Brackets & Bolts

Over 80 percent of the boating population trailer their boats, as opposed to keeping them in the water at a marina or private dock or in dry storage. For many, very little thought goes into the looks and performance of a trailer besides basic function.

However, trailer failures can stop a day on the water before it even begins and even causes damage to your boat. There’s a lot to know about the different types of trailers and trailer hardware, as well as the proper maintenance to keep your trailer towing smoothly. 

There are two main types of trailers: the bunk trailer and roller trailer. They are classified as to what method they use to support the boat. Bunk trailers have at least two fixed bunks that support the hull on either side of its keel. Roller trailers have multiple rolling wheels that support the hull, as opposed to fixed bunks.

The bunks of a bunk trailer are typically wooden beams wrapped in carpet. The wooden beams are held in place by metal brackets. On roller trailers, metal brackets support multiple non-marking plastic wheels.

There are varying opinions about which one is better or worse. Each trailer option has its pros and cons. Bunk trailers have no moving parts, while roller trailers can have dozens of wheels and pivot points that must move freely to support the weight of the boat hull as it is loaded and unloaded.

As far as upfront cost and maintenance costs, the bunk trailer is cheaper to buy initially and has fewer parts to wear out in comparison to the roller trailer. Roller trailers are more expensive upfront and the wheels must be replaced as they wear out. There is an argument that the bunk trailers are harder on the paint of your boat due to the friction of sliding the boat on and off bunks versus rolling it on and off.

As far as launching a boat is concerned, the roller trailer is much more straightforward. Simply disconnect the boat from the trailer and it will roll off. Bunks on the other hand require you to submerge the trailer further. For recovering the boat, some elect to “power load” the boat onto the trailer using the boat motors, while others prefer to winch the boat up. For an experienced captain, bunks and roller trailers don’t vary much as far as power loading is concerned. When winching, the low friction of the roller trailer makes it much easier in comparison to the high friction of bunks.

Some hulls are not designed to be trailered on roller style trailers, as the individual rollers may not have enough of a footprint to support the hull. On a roller trailer, it is crucial not to undo your winch strap or safety chain before the boat is backed down the ramp. Roller trailers can let a boat slide off prematurely if it is not secured correctly. 

The frames of boat trailers are typically made of two different types of metal, aluminum, and galvanized steel. Aluminum is a lightweight and corrosion-resistant metal, while galvanized is much heavier, but much stronger. Galvanized steel is a variant of steel that has been dipped in molten zinc, creating a corrosion-resistant layer of zinc.

Both galvanized steel and aluminum are designed to resist corrosion. In a saltwater environment, galvanized steel will rust away far quicker than aluminum. Regardless of what material your trailer is made out of, it will corrode and degrade eventually. For some, the reduced weight of aluminum is attractive, while to others the high strength of galvanized steel is a necessity. Galvanized steel is roughly two to three times stronger than aluminum, as well as two and half times denser. 

The components that attach to the frame of boat trailers to support bunks, rollers, and other accessories are typically made out of galvanized steel, zinc-plated steel, or stainless steel.

Zinc-plated steel is similar to galvanized in that both types of steel are coated in zinc to protect from corrosion. Zinc-plated hardware typically possesses a much thinner layer of zinc coating than galvanized. The coating of zinc on galvanized trailers is typically 1 mm thick while zinc plated is 0.2 mm thick. This results in the galvanized hardware being more corrosion-resistant than zinc plated. In the saltwater environment, this is something to consider when purchasing hardware. If the zinc coating of a zinc-plated material is removed through scratching or abrasion, that steel is very susceptible to corrosion in the future.

Stainless steel is another commonly used metal for trailer components. Stainless steel is strong and extremely corrosion-resistant. It is produced by mixing iron ore and chromium alloys and comes in different grades, with 304 and 316 being common in the marine world. While stainless steel is very popular, it does have its drawbacks. It is susceptible to a process called galling, where two stainless pieces create friction between two surfaces and essentially weld themselves together. This is most frequently seen when tightening fasteners down. 

How you stow your spare is something to consider. There are different styles of spare tire brackets, and it is important to find the best kind that suits your needs and how you plan to launch your boat. Pedestal-style mounts hold your spare tire up above the frame and well out of the way. The U-bolt style mounts around the trailer frame and through the mounting holes of your spare.

Being secured to the frame can get in the way of the trailer jack, and can remove your ability to walk down the frame of your trailer if that’s how you plan to launch your boat. It is a good idea to purchase a spare tire lock to deter thieves from stealing your spare tire while you’re out on the water. 

U-bolts are the most common way of fastening items to your trailer. Since every boat fits differently on the trailer, U-bolts allow for adjustment to different boats without having to purchase an entirely new trailer. They are used to hold the axle, rollers, guide posts, and almost any accessory mounted to your trailer. Whether you’re mounting additional accessories or replacing worn-out hardware, U-bolts are straightforward to replace.

When purchasing U-bolts, buy the correct size that correlates with the frame size of your trailer. Too large of a U-bolt won’t secure your items as well as they should be and too small will not fit around the frame of your trailer. 

Boat trailer bunk brackets are another type of bracket on your trailer. As the name implies, they are used to secure the bunks your boat rests on. If one of your brackets needs to be replaced, be sure to note the height and angle of the bracket you're replacing. Some bunk trailers utilize a bow roller to protect the keel.

These are typically installed on the cross members of the trailer. On hulls with a lot of deadrise, adjustable swivel top bunk brackets can be adjusted to support the hull at any angle.

• Keel Roller Brackets — Keel roller brackets attach keel rollers to the crossmembers of the trailer. They may be panel style, which accommodates a specific roller width, or split, which are in two pieces to fit any roller width.
• Vertical Bunk Brackets — Vertical bunk brackets attach to the trailer frame with U-bolts and hold vertically oriented bunks “sandwich-style” between two brackets.
• Swivel Bolster Brackets — Swivel bunk brackets are typically used to attach horizontally oriented (“flat”) 2 x 6” or 2x4” brackets to the trailer. Their design allows the angle of the bunk to be easily adjusted.
• Regular Bunk Brackets — Typically used for vertically oriented (“on edge”) 2 x 4” bunks for small watercraft trailers.
• Double U-Bolt Brackets — Like swivel bolster brackets, double U-bolt brackets are used to attach flat 2 x 6” or 2 x 4” bunks to the trailer. They attach to the frame with two U-bolts instead of one, though, making them stronger and more rigid.

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