Wood trailer chassis

[CLChastain]

Been skimming the tntt threads about wood trailer chassis, to supplement the little I already know.

Years ago, I read a book or vintage magazine article about home boatbuilding. It provided plans for the boat plus plans for building a wood-framed trailer for hauling the boat. It puzzled me, because I wondered if it wouldn't float when you backed it into the water to float the boat off of it. I figured maybe the wheels and axle weighted it down...

I also used to visit (and still do) Australian classic caravan forums that feature many homemade "bondwood" (plywood) camper trailers from the 40s, 50s and 60s that were being restored by vintage 'van enthusiasts, although many had been commercially manufactured. Member restore journals and images are fascinating. There were also aluminum and fiberglass oldies, but most were bondwood. One explanation I came across said there had been no aircraft manufacturing industry in Oz during WWII that had to diversify into trailers (like Spartan) after the war to stay in business.... But I digress. While most of the trailer chassis for the classic Aussie vans were steel, some of the homemade ones were made of wood timbers.

My question is ... for somebody with no welding or other metalworking skills, could a wood-framed trailer be feasible today, if it was well waterproofed, for a small standy such as I'm designing? My assumption is that it would be heavier than a comparable metal trailer chassis, but after skimming these tntt threads, I wonder. Since I've discovered "foamie" construction here, I've also wondered if a heavier wood trailer (if it IS heavier) might help lower the center of gravity for such a lightweight box and perhaps counter windage.

If it is feasible, the problem would be finding plans. The plans I remember reading about were for a boat trailer, but I don't remember where I saw it. Sam Rabl's "Boatbuilding in Your Own Back Yard" comes to mind (loved that book!) but I'm not sure that was it. Perhaps something like the Wanderbug plans could be upsized...

Any thoughts, suggestions? The wood chassis threads I've found here are about small teardrop designs. My favored standy dimensions are twelve long, seven wide, six tall. Apparently there are foamie standies in that size range, but I have this vision of a lightweight trailer box lifting off the trailer at highway speeds and floating in the air and landing on the ground beside interstate, crushed like an eggshell....

[CLChastain]

Incidentally, I have a steel trailer, from a 1970 or so Aristocrat LoLiner of the dimensions I want to use. It has a drop floor area. I hate it. I'm trying to get around using it.

[angib]

The problem with wood is how do you joint it? Big bolts look good but take away too much strength. If you are familiar with using epoxy and glass, it is possible but not at all easy.

The only way I would do a large all-timber trailer would be using a plywood double-floor maybe 12" deep - which is a lot of internal headroom to lose.

You might want to see this article on a plywood racecar trailer, though it sounds like a structural nightmare to me with the timber tongue just bolted to a 1/2" ply floor. I would like to hear how many thousand trouble-free miles this trailer has done before copying it. Note that it has some big metal plates where the axle attaches.



The same builder's previous racecar trailer was much more intelligent and a good example to copy:

http://www.westsystem.com/ss/projects-t ... taudacher/

[CLChastain]

Thanks, angib... That's a sharp looking car carrier.

I can't imagine anything larger than a regular 2x4-inch timber would be necessary to make a chassis for a trailer of the size and weight I have in mind, and some members would be even smaller -- 2/2, maybe. Bolts need not be so huge as to weaken the wood, especially if the joins are also epoxied... I suspect the leaf springs would be suspended from a metal hanger that would attach to a wood stringer the way it attaches to steel ones ... with bolts. The main thing I need to read up on is the tongue and coupler... I'm drawing a blank thinking about those parts on a wood chassis....

[aggie79]

I would not use 2x4s - particularly softwoods such as pine, douglas fir, etc. - or any other timber for that matter in a frame. Cut lumber has a grain. It works good in compression but not in torsion or tension. Timbers can have internal shear along the grain line when flexed. If you're going to build in wood, your better off building up framing members from plywood that has alternating grain directions.

[angib]

The basic requirement for the strength of a tongue is that it must be able to withstand a vertical load on the coupler of about half the total weight of the trailer- yes, that's half as in 50%. There is no way some 2x4s will provide that sort of strength unless they are assembled into a truss girder.

"But the tongue doesn't need to be that strong"? Well, most other trailers are, so why would a wood one be different?

[rowerwet]

I would use long metal straps bolted every few inches to spread the forces from the hitch out.
Even then you are getting into areas that you must get your engineering correct for everyone's safety.
Bolting a steel tongue on seems safer.

[rowerwet]

[quote="CLC]Apparently there are foamie standies in that size range, but I have this vision of a lightweight trailer box lifting off the trailer at highway speeds and floating in the air and landing on the ground beside interstate, crushed like an eggshell.... [/quote]
As the builder of a 13x6.5x4' foamie I can tell you our foam tears are bolted to the frame like any other tear. The floor is still wood of some sort, then the fabric skin is wrapped down under the floor and glued to it. The foam holds the roof up and the fabric ties the roof and walls down.
None have ever blown off the frame