All too often, boaters worry about what kind of trailers and tow vehicles are right for their boats and give short shrift to the vital link between the two - the trailer hitch. Picking the best hitch may not be as much fun as buying a tow vehicle or trailer, but it should be done just as carefully. The right hitch will keep the two working safely and efficiently, whereas the wrong hitch can be downright dangerous.

A trailer-hitch system consists of a frame bolted to multiple points on a tow vehicle's undercarriage, a fixed ball-mount platform or receiver box, hooks for attaching safety chains, and a hitch ball. Other components include a coupler, electric wiring harness, proper safety chains and a surge-brake cable. Hitches, couplers and balls are all weight-bearing components, and have maximum capacity ratings that are linked to the loads they will carry.
A trailer has both a carrying capacity (how much weight it can carry) and a Gross Vehicle Weight Rating (the carrying capacity plus the weight of the trailer). Make sure your trailer hitch is in the class that matches your trailer's GVWR and err on the side of caution when figuring out the load the trailer is carrying. That means adding extras such as fuel, gear and accessories onto the weight of the boat to get a final figure. The last thing you want is for your hitch to be pulling a trailer that's heavier than its rating. You can always tow a lighter load with a stronger hitch, but it doesn't work both ways. If you're in doubt, buy the next class up. Class I hitches, which are rated for up to 2,000 pounds of load-carrying capacity, come in four different designs: Frame-mount, bumper/frame mount, step bumper and bumper hitch styles. Of the four, a frame-mount hitch is strongest since it has bolted or welded attachment points on the frame of the vehicle. The bumper/frame hitch is also good for light towing, but it has one serious drawback: It tends to cancel out the crash-resistant design of most modern 5-mph bumpers, which flex on impact.

For heavy loads, a weight-distributing hitch spreads out tongue weight through spring bars so it's shared by all of the tow vehicle's wheels. Some automotive manufacturers require the use of weight-distributing hitches, while a number of trailer manufacturers caution against them. That's because many weight distribution hitches stop the trailer from surging forward, thereby eliminating the braking system on the trailer. Read the owner's manual of your trailer before you decide to install one. The hitch ball must be matched according to its rating. For Class I hitches, a ball of 1 7/8 inches is common. For Class II and III hitches, 2 inches is the norm. For Class IV, 25/16-inch hitch balls are standard. A ball that is too small will cause the coupler to bounce loose. Also note that different shank sizes will change the weight-bearing capacity of the hitch, even if the ball remains the same diameter. The weight-bearing capacities are on the top of the balls, and solid steel balls are recommended.

Hitch balls also have torque recommendations as to how tight the attaching nut should be. In general, for a Class I hitch ball, an 85-pound-foot torque wrench should be used. For Class II, use a 105-pound-foot torque wrench, a 235-pound-foot torque wrench for Class III, and a 300-pound-foot torque wrench for Class IV.

After the hitch ball, the coupler is the next most important contact point in the metal-to-metal connection between the trailer and tow vehicle. It's located on the very end of the trailer tongue and is connected to the hitch ball. It comes in two types: the hand-wheel type or lever type. Both styles have a coupler socket that fits snugly over the hitch ball, and a clamp that locks in place.
The difference in design is in how the ball clamp is controlled. In the first, you tighten or loosen the ball clamp by a hand wheel or screw knob. In the lever type, the clamp is controlled by raising or lowering a lever. Both styles are fine, but the lever is more common, because it gives an extra margin of safety by using a trigger-lock mechanism. The trigger lock must be released before the lever can flip up again to loosen the clamp. Many lever types also provide a place for a padlock, thereby insuring that the trailer will not accidentally disconnect from the vehicle as well as helping to prevent theft.

Safety chains, which are rated according to category weight, are the links that guarantee the trailer won't separate from the towing vehicle, even if the coupler-hitchball connection fails. Generally, a 3/16-inch chain is rated to 3,000 pounds, a 1/4-inch chain to 5,000 pounds and a 5/16-inch chain to 7,600 pounds.
Safety chains provide an extra margin of safety. Fitted with hook ends, they're attached to the trailer tongue or coupler. The chain hooks are then slipped through rings or holes on either side of the hitch ball. They should be criss-crossed in order to provide a small cradle for the tongue to fall into should it become disconnected, instead of having it drop to the ground and dragging. Make sure they're hooked up at all times - even if you're just making a short trip down the street to the launch ramp. The last two components in the trailer/tow vehicle link are the wiring harness and surge-brake cable. The cable is linked directly to the master brake cylinder, so if the trailer ever becomes separated from the tow vehicle, emergency brakes are triggered. Be sure to connect the wiring harness and surge-brake cable as the last step in the trailer hookup process. Once you have the proper hitch system, you can rest assured that the vital link will stay intact. Some step bumpers also rely on solid attachment points on the frame, but there are a number of aftermarket step bumpers that have no frame attachment points, making them structurally weaker. That lack of strength makes those bumpers good only for light loads, which don't include boats. Another undesirable hitch is the bumper-mount hitch. Most automobile manufacturers do not recommend using this hitch, attached by a chain to the bumper, because most modern bumpers aren't designed for towing. In addition to that, the galvanic action between the alloy in the bumper and the steel hitch can lead to corrosion.
For medium and heavy towing requirements, frame-mounted hitches are highly recommended. They are available in various styles, the two most common being the fixed ball-mount platform and the receiver hitch. Receiver-type hitches are the most versatile of the two since they allow owners to remove the ball mount and stow it in the tow vehicle. They allow for easy adjustment of hitch height, which is important if you want to carry different loads at different times.