How to Inspect a Used Boat Trailer Before You Buy

The capacity plate (or decal) gives the trailer's maximum design weight and the tires it came with. BoatUS notes the VIN is usually etched, mounted or stuck on the trailer, often on that same plate on newer trailers. On older trailers the decal is often faded or missing, which can make registration a hassle.

• Read and photograph the plate and the VIN.
• If either is missing or unreadable, find out from your DMV what it takes to get a replacement before you buy. BoatUS says some states let police or the DMV reissue a VIN plate at the owner's request.

The capacity on the plate is the gross rating, and BoatUS reminds buyers to subtract the trailer's own weight from it to find what's left for the boat, motor, fuel and gear. Discover Boating suggests weighing the loaded rig at a truck-stop scale with a full fuel tank and your usual gear aboard, and checking the trailer and tire ratings against that number, especially on a used package where gear has piled up over the years.

Also check the fit: the bunks or rollers should support the hull along its strakes and keel the way the trailer maker intended, and the boat should sit with the transom close to the end of the bunks. Our bunks and rollers guide covers fit in detail.

Walk around slowly with a flashlight, then get down low.

• Rust and staining: BoatUS says to note anything that looks excessive and investigate further. Surface rust on a painted trailer is common; flaking, swelling or holes are not.
• Welds and joints: look for cracks at crossmember joints, the tongue and spring hangers. Rust bleeding from a weld line can be a crack.
• Straightness: sight down the tongue and frame rails for bends or twists.
• Galvanized trailers: BoatUS warns that acid bottom washes leave white streaks and attack the zinc coating. Patchy or white, powdery areas mean the protection is going.
• Fenders: they should be solid, not torn or loose, and cover the full tread width. People step on them, so push down on each.

• Size: if the axle looks undersized or replaced, BoatUS suggests comparing its cross-section to what the capacity plate calls for.
• Straightness and alignment: uneven tire wear can mean a bent or misaligned axle, according to Discover Boating.
• Hidden rust: BoatUS warns that axles rust from the inside when water can't drain out of the tube, which can lead to sudden failure. Look for heavy scale, pinholes or rust streaks at the ends, and ask whether the axle is sealed or has drain holes.
• A slight upward bow is normal. Dexter explains that many axles are built with a deliberate upward bend called camber, which flattens out under load. Don't mistake it for a bent axle; look instead for one wheel leaning in or out more than its partner and for uneven tire wear.
• Axle ID: Dexter axles made after April 2001 carry a lot (serial) number near the center on the rear side of the beam, under the Dexter name; rubbing chalk over it helps you read it. Photograph it so you can order the right parts later. Ask the seller for the original purchase paperwork too: Dexter's axle warranty is written to the original purchaser.
• U-bolts: the U-bolts that clamp the axle to the springs sometimes rust through first, according to BoatUS's roadside data. Look closely at the nuts and threads.
• Ground clearance: BoatUS suggests at least about four inches at the lowest point of the trailer.

BoatUS notes leaf springs rust long before the frame and are often a sign of age rather than neglect, so plan on replacing them if they're crusty.

• Look for cracked or broken leaves, leaves that have shifted sideways, and springs that sag flat.
• Check the hangers, shackles and (on tandem axles) the equalizer for cracks, elongated bolt holes and bolts worn thin.
• On a torsion axle, look for one wheel sitting noticeably higher or lower than its partner and for cracks where the axle tube mounts to the frame. Look for weld beads on the axle tube or its brackets: Dexter warns that welding on its Torflex torsion axles can damage the rubber suspension inside, so a previous owner's welding repair is a red flag.

Our axle and springs guide explains what each part does.

Wheel bearings and hubs cause more than 21 percent of BoatUS TRAILER ASSIST calls, second only to tires. With the wheel chocked and the trailer safely jacked and on a stand:

• Grab the tire at the top and bottom and rock it. BoatUS says bearings shouldn't show wobble or excess play.
• Spin the wheel and listen for grinding or rumbling; feel for roughness.
• Look for grease slung onto the inside of the rim, which BoatUS says can point to a problem (often a failed seal).
• Note whether there are bearing protectors on the hubs.

Ask the seller when the bearings were last repacked or replaced. Discover Boating suggests inspecting and repacking every three to five seasons even with protectors. If nobody knows, budget for a bearing service before your first long trip.

Brake requirements are set by each state. BoatUS says 35 states require brakes once the trailer is rated for 3,000 pounds or more, while others set the line anywhere from 1,500 to 4,500 pounds; some, such as Florida, require brakes on every axle, and some require a breakaway device. If you're buying out of state, BoatUS warns that retrofitting brakes on another axle can be expensive.

• Identify the type: surge (a hydraulic actuator built into the coupler), electric, or electric-over-hydraulic. Make sure your tow vehicle can run it.
• Surge brakes: check the fluid level and color in the master cylinder on the tongue, as Discover Boating suggests, and look for leaks.
• Look at brake lines for rust, kinks and flattened sections.
• Look through the wheel or behind it at the drums or rotors for heavy rust and scoring.
• Ask when the brakes were last serviced. BoatUS's rule of thumb: if the trailer has brakes, inspect them carefully.

Tire problems are the most common BoatUS TRAILER ASSIST call, at 44 percent.

• Age: read the DOT code on the sidewall. Under federal tire-marking rules the last four digits give the week and year it was made: "3519" is the 35th week of 2019. Discover Boating's checklist says tires more than six years old should be replaced, citing the National Transportation Safety Board.
• Dry rot: BoatUS says dry rot gets most trailer tires long before the tread wears out. Look for cracks in the sidewalls and between the tread blocks, and for bulges.
• Type and rating: Discover Boating says trailer tires should be ST (Special Trailer) type. Compare the size and load range with the capacity plate, as BoatUS suggests.
• Tread: use the penny test BoatUS describes: if you can see the top of Lincoln's head with the penny upside down in the center groove, the tread is done.
• Spare: check it the same way, and confirm the lug wrench fits.
• Cheaper replacements: Boating Magazine warns that tires on a used trailer have often been swapped for less expensive ones with too low a load rating. If the tire-and-load sticker on the frame has faded away, it suggests taking the trailer's model number to the trailer maker and asking for the original tire size, rating and pressure. Inflate to the pressure molded on the sidewall; trailer tires usually run much higher than car tires.
• Tread that looks odd: Boating's writer has had tires with internal ply separation, where the tread bulges and wobbles. Uneven wear on one tire, or tread worn to the cords on one side, can mean a bent axle or spindle, so go back to step 4.

Old tires on a good trailer are a bargaining point, not a deal breaker, as long as you replace them before you tow it any distance.

Hook the trailer to your vehicle, or bring a light tester, and check running, brake and turn lights with a helper.

• Make sure the trailer plug fits your vehicle's connector, or that you have an adapter for the drive home.
• BoatUS says all wiring should be insulated and secured with supports at least every 18 inches. Look for chafed insulation and scorch marks at bends, the tongue hinge and near moving parts.
• Most boat trailers need red side markers toward the rear and amber markers or reflectors toward the front, according to BoatUS, and trailers wider than 80 inches need three red identification lamps across the rear.
• A dead light is common and usually a cheap fix (bulb, ground or socket), but a trailer with dead lights shouldn't go on the road. See our trailer lights guide.

• The coupler should be marked with the ball size and its capacity, and BoatUS says those should match the capacity plate. Check that the latch closes tightly on your ball with no slop and that it accepts a pin or lock.
• Look for cracks around the coupler bolts and the tongue.
• BoatUS says the safety chains should be long enough to cross and short enough that the coupler can't hit the road if it comes off the ball. Check the hooks and links for wear and rust.
• Crank the tongue jack through its full travel and check the wheel and the swivel lock.

• Work the winch: it should ratchet and lock cleanly, and the handle shouldn't slip. Replace a frayed, sun-faded or cut strap before you load the boat.
• Look at the bow stop and its bracket for cracks and loose bolts.
• Bunks: push on the carpet. Rotten wood under worn carpet feels soft or crumbles. BoatUS describes a trailer whose bunk bracket nuts loosened until the boat pressed the fenders onto the tires and shredded one on a long trip, so check every bracket bolt.
• Rollers: they should spin freely without flat spots or cracks.

BoatUS's paperwork checklist:

• The seller should have proper ownership documents for both the boat and the trailer.
• The VIN on those documents must match the trailer. If the VIN is missing, unreadable or doesn't match, expect trouble at the DMV and possibly a replacement VIN process.
• Get the trailer title if your state issues one (some states don't title trailers) and a bill of sale. In some cases you may need a separate bill of sale for the trailer.

If anything is missing, BoatUS warns, you'll spend time convincing state agencies you own it. Our used-boat paperwork guide covers liens and title checks for the boat side of the deal.

With the seller's OK, hitch up and drive a few miles on local roads.

• The trailer should track straight behind you without wandering or swaying.
• Brake gently: trailer brakes should engage smoothly without grabbing or pulling.
• Stop and feel each hub carefully with the back of your hand. BoatUS's roadside crews say a hub that's hot to the touch is a bearing on the verge of failure, and a dragging brake can cause the same heat. All hubs should feel about the same.
• Recheck the lights after the drive.

Add up what you found. Lights, tires, a strap, bearings and springs are routine, affordable fixes. A cracked frame or crossmember, a rotted-through axle, a missing VIN with no clear path to replace it, or a trailer rated below your boat's real weight are much bigger problems. Use your photos to negotiate, or walk away.