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Tyrtill wrote:I can’t tell you for sure the thickness its either 1 1/2” foam or 2” foam. Looking at it I think its the 2” but I’m not sure.
With this foam its minimum 25psi crush so it will dent with point loads like elbows and knees however I would guess even a thin layer of wood or fiberglass would prevent that. Probably even a thick carpet pad or blanket.
If you are doing a full wrap it should do a 16” span. One of the negatives of fiberglass vs pmf is that if it bends much at all the fiberglass will crack where the pmf will allow flex.
Another work around might be to put foam ribs on the bottom to take up space between the floor and the roof of the vehicle and then it will still be light and allow you to reduce your unsupported spans.
You mentioned that the aluminum frame would be in from the edges. I don’t think the foam will cantilever well so make sure you test that.
Thanks a lot for your points, taken out by your experience with surfboards. Even though pressure dings, aren't of considerable importance, for the intended use of my roof top tent , do you think that a foamie floor wrapped with glass+ epoxy, covered 100% with a 10cm memory foam mattress, will it be as vulnerable as a surfer board, to pressure dings ? 10cm memory foam mattress, wouldn't protect it considerably? Thanks in advance for your thoughts.TinkerTailor wrote:Hi everyone,
A quick note on fiberglass over foam and compression strength, knees, heels, etc.
I'm not a pro, but I have been shaping my own surfboards for over 20 years and have some experience there. Standard glassing schedule for the top or deck of a shortboard is one layer of 6 oz. and one layer of 4 oz. cloth. Often one of the layers will only cover the area of the deck on which you stand. The bottom of a board is typically glassed with one layer of either 4 oz. or 6 oz. cloth. Adding a gloss coat of resin over the laminating layer (as opposed to a sanded finish) may help resilience a tiny bit, but comes with more weight. Competition boards will have lighter glass and are considered semi-disposable, since professional surfers are sponsored by their surfboard manufacturers.
Even with the two layers of cloth over foam, dents from knees, heels, and even bony ribcages are so common as to be considered inevitable (referred to as "pressure dings" - dents that don't puncture the glass and thus don't break the watertight seal).
Since I hate sanding fiberglass more than I hate sanding wood, I have moved to vacuum bagging wood or cork skins over XPS foam for my boards. In my own experience, 1/8" plywood over foam is significantly more resilient in terms of compression strength than fiberglass, and laying up a sandwich panel for a floor would likely be simpler to construct as well as less expensive than to glass it.
If you're interested in the process for skinning a foam surfboard with wood skins, check out this blog post by the very kind master craftsman Grant Newby, whose process I now use Though I can't get hold of milled paulownia skins and use poplar bender ply instead. Might give foamie builders some interesting ideas!
https://woodensurfboards.blogspot.com/s ... vacuum+bag
TT
10cm memory foam mattress...
I'm sure that 20cm will be a lot better. But since I want the rtt to have max outer thickness of 25cm to be aerodynamic enough, not to increase my car's diesel consumption considerable, 10cm matress is the max I can afford, so I can fit in there 2 pillows and 2 spread sleeping bags, when closed. 10cm matress also is a big step up in comfort, compared to self inflating camping mats, I used so far :-)tony.latham wrote:10cm memory foam mattress...
Not to hijack your thread, I hope that's deep enough. Ours is 20 CM. 12.5 CM medium density foam and 7.5 CM of memory foam. It's dreamy. Years ago we had an 8 CM foam mattress and it was too thin.
Tony
I want the rtt to have max outer thickness of 25cm...
Pmullen503 wrote:Are you going to have enough wood frame thickness to securely bolt your floor to the trailer? I would suggest you increase your framing to 3x3 cm. You said someday you may want to build a teardrop on top of your floor. You'll want something solid to attach your walls to.
What does your trailer weigh? Are you worried about saving a few kg on the floor when your trailer alone weighs 100 kg or more?
Thanks again for your very helpful thoughts.Tyrtill wrote:
The red parts are cantilevered and would probably snap the foam without either a lot more glass or a little support.
I would recommend running the wood the other way to support this cantilever or put some foam runners parallel to the aluminum along the edges.
Just out of curiosity you say this is going on a trailer? If you can have the support structure for the floor be part of the trailer than you can probably just have a perimeter of wood in the floor plus maybe one crossmember down the middle just for attachment points. The aluminum runners probably wouldn’t be necessary unless there is something I’m missing.
If yo look at the early photos of my build you will see that the foam under my floor just sits on the trailer cross members and is supported that way. Then there is a 15/32 plywood layer on top of it for crush protection so feet don’t cause dents. The plywood layer also gives me something somewhat substantial to bolt to. There is NO wood cross pieces or perimeter in the bottom layer and I could carefully walk on it.
What I’m saying is you could make the camper super light if you had the trailer doing the supporting.
With the mattress and some fiberglass holding the unit together all you need is something for the hold down bolts to grab. Probably 2x2s running along the inside corners of the long sides would suffice.
You are absolutely right for tear drop trailers. But in my case, is a roof top tent. Rigid roof & floor, fabric sides. No cabin :-)GPW wrote:I hate to throw a Skunk in the camper , but the Floor is Everything !!! It supports the whole cabin , and the people inside … JMHO, I prefer a stout floor and a Lightweight cabin … With a light PMF Foam cabin , we’re still waaaay lighter than the commercial units … ( last longer too)
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