One of the most original details in the Pop 25 is referred to its twin keels. The concept we adopted is slightly different from what is usually found in other twin keel sailboats, since it is a general rule that they are built with foil shapes, which are excellent from the stand-point of hydro-dynamics, but are expensive and laborious to build.
In the case of the Pop 25 we specified laminated “grade A” steel plates, the easiest material to be found anywhere. The bulbs are also specified to be made from “grade A” steel rods in the shape of torpedoes, easy to be fabricated in any average sized lathe.
One of the advantages of this bulb-shape is the fact that the boat can stand on those bulbs whenever it is stationed in a flat surface. It is also invaluable when the boat is moored where the tide range requires two daily groundings at every ebb-tide.
One of the strong points in the Pop 25 design is the fact that it can stand on its twin keels when stationed in a flat horizontal surface without the need of expensive cradles. Render: Murilo Almeida
The bulbs may be optionally built in cast iron, or even in cast lead (not so recommended for its softness), if the facilities for making them this way in your area are more favourable, something we believe to be quite improbable. The only care it must be taken is to change the diameter of the cylindrical part to result in the same weight (256kg), since the density of cast iron is slightly smaller, and lead is considerably higher. In these cases the bulbs are attached to the keels by means of four 20mm bolts welded to dents made in the fin tips and bolted in countersunk holes drilled underneath the bulbs.
The leading and trailing edges of the fins can be easily made using a grinder for that, since it is not such a hard work to do it manually. Notwithstanding, any workshop might have tooling to do it by other means. The plates should be ordered already cut to its longitudinal shape, be it by CNC file, or in the traditional manner.
The keels attaching system is very sturdy, since it consists of two independent ways of fixing them to the hull working together: a 8mm steel flange welded to each fin root bolted to the plywood laminated keel, having its upper side embedded in sealant, and a pair of L-bars for each keel, bolted to the fin’s arms that intrude inside the boat, which are then bolted against Station 5 bulkhead. The keels should receive an anti-corrosion treatment before being installed, be it epoxy anti-corrosive protection or hot-deep galvanised treatment.
The keels system employed in the Pop 25 is more affordable and easier to be fabricated than others generally found in twin-keel sailboats, which are in most cases cast in iron or lead, or in some other cases having lead poured inside steel boxes built with the chosen hydrofoil. In the Pop 25, the fact that they are made from steel plates make them possible to be built in any place where there is a steel workshop.
These keels where produced in a workshop located in the same suburb where the builder was constructing his boat. It is still missing attaching the flanges and applying the anti-corrosive protection. Photo: Daniel D’Angelo.
Considering performance, twin keels are advantageous if compared to mono-keels for the reason that they increase lateral resistance when the boat heels up to the angle they make to the centreline. On the other hand they increase wetted surface, which represents extra resistance when sailing in light air conditions. Taking into account the shallower draught typical of twin keel design, they constitute an excellent choice for cruising sailboat.
Flange already welded to the fin. Photo: Daniel D’Angelo
Fin-keels - 20mm thick steel plates.
Fin-keel - 65kg
Note: The two battery banks weighting approximately 90kg each are considered internal ballast and should not be omitted, not even partially. In case an electric inboard motor is not the auxiliary propulsion chosen, if the banks are intended to be reduced, an equivalent ballast should be put in place so the weight of the internal ballast is maintained.