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Pantanal 25

How to build the Pantanal 25


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 with a consequent small loss in performance, especially when under sail. This method of construction is easy and quite quick to be accomplished, 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 these processes aren'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 moulds on the upper face of the building grid according to the following spacing:
The first mould is positioned at station 0.5. The fourteen other ones are placed at 480 mm intervals and the transom mould 400 mm abaft mould number fifteen. Fix the moulds in their places, taking care to match their positions, from first to ninth with the fore face of the moulds coinciding with the 480 mm spacing line and from there aft, reversing the moulds position. Beveling and fairing aren't required when proceeding in this way, representing an important saving in time of construction.
It's important to protect the edges of the moulds with an externally 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 first 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. If high density foam is difficult to be purchased in small quantities, marine plywood may be employed in its place. 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 (colloidal silica or micro sphere) 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 outside face of the foam is sanded to ensure a fair finish. Make a 2 mm rabbet with a circular sander on the 75 mm next to the sheer line to allow for the overlap of the deck lamination. (See detail in sheet 5B).
Now the hull is ready for the fibreglassing of the outside lamination. Employing epoxy resin to saturate the glass, apply two layers of 500g/m2 bi-ply material, overlapping 500 mm to the other side of the hull, this way duplicating in this area the thickness of the lamination. Finally the false stem at the lower tip must be installed. First bond a foam triangular patch already roughly faired to the lower part of the stem. Then, after the glue is set, carefully complete the fairing in place and apply over this patch the same lamination specified for the hull, overlapping the first layer in 50 mm and the second one in 100 mm. Sand the whole hull's surface after the resin is cured. When peel-ply is employed this is practically unnecessary.
Then apply an epoxy primer over the whole surface, except for the 75 mm rabbet next to the sheer line, since at this margin the hull is going to be bonded to the superstructure. Don't paint also the area around the bearing tube hole on the starboard topside, where the bowsprit will be attached.
When this task is completed, it's a great occasion to call the close friends for a barbecue, since it's time to turn the boat upside.

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, and also a patch where the shrouds chain plates will be installed. The lamination is single skin in the keel area and reinforced where the chain plates will be fixed. On that spot high density foam is inserted to reinforce the chain plate region. Before inserting the high density foam it's important to apply at the shroud chain plate location where the foam was removed two rectangular patches of cloth on the bottom of the rectangular hole opened there, laying on the inner side of the external lamination. Then apply two other cloth layers overlapping the hole walls which should be chamfered. Only then insert the high density foam and apply the inside secondary lamination. (See detail in sheet 5A). If wooden strips are employed there is no need to remove the strips, but it will be required an extra external secondary lamination over the hull's outside lamination.

Building the interior


Once the internal lamination is completed, the next task is the installation of the keel case, floors, bulkheads and furniture partitions.
The keel case, a rectangular box with rounded edges, is made over a male plug. The easiest way to make it is to apply the first layer of lamination around the plug and cut the after face vertically with a sharp edge tool. Then open slightly the laminate, remove the plug and proceed with the application of the remaining layers of lamination. After installing the keel Delrin or UHMPE (ultrahigh molecular-weight polyethylene) bearings, the case is ready to be installed. Apply the secondary lamination specified in sheet 5B to bond the keel-case to the hull bottom. After doing it, open the hole for the lower bearing. One way to make it is, after marking the rectangular area to be cut, to open four holes, one in each corner, and cut the rectangular hole with a jig-saw. There is no inconvenience if the cutting line isn't absolutely precise. If a small gap is left it can be filled with epoxy putty as far as the keel-case is correctly positioned. The bearing slot for the fin-keel must have a 0.3 mm maximum tolerance at each side, to prevent undesirable noises when the keel tilts.
Floors are installed only after the keel-case is firmly fixed to the hull bottom. Prepare the shape of the floors with rigid polyurethane foam and encapsulate them with the lamination specified in sheet 5B. Finally install the PVC foam sandwich brackets which join the floors to the keel-case, as specified in the plans, attaching them with secondary lamination.
Next the transverse bulkheads, which full size patterns are given in CD, are constructed in sandwich over a lamination table.
Carefully mark their positions on the interior with a pilot pen and fillet with epoxy with filler both sides of their edges. When the putty is cured, apply fibreglass tapes according to information given in detail in sheet 5B.
The remaining furniture partitions and the anchor rode well are made in a similar way as the transverse bulkheads, except that for them there aren't full size patterns. When finishing this work the interior is ready for the finishing work. The apparent edges of all bulkheads should be covered with a light cloth tape and then the whole interior is ready for sanding and to receive the finishing paintwork.

Building the Superstructure


Once again the moulds are fabricated by laser or miller cutting. They are also assembled over a rectangular grid, which in case the hull and the superstructure aren't built simultaneously, may be the same one.
The deck is built in a similar way to the hull, except that instead of strips it's employed foam panels. The radius between the trunk coach roof and the sidewalls is too small to allow for foam panels to bend over the moulds. On that place it's necessary to apply foam strips, as were employed during the hull construction.

When putting the foam panels in place, the bonding of a panel to another is made with sharp angles. The concave angle is later filleted according to the radius specified in the plans and the convex one rounded to specifications with a sanding tool. (A surform plane or a pad with sandpaper are quite adequate for the job, but with skill and some care, an electrical sander may also be employed). Only then the secondary lamination is applied. Insert high density foam, or, if not available, marine plywood patches, where fittings will be installed. (This is shown in sheet 5A.)
The outside lamination is applied after fairing the foam. When the fibreglassing is concluded, the whole superstructure is sanded. Then the deck is ready to be turned turtle for the inside lamination. Again round the convex edges employing a sanding tool and fillet the concave ones with epoxy with filler. The inside lamination is applied in the same way as the outside. After sanding the internal surface, cut the lifting-keel beam foam core and bond it to the ceiling. Then laminate it integrating to the superstructure.
Following, the hull is bonded to the deck. When lowering the deck on top of the hull, the bulkheads will fit very close to perfection under it. If in any particular point bulkheads and superstructure don't fit as a glove, if it's left a gap, this will be filled with epoxy putty, but if there is a lump instead, this lump requires to be removed with a surform plane, rasp or sanding machine.
First bond the topside edges to the underside of the deck, employing the same epoxy putty used to join the foam edges. Next fillet the inside edge all around the boat and apply the internal deck to hull secondary lamination. Then fillet all bulkheads to the superstructure and apply the secondary lamination tapes at their both faces. Finally make the round radius specified along the sheer line and apply the hull-to-deck joining lamination, overlapping the topsides lamination along the 75 mm rabbet
The bowsprit bearing tube is fixed at this stage.
Only after applying the finishing coat of paint, systems, fittings, drop keel and rudder gudgeons are installed. Next step is to invite your friends for the first trial.