The DuraKore planking was prepared by sanding off any high spots created by excess cured resin from strip planking joints on the hull, before fibre glassing. Due to the care I took in making sure all of the planks lined up to each other and have been supported well with battens etc, I did not have much preparation to do.
Tony Graingers MTB920 Trimaran plans were very easy to follow, taking away any uncertainty in what was required in terms of the glass layup or in fact the entire building project. Due to the potency of DuraKore, the glass layup is relatively light and just one layer of glass material was demanded. This was bidirectional 270gm and had to be laid so the fibre was 45 degrees to the planking. Here is an important tip I learned the hard way. If resin is applied to wood surfaces during the morning as the day is warming up, then as the resin cures and hardens the wood is breathing out expanding air as it is also warming up, and the result is bubbles of air trapped under the cured glass.
I had to cut these bubbles out. The best time to apply resin to glass over DuraKore of wood is when the temperature of the day is about to turn cooler for the day, as the air in the timber contracts and blows off the resin into its pores leaving no bubbles. A boat building shop would most probably have temperature controlled for fiber glass work. The layup at 45 degrees across the boards acts as diagonal bracing, just as the diagonal frames of old wooden frame ships were supposed to provide bracing in a wooden vessel. The bonus with glass fibers is that they provide that bracing over every cm of the hull and not only in specific regional areas of a bracing frame. I overlapped the fibreglass fabric by 70mm at the fabric borders, for continuity of load transfer from one fabric to the other. When the resin was wrapped in I applied release fabric over top of the wet fibreglass.
The release fabric called Peel ply may not bond to epoxy or polyester resins, and when vacuum bagging is used the cloth separates the breather material from the laminate, while the excess resin has been forced out of the laminate layup. In my project no vacuum bagging was utilized, but some excess epoxy does wick through the discharge fabric and might be easily peeled off after the laminate cures. See Garolite as well. Another bonus using that fabric was that it leaves a smooth textured surface which can be bonded to without any additional preparation. After the release fabric was removed I decided to use the West System fairing method that was an over kill for my project as my photos show I had a very reasonable hull with no humps. Bumps or hollows.
Fairing the hull The west system fairing involves troweling on a light weight epoxy resin fairing compound using a notched plasters float, leaving a great deal of epoxy guide rails spaced about 50mm and about 3-4mm higher than the hull surface to heal hard. If the hull isn’t very fair then higher railway lines will be needed. Once they were cured then I used a 1M homemade long board with sanding paper attached to it and carefully sanded the tops of the cure epoxy guide rails of fairing down to ensure the where the overlaps in the glass were, the epoxy guide rails are the thinnest in height and approximately about half the distance of the board the guide rails would be a couple of mm high and less height the further away from the overlap you went. Essentially a flat surface is made across the tops of the railway lines. With a flat float with the hardened epoxy guide rails as guides, I toweled on the fairing filling in all the spaces involving the guides.
I learned not to play the fairing too much as it only made the end worse. When the fairing was implemented I let it heal, then got the board out again this time with finer grit to carefully sand the filler to the epoxy guide rails, taking care not to take too much of them as that would basically produce a hollow. After this coat cured, there were a few small local areas that need little more focus, but nothing much. When the fairing was finished the hull had to be turned over so that the temporary mould frames could be removed. Turning the trimaran main hull What I did was to create a cradle over the hull, and locked the hull into the cradle so that it wouldn’t move as the hull was being turned. I rigged up chain blocks to do this, and attached them to the rafters of my shed, and on the cradle. This way the hull wasn’t going to be damaged by chains or ropes etc..
It proved to be an excellent method on turning my hull. These datum’s would prove very helpful later when I had to stick to the drawings for the installation of bulkheads, floors, seats and bunks etc, including the installation of the deck and cockpit flooring and chairs.
I repeated the preparation process for the use of fiberglass that I did for the exterior of the hull. For the interior however I used 200gm unidirectional glass with the directional fibers set up across the planks at 90 degrees to the board edge joints.
This layup given the strength that wooden frames could have supplied in tying all the wooden plank edges together and transferring the loads, but once more the 200gm unidirectional glass gives a superior job along every square millimeter of the hull from the gunnel down to the kelson, and back up to the opposite gunnel, from bow to the stern. This is unlike the previous methods of wooden frames that were spaced and just provide their strength locally. The hardwood veneers traveling the length of the ship supply strength fore and aft. Because of these advantages, the weight of the fiberglass used is pretty mild and when applied to DuraKore, the strength of the hull is really immense. You can see excellent photos of the glassing, fairing and turning the hull in my blog site.