Trailers Built For The Long Haul
- Feb 1, 2001
Glossy paint, swing-out saddle racks, loading lights--a new horse trailer can enchant you with options. But buying a trailer is like buying a horse. Your purchase examination goes beyond the chrome to evaluate individual parts. Just like a horse, a sound trailer requires sturdy construction and fluid movement. This enables your trailer to sustain years of use from horses and withstand hazards on the highway. A better-built trailer can endure impact, vibration, and weather better than its competitors.
When you're assessing any trailer, look for a vehicle that's engineered to be roadworthy. Learn how to judge its "stance" at a standstill, and its performance on the road.
The trailer is a combination of stable structures and moving parts. In the simplest terms, a trailer is a box secured to a chassis.
Trailers are designed and built from the floor up. A subframe's structural members form the trailer's integrity. The subframe supports the frame (the box) and a stout plank floor with the size and spacing of its cross members. These beams run perpendicular to the trailer's sides, or bottom rails.
Rails form the frame's bottom and top. Carl Turnbow, who's built Turnbow trailers for 41 years, says, "To build a strong trailer that will withstand a lot of abuse and years of service, you've got to have a good frame, a strong bottom rail, and a strong top rail."
Typically, the subframe and frame are welded of square metal tubing in a post and rail construction. Corner posts are vertical, along with the side posts (also called uprights or standards). Posts are concealed by the wall panels, or sidewalls. Walls can consist of three layers: interior surface, insulation, and outer skin.
On today's trailers, the front or "nose" is usually flat and squarish, with rounded side edges and radius corners at the top. The rounded design helps the trailer move more easily through air. Some models feature a streamlined, aerodynamic V-shaped nose.
A trailer is pulled through either a neck, as in the gooseneck shape, or through a tongue, which is a V-shaped section on the bumper pull trailer. The gooseneck tapers forward from the trailer body to form the nose. Its "drop"--the steel section that joins the neck to the coupler--is supported by gussets (triangular corner supports). A gusset on each side strengthens the joint.
The coupler, attached to the neck or tongue, hitches the trailer to a towing vehicle. The gooseneck coupler fits over a ball in the bed of a pickup truck; on a bumper pull trailer, a clamshell device connects the ball of a hitch to the trailer. A coupler has a rating capacity of the maximum weight it should pull, which can differ from the trailer's rating capacity and the capacity of the trailer hitch ball.
The trailer's roof can be flat or arched. Generally the roof is secured and braced to the top rail and struts.
Sundowner Trailers engineering manager Vic Cook says, "The floors, walls, and roof should be designed to work together so they will provide strength, the ability to flex and absorb shock and stress, and protection and accommodation of the particular cargo."
The trailer's undercarriage contains the moving parts of the running gear and suspension. Wheels turn on axles, and springs suspend the body and absorb vibration and shock. Most of today's trailers replace springs with rubber torsion suspension, so the axles themselves absorb the shock from the wheels. Rubber cushions the axles.
On a tandem-axle trailer, the two axles are each rated at 3,500 pounds. However, Tom Scheve of EquiSpirit Trailers says, "The trailer is rated at its weakest link. A trailer using a 5,000-pound coupler is rated to hold only 5,000 pounds." So the lower coupler rating overrides the 7,000-pound rating of the axles.
Wheels are 15 to 17.5 inches, with radial tires. Electric brakes--a combination of magnets, shoes, and drums--slow the trailer's forward motion when the towing vehicle brakes.
The length of axles affects wheel placement. Longer axles, measuring 102 inches wheel-to-wheel, place wheels on the sides so that no wheel wells protrude into the horse stalls.
Another moving part is the landing gear or jack. It supports the trailer's front weight when the trailer isn't coupled to a towing vehicle. On a gooseneck, the landing gear cranks up and down to raise or lower the front of the trailer and the coupler. On a bumper pull trailer, the jack adjusts the height of the tongue.
Trailer builders use materials and methods from the recreational vehicle, automotive, and even aircraft industries. Materials may include metals, plastics, rubber, vinyl, and wood.
Trailers usually are made of one of three types of metal alloy: all-steel, all-aluminum, or a steel frame with aluminum skin. Each metal has its own advantages in strength, durability, weight, and/or cost. Whatever the covering of the trailer, it must resist impact and be durable. Metal can fail by cracking, bending, shearing, or denting.
Steel is known for its strength. Even all-aluminum trailers use stainless steel fasteners, along with steel axles, neck, tongue, and coupler. A stainless steel "stone guard" can prevent dam-age from objects hitting the trailer front. How-ever, when protective paint gets chipped, non-stainless steel can rust. Steel's pluses are its strength and durability; the drawbacks are its heaviness and potential for rust.
Corrosion degrades metal alloys with chemical or electro-chemical reactions. Moisture rusts steel through oxidation, although aluminum also can corrode, especially from horses' urine. "Urine is alkaline," says Scheve. "An aluminum floor can deteriorate down to powder."
There is help in barriers that protect metal alloys from corrosion. Galvanized steel (normally used for pipes and tubing in the frame) has been coated with a zinc-iron alloy to protect the steel and resist rust, and has a textured, mottled shiny surface from crystallization of the protective alloy. Flat sheet-type components like the roof and sides are usually made of galvaneal steel, which is galvanized steel that has been reheated to smooth the surface, eliminate the shiny appearance and prepare it to hold paint better. These coated steels can be scratched lightly and still resist corrosion, but welding will break down the protective chemical barrier.
Another metal option is aluminum, which can be extruded (thickened by combining with other pieces of aluminum) to increase its strength. This process yields stronger, thicker pieces that can be formed shapes as opposed to flat sheets. Aluminum shapes include I-beam supports in the subframe, posts, rails, sheets, and floor planks.
"Important variables for aluminum include the thickness of the extrusions and sheeting, and the type of alloys used to produce it," says Kirk Turnmire of Featherlite trailers. For example, the sheeting that forms the exterior skin can be 0.04, 0.05, or 0.063 inches thick. Aluminum allows the trailer to be lighter weight, but is more easily damaged than steel.
Fiberglass is used by some companies in some components of trailer construction, such as the roof. Scheve says, "We mold tubular steel right into the roof, so the steel is like roll bars. Fiberglass is a good insulator, it's lightweight and easy to repair, and it will last you as long as the rest of the trailer."
Floor planks typically are made of two- inch-thick, pressure-treated wood. Alumin- um trailers often use extruded aluminum planks that are corrugated to encourage liquid drainage.
Rubber sheeting--riveted or bonded in place--protects interior walls and floors, although many trailers still cover floors with removable (and easily cleanable) rubber mats. Vinyl-covered foam padding can cushion stall dividers.
Manufacturing Methods And Specifications
Parts are fabricated, or shaped, then assembled into the vehicle according to engineering specifications. Turnmire described the first step as "pre-cutting aluminum extrusions and building and/or assembling component parts (axle subframe, hitch assembly, etc.) in specially designed jigs, or patterns. While these components are being fabricated, the roof and floor are constructed, also in specially designed jigs."
Components are made separately for attachment. A one-piece roof-shaped of metal or fiberglass-eliminates seams and possible leaks. Rear doors can be constructed of layered panels to be as thick as two inches.
Knight says, "Each trailer's nose and hitch, sidewall, rear door assembly, and roof are introduced into the assembly line as a separate unit, then brought together using Tig welding, semi-trailer industry standard Huck bolts, and compression rivets."
The subframe's floor supports are crucial. Builders space cross members eight to 12 inches apart, using I-beam, T-beam, J-channel, or angled steel beams.
Because a trailer is a box, its joints must align to form correct angles. Corners must be at 90 degrees to result in posts and rails that are straight at the trailer's four corners. Turnbow emphasized the importance of a square, plumb trailer. "Setting it up on the (assembly) line, it's got to be level and square. If you don't get it square and level, it won't perform on the road as well." He noted that an out-of-square frame--where one side is lower than the other--won't track smoothly.
Company representatives mention crucial methods. "The way walls are constructed is another important fea-ture in the design of horse trailers," said Jeff Knight of Exiss Aluminum Trailers. "The strength of the wall and its components are also important for the support of the dividers and latches that separate the horses."
Cook names the axle attachment and neck as critical areas of the structure. "The axle attachment area requires rigidity and strength compatible with the weight of the combined trailer and cargo. The axles need to be installed in line and true to the coupler or attachment point of the tow vehicle and located at a distance from the coupler or attachment point to insure stability when the trailer is loaded in a reasonable fashion.
"The neck of the coupler must also be able to meet all of the criteria for the axles, and be attached to the trailer in a secure way which will discourage shock and stress from being localized at one point, but rather distributed to as much of the entire structure as possible."
Another important design consideration is that joints resist vibration, since over time vibration will shake parts loose from each other. Turnmire explains attachments of components as crucial to trailer structure: "Common methods include welding, which is used to join similar metals for a more structurally sound trailer; riveting, used to secure lighter skins; and Huck bolting, which is used to join dissimilar metals."
Strong welds resist cracking, especially at stress points like the coupler and the drop of the gooseneck. "The fit of the joint, thickness of material, and a clean weld surface are required," says Cook. "The type of weld desired needs to be evenly distributed between the joined parts."
Mechanical fasteners lock parts in place and should not push out. Rivets, or headed metal fasteners, join parts by fitting the rivet's shank through a hole in each piece. The Huck bolt is an industrial fastener. Some manufacturers attach the trailer's skin with a strong, double-stick tape so no rivets dent the metal.
"Rivets are selected with proper strength, grip range, and diameter for the purpose intended," says Cook. "You need to take into consideration shear strength, holding capability, and sealing requirements when choosing rivets."
Seals and gaskets must block air and light. "Make sure that no light is visible inside the trailer when the doors are shut," says Turnmire. "A smoke test is often used, particularly on custom trailers, to detect leaks."
The trailer's exterior finish must deflect the effects of weather. Manufacturers use automotive processes to bond paint to metal walls. All exposed steel should be painted, and the subframe on all trailers should receive a protective undercoating.
Manufacturers self-assess their manufacturing methods through quality control, and "road test" new or updated models with and without horses loaded.
"Exiss spends numerous hours using the latest engineering software in the design phase of our trailers," explains Knight. "Through computer simulation, we test the strength and structural integrity of our designs before we begin the manufacturing process." A prototype built after computer testing is then tested on the road.
Most manufacturers offer warranties of up to seven years on certain structural components.
Trailers must meet certain U.S. regulations described by the Federal Motor Carrier Safety Administration (see them at http://mchs.fhwa.dot.gov/rulesregs/fmcsrhome.htm). Other than that, few cite any industry regulation. Some are members of the Recreational Vehicle Industry Association (RVIA, www.rvia.org), and register their trailer living quarters that are manufactured to RVIA standards.
Many manufacturers (around 100) are also members of the National Association of Trailer Manufacturers (NATM, www.ntam.com), which has compiled relevant structural manufacturing information from different trailer industries, applicable laws, and recommendations from various sources on trailer design. Ronald Jackson, president of CM Trailers and past president of the NATM, says, "Our primary goal at the NATM is to address trailer concerns and draft manufacturing guidelines for the small trailer under 26,000 pounds gross vehicle weight rating. We meet annually and exchange information with our competitors and the manufacturers that supply our materials. The education goes in both directions, and that's the gist of what the association represents--to exchange information in order to make safer products." The NATM is not a regulatory agency, but it does offer a voluntary manufacturing plant inspection service to its members.
Safety And Comfort Systems
One of the more important safety systems of a trailer is the electrical system that powers the brakes and exterior and interior lights. Wiring must be installed properly, and ideally with no wires exposed to the elements.
To load and unload the horse, the entry system has one or more doors and possibly ramps. Dividers separate horses into stalls, and the slam latch on dividers simplifies placing horses in a slant load trailer. All hinges and latches should open easily and close doors and windows securely, and be sized and placed for security and safety.
"Everywhere we can, except on ramps, we use a continuous hinge," Turnbow says. "On the door, it goes from the top to the bottom. It gives you more durability over the long run."
Air circulates through windows and roof vents, permanent or removable feeders allow the horse to eat hay in transit, and storage areas carry equipment. All of these features vary in size and placement, and should be selected for your specific needs.
The horse trailer also might include a separate compartment for humans, usually positioned at the vehicle's front. The area can be a tiny dressing room or living quarters as luxurious as a motorcoach. The more elaborate the living quarters, the more complex the systems of air conditioning; fuel for heating and cooking; water, sewage, and water heating for restroom, shower, and kitchen, and electrical power.
When evaluating a trailer, test the integrity and usability of all systems. You should ask yourself questions such as: how easily do the doors and ramps open and shut? How hot will the trailer be in the summer? On a slant load, can you swing the rear saddle racks out of the way to open the rear doors fully?
As you "vet" any trailer, look for strong components to improve safety and comfort. A sound trailer assures durability and long-term value of your investment.
For more information on trailers, see these recent articles in The Horse: "Trailers 2000," March 2000 issue (http://www.thehorse.com/ViewArticle.aspx?ID=154); "Shop the Used Trailer Lot," July 2000 issue or (http://www.thehorse.com/ViewArticle.aspx?ID=193).
Also, you can join discussion forums at the www.horsetrailersonline.com web site.
(Inclusion in the following list does not imply endorsement. If you are a manufacturer of trailers and are not listed here, please contact email@example.com to be included on this list on our web site.)
452 South Park Avenue West
Twin Falls, ID 83301
11301 South I44
Oklahoma City, OK 73173
Circle J Trailers
312 West Simplot
Caldwell, ID 83605
PO Box 137
West Jefferson, OH 43162
8222 Southwest 8
Oklahoma City, OK 73128
PO Box DL
Reno, OK 73036
PO Box Drawer C
Hwy 81 South
Chickasha, OK 73023
Hawk Trailers, LLC
1220 Depot ST
Manawa, WI, 54949
Kiefer Built Trailers
305 East 1st
Kanawha, IA 50447
PO Box 10-307 West Parker
Plumerville, AR 72127
715 Range End Rd.
Dillsburg, PN 17019
Duncan, OK 73533
9805 South State Hwy 48
Coleman, OK 73432
PO Box 46
2525 State Rt. 41
Cynthiana, OH 45624
About the Author
Award-winning writer Charlene Strickland lives in Bosque Farms, N.M. She has published 8 books and over 600 magazine articles, and is a member of the International Alliance of Equestrian Journalists.
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