We purchased a used aluminum drift boat a couple years ago, which has been great to float white water to flat water. The fully outfitted boat and trailer only cost about $3000 and was water ready. We've enjoyed countless fishing, crabbing, and just lazy float trips in this boat and it's been worry free until I started to take a close look at the trailer this winter.
These aluminum boats are super durable and are basically maintenance free. However, the trailers (most of them steel tubing) do not live nearly as long as the boats due to rust. After close inspection of the trailer, I noticed lots of rust and in many places the tubing had rusted clear through. I started to price out new trailers and quickly found that they start at around $1500, which was half of the overall cost of the boat. I did some quick calculations and realized that I could easily build one for $500 - $700 dollars in materials.
So, I designed, fabricated, prepped/painted, and have already put over 2,000 miles on my new trailer without any worries. In this Instructables article I'll walk you through the process from inspection of the old trailer through final assembly and use of a newly fabricated one.
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Step 1: Inspecting Your Boat Trailer
The boat and trailer were manufactured in 1996, so at 20 years old I wasn't surprised to see the trailer showing some rust through the paint. With the boat on the trailer the rust didn't look bad, and I had planned this winter to put a fresh coat of paint on it. After I pulled the boat off to take a closer look, I quickly found that the trailer had a considerable amount of rust and frankly was not safe traveling down the road. When the boat was removed, I was able to see many spots where the trailer had rusted clear through many of the main structural components.
At this point I knew a coat of paint was not going to fix this trailer, and it was time for new one. Through my inspection, I did notice that the axle, leaf springs, wheels, etc. where still in good shape and had nothing more than a little surface rust on them. Other than the axle assembly, the trailer was scrap.
Step 2: Measuring the Existing Trailer
Since I had an existing trailer, I didn't have to build a trailer off from the boat dimensions. I was able to take measurements off the existing trailer and use it as a pattern for my new design. This obviously simplifies the design and overall task. There are a few key measurements I wanted to ensure I had captured correctly. The axle and bow rest placement relative to the two main boat supports are critical for proper balance of the boat and trailer. Other than these few critical dimensions, the rest of the trailer I just taped out and captured in some basic sketches.
Step 3: Trailer Design
For the overall layout and detailed design of the new trailer I used Autodesk's Fusion 360 product. With Fusion, I was able to easily layout the entire trailer virtually before I ordered or cut any material. Fusion also provides simulation software that allowed me to constrain and load my virtual trailer design to validate that it could easily hold up to 1,000 lbs load. The image attached shows overall deflection at the 1000 lb loaded condition.
In the new trailer, I did want to incorporate two design changes from the original. The first was a segmented rear roller system. The original trailer had a single long roller that didn't allow the boat to easily pivot during loading. In the new design I incorporated a series of 5 rollers that would rotate independently allowing the boat to more easily pivot while aligning the boat during loading. The second change added diamond plate landings that would allow you to easily get in and out of the boat while it was loaded on the trailer. Other than these two advancements the new design was a very close replica of the original design.
Step 4: Frame Weldment Layout
For the first fabrication step I started by cutting the main frame components from steel tubing ( 2in x 3in 0.125in wall). After cutting out the frame components, I laid them out to ensure a good fit.
Step 5: Assembly and Welding of the Frame Tongue
The initial step in welding together the frame is to weld the tongue to the first cross member. To do so, square the two components together (the tongue is perpendicular to the first cross member), tack weld the components, recheck squareness, and then complete by welding around the mating surfaces of the two components. Once complete, add the two cross angle support stiffeners. With the tongue welded together, it will be the basis of the rest of the trailer. Take time to ensure squareness and fit of these components, as the rest of the trailer will be based off of this initial assembly.
Step 6: Completing the Frame Weldment
Now that we have the trailer tongue assembled and welded together, we can layout the rest of the frame sections. You'll want to shim the entire frame up off the ground so that you'll be able to both clamp and level the full frame. To shim the frame I used lumber to first get the structure off the ground, and then used small pieces of sheet steel ranging in thickness to shim up and down each corner of the frame. Using a level, a square, and clamps, work your way throughout the frame shimming and positioning as needed to assemble and fixture the whole frame.
You'll have three goals in assembling the frame:
- Ensure that the whole frame is level (both down the length of the trailer and across the width).
- Ensure that all right angle joints are square. I use a large framing square, which works quick well.
- Ensure that all joints are assembled tightly together.
Once you have the entire frame in position, cross tape both far corners from the tongue to ensure that the entire frame is square. With the whole frame tightly clamped together, you can use a large hammer to adjust the frame such that you get the same measurement when cross taping between the tongue and far corners.
Check your joints and recheck that the frame components are still in level. Then, work your way around the frame and tack weld the entire structure together. These tack welds should be large enough to hold the frame together, but not so heavy that you introduce a lot of heat in any single area. Now that the frame is all tacked together, I would again check both level and squareness before fully welding it all together.
If you are satisfied with the setup, now you can begin welding up the entire frame. To do so, you'll want to balance the heat across as much of the frame as possible to help prevent warping. If you simply start welding in a single location and then work your way around the frame, you'll likely find that the frame has warped from heat. By welding a single seam and then moving to another location on the frame to start another weld, you will have distributed heat more evenly throughout the frame reducing overall warping. You will want to continue this process around the whole frame until complete.
At this point the main frame weldment is complete! Notice in the images above that I also added wire guides and ran lightweight cable through the assembly before welding it together. These guides and cable will allow me to easily pull the wiring harness through the frame in my final assembly. Had I pulled the wiring harness through the frame tubes prior to welding, I could have melted or damaged them during the welding process. It's much easier in my opinion to run a cable and pull the wires through in the final assembly.
Step 7: Mounting the Axle to the Frame
Now that the frame assembly is complete, we can locate and weld on the leaf spring front and rear hangers.
The placement of these hangers is important, so you'll want to take extra care to ensure their location is correct before welding them to the frame. If you remember we took extra care in measuring the exact placement of these hangers from the original trailer. Once we have them located, clamped, and welded in place we can flip the frame over and attach the axle.
Before we flip the frame over, now is also a good time to add the tongue skid. This will save us from needing to flip the frame again later or from needing to weld from below.
With the axle now assembled, we can more easily move the trailer around as needed.
Step 8: Assembling the Fenders and Steps
Creating the components to mount and build the steps is where having a good CAD model really pays off. There are several components to create and getting them to fit together is quite easy since we're able to build them from the CAD geometry.
The most difficult part of this assembly is creating the mates against the shaped fender. I have a 3 axis CNC mill, so I was easily able to cut the compound curve directly from my CAD geometry. This made for a really nice fit that was easy to weld and blend together. If you don't have access to a CNC milling machine, not to worry, you can layout directly on the material from your CAD design. Then cut the shapes by hand using a saw, torch, or a cutoff wheel and then simply grid to fit. Taking time here to ensure a nice fit will certainly pay off in the overall aesthetics of the trailer.
Step 9: Roller Assembly
To assemble the multi-segmented roller system, we first construct the 6 mounting tabs. The rollers will be assembled with a stainless steel 3/8 inch solid rod that will pass through the rollers and tabs. Alignment of these tabs will be critical to ensure the following: centering of the rollers, clearance for each roller to rotate freely, and to ensure that the SS 3/8in rod can pass through them all. The ends of the rod should be drilled to accept a hinge pin or cotter key.
Step 10: Prepping for Paint
I had originally planned to have the trailer powder coated, however I found that due to the size the price was considerably more than I wanted to spend. After all, this was just a simple trailer for fairly inexpensive boat. So, after doing some research online, I found that many have had good luck just using brush on Rust-Oleum.
To prep the trailer for paint, the task is to grind welds and any weld splatter that you want cleaned up prior to painting. This is a dusty and dirty job, so make sure you're dressed to get dirty. I use a 4 1/2 inch angle grinder, which cleans things up very nicely.
Once, the trailer is completely ground and free of any defects you will need to clean it with solvent. I use Xylene to remove all dust, grime, and grease/oil from the frame. Xylene can be purchased at any paint store or home improvement center. Be sure to read the warning before using, and make sure you're in a well ventilated place before using a solvent like this. I prefer to do this kind of work outside.
Take your time to clean the trailer very well.
Step 11: Paint
For paint, I chose brush on Rust-Oleum after doing some internet research on trailer painting options. After a quick google search I found that many people had good luck with this approach. First I used the clean metal primer, which comes in white and has a bit of a chalky finish to it. One coat covered the trailer nicely, however I did do a little touch-up to the primer coat before painting with the protective enamel. After allowing the primer to dry, I applied two coats of the protective enamel. I found it almost impossible to eliminate all runs when putting on enamel paint. However, I worried less about the runs and more about the protective finish. I coated the trailer very heavily in hopes that it will help me get years of lasting coverage.
Overall the paint turned out really well, and the Protective Enamel has a very nice shine after it dries.
Step 12: Final Assembly
Once the paint was dry, it's time for final assembly! Only a few things to do here before we're complete.
- Installation of lighting and wiring
- Chase the wire harness throughout the frame using the previously installed cable and routing guides
- Install LED light housings
- Complete the wire connections. I purchased a complete light set, which came with everything needed and a nice easy to follow schematic.
At this point, the trailer is now complete and ready to be tested!
Step 13: End Result
This is the first trailer I've created and found the whole job to be manageable and very rewarding. Hopefully you found this Instructable helpful and I would enjoy any feedback you might have.