|Trailers fishtailing behind the tow car is a serious problem. |
Make sure the boat is secured to the trailer and cannot move. A boat moving or the trailer flexing under the boat is unacceptable, illegal and unsafe. Make sure the boat is heavily tied at the front and sides. Use webbing load binders pulling from the frame at the rear if the suspension up over the deck. If you have a trailer swaying, it is essential that you make sure the boat stays with the trailer.
Fishtailing is caused by misalignments by the car and trailer. It is important to understand that the geometry and weights of the car and trailer/boat need to be evenly distributed. Because boats have reasonably high wind resistance and centre of weight, external effects like wind and road camber cause misalignments that can start up sway on poorly aligned or balanced trailers.
Never, never, never drive with a trailer continually swaying. The axles are simply not capable of surviving the continual loads if a swaying trailer. I have seen fatigue faulures on axles cause an accident writing off the trailer and load because the driver refused to slow down.
Never try and speed up to get trough the swaying. This increases the energy out of control and increases to likely hood of an accident. There is no garanteed way of contolling a swaying trailer, keep you eyes ahead on the road(its very important that you watch where you want to go), back off gently and slowly and steer sraight ahead. If its happening on a corner, you have higher risks but the same techniques are your best option.
Never fight the sway with steering corrections or rapid braking or accelleration. Be smooth and slow the combined speed slowly.
Traditional thinking is that drawbar weight needs to be about 100Kg for a RL 24. Use a set of bathroom scales to check what your drawbar weights when the boat is fully loaded.
Now assuming you have a reasonable drawbar load, what next. You could buy a new trailer but new trailers also sway sometime.
The condition of your car and its suitability to tow need to be questioned. Have you tried towing with a different type of car? If the swaying goes away, bingo, if not lets move to the trailer.
Trailer hitches, load distibutors and antisway bars are all accessories caravan places will sell you to hide the problems. My experience is that most of these devices increase the loads on the car and trailer so be careful.
Check the condition of the trailer. If it is a tilt trailer, look for movement in the drawbar or signs of flexing. Rectification may need a workshop.
Check the wheel bearings for movement, absolutely minimal movement is allowable in your situation. If there has been damage to axle stubs due to failed wheel bearings, a new axle and bearings may be needed.
The trailer suspension needs to be in good condition, no more than surface rust on the springs and be sure the U bolts are in good condition. A sping siezed solid with rust will upset the tracking of the trailer.
Get a tape measure and measure the triangle made by the drawbar and each wheel bearing. Check that the wheels are the same distance from the center of the trailer. The geometry of the trailer needs to be the same both sides.
Check the tyres are in good condition and similar types on each side. Check tyre pressures. These tyres are as important as the ones on the front of your car. If you have to change tyres on the trailer use TOYOs or other tyres with a great reputation. Its false economy to save money on trailer tyres.
The great thing about most boat trailers is that they are adjustable for lots of different boats. If all the other stuff seems OK, its time to look at changing the geometry of the trailer. It might pay to have this done by a workshop but if you are mechanically competent, you could look at this yourself. Basically the idea is to change the wheelbase (distance from the drawbar to the axle) of the trailer. Firstly check that you have all the stuff in the boat packed with the heavy stuff low and near the axle. Check the drawbar weight. The idea is to shift the axle and boat backwards, or forwards to change the geometry of the trailer. Make sure after all adjustments that the drawbar weight is between 70 - 100 Kg. As I said, this is a big job that may need a workshop.