Foamie floor

[Pmullen503]

Now I understand what you want.

Those aluminum rails go on car top cross bars so in effect all the perimeter edges are cantilevered. In that case the perimeter wood spars are spreading out the stresses. You should make them deeper. Notice how the base of the unit in the photo is like a box or maybe the base is that thick. Those vertical sides make the whole unit stiffer. Note the corners, the round corners reduce the concentration of forces there. A wooden square corner will need really strong joinery and probably a metal corner brace as well. I would use thicker foam too, that would increase the stiffness without adding too much weight.

If you can make a platform that would work on the roof top like that, it will be more than strong enough for a trailer where its supported around the perimeter.

[gregkn73]

Now I understand what you want.

Those aluminum rails go on car top cross bars so in effect all the perimeter edges are cantilevered. In that case the perimeter wood spars are spreading out the stresses. You should make them deeper. Notice how the base of the unit in the photo is like a box or maybe the base is that thick. Those vertical sides make the whole unit stiffer. Note the corners, the round corners reduce the concentration of forces there. A wooden square corner will need really strong joinery and probably a metal corner brace as well. I would use thicker foam too, that would increase the stiffness without adding too much weight.

If you can make a platform that would work on the roof top like that, it will be more than strong enough for a trailer where its supported around the perimeter.

I knew my description and sketch wasn't good enough, to understand details :-)

The plan of mounting onto trailer, is on similar cross brasses , not on its perimeter.

So please give me numbers. How thick of a foam and most important, how deep and thick the wood slats of the perimeter? 5cm XPS foam and 1cm*5cm wood slats for the perimeter, would it be enough , to withstand cantilevering forces? Thanks in advance .

[Pmullen503]

Maybe a structural engineer will weigh in.

But 50 cm will be better that 30. For a beam, doubling the depth gives 1/8 the deflection under the same load. So increasing the thickness of the foam helps a lot. I would move those internal wood spars closer to the sides: 1/4 width and 3/4 width instead of 1/3 and 2/3. Less of the platform would be cantilevered on the sides. Same principle for the bars on the car, as close to 1\2 the length as possible. Your center of gravity is closer to your head than your feet so cantilever the "head " end less than the "feet" end.

[gregkn73]

I would move those internal wood spars closer to the sides: 1/4 width and 3/4 width instead of 1/3 and 2/3. Less of the platform would be cantilevered on the sides.

By doing so , the distances between the wood spars will be 30,60,30cm respectively. The 60cm unsupported width of foam, won't have any tension issues? Does the increase of the thickness of the foam , from 3-->5cm , compensate the increase from 40->60cm , of unsupported foam in the middle and the related tension issues?

[Pmullen503]

The 60cm is supported on both sides, the 30cm is cantilevered, the bending moments are similar.

[gregkn73]

The 60cm is supported on both sides, the 30cm is cantilevered, the bending moments are similar.

Now I got it

[KCStudly]

I don't understand why everyone keeps saying that FG is brittle. They clearly are just propagating the experience of other people under different circumstances.

While trying to decide between PMF and epoxy/glass weave for myself, I tested. I actually tried it for myself. Now maybe a thick slab of laminated FG cure will be so strong that when you eventually get it to fail it might snap, but that's just not how a couple of thin layers of 6oz cloth works when laminated lean over extruded foam.

After years of curing, to this day I can still fold my test coupon into a U-shape (glass to the outside of the bend)... that's 2 plys of 6oz weave over 3/4 inch thk foam board (though with the weave not filled, primed or painted, and only laminated on one side)... and it comes right back. No cracking, no delamination, nothing.

Whack the face of the panel against the pointy corner of the bench fairly hard and, what do you know, it didn't shatter, splinter or crack. In fact I couldn't find a mark.

Not only that, but 8oz canvas glued with TB2 and painted with 1 coat of latex on the exact same size and shape of foam weighed exactly the same as 2 plys of 6oz glass and epoxy.

gregkn 73 is right, the strength of that FG topper tub comes from the perimeter walls of the tub acting as vertical stiffening, and the ribs formed by the raised channels where the metal channels recess. Look how tall those tub walls are; very deep resulting in a strong moment of inertia.

One last thought, if the RTT OEMs could get away with making their products lighter and easier to install, don't you think they would? All engineering is a compromise. If you want it lighter you either have to sacrifice durability, longevity, or cost of materials and manufacturing. If you go too light it could fail altogether. Just saying.

Using vertical ribs underneath the RTT floor longitudinally in the direction of travel would not increase the wind resistance so dramatically, but when properly filleted and glassed into the underside of the floor would add a bunch of stiffness. Could even be inverted like the ribs in the glass RTT, then subtract these bumps from the foam layer. Think of it like the ribs in a pickup truck bed or the roof in an old large American station wagon.

[greygoos]

I am currently building a platform for a RTT with a sandwich of 1 1/2 inch foam, 2 X 2 and 5mm top and bottom ply. 2 X 2 are 16 inches on center. Platform is 98 inches long and 56 inches wide. It is a folding type. Unless you are going to stand on the floor I think that is all that is needed. I go about 300 and have crawled around the floor with no problem. The kids walk all over it and no issues. I had a Smittybilt several years ago and when I knelt on their aluminum floor you could feel and hear the crackling of the foam underneath. There is a build on here where the builder used 2 inch foam with I believe 040 aluminum on top. No other support except for the cross pieces of the trailer.

[gregkn73]

I am currently building a platform for a RTT with a sandwich of 1 1/2 inch foam, 2 X 2 and 5mm top and bottom ply. 2 X 2 are 16 inches on center. Platform is 98 inches long and 56 inches wide. It is a folding type. Unless you are going to stand on the floor I think that is all that is needed. I go about 300 and have crawled around the floor with no problem. The kids walk all over it and no issues. I had a Smittybilt several years ago and when I knelt on their aluminum floor you could feel and hear the crackling of the foam underneath. There is a build on here where the builder used 2 inch foam with I believe 040 aluminum on top. No other support except for the cross pieces of the trailer.

Is it easy , to upload some photos of your platform? And can you give me the weight of it? Thanks in advance

[gregkn73]

One last thought, if the RTT OEMs could get away with making their products lighter and easier to install, don't you think they would?

.

I can think at least, two reasons why they didn't :-)

First they overbuilding them. I won't. If I make it , to sell it, I would overbuilt it also.

Second reason, it is easier , quicker, and most cost effective, to make them just with polyester resin and fiberglass , over a mold. Skin on frame, stitch and glue , foamie , can give lighter RTT, but are not so cost effective methods.


PS Thanks for your experience with fiberglass and epoxy over foam.

[greygoos]

I am currently building a platform for a RTT with a sandwich of 1 1/2 inch foam, 2 X 2 and 5mm top and bottom ply. 2 X 2 are 16 inches on center. Platform is 98 inches long and 56 inches wide. It is a folding type. Unless you are going to stand on the floor I think that is all that is needed. I go about 300 and have crawled around the floor with no problem. The kids walk all over it and no issues. I had a Smittybilt several years ago and when I knelt on their aluminum floor you could feel and hear the crackling of the foam underneath. There is a build on here where the builder used 2 inch foam with I believe 040 aluminum on top. No other support except for the cross pieces of the trailer.

Is it easy , to upload some photos of your platform? And can you give me the weight of it? Thanks in advance

This picture shows the framing with the insulation board on one side and the plywood cover on the other. i havent done a complete weight but will guess at 60 pounds. Have you looked at the DIY Roof Top Tent group on FB. Lots of builds and ideas.

[WoodSmith]

I'm far from an expert, but I am doing something similar. I'm building what I'm calling a Trailer Top Tent which I plan on putting atop my utility trailer.

My construction is a 3/4" poplar frame, filled with foam and TiteBond 2 laminated with 1/4" plywood (both sides). There is now a 3/4" x 5-1/2" frame glues screwed and epoxy filleted to the floor to add rigidity. I can lift this floor alone, but I would have a hard time putting it on the roof of a car. Two people can do it easily. When this picture was taken I was frankly rather impressed at how little deflection I saw. The sawhorses are further apart than the support will be on my trailer, so I didn't bother getting numbers. In my case, the center hole through which my kids legs are dangling is a removable hatch that will have a removable leg so it can be used as a table.



I actually plan on getting a weight for the pan as I'm calling it, but it is currently threatening a T-Storm and I don't feel like getting caught out!