Few things are more disconcerting for those new to boat towing than when the loaded trailer sways after a semi blows past, when the hitch hits ground when you're driving across raised railroad tracks, or when the back of the trailer scrapes as you pull into a gas station.
The common denominator among all three of these anxiety-inducing scenarios is that the towing setup between the tow vehicle and the trailer needs adjustment. To eliminate these problems, tweak the hookup between the trailer and tow vehicle, select the appropriate hitch shank, and adjust the hitch-ball height so the trailer frame is positioned parallel with the ground.
Nice & Level
If the trailer frame is angled upward or downward, then the hitch-ball height needs to be changed to bring the trailer frame parallel to the ground. Here's where fixed-type hitch shanks that have a "step" for the hitch ball may be all that's needed to put the trailer at the proper angle. The rise or drop afforded by flipping the hitch shank so the step is up or down can change trailer tongue height by three inches or more, depending on the design of the shank.
Another hitch-shank option is one that offers an adjustable ball. Such a shank is ideal for those who tow different trailers during the year, say a boat trailer and a small utility or ATV trailer. Adjustable-ball shanks with either a four-inch or a six-inch drop will work for a wide range of half-ton 4x4 pickup applications. Shanks with even more drop work well with heavy-duty 4x4s and lifted trucks/SUVs. If you use an adjustable shank, make sure it's also rated for the weight you're towing.
Boat owners towing bigger boats should pay close attention to tow ratings and the stipulations regarding the use of towing "on the ball" versus using a weight-distributing hitch.
Most vehicle manufacturers recommend that 10 percent to 15 percent of the trailer's loaded weight be on the hitch when towing. However, if you're towing a larger boat, say one longer than 24 feet or so, your tow-vehicle manufacturer may recommend a weight-distributing hitch. (See sidebar.) You also must be careful that the desired tongue weight doesn't exceed the capacity of either the hitch or the vehicle specifications. But for conventional, weight-on-ball setups, keeping to the 10 percent to 15 percent weight-distribution recommendation will help fight trailer sway. How, you ask?
Tongue weight serves as a proxy measurement for the center of gravity (CG) of your loaded trailer. You want the CG — the imaginary point on the boat/trailer combo where the whole thing would balance if you could rest it on a (very) sturdy post — to be in front of the contact patches of the trailer tires. In other words, you want the boat to be bow-heavy on the trailer. This is because the friction of the tires rolling on the road creates drag, which acts as an antidote to sway by gently tugging the rig back into line with the tow vehicle if some force (remember that fast-moving semi?) happens to push it side to side.
If the CG is even with the trailer tires, the drag from this friction won't correct the sway; if it's behind the tires, the results can be spectacularly bad. The drag will act to exaggerate the forces behind the sway, potentially leading to a total loss of control. If you've ever driven through a deep puddle on the side of the road and felt a moment of fear as the car pulled to the right, you know what a sudden application of drag can do to vehicle stability. If you imagine a similar force, amplified by the long lever arm of the trailer, pushing sideways on the rear end of your truck, you'll begin to understand how things can go bad quickly.
If your trailer is extra tail heavy, it's possible to lift the rear of the truck enough to impact traction. You may discover that this is the case when you can't pull your loaded trailer back up the ramp. It's also possible to have too much tongue weight, which can put so much down force on the back of the tow vehicle that it lifts the front end up, impairing steering. And on tandem-axle or triple-axle trailers, too much tongue weight will also cause uneven loading on each axle, which can lead to blowouts on the affected wheels.
If you find that your tongue weight is just slightly out of the recommended range, you may be able to shift stored gear forward or aft to correct the problem. Just make sure that what you've stowed will stay where you placed it. Even a heavy cooler can make a big impact if it's stored all the way forward in the bow or at the stern. However, if you find yourself well out of the recommended range, the trailer will need to be adjusted to shift the boat fore or aft a few inches until the problem is remedied.
When Do You Need a Weight-Distributing Hitch
Tongue-weight is defined as the amount of weight a trailer places on the hitch ball, and there's a specified limit to this number that vehicle manufacturers place on every tow-capable vehicle they make. Your trailer's loaded weight, multiplied by 0.1 or 0.15, yields the recommended tongue weight to prevent trailer sway. You must be certain that it also falls within the specs for the hitch and vehicle capacities. (Remember that tongue weight counts against a truck's payload capacity.)
If the trailered weight is greater than a certain amount (usually more than half the weight of the tow vehicle), a weight-distributing hitch is needed; a sway-control device may also be necessary. For example, if you're towing a boat/trailer combo that weighs, say, 6,000 pounds behind a half-ton pickup, the truck likely needs to be equipped with a weight-distributing hitch, and the rig must place at least 10 percent of the tongue weight on the hitch ball. The same applies in scenarios involving three-quarter-ton or one-ton pickups towing boats that weigh more than, say, 7,000 pounds, which is around the trailered weight at which Ford, Ram, and GM require weight-distributing hitches be put into play. Both Reese and Equal-i-zer make weight-distributing hitches designed for boat trailers with surge-type brakes.