Severe salt water corrosion on a boat trailer.

How to check a boat trailer

When buying a used boat it always pays to remember that fundamental rule of nature, which says that just about any man-made object that’s in regular contact with water (particularly saltwater) requires a lot of maintenance.


Inspecting a boat trailer

The rule is especially true for boat trailers. One moment it spends months in someone’s backyard and suddenly it’s submerged in something as harsh as the marine environment. It’s a life of extremes and unfortunately, it can lead to all sorts of problems — problems you may not know about when you shell out cash for a boat, but can create all kinds of headaches, possibly even before you make it onto the water.

Fortunately, there’s a lot that buyers can do to avoid walking away with a failure-trailer. And best of all, you don’t even need to be an expert.


Corrosion on trailers

Corrosion kills trailer components, so it should be the first thing on your list of things to look for.

Start with a “hammer test” where you strike a hammer on different points of the trailer body. A metallic ringing means the metal has retained its integrity, while a dull “thud” could mean corrosion has set in.

Next, raise the trailer on a jack and have a good look underneath. Is there any obvious damage, or telltale reddish-brown corrosion? Take your time, especially on the lower half. This is the bit that gets immersed in the water and it can hide some nasty surprises.

If you’re satisfied with the body, then check the front of the trailer for cracks and other signs of stress. Check that the coupling is firmly bolted on, or otherwise soundly attached.

Next, inspect the brakes. These are the number one source of problems with boat trailers, so check the discs and callipers for corrosion, or excessive wear. Also, ensure any mechanical brake-cables, or hydraulic-brake reservoirs are in good condition.


Axles and suspension

Look at the suspension and axles. If you can see between leaf-spring suspension-layers of steel, then they need replacing. Check the wheel bearings too, because they are some of the most vulnerable components on a trailer; especially, if the former owner didn’t perform regular maintenance. Look for wear, and give the wheels a spin. Any rocking, or funny noises, suggests they need replacing.

While you’re at it, check the tyres. Are they cracked, peeling, or out of shape after sitting in someone’s back yard? Wheels and tyres are relatively inexpensive to replace, but you don’t want to take home a trailer that can’t support the weight of the boat, so make sure the load rating is correct. 


Now move onto the rollers. Older, or cheaper models, may have rubber trailer rollers that are often in poor shape, so these may need replacing with ultra-modern polyethylene components.

Skid trailers are less likely to need replacing, but don’t underestimate the abrasion damage that dirt-prone skids can do to a fibreglass hull.


Test the brakes

Brakes are the number one source of headaches in used trailers (above). Indeed, you’d test-drive a boat before you spend many thousands of dollars, so why neglect to do the same for the boat trailer?

Hook it up and test the lights. If none of the lights work then it’s possible there’s a problem with the wiring, but if only one is out, it could be the individual globe.

Obviously, you need to check the trailer’s braking capacity. This won’t be too hard for smaller boats, where you just hook it up on your own vehicle, but this can get a bit tricky on bigger boats.

Under Australian law, loads exceeding 2000kg must be able to automatically apply full brake-pressure for at least 15 minutes if the tow vehicle is accidentally separated. This is handled by a breakaway-system, which must have a controller installed inside the vehicle. An easy way to test this is to have it demonstrated in the seller’s vehicle.

Trailer Winch

Finally, check that the winch is in working order when you retrieve the boat. Look for any bending, or damage on the ratchet and winch-post, and check the cable or strap for excessive wear or damage.

Hopefully, the boat will have been launched and retrieved successfully by now, and the trailer passed all the points mentioned above. All you need to do now is tell the seller he’s dreaming unless he drops the price by a few grand…


Originally published in TrailerBoat #254, April / May 2010.