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
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
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
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
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
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.