Boat Trailer Parts Tutorial and Diagrams

Tom Wiesen

Boat trailers are built from components with specific names. Learn here what each part is called so you can communicate effectively to replace, repair, or upgrade your boat trailer parts. 

It’s as important to know the details about your boat trailer as it is to understand the parts of your boat or car. Learn the part names and the maintenance required to keep your trailer operating like new for years to come.

Identifying Parts Common to All Boat Trailers

Starting at the front of the trailer, the first part is called the coupler. The coupler is the moving part that clamps down on the ball to secure the trailer to the vehicle. Keeping this part lubricated so the coupler lock fully engages and there’s no surprise release is essential.

A surprise trailer hitch release brings us to our next item, the safety chains. Safety chains play a vital role as a backup attachment to the vehicle if there is somehow a failure in the hitch system. 

If your trailer breaks free from your vehicle, not only will your boat get wrecked, but it is a hazard to others. Furthermore, for liability reasons, a trailer separated from the vehicle becomes a vehicle in itself in terms of liability. 

If someone else gets injured or property gets damaged from a loose trailer, you’ll wish you had that special insurance on your trailer. Take the safety chains seriously. Hooks that clip shut are preferred over open hooks.

Next, working our way back on the tongue of the trailer, we have the jack. Keep the jack lubed for trouble-free operation. After using the jack to lower the trailer onto the vehicle hitch, close and lock the coupler, fasten the safety chains, and then raise your jack all of the ways. 

Without a doubt, the most common way to ruin your jack is to forget to raise it fully and start driving away. Then the jack gets bent, and you can’t raise or lower it. It happens, but don’t let it happen to you.

Another item at the front of the tongue of the trailer is the electrical plug for lighting and trailer brakes (for larger trailers). The plug is on a length of flexible cord so the trailer can turn without pulling on the plug. 

Get the cord length right by wrapping it to support the cord if needed. If the cord or the plug drags on the ground while driving, it will surely need repair.

Working back on the tongue, we now have the winch and the winch stand. Often, trailers are built with bolt-on winch stands, and sometimes the winch stand is welded to the frame. 

The winch is equipped with either a cable or a strap that coils onto a spool. This controls the boat during launch, retrieves the boat when pulling the boat out of the water, and secures the boat’s bow to the trailer during transport. Be sure your winch is rated higher than the weight of your boat.

Keep the winch lubricated for smooth operation. The last thing you want is for the locking mechanism to release unexpectedly, and your boat slides off of the trailer while going down the road at speed. 

It is equally important to lubricate the latch of the hook that’s on the cable or strap. Make sure it’s functioning as it should so it stays attached to the bow hook of the boat and your boat remains securely fastened to the trailer.

The next part of the trailer is the bow stop. It is either a rubber bumper, a carpeted V-shape, or two padded vertical pipes that the bow nests into. Make sure that you have padding here, or the bow trim of your boat will get damaged.

Near this point on the trailer, you may have a spare tire. Just like for your car, a spare tire is a good thing to have because flat tires never seem to happen at a good time.

Bunk Trailers and Roller Trailers

Now we have the parts of the trailer that the boat actually sits on. Oftentimes these are carpeted, or rubber padded bunks that are like rails that the boat bottom sits on. When loading the boat on a bunk trailer, it is important that the boat is centered, so the bunks nest into the sweet spot on the bottom of the boat.

Other trailers have a system of rollers. When using a roller trailer, the boat is winched on and off of the trailer. This is an ideal system for a solo operator because the winch enables a sure and steady loading and unloading while the boat is naturally directed to the sweet spot where it is centered.

By contrast, a bunk trailer is best with a boat driver on board and a vehicle driver. The trailer is backed deep enough into the water, and the driver literally drives the boat onto the trailer. A rehearsed team will just give a go signal, and the boat driver applies some throttle as the vehicle driver pulls forward. The whole process is seamless and painless. 

If a boat on a bunk trailer is not nested fully into the bow stop, the vehicle driver can go forward and then hit the brakes to get the boat to slide forward on the wet bunks and nest the bow into the bow stop. Of course, use moderation with the speed and braking to avoid damaging the boat bow and trim.

Overall, bunk trailers are far more commonly used than roller trailers. They are simpler, have fewer moving parts, and are less maintenance. And of course, they cost less than roller trailers.

Boat Trailer Bunks

Boat trailer bunks are made from marine plywood, hardwood, or a composite material that’s like a hard plastic wood. The bunks are either covered with carpet or rubberized plastic to pad the bottom of the boat. Be certain the bunks have structural integrity so you don’t end up with the bottom of the boat sitting on a steel bracket.

Roller Trailer Parts

Keel Rollers

In terms of keel rollers, there is a wide range of sizes and forms to choose from. Keel rollers run the length of a roller trailer, usually down the center. 

Wobble Rollers

On a multi-roller trailer, wobble rollers are critical. They are the key to loading and unloading your boat, and it is imperative to keep these rollers lubricated and in good condition. 

Older trailers may have rollers that lack integrity because the rollers are cracked, broken, or have flat spots. This not only makes it a challenge to launch or recover your boat, but also can cause damage to the bottom of the boat if the weight is not distributed properly.

Multi Roller Brackets & Hardware

This configuration requires many different brackets and hardware, so multi roller trailers have many moving parts. It’s uncommon for these parts to come in a kit form that includes everything you’ll need.

Boat Trailer Tires and Wheels

The most overlooked maintenance item on any trailer is to grease the wheel bearings every year. It is easy to overlook because it’s out of sight. However, repeated submersion in water, followed by baking sun, leads to corrosion and degradation of the grease. If your wheel bearings wear out or lock up going down the road, the wheel can come off and cause an accident.

Boat trailer tires need to be closely monitored. Because boat trailers often spend time baking in the open sun and being subjected to the elements, tires can degrade even though they have a few miles on them. Closely inspect the sidewalls, especially near the bead for cracking and signs of drying out.

Boat trailer tires have a special ST rating. These tires have a stronger sidewall than passenger cars or light truck tires. Also, the load rating for boat trailers tends to fall into the B or C category. 

Radial tires are the best and run cooler for long hauls. Consult a boat trailer shop like Trailers and Transport to learn about the best tires for your trailer and load.

Larger boat trailers are equipped with trailer brakes. These brakes are electrically activated, and it’s important to have them functioning properly. A heavy boat behind a truck needs extra braking power on the trailer, so the load doesn’t pass up the tow vehicle!

Boat trailers have fenders that cover the wheels to keep mud and water from spraying up on the boat. There is often a step up and a place to stand on top of the fender. This is nice and useful customization, so you can get in and out of the boat easily when it’s on the trailer.

Next are the trailer taillights. These are special submersible lights that are watertight. A standard trailer light would simply fill with water, corrode, and quit functioning in short order. Some trailers are equipped with LED lighting along the length that adds nighttime visibility to larger rigs and also looks great.

At the very rear are vertical bars that are guides to direct the boat to be centered when loading and unloading. These guides are generally padded with rubberized plastic. 


Boat trailers are generally built from individual components that are bolted together. By understanding the individual trailer parts, and the basic maintenance required to keep them functioning properly, it’s possible to keep a boat trailer functional for decades.