Thread: Number of axles on a boat trailer

Originally Posted by Tasmerican

Hi guys,

I'm in the process of restoring an old boat trailer that I picked up for a song. Everything's been disassembled and repaired, and I'm just getting ready to start putting it back together again. Once it's complete, I'm going to have to get it checked as it's been out of rego for some time.

The trailer is about 6m long and 1.5m wide. It won't be more than 2 tonnes GTM. There was one axle on it. I've had a look through the VSB1, but can't find anything about the number of axles that are required. Does this mean I'm okay to leave it as having one axle?

Any guidance is much appreciated!

It would depend on the axle, bearings and the springs also the condition of these as they are the limiting factors
What size is the axle, size of bearings, also the width, thickness and number of leaves in the spring? Take these details to a spring/axle supplier/manufacturer to get ratings,
if these are each over 2 tonne then it shouldn't be a problem. Other wise you will need to go to a tandem axle assembly, beware that most tandem assemblies are usually rated at about 1.8 tonnes. You will need a heavy duty suspension.
It is usually the thin end of the axle/bearing that gives problems.
Is the trailer going to be braked? As it could be a problem with insurance on the towing vehicle.
In SA we are only allowed a certain amount of overhang past the rear axle, you might need to check up on this.
Kryn

Thanks for the response!

I'm not sure about the size of the bearings. The axle is 40x40 RHS, but I don't know the thickness. Both the axle and bearings are in pretty good shape. I bought new springs, and just checked them; they're 1350 kg, so I guess that's going to need to be my maximum weight. It's not really a problem, since my boat is fairly light. I've also got brakes on there - the mechanical disc override variety.

Am I right that the total weight of trailer and boat together will then be 1350 kg? (Is that GTM?) Also, does that mean that I need to make sure the tyres are rated to 1350 kg each, or half of that (675 kg) each?

I'll have to look into the overhang - not sure what they allow here in Tas!

Before you fit the springs, please check your axle bearings. I highly doubt the axle will be RHS, particularly if it's only 40 x 40. A solid beam axle is turned from 40mm sq. Duraflex, but the two combinations of bearings that can be machined onto this is either "LM" (Holden inner & Holden outer) or "Composite" (Holden inner & Falcon outer). The LM is rated to 1000Kg, and the Composite to 1100Kg. Either of these two will then be your maximum rating without upgrading the axle.

I only ever recommend having the springs rated equal to or less than the axle.

Bearing numbers will help identify what you have.
Holden inner (large) 67048
Holden outer (small) 11949 (has same journal diameter as the thread on the end of the axle)
Falcon outer (small) 12749 (bearing journal steps up to a larger diameter than the axle thread)

As Kryn has said, you can have a single axle raed to 2000Kg.
Actually, you can get a single axle setup rated to over 4500Kg and still be perfectly legal, and this is why there isn't anything in the VSB1 regarding the number of axles. The only limiting factor to weight limit on a trailer is its weakest link. This can be the axle bearings, suspension, wheels and/or tyres, coupling, and chain all have ratings that effect the trailers rating.

Originally Posted by Tasmerican

Am I right that the total weight of trailer and boat together will then be 1350 kg? (Is that GTM?) Also, does that mean that I need to make sure the tyres are rated to 1350 kg each, or half of that (675 kg) each?

The two ratings given for trailers is ATM, and GTM. The ATM (Aggregate Trailer Mass) is the weight of the complete trailer, fully loaded, sitting on its own, on a weighbridge. The GTM (Gross Trailer Mass) is this same trailer hitched up to a tow vehicle with only its wheels on the weighbridge. The difference between the two is then your ball weight, a known requirement for the towbar on the tow vehicle.
Your tyre rating needs to be in excess of half the GTM. The two braking limits (750Kg and 2000Kg) are also measured at GTM.

Originally Posted by Tasmerican

I'll have to look into the overhang - not sure what they allow here in Tas!

Section 17.2 in the VSB1. The rear overhang is measured from the centre of the axle (or axle group) to the rear most point of the trailer and its load, and cannot exceed the front load space (centre of axle to front of boat in your case), or 3.7M. There's no reason why it should be any different in Tassie to the mainland.