Is My Vehicle Rated to Tow This Boat? Towing Capacity, GCWR and Tongue Weight Explained

• Open the towing section of the owner's manual. Many makers list towing capacity and GCWR by engine, axle ratio, cab, bed and drive (2WD or 4WD). Find the row that matches your vehicle, not the best one in the chart.
• Look at the certification label on the driver's door jamb. It lists GVWR and front and rear GAWR. A nearby tire and loading label usually shows payload.
• Note whether you have the factory tow package. BoatUS points out that these packages can add parts you can't bolt on later, such as a different axle ratio, extra cooling, a heavier alternator, sway control and load-leveling suspension. The rating often assumes those parts.

Photograph every label and chart so you have them on your phone.

Find the trailer's capacity or VIN plate. EZ Loader, for example, puts its VIN sticker on the inside of the front frame rail on the passenger side, with a decal under the tongue. The plate shows the trailer's GVWR and usually tire size and pressure. Also check the tire sidewalls for their load rating.

If the boat plus gear comes close to the trailer's capacity, you have a trailer problem before you even get to the tow vehicle. Leave yourself a margin rather than running right at the limit (our pre-trailering checklist covers the usual rule of thumb).

Brochure "dry weight" leaves out a lot. Load Rite's method for sizing a trailer is a good reality check:

1. Start with the boat's dry hull weight.
2. Add the outboard or engine weight.
3. Add fuel at about 7 lb per gallon of tank capacity and fresh water at about 8 lb per gallon.
4. Multiply the total by 1.1 to allow about 10 percent for batteries, electronics, coolers and gear.
5. Add the trailer's own weight (from the maker or the scale).

Owners are often surprised: a "3,000 lb" boat can easily be well over 4,500 lb on the road once the trailer, fuel and gear are counted.

A certified truck scale (CAT scales at truck stops are common) gives you real numbers for a small fee. Load the rig the way you actually tow: fuel, gear, coolers, passengers or their weight.

Weigh 1: the whole rig. CAT Scale's instructions for a truck and boat: steer axle on platform 1, drive (rear) axle on platform 2, boat trailer on platform 3, with everything on the scale. CAT notes its scales give axle weights and a total, not individual wheel weights. Very light rigs (under about 2,000 lb total) may need a call to their help desk.

Weigh 2: the vehicle alone. Unhitch in the lot (chock the trailer wheels first), then weigh just the vehicle with the same people and cargo aboard.

From the two tickets you can work out everything:

• Combined weight = Weigh 1 total. Compare to GCWR.
• Loaded vehicle weight = platforms 1 + 2 from Weigh 1. Compare to GVWR.
• Rear axle weight = platform 2 from Weigh 1. Compare to rear GAWR.
• Tongue weight = (platforms 1 + 2 from Weigh 1) minus (Weigh 2 total). BoatUS uses this same "hitched minus unhitched" method.
• Loaded trailer weight = platform 3 from Weigh 1 plus the tongue weight. Compare to the vehicle's towing capacity and the trailer's GVWR.

A made-up example: Weigh 1 shows 3,300 + 3,700 + 4,200 lb = 11,200 lb total. Weigh 2 shows the truck alone at 6,550 lb. Tongue weight = 7,000 minus 6,550 = 450 lb. Loaded trailer = 4,200 + 450 = 4,650 lb. Now check each result against your own labels. If any number is over its limit, the rig is overloaded, even if the others are fine.

Leave a margin. Discover Boating's trailer-law page suggests not going over about 80 percent of the vehicle's maximum towing weight, and reminds you to weigh with the boat's fuel tank full and your usual gear aboard. Being "just under" the sticker number leaves nothing for hills, heat, headwinds or the cooler you add later. The same page notes that states also limit trailer length (roughly 30 to 60 feet, depending on the state) and the combined length of vehicle plus trailer (about 50 to 85 feet), and that most states treat a load wider than 8 feet 6 inches as a wide load needing permits or flags.

Divide tongue weight by loaded trailer weight. In the example, 450 divided by 4,650 is about 10 percent.

Sources differ a little on the target. BoatUS's tongue weight article says 7 to 10 percent of total trailer weight, while BoatUS's hitch article notes about 5 percent is normal for many trailered boats. Too little causes sway at highway speed; too much makes steering light and overloads the rear axle. Stay inside your vehicle's and hitch's tongue limits whatever the percentage.

To change it, move heavy gear fore or aft, empty water tanks, or move the winch stand so the boat sits farther forward or back. BoatUS says to do that at home, never on the shoulder.

The hitch, ball mount and ball are rated separately, and the lowest rating in the chain is your limit.

• Read the label on the hitch cross tube. Boating Magazine notes most receiver hitches show a weight-carrying rating, and many also show a higher rating that applies only with a weight-distributing system.
• Classes are a rough guide, not a rule. Published class ratings vary by source (BoatUS describes Class III as 5,000 lb and up; Boating Magazine lists Class III up to 6,000 lb), and BoatUS calls Classes IV and V more of a marketing term than an industry standard. Go by the label, not the class name or the receiver size.
• A bigger hitch never raises the vehicle's rating. If the truck is rated for 5,000 lb, a 10,000 lb hitch still means 5,000 lb.
• Boating Magazine says to forget step-bumper hitches for boats; they're relics.

• Ball size must match the coupler. Common sizes are 1-7/8, 2 and 2-5/16 inch. The coupler size is stamped near the latch and the ball is marked on top. Boating Magazine warns that a ball that's too small can let the trailer pop off; one that's too big won't let the latch close.
• Ball rating: the gross trailer weight rating stamped on the ball should be at least your loaded trailer weight, and the ball mount's rating should match the hitch.
• Shank diameter must match the hole in the ball mount. A loose shank can work loose or snap.
• Drop or rise: choose a ball mount that leaves the trailer frame level when hitched. A nose-high or nose-low trailer changes tongue weight and how the brakes and axles share the load.

Brake rules are state law and the thresholds differ. BoatUS says most states require brakes on trailers over 3,000 lb gross, and many experts recommend them from 1,500 lb up; a few states set the line lower than 3,000 lb. Some states also require brakes on every axle or a breakaway system. Check your own state's DMV or vehicle code, and the states you'll pass through.

Boat trailers usually use surge brakes (our surge brake guide) or electric-over-hydraulic brakes with an in-cab controller (our trailer brake controller guide).

A wide boat or trailer can block your normal side mirrors. Most states require that you can see the road behind your rig, and many set rules for mirrors when the load blocks the view. If you can't see past the boat on both sides from the driver's seat, add extended towing mirrors (clip-on or replacement) before the trip, and check your state's rules.

The heaviest moment is often pulling a wet boat up a slick ramp:

• A light 2WD vehicle with the drive wheels on algae can spin. 4WD or a lighter rig helps; so does keeping the vehicle's drive wheels out of the slimy zone.
• Front-wheel-drive minivans and crossovers have an extra catch: tongue weight lifts the front of the vehicle, right where the drive wheels are. BoatUS's ramp tips say a front-wheel-drive vehicle that spins may grip better with less tongue weight, the opposite of a rear-drive truck. If your rig only works with everything going right, it's too close to the limit (our solo launching guide has the full list of wheel-spin fixes).
• BoatUS notes that with surge brakes, the trailer brakes don't help while you back down a ramp; only the vehicle's brakes hold the whole rig. With heavier boats, that's a real strain.
• Boating Magazine warns that weight-distributing spring bars that are too stiff can cost rear-wheel traction on a slippery ramp, and some can bind surge brake couplers.

Take a short loaded drive at road speeds in a safe area. Feel for sway, a bouncing rear, light steering, or a soft brake pedal. BoatUS also suggests stopping after the first 50 miles or so of a trip to check the hitch, chains, tires, hubs and load. Weigh again any time you change the boat, engine, fuel tank, tow vehicle or what you carry.