Pop 25

Simplicity and speed of construction, together with extreme toughness, are the main attributes of the Pop 25. The hull is built upside-down, and the basic materials employed in its construction are marine plywood, wooden strips and epoxy resin. All pieces of the boat, except some bunk-boards, are bonded with this resin and the whole interior is saturated with two coats of it.

The hull is assembled over eleven bulkheads or semi-bulkheads strategically placed at full stations, except for the stern scoop transom, which is placed at the Station 10.7. All these transverse structures, which we call Sections, are easy to be built, since they are made of plywood panels and straightedge cleats attached to their faces. These Sections are joined by 20mm x 20mm stringers, which fit in slots previously opened in the sections when they were pre-fabricated at the workbench. They will serve as support for attaching the double-walled hull topsides and the 10mm plywood laminated bottom keel. The 2 x 6mm plywood laminated bilge panels are attached only after the topsides and laminated keel are installed and their edges faired.

Pre-fabrication of sections and stem: The Pop 25 hull is built over eleven transverse structural components (Sections) and the stem, a straight-edged piece of wood with a trapeze shape in its cross-section, which can be either be built from a stock of lumber, or be laminated employing 20mm planks for the purpose (our preference). It is given in the plans the full size drawing of its cross section, and being a straight piece, it is a piece of cake to make it.

This step in the construction is quick to be accomplished and is very pleasant.

FIG 1 - SECTION 3 BULKHEAD

The plans show each Section from both sides with all its parts and there is a special sheet showing the plywood cut-outs for with their measurements labelled, so one had to be extremely absent minded in order to commit any mistake . Besides, most details are drawn aside in full scale, making each Section absolutely clear to be understood.

Assembling the hull: Once finished the construction of the Section, the next step is preparing a building grid ( rectangular frame made of wood or metal measuring 7.40m 1.20m with its upper edge levelled) to lay the sections on it. It should be fixed in each Section a pair of temporary legs 1.2m apart, except for the two first ones, with the correct length to keep all Sections design water lines at the same hight above the building grid. Then all sections should be placed on the building grid in their respective Station positions and the Stem Post should be fitted on the foreside of the building grid.

FIG 2 - SECTION 5 BULKHEAD

The next step is to join all Sections and the Stem with 20mm x 20mm stringers which fit in notches previously opened when the Stations were fabricated at the workbench. Since these stringers make very smooth curves in one direction only, assembling them is a very easy task, requiring only bevelling the bottom edge of the notches to adjust for the gentle curves of the hull shape. Once all stringers are fit in place all stations should be also bevelled around their contour to allow the plywood sheathing to de attached without leaving gaps between them and the bulkhead frame edges.

FIG 3 - DOUBLE-WALLED TOPSIDES CORE STRUCTURE

As the structure becomes firm enough after joining the bulkheads with the stringers, it is then that the bevelling of all frames takes place, using a hand plane for the purpose. The Stem is previously bevelled to its proper shape, not requiring any adjustment.

Then it's time to build the hull's topsides. The Pop 25 adopts the unique method of making them double-walled employing 20mm x 20mm horizontal stringers as spacers between the inside and the outside walls. To shorten the areas of the panels between stringers, segments of frames are fitted vertically between stringers in each Station position. Then, before the outside wall is attached, all empty spaces should be saturated with two coats of epoxy resin and then filled with foam, so in case of a puncture in the outside wall the panel will not be flooded. Besides, the foam will enhance the thermal insulation of the interior.

Once concluded the topsides, the hull is already as rigid as a rock. Then the next step is the construction of the laminated keel. This is done bonding three layers of 10mm marine plywood over the bulkhead floors, creating a large panel of extreme rigidity.

Finally the two bilge panels are laminated in place. These are laminated with two layers of 6mm marine plywood over the bulkheads bilge frames.

Since all pieces of the hull are glued to each other along the whole construction, it is perfectly admissible to employ ordinary iron nails to attach the parts while the glue isn't set, and removing them after the resin is cured. This represents good savings in time and money.

The last piece to be attached to the hull is the stem cap. This part is similar to the stem and for its construction it is also provided a full size drawing of its cross section.

After rounding the sharp edges along the chines and stem cap, the hull is ready for its fibreglass encapsulation. This is done applying two layers of 300g/m² fibreglass bidirectional, or biaxial cloth, over the whole hull's surface, impregnated with epoxy resin.

After sanding, fairing and applying a coat of epoxy primer the hull is ready to be turned over.

Building the interior: The interior layout construction is quite advanced when the hull is turned upside all the transverse walls belonging to bulkheads are already pre-fabricated and cleats that support longitudinal panels are also in place, clearly showing how the work will proceed.

The first step after turning the hull over and detaching the temporary legs that supported the Sections on the building grid is building the two longitudinal bulkheads along the 300mm bulwark stringer that limits the cabin corridor. Abaft Station 7 this longitudinal bulkhead separates the aft double berths from the cockpit.

All bunk-boards and saloon settees are supported by the stringers placed 200mm above D.W.L., a building simplification that represents a shortcut in time construction

FIG 4 - INTERIOR CONSTRUCTION

Other furniture, the vanity basin counter, the galley, the navigation table and the two shelves behind the saloon backseat are supported by the 500mm hull stringers.

FIG 5 - BUILDING THE INTERIOR FURNITURE

Building the deck, cabin trunk and cockpit: The Pop 25 employs an original system to build the deck and coach-roof. Instead of doing like most other boats, where the ceiling is fitted after the deck and the coach-roof are already built, in the Pop 25 the ceiling is made in the first place, over it being installed stringers and beams, and on top of these reinforcements is applied the deck and coach-roof sheathing. To make things simpler, the bulkhead beams are straight, the ceiling being curved only in the fore and aft direction. Deck and coach-roof cambers are obtained by means of flat based and curved on top beams installed over the ceiling. As with the hull topsides, the empty spaces between ceiling and coach-roof, after being saturated with two coats of epoxy, are filled with foam. Doing in this way, besides ensuring an efficient thermal insulation, also allows the installation of flush cabin lights, and hiding the electrical wiring inside the core of the double-walled structure.

FIG 6 - THE CEILING IS BUILT BEFORE THE DECK IS LAYD IN PLACE

After installing the deck ceiling, the next part to be built is the cockpit. This is not double-walled, since the compartment under it doesn't require thermal insulation.

Before installing the deck sheathing it is necessary to build the bowsprit. The bowsprit is a wooden pole of square cross section built in place employing four 20mm thick planks.

After installing the deck over the core structure (stringers and deck beams) the cabin trunk side walls should be laminated in place in a similar way as it had been done with the laminated keel. The coach-roof is made in the same way as the deck, with the ceiling being installed first, followed by coach-roof core structure and the coach-roof sheathing.

The two wooden prismatic boxes that serve as bearings for the stern post tunnels must be built before the transom scoop sole is fitted.

At this stage, after constructing the companionway hatch according to the details contained in a special sheet for this purpose, after rounding all sharp convex edges,and filleting the concave ones, the superstructure is ready to receive de fibreglass encapsulation.

Once concluded the painting job, deck hardware, keels and rudders should be installed and the boat is ready for launching.


LIST OF MATERIALS
DIMENSIONS
1
HULL


1.1
Laminated keel
15 sheets

1.2
Intermediate panel
6 sheets

1.3
Topsides


1.3.1
Inside wall - 6mm marine plywood
8 sheets

1.3.2
Outside wall - 6mm marine plywood
8 sheets

1.3.3
Topside core chine log
(2x) 20mm x 40mm x 7.6m
0.0122
1.3.4
Topside core stringers
(12x) 20mm x 20mm x 7.2m
0.0346
1.3.5
Topside core sheer clamp
(2x) 20mm x 40mm x 7.2m
0.0058
1.3.6
Vertical reinforcements
20mm x 20mm x 16.7m (total)
0.0067
1.4
Stem
(5x) 20mm x 140mm x 0.99m
0.0139
1.5
Stem cap
(5x) 20mm x 140mm x 0.98m
0.0137
1.6
Bowsprit


1.6.1
Top and bottom cleats
(2x) 20mmx 40mm x 0.70m
0.0022
1.6.2
Side cleats
(2x) 20mm x 40mm x 0.70m
0.0011
1.6.3
Tip central reinforcement
(2x) 20mm x 40mm x 0.08m
0.0002
1.6.4
Root central reinforcement
(2x) 20m x 40mm x 0.10m
0.0002
1.7
Sheer clamp
(2x) 20mm x 20mm x 7.20m
0.0058
1.8
Skeg - triangular wooden block
(2x) 20m x 155mm x 530mm
0.0033
1.9
Electric motor support (suggested)


1.9.1
Base cleat
20mm x 40mm x 0.60m
0.0005
1.9.2
Core - solid wood
20mm x 240mm x 0.60m
0.0029
1.9.2
Outside layers - 10mm marine plywood
0.2 sheet

1.10
Chainplate plywood reinforcement
0.2 sheet

1.11
Throughull wood reinforcements
(2x) 20mm x 75mm x 100mm
0.0003
1.12
Hull stringers
(6x) 20mm x 20mm x 100m
0.004
1.13
Rudder - 6 x 6mm plywood and 1 x 10mm
1 sheet 6mm & 0.2 sheet 10mm

2
DECK


2.1
Deck and coach-roof plating - 6mm marine ply
6 sheets

2.2
Core deck beams
20mm x var. height x 12.6m
0.0102
2.3
Ceiling - 6mm marine plywood
6 sheets

2.4
Stringers
20mm x var. height x 29.6m
0.0237
2.5.1
Deck core sheer clamp
(2x) 16mm x 32mm x 7.60m
0.0097
2.5.2
Deck core carling
(2x) 20mm var. height x 6.0m
0.0096
2.5.3
Deck core sheer clamp reinforcing strip
(2x)16mm x 20mm x 7.10m
0.0045
2.6
Central stringers
(2x) 20mm x 40mm x 3.66m
0.0059
2.7
Bulkeads superstructure beams
20mm x 40mm x 25.3m (total)
0.0202
2.8
Cabin trunk side walls - 6mm marine ply
7 sheets

2.9
Coach-roof plating - 6mm marine plywood
1.5 sheets

2.10
Coach-roof core beams
20mm x variable height x 6m
0.0048
2.11
Coach-roof core stringers
20mm x 40mm x 3.9m (total)
0.0031
2.12
Coach-roof core outside clamp
(2x) 16mm x 40mm x 3.66m
0.0047
2.13
Cabin trunk front wall - 10mm marine plywood
0.5 sheet

2.14
Intersection cabin trunk front wall / deck
(3x) 20mm x var. lenght x 0.82m
0.0020
2.15
Coach-roof reinforcement at mast position
(6x) 20mm x 40mm x 310mm
0.0026
2.16
Mast step base
(8x) 20mm x 30mm x 310mm
0.0015
2.17
Mast step rectangular box cleats
(2x) 20mm x 20mm x 600mm
0.0005
2.18
Toe-rail
(2x) 20mm x 20mm x 4.60m
0.0037
2.19
Cockpit coamings


2.19.1
Base transverse cleat
20mm x 20mm x 1.40m
0.0006
2.19.2
Side cleat
(4x) 20mm x 20mm x 1.30m
0.0021
2.19.3
Bottom plank
20mm x 210mm x 1.40m
0.0059
2.19.4
Outside wall - 3x 6mm plywood (laminated)
1.5 sheets

2.19.5
Inside wall - 10mm marine plywood
0.5 sheet

2.19.6
Intermediate panel - 10mm marine plywood
0.5 sheet

2.19.7
Top panel - 2x 10mm marine plywood
0.5 sheet

2.19.8
Top cap base plank
20mm x 85mm x 1.29m
0.0022
2.19.9
Coaming bulkheads -10mm marine plywood
0.25 sheet

2.20
Transom platform sole - 10mm marine ply
1 sheet

2.21
Transom platform stringers
20mm x 84mm x 2.54m
0.0043
2.22
Transom transverse reinforcements
20mm x 84mm x 2.54m
0.0043
2.23
Rudder post tunnels side cleats
20mm x 100mm x 0.90mm
0.0018
2.24
Rudder post tunnels spacer cleats
20mm x 60mm x 0.87
0.0010
2.25
Cockpit floor - 10mm marine plywood
0.5 sheet

2.26
Sliding companionway hatch
See separate drawing

2.27
Deck hardware reinforcements
Thickness - 20mm

2.28
Transom convex cap - 4 x 10mm marine ply
0.5 sheet

3
TRANSVERSE STRUCTURAL COMPONENTS


3.1
Frames at bulkheads
20mm x 40mm x 19.5m
0.0156
3.2
Builkhead and other interior panels - 10mm ply
7 sheets

3.3
Bulkhead floors
20mm x 40mm x 17.5m
0.0140
3.4
Fin keel fixing cleats at bulkhead
(4x) 20mm x 200m x 370mm
0.0059
3.5
Transverse members on bulkheads & interior


3.5.1
20mm x 20mm cleats
20mm x 20mm x 35m
0.0140
3.5.2
20mm x 40mm cleats
20mm 40mm x 25m
0.0200
3.5.3
20mm x 50mm rails
20mm x 50mm x 2.5m
0.0025
3.5.4
20mm x 70mm trims
20mm x 70mm x 2.5m
0.0035
4
LONGITUDINAL COMPONENTS


4.1
Plating - 10mm marine plywood
5 sheets

4.2
Fore and aft longitudinal components


4.2.1
20mm x 20mm cleats
20mm x 20mm x 30.0m
0.120
4.2.2
20mm x 40mm cleats
20mm x 40mm x 12.0m
0.0096
4.2.3
20mm x 50mm rails
20mm x 50mm x 2.5m
0.0025
4.2.4
20mm x 70mm trims
20mm x 70mm x 2.5m
0.0035
5 GLASS CLOTH REINFORCEMENT LAMINATION


WEIGHT g/m2 AREA m2 WEIGHT OF FIBRE THICKNESS
5.1 2x CLOTH 300 g/m2 600 g/m2 17 m2 10.5 kg 1 mm






5.2 2x CLOTH 300 g/m2 600 g/m2 14 m2 4.5 kg 1 mm






5.3 2x CLOTH 300 g/m2 600 g/m2 22 m2 30 kg 1 mm