Work is finally progressing again on the trailer, with laminating in process:
And laminating on the outside finished:
There are 5-6 layers of 300 gram/m² cloth on it. The sides have only 4 layers of cloth. The bottom has one layer of 550 gram/m² followed by 3 layers of 300 gram/m². I hope I'm in the ballpark with that. Strength is not the issue I worry about, but rigidity is. I'll probably be adding a layer of 550 gram/m² on the sides and/or strips of wood to provide more stiffness without increasing weight too much. The bottom will be made in sandwich construction, with 20 mm of extruded styrofoam added and then glassed over.
In hindsight, I should have added a layer of extruded styrofoam at the top and bottom of my styrofoam plug and cutting it in shape with the hotwire knives along with the white expanded styrofoam. That way the extruded styrofoam would have automatically ended up as an integral part of the lid and bottom. Now I need to put in extra work to install foam in the roof and lid. Lesson learned....
The particular glass cloth I used ('keper' woven; not sure of the English word for it) is very pliable in both directions, which makes it ideal for the double curvatured surfaces. Impressive how well it shapes up. Only rarely need to cut it in to go round double bends. Much more pleasant to work with than standard 90 deg. cross-woven cloth.
All went relatively smooth, apart from one issue: outgassing of the styrofoam when the box became fully closed (completely covered in cloth and epoxy). As the temperature was rising in the shed, so did the temperature of the styrofoam core and the air in it - all 137 liter of it. A large (15 cm diameter) blister developed in the side. After ejaculating some colourful language that I won't repeat in this family-oriented forum, I grabbed a knife and made a cut in the blister. That let the overpressurized air out, after which the blister skin could be pushed back in place; it was in the gelling phase, so no permanent damage done. Looking at it now you can't see what happened. But it sure made my heart skip a few beats as I walked into the shed to get something and then noticing this large blister....
I've been working wet-on-wet, which with the current temperatures allows intervals of many hours. Which is nice, so I have time for other things too like sleep.... It's important to put the next layer on while the previous layer is still in the gel phase and before an amine blush develops.
The box is now postcuring inside, in a make-shift construction of a table with sheets hanging from the sides, and a 750W radiant electrical heater providing the heat. Needless to say it's now pretty warm in here....
After the epoxy has completely cured, the lid will be sawed off and the styrofoam core removed (I may leave a small layer of it in the lid, which will then be glassed over - we'll see if I can make that work, cutting the styrofoam with a still-to-be-made special hotwire knife). If it doesn't work, it'll be a piece of extruded styrofoam in both the lid and the bottom.
Then, when the shell has been scooped out, I may or may not add a layer of 550 gr/m² from the inside to the sides and other places that might benefit from it. And add wooden stringers in strategic places to make it a bit more rigid.
So far, it has been going relatively smoothly. Also got to know a few boat builders in my area who were very helpful in supplying epoxy and glass cloth at VERY competitive prices (their cost) and gave many tips. Spent a few hours in one of the shops, talking to a guy (who happened to originate from my town but now lived and worked elsewhere - but I recognized his accent :-) ) building *very* nice boats - vacuum bagging entire hulls in epoxy/polyurethane sandwich construction. I felt like a kid in a candy store, admiring everything....
