The trick is to slow down quickly but not suddenly while keeping things under control. It takes practice and experience towing trailers which most people don’t have. (Obviously the best advice is to not exceed recommended speed limits in the first place).
Larger trailers and most multi-axle trailers have electric brakes that will prevent this type of trailer sway. Apply a little bit of positive braking on the trailer while accelerating the towing vehicle slightly at the same time and it will bring the oscillation under control.
another stupid question by someone that has never towed anything…if i buy a boat and a trailer, how do i balance the trailer to make sure most of the weight is upfront?
is there a way to do this…you can’t just move the boat up can you???
Most trailers have stickers on them indicating the recommended and maximum tongue weight. The tow vehicle will also post it’s maximum towing capacity either on a sticker or in the owners manual. As indicated in the video linked above, you want at least 60% of the weight towards the front.
A properly matched boat/trailer combo should already be configured to position the weight properly for towing. Many larger boat trailers have configurable rollers that can be moved forward/backwards for correct balancing and you can also move the front winching post along the main tongue rail. It’s something most amateurs shouldn’t mess around changing from factory settings.
ETA: Most boats are already weight-forward by design while towing. If you look at a boat on a trailer, you should see at least 2/3 of the length is forward of the wheels… Sailboats and some power boats have weighted/lead keels that lower the center of gravity. Most of the rear weight is engine and you can throw off the center of gravity pretty easily by adding a few hundred pounds of gas + gear in the back.
Pickup trucks actually make terrible tow vehicles because of the lack of weight over the rear drive wheels. A little bit of ballast in the bed helps to maintain traction. (Newer trucks have traction control systems and tow packages designed to minimize this type of trailer sway).
Here’s a good explainer on how to configure a boat/trailer setup including weight distribution (I recently had to replace my Shorelan’r trailer and used this guide to find the right sized trailer for my boat): ShoreLand'r.com - Boat-To-Trailer Step #1
You can definitely feel it when it starts happening. No need to use your mirrors.
It’s a sphincter-clenching experience you never forget.
I sped plenty when I was younger, but now I basically never go over the limit. Somehow I can still get where I’m going on time. A lot of lives and property would be saved if people moved just slightly slower.
My thought was that the boat seemed to come out of it better than the car did. And along related lines, the late great Patrick McManus on properly attaching your trailer:
" Going down a steep grade, you glance out the side window and notice some idiot trying to pass you on the wrong side. Then you see it is your trailer! Oh, it is a thrilling sight, I can tell you, especially if the trailer is carrying an eighteen-foot boat. Some people are thrilled right out of trailering. Others vow never again to try to get by with the too-small ball when only the just-right ball will do."
Yeah that was my feeling too. Its the wake vortex from the car it is overtaking. Another factor is that he overtook on a descent into a little valley (making acceleration easier) but at the bottom there might have been a creek (common in Australia) with a bridge. Often the surface going on to the bridge is not smooth so he got some vertical and possibly lateral impulse from that as well.
Tank slapping in a trailer is one of those things that gets people because intuition leads you to the wrong move. It’s caused by the trailers’ velocity exceeding the truck. There are three things to prevent it:
Weight biased forward and hitch level or angled slightly downward
Equalizer bars which transfer weight between truck and trailer. These are particularly important with live loads like horses where the center of gravity on the trailer moves.
Proper electric trailer brakes driven from the vehicle (none of that magnetic inertial nonsense) and calibrated to engage slightly before the vehicle when the brake pedal is first touched.
There are two ways to recover when it happens:
A proper electric trailer brake system in a tow vehicle will have a manual engage button or lever in the truck. Tap that and trailer will straighten right out, problem solved. No wrecked boat, no dead horses.
SPEED UP. This is the one that gets people. The trailer is tank slapping because it is trying to pass you. It is going faster than you. Speed up, straighten it out, and then slow down gently to regain control.
Source: A lifetime of hauling and wishing most people on the road knew even the first thing about how trailers behave.
One of my old neighbors buried the nose of his boat trailer in the ditch in front of my house because of this mismatch. It was a good thing he hadn’t gotten out on the higher-speed roads yet.
I was a fairly newb years ago when I was pulling a boat trailer behind me. I was going down the steep-ish side of the Sunol grade on northbound 680 just outside of Fremont, California. Passing the CHP truck scales, the trailer started swaying something crazy. I could hear the trailer tires squealing at each extreme of the sway, and I could feel my sphincter clenching as I tried to figure out how I’d recover from the crash that was imminent.
Somehow, my intuition was telling me to not hit the brakes (trailer was single axle, no brakes, loaded with a 17 foot inboard/outboard family style vessel). I was headed downhill, so I just kept the speed going as steady as I could without increasing, and toward the bottom, I gently tapped the truck’s brakes when the trailer was in line with the direction of travel. Somehow, I got it under control. Almost had to stop and change my pants, it was freakin’ SCARY. It’s probably been THE scariest experience in a vehicle in my life.
Later, after thinking things through and talking with grizzled older and experienced boaters/trailer’ers, I determined that the boat wasn’t fully seated at the front-most position on the trailer, ie, too much weight behind the trailer axle. From then on, I cranked that boat as far up the trailer when hitching it up from the water as I could.
That boat is long gone, when home to the girlfriend’s parents along with the girlfriend, but I have a boatload more trailering experience these days. You really gotta have your wits about you when pulling a load, no matter how small. These guys doing 85mph up highway 80 to get to Tahoe with their 3-axle beasts don’t freakin know what they’re doing. Clamping down on trailers should be a priority of the highway patrol.
BTW, in that video, I’m not sure what that guy was thinking, accelerating toward a blind hilltop with such a heavy load. He needed to just sit back and take it easy. But damn, those guardrails did their job!!
I have a very large tow-behind (not 5th wheel) camper. I’ve experienced trailer sway a couple of times with it. Braking steadily, not sharply, is the fix; avoiding sway is the only cure.
There is no panacea that will prevent sway. You have to do a lot of things that add up to preventing sway:
Pay attention to the vehicle’s handling. By the time you feel sway in your butt, your trailer is already in trouble. You must respond quickly!
Speed. I don’t exceed 69mph because somewhere around 76mph my trailer will start to sway.
Patience. I may be an awful type-A behind the wheel of my overpowered car, (yes, that was me glowering in your rear view mirror) but when I get in the truck to tow, I am a completely different driver. Following and stopping distances are increased, I happily stick to the right lane and allow and encourage others to pass, I watch speed limits, and other traffic signs all become very important.
Weight distribution. Keep tongue weight close to 60%.
Slack tanks. Either drain or fill the water storage tank. A half-full tank will slosh around making for unexpected control problems.
A weight distributing hitch will shift weight to the front of the tow vehicle, giving the front wheels more traction and steering authority.
Increasing the weight shifted to the tow vehicle will reduce sway by a little bit more.
Anti-sway bars provide extra friction inhibiting the trailer from turning independently from the tow vehicle.
The wind resistance of a giant trailer is awful in the best of conditions. Headwinds, tailwinds, and crosswinds all reduce stability to an amazing degree. On days when prairie winds are up, I stay off the freeways and look for side roads no faster than 60 mph. Drives my spouse crazy, but she’s not driving now, is she?
Rain. Slow down, and if the roads might have standing water, it’s a good time to look for a diner.
A right-sized tow vehicle. The tow vehicle must have a long enough and wide enough wheelbase for the trailer. The lighter and smaller the tow vehicle, the worse the problems will be.
Properly adjusted trailer brakes are essential to recovery from sway. As part of the hitching process, I test the trailer brakes literally every time I drive away after hitching up.
I don’t know because I don’t have a boat, but it seems to me a boat is aerodynamically shaped to reduce traction. The faster you drag it, I expect the more it wants to fly. But I don’t think that’s what stumped Aussie McBoatbutt.
What the F***? I can hardly believe I am reading this. In UK and Europe max speed limits when towing are much lower than max speed limits for other vehicles. For obvious reasons. E.g. UK max limit on motorways is 70mph, but if towing, it is 60mph. On main roads (single carriageway) max limit is 60mph but 50mph if towing.
Is it really legal to drive at 69mph (or 76mph) when towing, where you are?
