How to set up your trailer correctly. 

 May 6, 2020

By  AndrewVR

It is important to have a roadworthy trailer that is properly rated, designed, fully engineered and certified to carry your boat. With highway speeds up to 110km/hr, an unbalanced or incorrectly fitted boat, together with a poorly designed and mechanically stressed trailer can be a deadly combination!

Very important issues to consider are:

a) Are you within the allowable Aggregate Trailer Mass (ATM), as per the compliance plate?

Note: ATM kg = boat (kg) + trailer (kg) + weight on the vehicle tow-ball (kg)

b) Is your load C of G (Centre of Gravity) as low as possible? Properly dimensioned trailers with low road profiles that allow for a low C of G are safer, more stable, and also easier to use when launching and retrieving. Check your chassis because newer technology torsion axles allow the load to ride on the axles whereas spring axles suspend the load higher on a sprung chassis.

1. Preparing the trailer

Typical trailer configurations are shown below. None is less safe than the other provided the load is being properly distributed and carried. For all boats a hull inspection will determine the initial positioning of hull supports (rollers, slides, etc), prior to first loading the boat.

2. Placing the boat on the trailer

You will need to know your approximate total loaded boat and trailer kg, and also be able to measure or accurately estimate the trailer tow ball kg resting on the car.

The trailer winch is used for initial loading of the boat on your trailer. But note that setup of the winch post and bracket is the last adjustment to undertake when setting up any boat trailer.

Winch the boat onto the trailer until approximately 8% of the total estimated weight of loaded boat and trailer is measured at the tow ball, moving the boat forward or backward to suit if needed. It may even be necessary to move the axles to suit, and if so, a bolted axle design will make this much easier.

Once the boat is positioned the roller and bunk supports can be adjusted to distribute the keel and hull loading. A boat’s keel is always the strongest area of support. And unless your hull is specifically designed otherwise, the keel should take approximately 80% of the load with side supports taking the remaining 20% load.   

3. Adjusting the Winch Post

In this final step, and with the boat now properly supported, it’s necessary to ensure that the trailer chassis is relaxed, un-stressed, and level. This is achieved by taking the weight off the jockey wheel or tow ball, and instead using jack stands to support the chassis under the boat.

The winch bracket and winch post are now to be adjusted to meet the bow eye in a way that ensures the winch strap draws horizontally and does not induce any upwards or downwards bending stresses into the trailer when the boat is fully winched. 

4. Securing the boat

Care must be taken to ensure that any devices used to secure the boat to the trailer are fit for purpose and do not induce excessive forces resulting in bending or stressing of the trailer frame.

This especially applies when using rachet-straps and turnbuckles which easily apply tons of force – excessively more than needed for safe and secure trailering. Overly tight securing of the boat will bend a trailer chassis, change the even distribution of boat supports against the hull, and make the trailer more rigid where in fact it needs to flex. Together the effects of over-tightening have the potential to crack and destroy the chassis and damage the boat hull.

5. Simple checks for safe and happy trailering!

  • The centre of gravity must be kept as low as possible
  • The weight must be carried over the axles with approx. 8% of both the trailer and boat weight evident on the tow ball, and the ATM not be exceeded
  • The trailer must be allowed to flex to allow even distribution of stress. Conversely, the boat must not be overly secured resulting in bending stress in the trailer chassis

Trailer Tips by Spitfire Boat Trailer SA

Andrew van Ryneveld – Adelaide

0450 731 952

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