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Boat trailers and brakes
  |  First Published: November 2005



I’m being a bit dramatic in saying it, but boat trailers and brakes are really an inseparable pair that need tender loving care to make sure their union is long and happy.

If you have a boat, motor and trailer (BMT) package that weighs 750kg and over then you need to have override mechanical or hydraulic brakes.

If the BMT package weighs up to 2000kg you have to brake only one axle with an electro hydraulic brake system. That is usually done with override mechanical brakes or override hydraulic brakes.

Last but not least, if your BMT package goes over 2000kg then you need to have a brake system that’s controlled from the cab of the tow vehicle. It must have a fully-approved breakaway system and all the axles must be braked.

These units are normally based on an electric-over-hydraulic system or an air-over-hydraulic system. There are other options out there like vacuum systems, which we will not be discussing in this article as they’re not commonly fitted to boat trailers any more.

Under 750kg

When considering the weight of your BMT package you need to allow for all the gear that normally goes in the boat as well. That means fuel, esky, anchor, ice, safety gear, fishing gear, clothes and more. Consider all of these items when working out if your BMT package exceeds the 749kg threshold for brakes.

News flash! Most boats over 4.5 metres will weigh 750kg or more. If you have an open dingy you should be fine but as most boats now seem to be fitted with casting platforms, live-bait tanks, under-floor fuel and the like, you might just be surprised. I know of one boat brand whose models of 4.35 metres and up require brakes to be legal.

Most smaller boating rigs are sold on the basis that the BMT package in the dealer’s yard will be under 750kg and therefore does not need brakes. The unit could weigh 700kg when you purchased it but there’s still the added weight of gear. Once that’s added you might be over 750kg and therefore an illegal rig.

Check carefully to make sure you have enough weight margin to allow for carrying the normal gear you take away boating. If in doubt, I recommend you ask your dealer to fit brakes. It will cost you more initially but will save you money in the long run. If you have an accident and the unit exceeds the minimum requirements for brakes, there is a long list of offences you could be charged with or even worse, your insurance could be denied given that the unit isn’t legal.

750kg to 2000kg

From 750kg to 2000kg you will normally find trailers fitted with override mechanical or hydraulic brakes. These brakes are also referred to as inertia-type systems. The weight of the rig causes the coupling to compress during braking, which pushes a lever that will either pull a cable or push a piston to engage the brakes. You’ll hear lots of discussion on which system is better but the reality is that both work, both are legal, and in certain situations one system will outperform the other. In most cases, the dealer makes the decision for you when you buy the BMT package.

I like the mechanical system. It has its little issues and you need to make sure that you keep the cable adjusted correctly but it is fairly maintenance-friendly.

Both systems require very little maintenance and if carried out as part of your normal bearing service schedule, you should have very few problems with your brakes over the life of the trailer.

Over 2000kg

The same applies for this weight point as for the 750kg mark. Make sure that the unit has enough spare weight capacity to allow for gear.

The biggest killer in these units tends to be fuel. It’s not uncommon to see a boat at 6.5m carrying 200L to 250L of fuel. That means 200kg to 250kg of extra weight. It also means more people and therefore more gear. If the unit has a weight of 1800kg, and that is the weight of the BMT package dry or with a token amount of fuel, once you’ve set it up for use it will be over 2000kg and will require the appropriate brake system.

Most of the BMT packages over 2000kg are fitted with electro-hydraulic brake systems. This means an electronic brake controller from the cab of the tow vehicle controls the units. When you put your foot on the brake the unit sends a signal to a control unit mounted on the trailer that will start a pump and pressurise the hydraulic brakes on the trailer. There are other systems out there that work on the same principle but do so based on an air-over-hydraulic system rather than an electric one.

Having used both, I’ve found the electro-hydraulic systems more to my liking and easier to set up. That’s not to say that the other units are bad, just that I prefer electro-hydraulics.

The requirements for a system over 2000kg are that the brakes be controlled from the car and that the trailer is fitted with an appropriate break-away system. Should the trailer disconnect from the tow vehicle, the trailer’s brakes will automatically activate and stop the trailer from rolling down the road. Most break-away systems are fitted with a little battery to activate the brakes in the event of a detachment. These batteries need to be kept charged. Some units come wired with charging circuits and some don’t.

Batteries will also discharge themselves on a daily basis. It may be only 1% to 2% per day but you need to keep that in mind if you’ve let your boat and trailer sit for a while.

These types of brakes normally require very little maintenance and if carried out as part of your normal service schedule they will be very easy to maintain. Check and service the calipers as part of your wheel bearing schedule and give the unit a complete brake fluid flush every 6 to 12 months.

Be prepared

Brakes are one part of a trailer that most people tend to avoid like the plague for fear that they’ll add too much maintenance to the trailer and will never work.

Most companies now use galvanised discs and calipers as a minimum standard and most fittings are galvanised, too. You really don’t have to spend a lot of time looking after your brakes. And when you think about it, they could be the difference between you being able to stop or crashing into something.

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