Plywood Thoughts - Teardrop Trailer

Hi all!

This is my first post although I've lurked many times.  I've got a new project coming up that is a little different but very similar to a wooden boat - a teardrop trailer.  Yes, there is a site for building these but I would really like your opinions as I feel that the design parameters and construction of wooden boats and the elements that they encounter are similar to what I am encountering.

I will not be covering the trailer in aluminum or FRP.  It will be painted.  It will be plywood with the necessary internal framing/insulation.  It will either be 1/8" thick or 1/4".  Ok - maybe 1/2".  I am designing a lightweight trailer so weight is a consideration.  The size of the trailer will mean that there will be plywood seams.  And of course, I will be bending it in the teardrop form.  

I live in Boise and have not been able to find a local source of marine plywood (we are the land of aluminum jet boats I guess).  Even my local supplier of wholesale lumber/plywood that I use for cabinets and furniture couldn't help.  I did talk with a local wooden boat builder and he gets his material from Edensaw in Washington or Strata in Santa Ana Ca.  I've had one quote for shipping what I need with a cost of $225 just for shipping.  I could do a long road trip to get this plywood but I thought I would ask your opinions first.  I feel that other material available locally may suffice.

I can find exterior plywood, ACX in the various thicknesses that I need.  I also can easily purchase Baltic Birch (the supplier says Russian).  I haven't found a source in MDO although I haven't looked very hard for it.  

Okay - enough background, time for the questions.  First, what would you use?  

Much of the reading that I've done here basically tells me that if I use fir plywood, I can expect it to check unless I coat it with fiberglass cloth and epoxy resin.  True? 

My gut tells me to use cloth and resin anyway (even though I don't have a lot of experience with it) because I will have plywood seams and exposed plywood edges.  So, I ask myself, why not cover the whole exterior?

And finally, my research on the BB shows that it is not made with exterior glue or rated for exterior use.  But, if I encapsulate it in cloth & resin, will that be okay for this project?  The BB would form the roof/front/hatch of the trailer.  The width of the trailer is just under 5' so my material waste would be minimized.  All my seams would land on framing underneath.  The use 4' wide material means more roof spars.  I can also get the BB in 1/8" thickness and use 2 layers to form up the bends.

Thank you in advance for your thoughts/opinions/guidance.

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Permalink Reply by Rick Newman on March 18, 2014 at 7:14am

The issue with non-marine plywood and wooden boats is intrusion through damage of water into the core of the plywood. You shouldn't be hitting too many rocks in your travels other than gravel on the front of the trailer. However you could either place some aluminum or additional fiberglass along that surface. If the rest of the plywood is covered with four or six ounce fiberglass cloth and a quality epoxy resin and either paint or varnish your checking problems will be conquered.

There is another plywood supplier in SLC, but my hard drive (brain) is too full and I can't remember it. Since you aren't immersing your trailer in water but protecting it from the entry of water with a coating of fiberglass in my opinion you can use non marine plywood. Obviously the edges of your plywood need to be protected too. Where will you store the trailer? If outside can you provide some sort of cover or shelter from snow and rain. Not that it won't be protected from moisture but why let moisture collect needlessly on the surface.

I have left a section of 1/4" Baltic Birch outside where moisture can indirectly attack it. It has developed black spots but suffered no delamination problems. I used the BB as the bottom of trays on my boat, they are laminated with six ounce fiberglass and water based polyurethane outdoor finish from General Finishes.  The boat does infrequently get water in the trays but has been covered during the winter months and tilted up to keep water and snow from collecting.

How long before you will be building your trailer? I ask because you may be able to do some test pieces with a variety of plywoods laminated with epoxy and fiberglass leaving them outside to see what occurs.

I am familiar with the teardrop trailers and admire the workmanship and designs that are exhibited on the web site you mentioned.

I would love to see pictures and hear about the details of your project, will you be doing some sort of a blog or series of posts somewhere?

Best of luck;

Rick Newman

Permalink Reply by Ken on March 18, 2014 at 3:32pm

Rick,

Thanks for confirming the checking issue.  As I am in the design stage, I can take the time to really think about the plywood edges.  I have also thought of how to store the trailer in the winter which is when we get our snow and rain.  I am planning on making a shed and also using a breathable cover on the trailer.  That'll be another project for thread injector!  And that's great info on the BB.  I thought it could take some abuse.

When you say additional fiberglass to protect the plywood from gravel hits, what is your definition of additional?  I had thought to use 4 oz cloth all over.

I'm not in a hurry to start this project as summer is just around the corner and I plan on playing outside as much as possible.  I can hear the call of the mountains.  This trailer will be our retirement RV.  I plan on pulling it with a small car hence the need to design it right.  I've got an initial trailer frame drawn up and I need to run the calcs.  I think its a little too beefy. This is where I should be able to save the most weight.

Once I begin the build, I plan on sharing it on the http://ww.tnttt.com/ website under the Build Forum.  And those guys do build some beautiful trailers.  Mine will be more function - hence my desire to paint it.  I'll save my detailed woodworking for my cabinets and furniture.  (But I do have to keep telling myself that it's just an upgraded tent!)

Permalink Reply by Rojo on March 18, 2014 at 4:09pm

Hey Ken

I'm in Boise too. Did you try to special order ply through BMC West? I haven't tried them yet, but I saw a thread on some site or another where someone had some success there. I know Crosscut Hardwoods in Portland also sells marine grade ply and is a little closer to us than Seattle.  I think the place Rick is thinking of in SLC is called Macbeath's.

Let us know what you decide.

Permalink Reply by Ken on March 18, 2014 at 4:15pm

Hey Rojo!  No, I haven't tried BMC as yet.  I did try Franklin BS, Intermountain Wood Product, High Desert Hardwood and Capital Lumber.  I went by BMC the other day but didn't have time to stop.  I'll call them in the next week or so to see what they can come up with.  Thanks for reminding me.  And thanks for the source in Portland.  I've been googling to find one w/o much success.

Permalink Reply by Rick Newman on March 18, 2014 at 4:50pm

Macbeath's, that's the place. I heard a report on the radio yesterday that stated that while some of us older folks thought we had memory issues with not remembering things it is actually that are brains are so full of information that it takes a while to sort through everything stored there before the answer we are looking for appears. Hence our hard drives are just approaching a state of "fullness" that requires a longer "seek" time than those with fewer experiences or opportunities for data storage. If I could make money from those tidbits I remember or from telling stories about life I would be a monetarily rich man. Just not an old guy with lots of stories and a mind for trivia!

When I say more fiberglass I was thinking about some 17 to 20 ounce triaxial weave fabric. Something with some real meat to it. I think that aluminum would be more easily replaceable and less expensive. Even some 1/4" diamond plate could work out and the diamond embossing would help to hide blemishes. I look forward to seeing what you build. Have you checked out Fiberglasssupply.com yet. They are located in Washington so the freight costs are too bad and they offer a good selection of products and good service. I have no connections with them just had good luck with their products and service.

Good luck,

Rick Newman

Permalink Reply by John Weston on March 20, 2014 at 9:35am

myself, I would use MDO in 3/8 or 1/2. tape all seams with FG and diamond plate the front. use a good primer and finish with a good deck paint. see, that was easy. now get to building. I can call over to Shelton there is suppose to be a plant that makes MDO and get a cost. Shelton is next to Olympia. the drive over and back would prob be cheaper then shipping cost.

JW

Permalink Reply by Ken on March 20, 2014 at 6:53pm

Rick,  did you use the General Finishes Exterior 450?  I've shot gallons of their interior Enduro-Var.  Also brushed it.  I love that it is a w/b with an amber tint.

Steve - I started looking at MDO last week.  I like everything about it except the weight.  And, I could only see that the smallest thickness is 3/8".  That would be fine if I didn't plan to make a SIP type wall - structural insulated panel.  

Once I have the design a little further along, I will compare all of the weights of the various constructions that I have in mind including MDO.  I started the spreadsheet last night so that I will be able to calculate all of the weights easily.  I will inquire locally to see if it is available if I see myself using it.  Thanks for the offer.  

Permalink Reply by Rick Newman on March 20, 2014 at 8:56pm

Ken I used General Finishes Exterior 450. So far so good. It sprays well and looks good. I haven't opened the cover all winter but I soon will. to see how it sprayed out look at the pictures on my page.

Rick N

Permalink Reply by Ken on March 21, 2014 at 5:13am

Some really great photos of the work of some very fine craftsmen!  I always thought it would be great to row the MF Salmon or main Salmon in a drift boat.  But I think I would need to bring some fiberglass repair equipment along with me as I'm just a kayaker and hitting rocks has always been part of the fun and I bring that mentality over with me when I'm rowing.

Ken

Permalink Reply by Rick Newman on March 21, 2014 at 8:13am

For the most part the hits are along the chine, hence its design to be easily replaceable. You will hit rocks, what I find is most important is what and how many rocks you miss! I built the floor of my boat hopefully exceedingly strong in hope that any damage I suffered would be minimal and that I could continue my trip with minimal repairs until I got home. The fiberglass and other fabrics commonly used in our builds have the greatest strength when under tension. That means that having it on the inside of the boat provides the greatest strength. so the thicker the interior laminate built with the strongest fabric provides more resistance to puncture. I chose S-glass over the more common E-glass, not much more cost but increased strength.

In my opinion an almost unbreakable boat could be built but the cost would be much beyond my budget.  Could it have the draw as a nice wooden boat, I think not.

At high water I found the Middle Fork to be a very busy place to row especially with a Lower Main Salmon style load! What I really enjoy about my 16' Greg Tatman boat is its performance with a light load. I was also a kayaker and and open whitewater canoe guy and loved the ability to put those boats where ever I wanted. Eddy turns, swiveling around rocks almost possible in my boat. I use the chine to help make turns, leaning it purposefully to one side to carve a turn or front or back ferry. I like to turn my oar blades parallel to the river surface and do a bracing movement much like in a canoe or kayak.

You have joined a great group of folks, welcome aboard. It will be interesting to see how long it before you start planning your boat build too.

Rick N

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