The Weighbridge Doesn't Read Brochures: Working Out What Your Car Can Legally Tow

You've found it. A tidy 5.5-metre cuddy, two seasons old, and the advert says 1,400 kg on the trailer. Your estate car is rated to pull 1,500 kg. Job done, deposit sent, see you at the slipway.

Except the 1,400 kg was someone's memory of the boat dry, with no fuel, no anchor, no battery, no outboard and no trailer. And 1,500 kg on your car's plate was measured with a driver and a quarter tank of fuel, not two adults, a dog, a coolie-load of kit and a full tank. This is the bit where a nice afternoon turns into a weighbridge visit and an awkward phone call to the seller.

None of this is exotic. It's just arithmetic that nobody does until it's expensive.

Three plates, and only one of them is the boss

There are three sets of numbers in play and they don't negotiate with each other.

First, the vehicle identification plate — usually under the bonnet or on a door pillar. It gives you four figures: gross vehicle weight (the most the car can weigh loaded), gross train weight (car plus trailer plus everything in both), and front and rear axle limits. Subtract the GVW from the GTW and you've got a working figure for towing capacity. It won't always match the handbook, because the handbook often quotes a lower limit for gradients or for certain engine/gearbox combos. When the two disagree, the smaller number is the one that keeps you legal.

Second, the trailer plate. That gives you the trailer's maximum authorised mass (MAM) — the most it's designed to weigh fully laden — plus the axle limit and, if it's braked, the coupling details.

Third, your driving licence. More on that in a moment.

Some older cars have no GTW on the plate at all, only a towing limit buried in the handbook. In that case the handbook is the referee. Not the bloke on the forum who swears his identical car pulled 2,200 kg to Cornwall without a murmur.

Your photocard is not the licence you think it is

This is where a lot of UK buyers get caught out, and it has nothing to do with how well they drive.

Passed your car test before 1 January 1997? You almost certainly have category BE by grandfather rights and can tow a trailer up to 3,500 kg MAM behind a car. Passed after that date? Your entitlement depends on when and on codes printed on the back of the card. Between 2013 and 2021 a lot of drivers took a short B96 course to reach a 4,250 kg combined limit rather than sitting the full BE test. And since 16 December 2021 the rules were relaxed again, so a standard category B licence now covers a trailer with a MAM of up to 3,500 kg — subject to the car's own limits.

The trap for anyone shopping in 2026 is that the car and trailer must both be within your entitlement, and the plated figures are what count, not what the outfit actually weighs on the day. A two-tonne trailer is a two-tonne trailer to the law even when it's empty and you're only moving it four miles to the yard.

Nine out of ten buyers will be fine. The tenth needs to look at the back of the card before falling in love with a boat, because upgrading a licence is a slow, expensive way to fix an impulse purchase.

The plated weight is the only weight that matters

This catches out nearly everybody. A trailer plated at 1,800 kg counts as 1,800 kg against your licence and your car's towing limit, whether it's carrying a boat, a pile of leaves, or nothing but a spare wheel.

Which cuts both ways. A trailer plated at 2,000 kg but only ever loaded to 1,500 kg is still a 2,000 kg trailer on paper — that's the number your insurer, the police and the DVLA will read. If it's over your limit, you can sometimes have the trailer re-plated lower by the manufacturer, but that's a paperwork exercise with a real cost and a hard ceiling.

Then there's the honesty problem. Manufacturers weigh boats in conditions no boat ever leaves the factory in. Add fuel at roughly 0.85 kg a litre (a 120-litre tank is north of 100 kg), an anchor and chain, a battery or two, fenders, warps, a liferaft, the outboard if it's been off, plus whatever lives in the locker that you haven't looked at since March.

The fix is embarrassingly cheap: find a public weighbridge — councils and scrap yards run them, a tenner or so gets you a ticket — and weigh the whole outfit loaded exactly as you'd tow it. Keep the ticket. If you ever get stopped, or have a claim, that piece of paper is worth more than any conversation.

Noseweight, payload and the family in the back

Towing capacity isn't the only ceiling. Every kilo of downward force on the towball comes out of the car's payload, and a typical family hatchback's payload is smaller than you'd guess — often around 450–500 kg once the driver is accounted for.

Two adults, two teenagers, a full tank and a boot of luggage can eat most of that before the trailer is even hitched. Add 75 kg of noseweight and you're very close to the line. This is why some outfits that are legal with a solo driver are over the rear axle limit with a full car — and rear axle overload is the one that quietly destroys tyres and, in a claim, your credibility.

A rough starting point: keep the trailer's laden weight at or below about 85% of the car's kerb weight if you're new to towing. It isn't law, it isn't in any statute, and plenty of experienced drivers ignore it. But it is the difference between a calm 60 mph on the A38 and a trailer that wants to steer the car for you.

Two very different skills: slipway and motorway

Towing a boat asks the car to do two jobs that pull in opposite directions.

On the slipway, you want traction. Wet algae-covered concrete at 10% is a genuinely slippery surface, and a front-wheel-drive car with its driven wheels on the dry bit at the top of the ramp is doing well to get a light boat back out. Weight shifts rearwards as you climb, which is precisely the wrong direction for a FWD hatchback. All-wheel drive helps enormously; a low-range gearbox helps more. And if the ramp is steep, the trailer's brakes (overrun, typically) do nothing useful in reverse.

On the motorway, you want stability. That means noseweight set properly, the load centred over the axle rather than hanging off the back, tyres at the right pressures on both car and trailer, and a sensible speed. A trailer that's happy at 50 mph can become a handful at 70, especially in crosswinds or when a lorry passes. If your boat is a high-sided cuddy with a lot of windage, take that seriously — it isn't a caravan, but it isn't a low-loader either.

Also worth checking before you commit: over 750 kg MAM the trailer must be braked, and it needs a breakaway cable — not a chain — attached to a proper point on the car. Lighting boards fail. Test them every single trip, ideally with someone standing behind while you work the pedal.

The insurer's question is a different question

Your policy will want to know that you tow, what you tow, and how often. Some will load the premium, some will add an endorsement, and a fair number quietly exclude damage occurring while launching or recovering — which is exactly when things go wrong. Trailer cover is often a separate matter entirely; the boat may be insured, the trailer may not be.

Tell them the truth and get the towing confirmation in writing. If a claim goes sideways because the outfit was over the plated limit, 'the salesman said it would be fine' is not a defence anyone has ever won with.

And then there's the driveway

One last, unglamorous calculation. A 1,800 kg outfit on a single axle puts a lot of point load on whatever's underneath it — block paving over a shallow sub-base is not the same as a concrete pad, and a trailer parked on a slope with the jockey wheel digging in will leave a mark you'll be explaining for years.

Check your deeds, your tenancy, or your neighbours' patience. Plenty of UK properties have covenants or lease terms that quietly ban trailers, and a boat on the drive is a far more visible thing than a boat in a marina. Add a hitch lock, a wheel clamp and, ideally, a post you can chain to. Trailers are stolen more often than boats.

None of this is meant to put you off trailer sailing, which remains the cheapest route into boat ownership this country offers. It's just that the maths comes first. Get the plates out, take a photo of the VIN sticker, read the back of your licence, and put the whole thing over a weighbridge before the survey. Then the only surprise left is the weather.