Events Intervene

As can reasonably be expected, various random events have intervened to cause further delays.  There was a disconnect between what I thought I ordered for the oak slats and what I actually specified.  That drove the need to step back and recalculate.  We encountered several issues during our test rib build that have driven a minor structural redesign (more on that later).  But, that's why we did the test!

Further, a dead refrigerator, a broken car windshield and a computer that won't display any video complicated efforts to move the TD forward.  The windshield is being replaced as I type, the fridge service is tomorrow (hopefully it is repairable) and the computer, well, a new video card and a replacement power supply both failed to make a difference.  The computer is an auxiliary one anyway, mostly used as a print server and to run SETI, so it can wait.

The Test Rib

In review, we decided to build a test half-rib from red oak that we cut ourselves, but later switched to building a full 8-ply rib from white oak that we sawed to 1/4" from an 8/4 board that was nominally 1-13/16" thick.  The overall length of the full rib is 18', and we could not get an 18' board, so each ply had to have at least one joint.

We cut and dry-fit the first four layers, then cut the other four without laying them into the mold.  We decided to attempt two joints in one ply to maximize the utilization of the wood.

Given that we only have so many hands, that the open working time of the glue is critical, and that handling a bundle of glued and slippery boards 18' long into position in the mold seemed daunting (for good reason!), we decided to attempt only four plys on the first gluing, subsequently gluing up the other four and adding them to the first four.

But while we were applying the glue to the slats we realized that the time it was taking to spread the glue mandated that we put the first three plies into the mold before it was too late.  A few days later we removed those first three from the mold and prepared for the next step.  Here is a photo of the first three, positioned on the base trailer to give a sense of overall size and shape:

It was pleasing to see the rib in place.  Clearly, though, this teardrop will not qualify as "tiny," and that is by design.

Next we added three more plys to the assembly, then finally the last two.  Here are some photos showing the full eight plys in the mold:

 - View at Rear (Hatch Area) -

- Clamping Station Detail -

- Shallow Portion of Curve -

Overall, we were very pleased with the 2x4 blocks screwed to the work table and the use of shims to clamp at each station.  As you can see, we occasionally added a clamp between stations to pull the layers together.  

Since the rib is wider than the target 1-1/2", we will flatten one side somewhat, then run the rib through the table saw in two passes (one for each side) gradually bringing it down to the 1-1/2" desired and evening out the sides.

Lessons Learned

The first lesson is that attempting to lay up a full rib with all eight plys just isn't workable; we don't have enough hands and glue working time.  

The second learning is that it will be much easier to do the laminations if no joints are involved in any ply.  As the bundle of slats is being positioned in the mold the layers have a tendency to slide relative to one another.  Even one joint in each layer is challenging because you have to move one layer relative to two other layers without disturbing their joints.  Since we cannot get 18' lumber, that means we have to build the ribs in two sections - front and rear.  By bringing the sections together at a cross-member we will be able to retain structural integrity while vastly simplifying the lamination process.  We will be able to glue up 8 slats no more than 10' long, get them into the mold and clamped without difficulty.  While this doubles the number of laminations required, it will be achievable.

The next step is to calculate the longest possible rib section length that can be created from our milled stock, and determine if that length can work with the positioning of the partition that separates the cabin from the galley.  If not, then we will position an oak cross-member at an optimal point in the curve to join the sections.  More soon!

Interregnum

For those of you following this blog, we find ourselves in an interregnum.  The oak slats to laminate the ribs are on order but not likely available for another week or better.  Sean and I have been working to create a test lamination, but that has progressed from a half-rib from red oak to a full rib from white oak.  We bought the white oak board (8/4 x 5-1/2" x 14'), reviewed our techniques, and finally today ripped the slats.  Tomorrow we will size them to 1-5/8" wide and prepare for the actual lamination.

Stay tuned!

Building the Teardrop

The Building

 As I mentioned in the Welcome message, the teardrop is being constructed in my friend Sean's yard.  To facilitate this, he put up a temporary building as shown below.

At 12' x 20', this space will be more than adequate.  It will accommodate the work table we envision, and it will allow us to assemble the entire trailer under cover.

The Table

To facilitate construction of the laminated ribs and the trailer sides we determined that a table was required.  The overall dimensions needed to be 5' x 12'.  Sean determined that we should build the table structure from 6" heavy duty steel studs and channels, covered both sides with 7/16" OSB with dimensions of 4' x 12', and a top layer of 3/4" fir plywood to the full 5' dimension with the edge reinforced by 2x6 fir.  The table rests atop two custom-sized saw horses.  The top layer of plywood was painted white to enhance lines drawn for the layout.

Once the table was complete we proceeded to draw the profile on it.  This required the addition of two "wings" - one at the end in the foreground of the above picture to locate one of the two foci for the rear ellipse, and one at the far corner in the above photo to accommodate the rear section where it drops below the top of the trailer edge (part of the hatch area.)


We located the two foci for each ellipse, and using braided steel line, drew the ellipse sections using the "string" method.  In this method, each end of a "string" or line is affixed to one of the two foci.  The overall length of the "string" is the sum of the distance between the two foci plus twice the additional distance from one of the foci to the extent of the ellipse on the line connecting the foci.  

Once the curves were drawn using the steel line we used a spline, positioned periodically by fasteners, to create the true, fair curves.  This compensated for the fact that the steel line method created inaccuracies when the awl intersected the grain of the plywood in an unfavorable manner.

Following are the two ellipse layouts, each also showing the extent of the ellipse where it intersects the trailer:

Once the profile was drawn on the table, the next step was to lay out the clamping stations for the laminations.  We decided to screw 2x4 blocks to the table on both sides of the lamination profile.  The lines drawn were the outside of the profile, so we measured 2" inside that and affixed a block, the end of which had been slightly rounded to avoid flat spots on the lamination.  We used a standard 1-5/8" piece of 2x4 plus shims to locate the outer block.  The view below shows some stations at the hatch reflex area with some steel bands used to check fairing of the curve:

 Here is a view with all the stations installed, viewed from the front of the profile; note the addition of a wing at right (center top of the curve) to mount the outside clamp blocks:

 After installing all of the stations we ripped some red oak to 1/4" thickness in 10' lengths in order to do a dry run and prove that 1/4" stock would take the curves.  We used shims to position the laminate plys and mimic the clamping action required when glue is in play.  We ran the dry run with 8 pieces of 1/4" red oak bent to the tightest part of the overall curve.  Occasionally clamps were required to close the gaps.

The 1/4" oak was able to take the tightest of the curves without hesitation.  Our next step is to recreate the back half of the curve using glued laminations.

The Trailer and Cabin

The Trailer Portion of the Teardrop

Most teardrops, whether commercially produced or home-built, start with either a custom welded frame or a bolt-together frame, such as this one from Northern Tool.  The drawbacks are a) the frame is steel, which can corrode, b) the underside of the plywood floor must be carefully waterproofed, and c) the trailer has to be inspected and assigned a serial number by the state's DMV or DOT before it can be registered.

I opted instead to purchase a pre-built, all-aluminum trailer from Aluma.

The version I purchased omits the gate on the rear of the trailer; I also added a spare wheel and mounting bracket.  The 6310H includes a 3000# torsion axle.  It is 63" wide and 10' long.

The advantages here, in my thinking, are that the trailer is already road-legal, is highly corrosion resistant, and provides a solid platform on which I can build my cabin.

Cabin Shape - Profile

Before beginning to design the profile I spent a lot of time looking at what others have done.  None of the profiles I found were exactly what I had in mind.  They were either too "eggy" - almost an egg on wheels - or too angular.  None of them had the dimensions I wanted - a 10' long platform that was 4'6" to 5' high.  And so I embarked on learning a new drafting tool to design my profile.

Alibre Design is the program I settled on, mostly because it appeared capable and was relatively affordable in the consumer version.  I have to say, though, that it supports a workflow that was completely foreign to me.  It assumes you will begin with solid modeling and proceed to detailed drawings.  I just wanted to start with the detailed drawing.  I give Alibre's customer service high marks for helping me get there.

It took eight iterations (I call this one "Take 8", a tongue-in-cheek reference to Dave Brubeck) before I arrived at this profile:

This profile is a combination of two different ellipses with their horizontal axes aligned;  the ellipses join at the topmost point.  Keeping the horizontal axis of the front ellipse shorter provides for better headroom in the front, while extending the horizontal axis of the rear ellipse creates a very nice reflex in the curve which will be part of the hatch/galley.  With the ellipses extending ahead of and behind the limits of the 10' trailer bed, the overall length of the cabin grows to approximately 11' 1-5/8".

The dotted line is the floor of the trailer, but that will not be the floor of the cabin.  I will use 3 2"x6" running front-to-back, boxed in the front but open in the back and covered with 3/4" birch plywood for the base of the cabin as seen in the section below:

One side effect of this floor construction is that I will have two cavities, each about 29" wide by the 10' length of the trailer to store items such as folding tables, chairs, tools, and even (potentially) a screen room.  These cavities will be accessible from the open hatch since I will not box in the rear.

I wanted to build the side walls and front/top using a sandwich construction method.  For the side walls the inner and outer layers will be 1/4" Baltic Birch plywood with 3/4" x 1-1/2" oak structural components as appropriate.  These oak components will primarily serve to create the cavities that will be filled with rigid foam, and to provide solid attachment for doors, windows, galley partitions and other items as required.  With the entire surface of the plywood glued to the rigid foam and the oak members, the result will be a lightweight, rigid panel.  By running the side wall construction to the top of the curve I will be able to deduct 4" from the 63" width of the trailer, and thereby use slightly cut down 5'x5' Baltic Birch for the inside and outside of the front/top curve.

The front/top curve will be similarly constructed.  This presents a challenge - how to structure the curved front and top while achieving the same rigid panel result.  I decided to laminate six ribs to form the basis of the structure.  The two ribs at the walls will be 1-1/2" x 2", laminated from eight layers of 1/4" thick white oak.  The four inner ribs will initially be laminated as two ribs 1-1/2" x 1-1/2" in section from 6 layers of 1/4" white oak.  These will then be sawn along their length to create four ribs 3/4" x 1-1/2".  The ribs will be connected across the width of the cabin with 3/4" oak stock in a box pattern, with the voids being filled with two layers of 3/4" rigid foam.  (The 3/4" foam will conform to the curve without needing to be kerfed, whereas the 1-1/2" foam will not make the bends.)  The inside of the curved panel will be covered with a single layer of 1/8" Baltic Birch plywood, while the outside will receive two layers of 1/8".

All connections will be made with glue and screws, with the screw holes being pre-drilled to avoid splitting the oak.

Why white oak for the ribs?  I want to use oak for strength, and the supplies of white oak can provide somewhat more regular grain than red oak.  In a subsequent post I'll show how we set up a proof-of-concept using red oak, and the red oak worked great.  I don't know that the additional investment in white oak will pay for itself in the ease of working the laminated ribs, but I do know that when I leave it exposed and varnished under the hatch it will look very, very nice.

What the section above does not show is that the entire outside will be clad in pre-painted aluminum.  I'm thinking on a two-tone scheme using red and white that highlights the waistline on which the ellipses are based.  The front and top may be either white or natural aluminum in color.


In the next post I'll add some photos of the facility where the trailer will be built, the worktable we constructed for the purpose, and the clamping stations we have laid out for laminating the ribs.
  

Design Considerations

Why Design My Own?

There are a goodly number of teardrops on the market today being manufactured by small- and large-scale operations.  Prices range from around $5k to $30k and more.  (See the Orvis model here as an extreme example.)


Each manufacturer brings their own sensibilities to their products, and I have to admit that several available trailers caught my eye.  In the end, though, none fit my requirements just right, and I decided to "roll my own."


The primary consideration was that the available teardrops are generally limited to a 4' height.  I sleep in a chair, not on a flat bed, for two primary reasons:  1) My back hates being on a horizontal surface; I can take no more than a few minutes in a traditional bed, and 2) sleep apnea is an issue with which I am intimately acquainted.


Sometime around 1994 I had to fly to Fort Worth, TX, to a manufacturing operation of the company for which I worked.  I was stuck in the window seat on a 2-5-2 aircraft, and spent the flight from ATL to DFW forced to lean left but constrained by the next passenger.  Upon my arrival there I was in serious pain, as I had several years prior pinched a nerve in my lower back.


The conference room at our plant had, in addition to the customary tables and chairs, a sofa and a matching chair.  I found that, if I sat in that chair, all back pain subsided.  I convinced the plant manager to have his people move the chair to my hotel room for the duration of my stay.


I hadn't slept so well in many years.  Not only did the chair alleviate my back pain, sleeping upright addressed the apnea as well.  I haven't slept in a bed since.


I have determined that an Ikea Poäng chair with foot stool will suit me well.  It will fit into my design, it is lightweight, and should I decide to check into a hotel/motel for the night, I am not going to be constrained in my choices by whether or not they have an appropriate chair for my slumber - I can simply bring my own chair inside!

Teardrop Design Considerations

Sleeping comfort

As you might infer from above, the first consideration is that the cabin be large enough to accommodate sleeping in a chair.  That drives the interior height dimension.  Further, should my wife decide to join me on an adventure, it needs to be wide enough for the chair and a second person sleeping "normally."

Galley

Another consideration is an adequate but not overdone galley.  I'd like to have running water in a sink, but I am content with using a Coleman cooler for refrigeration.  A stove is a requirement, and I initially decided to do a built-in propane stove.  I also wished to have a grille, whether gas-powered or charcoal-based.  However, I went to Cabela's one day and was looking at their camping gear.  There I found a portable propane-powered portable grille that can fold and stow.  It also provides for a stove top burner with an optional part.  This is a perfect solution for me - both functions in one unit, not requiring an onboard propane tank with associated hose, not requiring the additional space of two units, easily replaceable should the need arise, and foldable/stowable.  Some teardrops go so far as to provide microwave ovens, hot water and other appurtenances, but I find those both unnecessary and resource- and space-intensive.

Stowage

The teardrop should be capable of carrying all the requisites for life on the road or in the campground - a table, chairs, and even a screen room - as well as a spare tire and the tools necessary to change it out.

Dual-voltage electrical system

Most RVs have an onboard dual-voltage (12v - 120v) system.  Some even include 240v (well, those are the behemoths built on bus platforms) and generators.  I want to have onboard battery capacity to get me through a couple of nights if need be, while being ready to plug into "shore power" - the 120v feed available in most RV campgrounds.  (I find it interesting that not only is this a nautical term, but the general components of boat and RV electrical systems show a high degree of overlap.)  No generator is desired.


The idea is that most of the time the systems in the trailer can run on 12v from battery.  My laptop computer can run from an available 12v power supply.  I have no requirement for a radio, DVD or TV system.  Lights, fans and ventilation can easily operate on 12v.  However, some components (such as the Coffee Maker - an absolute, non-negotiable requirement) require 120v. 


The hookup to my car provides for charging the battery while underway.  I have found an available converter/charger that takes an incoming 120v feed (from shore power while in an established facility), converts it to 12v and charges the battery.  Any 12v outlets/appliances run from the battery, while 120v devices run directly from the shore power feed.  When no shore power is available, the inverter section will take 12v DC from the battery and invert it to 120v AC.


Rather than having one 12v battery, my research indicates that one is better off with a pair of 6v golf cart batteries in series (thereby creating a 12v supply.)  Car batteries employ plates that are essentially lead-coated sponges.  By multiplying the surface area with a "sponge" form factor, they achieve a greater cranking amperage.  But these batteries do not hold charge for long or have long lives, since they are designed to deliver maximum amps over a short period of time and do not presume "deep discharge."  Marine "deep discharge" batteries improve upon this by making the lead coating on the sponge thicker, extending the life span of the battery.


Golf cart batteries, on the other hand, employ solid lead plates.  While they are not designed to deliver high instantaneous current, they deliver much longer discharge times and overall battery life.  This is perfect for my requirements. Golf cart batteries are typically 6v, so a pair of them in series will deliver the 12v required.


I've been looking at solar charging system as well.  Simply put, you mount a solar panel on your roof, feed the output into a charge controller, and connect to the battery.  These systems are not inexpensive.  Further, one has to assure that the solar system, the car charger, and shore power do not conflict.  Maybe, but not likely initially.

Light Weight, Durability

As I will be towing the trailer with my car, weight is a critical concern.  Obviously, the heavier the trailer, the lower the gas mileage.  I've been spoiled by owning a car that can achieve 36+ MPG highway.  To paraphrase a well-known actor/association president, those MPG will be pried "from my cold, dead hands."  Well, I know I'll give some up, but no more than necessary.


I live in New England, very near the shoreline.  Corrosion is a concern, though I probably won't be towing the trailer through a lot of snow and salted slush.  The typical teardrop is built upon either a custom-welded steel frame, or a bolt-together steel frame, such as this one from Northern Tool and Equipment.  Steel corrodes.  Further, when building a trailer on a platform of this type, the underside of the plywood floor must be properly waterproofed (and maintained.)


Aluminum trailers avoid the corrosion issue, and are light-weight.

Construction

Typical teardrop construction is based on the same sheet of plywood that drives the overall dimensions.  A sheet of plywood is bolted to the steel frame.  Two plywood slab sides are cut to profile, mounted to the platform and connected by 1x2 stringers or similar members.  The inside and outside of the curves are covered with 1/8" or 1/4" plywood.  The trailer is most often covered with painted or mill finish aluminum.  Some finer examples leave the exterior in wood, stained and varnished (or covered with resin), some trimmed with hardwoods.

The issues with that typical platform include the lack of insulation, flimsy construction (in my opinion) and a general sense of lacking longevity.

Further, such examples require the builder to have the trailer inspected by state authorities and a VIN assigned so the trailer can be registered.

I determined that I would build my trailer on top of an all-aluminum utility trailer from an established source.  The advantages are that the base trailer will be complete, including a VIN and DOT-approved lighting, that it will be lightweight and it will be resistant to corrosion, indicating expected reliability and longevity.  By selecting the heavy-duty axle version of the trailer, I can be confident of towing the trailer over dirt roads in the Western US without fear of it breaking down.


The base trailer I selected has a bed that is 63" wide by 10' long.  Both of those dimensions exceed the typical 4'x8' sheet of plywood.  The choice drives the selection of Baltic Birch plywood as a prime construction material, as it is available in 5'x5' sizes.


For the side walls I decided upon a sandwich construction, comprised of 3/4" x 1-1/2" structural members between layers of Baltic Birch plywood, filled with semi-rigid foam sheets, clad in aluminum.  This construction establishes a rigid, lightweight system (assuming all the layers are glued together.)


For the roof/front I decided upon a similar construction.  This drives the requirement for curved ribs matching the overall profile.  To create the curved sandwich construction I opted to create laminated ribs with solid cross-members infilled with rigid foam insulation and covered by Baltic Birch plywood.

The construction of the galley components will primarily be 3/4" birch plywood, giving the overall structure additional rigidity.  The hatch will be built from the laminated ribs and self-manufactured bead-board, exposed on the inside, to highlight the overall construction techniques and craftsmanship.

By selecting sandwich construction for both the sides and the top I hope to keep weight minimized.  Creating the laminated ribs for the curved sections becomes a technical challenge that I welcome.

The next post will begin to detail the construction methods selected and follow the construction process.

Welcome!

Welcome to Emmitt's Teardrop Adventures.  At the request of several friends, and in the interest of sharing learnings, I will use this blog to follow the process of building my own design teardrop.  Upon its completion I will chronicle my travels with it and share some of the photos that will be taken.

I wish to acknowledge from the beginning the participation of my very good friend of long standing, Sean Fox.  Sean is a sounding board, a (constructive) critic, and a partner in the construction process.  The trailer is being constructed in his back yard under a temporary building.  Without Sean's expertise and active participation in the construction process, this teardrop simply would not be possible.

There will be many other acknowledgements along the way, as well as links to sources and resources I have found useful.

What is a Teardrop Trailer? 

There are plenty of resources on the web detailing the development of the teardrop trailer, so I will not attempt to recreate that information here.  In short, a teardrop is a small travel trailer that became popular in the post-war years.  One could buy a manufactured model, or, following plans and directions in a number of magazines, build one from scratch.


The term Teardrop derives from the typical profile of these trailers - a rounded shape that often resembles a teardrop.  Many other shapes have also been classified as a teardrop given their similarity.


The typical teardrop is very simple, consisting of a cabin for sleeping and a hatch in the rear that provides access to a galley.  Often they are four feet wide, about four feet high and no more than eight feet long, a planform dictated by the standard sheet of plywood.  

The teardrop's relatively small size and light weight make it easy to tow without requiring a huge, expensive-to-operate truck.  That appeals to me!

You can get a sense of some of the historical designs here and here.

Why a Teardrop Trailer?

Well over a year ago my wife, who travels around the country to various botanical conferences and other gatherings, was musing about the potential of a teardrop as a place for her to sleep rather than paying motel/hotel rates.  In the end, she decided against getting one as it would take some time to realize the payback.


As I was considering retirement at the end of 2011 I needed to answer the question, "What will you do with your time?"  I have an abiding interest in nature and scenic photography, and traveling around the country in that pursuit could be quite expensive.  A teardrop will help keep expenses minimized during my adventures.

Besides, I just love a project like this one.  It will employ design sensibilities, problem-solving and craftsmanship skills.  And the end product will enable my Teardrop Adventures!

Next post I will introduce my thinking on a design that will work for me.