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How to Adjust Boat Trailer Bunks? – 4 Steps to Remember

Fact checked by William Hart

how to adjust boat trailer bunks

After a period of use, the trailer’s joints inevitably loosen and cause the bunk boards to tip to one side or rub against the boat’s hull. At first, it might only hinder the boat’s smooth transition from the sea to the trailer. But with time, it brings severe hull damage that costs thousands of dollars to repair.

Every owner needs to learn how to adjust boat trailer bunks and carry out the necessary steps before serious damage occurs. This article will walk you through four steps to balance out your boat’s trailer.

Table of Contents

4 Steps to Adjust Boat Trailer Bunks

What to prepare:

To properly adjust the bunks on your boat trailer, grab the following tools:

  • Torpedo level tool
  • Wrench
  • Screwdriver

Step 1. Adjust the trailer’s keel rollers


Keel rollers (also known as keel guides) lie in the center of the trailer, helping your boat roll on and off the vehicle smoothly. Before setting up boat trailer bunks, you need to inspect and adjust boat trailer guides so that they bear most of the vessel’s weight.

During this step, you don’t have to worry about Jon’s boat trailer bunks just yet. The same applies to other vessel types if you have them.

To begin, find the boat trailer keel guide positioned in the front, loosen the bolts underneath the trailer’s frame with a wrench and screwdriver, elevate the roller until it touches the boat’s keel, and tighten up the bolts.

Some trailers have one keel roller, while some have two to three. You should read the trailer owner’s manual or search for online setup pictures for this information. You must find and adjust all rollers that your trailer carries.

Step 2. Inspect the boat’s position on the trailer bunks

When you finish adjusting the keel rollers, start inspecting the trailer bunks.

  • Move to the vessel’s stern and see how it is sitting on the bunks. Are the sides of the bunk boards rubbing against the hull? How does your boat rest on trailer? Is it lopsided?
  • Move to the trailer’s wheels and check the distance between the wheel fenders and the boat. How far apart are they? Do you notice severe scratches on the hull?

The hull should neither touch the fenders nor stay too far away from them. When the boat is too high, you will have problems launching it, especially in shallow waters. Ideally, the hull and fenders should be 1.5 to 2 inches away from each other.

Step 3. Adjust the boat trailer bunks


Most trailers have adjustable boat trailer bunks, so you won’t need chainsaws or cutting tools to modify them. Once you identify your issue, grab your wrench and follow the corresponding solution below.

  • The sides of the bunk boards rub against the hull

The bunk boards are connected to the trailer frame by four bolster brackets topped with four swivel brackets. You will adjust these brackets until the boards are parallel to the ground and stop chafing the hull. Follow these steps:

  • Loosen the bolts on the bolster bracket with a wrench
  • Place a torpedo-level tool on one bunk board and adjust it so that it lies parallel to the ground and then tighten the bolts. Remember not to shift the height of the bracket.
  • Repeat the steps for the three remaining brackets
  • The boat sits too high or too low on your PWC trailer bunks

In this case, you need to adjust the height of the bolster brackets to lower or elevate the boat. You should:

  • Unfasten the bolts on the bolster bracket
  • Move the bracket upward or downward depending on your issue
  • Once you reach the desired height, secure the bolts with a wrench
  • Repeat the same steps for the other three

Note: If necessary, launch your vessel before carrying out the procedure.

Step 4. Adjust the winch stand

Now that you have the desired boat trailer bunk position, finish up by adjusting the winch stand. You don’t want redundant winch straps to touch the road and trap in other components as you tow the trailer behind your car.

You should loosen the nuts, move the winch stand slightly toward the front of the trailer, and secure the nuts. Simple as that, and you can adjust a boat on a trailer successfully.

Other Tips to Adjust Boat Trailer Bunks


Do not over-tighten the bolts on the trailer frame

It is tempting to secure the bolts on the trailer frame as tightly as possible, so you can avoid further adjustments in the future, but doing so can damage or strip the threads.

Plus, what if you adjusted the bolster bracket incorrectly? By securing the joints too tightly, you leave no room for readjustment.

Inspect the trailer regularly

The trailer bunks bear a huge amount of weight each time you winch your vessel onto them and tow the trailer behind your vehicle. The weight and bumpy roads will eventually loosen their joints, so you must adjust them regularly.

If you retrieve your vessel onto a trailer with lopsided bunks, the boards will rub against the hull and leave scratches, decreasing the value of your investment. Plus, when the protective paint is damaged, the elements can invade and destroy the frame of your vessel.

Pay attention to your safety

As you adjust the boat trailer bunks, pay attention to avoid hand injuries. Remember that you are working with heavy-duty bolts and brackets, and if the trailer collapses, your hands are under the entire weight of your vessel. If necessary, put on shock-absorbent safety gloves while carrying out this procedure.



Should boat trailer bunks move?

Boat trailer bunks should neither be wobbly nor too tight. If they move, the boat doesn’t sit on them securely. If they are too tight, their sides might scratch the boat’s hull.

How far back should bunks be on a boat trailer?

The bunks should lie as far back as the rear point of your vessel. In other words, your entire boat should fit on the bunks, leaving no overhang.

The vessel bumps and moves as you trailer it on the road, so any unsupported stern areas will be dented, especially if it has heavy outboard motors.

Should boat trailer bunks be level?

Yes, you should level the bunks with a torpedo tool every time you adjust them. You don’t want to spend time moving them around just to realize that they are not aligned properly.

Can I make boat trailer bunks at home?

Yes. You can also search for ideas online and make DIY boat trailer bunk brackets. The process might be time-consuming, though.


With a wrench and a torpedo level tool, you have learned how to adjust boat trailer bunks properly. So, don’t leave your vessel lopsided on the trailer or the sides of the bunk boards scratching the hull. When you finish adjusting, the boat’s transition from the water to the trailer will be much quicker and smoother.

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