#1. My preferred method is to use Kolb styling clay to form the basic cowl plug. Thats the same material and technique as I used when doing the 1/10 Volvo racing body some 15 years ago (link). The styling clay is the same that is used in the car industry when doing prototype designs at Volvo etc.
#2. When working with styling clay you heat the clay up to about 60+C in a owen and the clay softens so you can apply it etc. When cooled down to less then 25 deg you can start shaping it. The shaping is done with a combination of different special tools that I have made myself (copied from a guy that works at Volvo design). You also use other tools like profiled templates etc. Search for "styling clay" on Google and you get plenty of info - like these...
#3. When done with the shaping the clay plug is removed from the shape board and attached to std white laminated shelf board and a small bottom radius is added so it will be easier to mold.
#4. The 45 plug in the back and a 21 sized "180 deg wrap around exhaust" plug in the front.
#5. You can somewhat see that the 21 plug (bottom one) have a concave recess on the right rear part. That is to make more room for the wrap around exhaust.
#6. You need to have a couple of degrees of angle on the sides (minimum) as otherwise it will be hard to get the mold off the plug and also removing the finished molded cowl from the mold.
#7. You can hardly see it, but look at the center-line drawn on the base board. To the very front where you normally cut of the finished cowl I have made a small groove. That groove is just about visible on the finished cowl and there is one made to the mold in the rear also. That is really helpful (I think) when actually aligning the cowl to be fitted on the boat tub.
#8. The styling clay is a bit soft so its painted with 2K basecoat and 2K paint or clearcoat to get a smooth glossy finnish that will be easy to polish and mold.
#9.
#10. On the sides of the base board some additional base boards are attached to form a box around the cowl plug. The sides are about 15 mm higher then the highest point of the cowl plug.
#11. A soft clay is being used in all the corner joints (blue). Then its being prepared with wax (this + this) and release agent (PVA).
#12. Mold epoxy gelcoat brushed on.
#13. Mold epoxy resin mixed with cotton flock makes the corner fillets. Then I forgot to take pictures of the thin fiberglass cloth being applied though... But you use a couple of 163 g twill weave fiber glass cloth and epoxy resin to make a hard backing on the mold gelcoat and the filled corners as in this picture.
#14. Directly when your done with applying the two layers of fiber cloth (before it has set) you mix up a material called Poraver with epoxy resin and a small amount of foaming agent (about 55 g epoxy resin per 1L of Poraver) and start filling the box up... When that has hardened over night you sand the bottom flat and add a couple of layers of fiber glass and epoxy resin to seal the bottom of the mold. Leave to completely set for a couple of days.
#15. Remove the newly made cowl molds from the cowl plug and clean it out with water. Then carefully smoothen the surface with wet sandpaper and water. When that is done use your favorite polishing compound and polish the gelcoat. Done. Now you can start preparing your mold with wax etc... Good Luck With Your Own Molds! :)
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