich construction, the so called speed-strip construction method. Preferentially she is intended to employ PVC foam as core material, but optionally PVC foam may be substituted by light wood, resulting in a heavier hull and consequently a small loss in performance. This method of construction is easy and quite quick to accomplish, resulting in a light and sturdy hull.

Sheets 0 which are supplied in CD, or, if required, printed in paper, contain the full size patterns for hull and deck moulds, as well as the full size drawings for the transverse bulkheads. Moulds and bulkheads when precisely cut by numerical control have their heights above the building grid correctly defined, so positioning them on it becomes an easy task. The CNC file supplied in CD allows the fabrication of the moulds by means of laser or miller cutting. If this process isn't available locally, there is no restriction in resuming to the traditional method of cutting the moulds and bulkheads with the jig-saw. The smaller precision thus obtained is negligible regarding the final quality of the boat.

Label the position of stations on the upper face of the building grid and fix the moulds in their places, taking care to match the stations, from 0.5 to 7, with the fore face of the moulds and from there aft, reverse the moulds position. Beveling and fairing aren't required when in doing this way, representing an important saving in time of construction.

It's important to protect the edges of the moulds with non-adhesive tape to prevent any spilled glue to stick to them.

Attach the moulds to the building grid, taking care to ensure that they stay plumb and perpendicular to centreline. Next install the stem base mould, which is also supplied in full size pattern and joins to the #0.5 station mould. The stem is made with two pieces of PVC foam, being the one closer to the forepeak built with high density foam, since the forestay chain plate will be attached there. Marine plywood may be employed if high density foam is difficult to be purchased in small quantities. After firmly fixing the moulds in their places, the hull is ready to be planked with the strips.

Prepare 60 mm wide strips from 15 mm thick 80kg/m3 PVC foam. (The width is reduced to 30 mm if wood is employed). Fix the first strip with its lower edge coinciding with the sheer line. Then proceed applying other strips until reaching about two thirds of the hull's girth.. Use temporary nails to fix the strips to the moulds and apply epoxy with filler to join their edges and ends. Then start applying the strips from centreline until reaching the ones that were already laid in place.

Once the boat is completely planked, the temporary nails are removed and the outer face of the foam is sanded to ensure a fair finish of the hull. Make a 2 mm rabbet with the circular sander on the 75 mm next to the sheer line to allow for the overlap of the deck lamination. (See detail in sheet 5).

Now the hull is ready for the fibreglassing of the outside lamination. Apply two layers of 500g/m2 combined cloth, overlapping 500 mm to the other side of the hull, this way duplicating in this area the thickness of the lamination. Sand the surface after the resin is cured. If peel-ply is applied this is practically not needed. Then apply an epoxy primer over the whole surface, except for the 75 mm rabbet next to the sheer line.

Remove the moulds after turning the hull upside. Then sand the interior and remove with a chisel the foam at the central area where the keel case will be attached, where the lamination is single skin. (See detail in sheet 5A). If wooden strips are employed there is no need to remove the strips in that area.

Once the internal lamination is completed, the next task is the installation of bulkheads. These are bonded in place with secondary lamination.

The deck is built in a similar way as the hull, except that instead of strips it's employed foam panels.

Following, the hull is bonded to the deck and after applying the finishing coat of paint, systems, fittings, drop keel and rudder gudgeons are installed.

Roberto Barros
www.yachtdesign.com.br
Rio de Janeiro, June 2006