Trailer set-up
  |  First Published: July 2006

One of the things that can make a big difference to your day is how well your trailer is set up.

Why? Well, if your trailer has been set up correctly it will tow better, sit behind the car rather than wander all over the road and come on and off the trailer easily.

What’s involved

Trailer set-up covers things like roller and skid set-up and position, when to use rollers or skids (see previous issues of VFM for more information), the position of the boat on the trailer and the position of the suspension to ensure the correct draw bar weight.

Let’s start with the smallest trailers first and work our way up from there.

Up to 4.3m

Most 12-14ft (3.7-4.3m) trailers come with fixed or welded suspension, so you won’t be able to move or adjust its position. However, the boats that are placed on these smaller trailers are normally at the lighter end of the market and don’t have a lot of draw bar weight so adjustment is generally not needed.

Above 4.5m

Once you get to about 4.5m+ you may need to adjust the suspension forwards or backwards to attain the correct draw bar weight so that the rig tows correctly.

If you have too little draw bar weight the trailer won’t sit behind you when you’re towing. Instead, it will tend to ‘snake’ or sway from side to side. You may get into a situation where the trailer appears to sit behind you easily, but when you pass someone and pull back in front you’ll find the trailer wants to sway.

It’s not so bad if the trailer sways from the outset because you’ll notice it and be able to adjust your driving accordingly (i.e. reduce your speed to minimise the sway).

The second situation is more dangerous because you may not notice the problem until it’s too late. If you aren’t experienced and don’t know how to handle the problem, rolling the whole unit over becomes a risk. The worst thing you can do here is put your foot on the brake. A better tactic is to accelerate slightly to get the boat back into a ‘following’ situation and then decelerate the whole unit to a more manageable speed.

Fixing the Sway

You can fix the swaying problem by adjusting the suspension position further back on the trailer chassis, away from the front of the trailer. This will increase the draw bar weight and make the trailer follow the tow vehicle.

Trial and error will determine how far you need to move it. In most cases it won’t be very far. Just make sure you mark where you started from so you’ll know how far you have moved the suspension each time you make an adjustment.

Ultimately, you want the draw bar weight to be substantial enough to get the trailer to follow the car at all times. If it is too light the wheels of the trailer will follow the road surface and the trailer will go where it wants. Too heavy and you’re in danger of overloading your trailer tongue on the car, making the front end of the vehicle too light. This can affect the car’s steering, damage the suspension of the tow vehicle through overloading, and bend or break the draw bar of the trailer.

Draw Bar Benchmark

The old rule of thumb used to be 10% of the weight of the trailer and boat was needed as draw bar weight. While this isn’t a bad measure for some boat sizes, it doesn’t work when the units are at either ends of the spectrum.

Imagine a rig that weighs 100kg – that would mean 10kg draw bar weight, which would tow pretty badly. Or take something that weighs 4500kg; you would have 450kg down force on your trailer tongue. Not too many people have towbars that are rated for that king of weight.

I believe that smaller trailers to about 4.3m should be a good one handed lift – something that you need to bend down and take a good grip on and pick up.

For 4.5-5.8m trailers I usually recommend a two handed, knees bent lift.

From 5.8 to 6.5m under 2000kg ATM (aggregate trailer mass, maximum weight of loaded trailer) you can usually get away with 100-120kg depending on the layout and set-up of the trailer and boat.

Over 6.5 and 2000kg ATM the weights are determined by how they tow behind the vehicle, and the final weight of the whole unit.

Most towbars have a maximum down force rating of 350kg and I haven’t seen too many trailers with that type of draw bar weight.

The Bottom Line

The bottom line is that you should be able to tow your trailer/boat/caravan down the road at a minimum of 90km/h without the trailer swaying all over the road – nor should it sway when you pass someone, as long as you stay within the speed limit.

Launch and Retrieve

Here are a couple of ways to make launching and retrieving your trailer easier.

Small Trailers

Small keel type trailers are used for alloy or glass hulls and are pretty quick to set up. When you set up your boat on the trailer it needs to be done with a ‘nose up’ or ‘keel up’ angle, i.e. the boat’s keel needs to set higher at the front than at the rear. This allows the hull to roll off the trailer more easily.

To do this, first set your trailer on level ground. Next, check that the front keel-supporting roller is higher than the back keel-supporting roller by approximately 25mm. Occasionally, you’ll need to make the front even higher but most of the time 25mm will do. Bear in mind that it’s easier to do all this without the boat on the trailer.

Now you need to get the boat sitting on its keel on the trailer. Pull the boat forward until the rear of the boat overhangs the last keel roller by 50mm, and then adjust the winch post to make sure that the boat is securely held to the trailer.

The last adjustment is to move the side supports in or out until they clear the strakes or pressings in the hull and to push them up until they touch the hull. You don’t need to have a large amount of weight on the side supports as they are really only there to keep the boat from rocking from side to side. Keel-type hulls are designed to take the majority of their weight on the keel.

Larger Trailers

When it comes to larger boats, the same set-up applies as for keel-type trailers. It’s also pretty much the same for multi-roller trailers without keel rollers, except that you’ll be doing it with the roller packs on the outside of the trailer. The series of rollers and arms set up on the outer edge of a multi-roller trailer are normally between 1100mm and 1200mm apart, and you just apply the same principles as you would for a smaller boat.

The back roller pack becomes your lowest point. You then set the front roller pack higher than the back set by a minimum of 25mm; 50mm is common for larger boats. With these two packs set you can now drop all the other packs down low and out of the way.

Get the boat on the trailer and set up for length, with approximately 50mm of the hull overhanging the last roller. Once you have adjusted the winch post you can get under the lowered roller packs with a trolley jack (or you can crawl underneath and push them up by hand) and use the jack to push the stems (also called wood yokes) up until the roller packs are touching the hull.

Once the rollers are touching the hull you’ll probably want to give the jack about a half an extra stroke to get the roller packs to take up the weight of the hull. Unlike keel-type trailers, multi-roller trailers spread the weight of the boat over all the rollers.

Once you have done one pack, do the same pack on the other side and work your way through all the rest. After you’ve done all the packs you may need a few minor adjustments here and there, but 90% of the work should be done.

The only other adjustments are the individual arms in and out, to clear the strakes of the hull. When you first get the boat on the trailer and you’re pushing the roller packs up for the first time, you will be able to see if the rollers clear the strakes. If they don’t then you will have to undo the U-bolts that hold the arms and slide the arms in or out to get the rollers to clear the strakes of the hull.


Another thing to consider when you’re moving things around are the brakes. You will need to make sure you don’t pull them or break any fittings when you’re making your adjustments.

If you move the undercarriage of a multi-roller trailer there is a good chance it will be fitted with hydraulic brakes. You can tear the brake lines if you’re not looking to see how much adjustment you have in the lines.

In most cases you can move your undercarriage 200-300mm and the brake lines will allow it. Over that and you might have to check to see if it’s capable of being moved any further without undoing some of the retaining clips that hold the brakes’ pipe in place.

In all, a properly set-up trailer will allow you to easily tow your boat to and from the ramps. It should also launch and retrieve your rig without you getting stressed or frustrated.

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