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How To Adjust Boat Trailer Bunks

How To Adjust Boat Trailer Bunks
November 15, 2017 Ultra High

How To Adjust Boat Trailer Bunks | Carpet & Plastic Boat Bunk Guides

Overtime many boat owners in America will come to the point that they will need to either replace their existing boat trailer bunks or repair their existing bunk guides due to constant wear and tear. If you own carpet bunk guides you will no doubt notice that they constantly need replacing much faster than plastic boat trailer bunks. 

Carpet boat trailer bunks are generally designed for use with fiberglass hulls. If they are used with aluminium boat hulls, due to the two materials clashing, this causes an unhealthy friction between your boat and bunks which will cause them to rip or tear much faster. Plastic boat trailer bunks on the other hand for aluminium boats last much longer and have a far greater life span and performance rating. 

In today’s tutorial we go over the simple steps on how you can adjust your boat trailer bunks to make them suit your boats hull. 

Why Do I Need To Adjust My Boat Trailer Bunks?

Plastic-boat-trailer-bunks-12There are numerous reasons boat trailer bunks and bunk brackets need to be adjusted to suit your boats hull.

  1. When you buy a new boat and trailer from a dealer, many new boat trailers from major manufacturers are made on a production line. This means that every boat trailer from a particular manufacturer are all made the same before being shipped to a boat builder or dealer. All the dealers are concerned about is selling a new boat and trailer package to the customer. Rarely do dealers put in any work to make sure the boat trailer has been adjusted to suit the customers new boat. 
  2. If you own a boat already and looking at upgrading or replacing your existing boat trailer. The boat trailer you will look to purchase will not be suited to your boat. 
  3. If you own a boat trailer and looking to purchase a new boat, your boat trailer will not be suited to your new boat.

If you fall in to one of the above categories, you will need to learn how to adjust your boat trailer bunks and bunk brackets to suit your setup.

By correctly adjusting your boat trailer bunks to suit your boat, not only will it sit better on your trailer; it will provide a smoother ride while in transit, will help make launching and retrieving easier and if you have keel rollers on your trailer, the bunks will help to evenly distribute your boats weight on the rollers for a smoother setup and lastly, be overall safer.

Step 1 – Check your boat trailers keel rollers

The first step to ensuring your boat is sitting correctly on your boat trailer is to check that your boats keel is resting on the keel rollers that may be attached to your boat trailer. 

Approximately 70% of the boats weight is in the keel, so it is important that we focus on this area of your boat and that it is well supported.

With your boat on your trailer, climb or position yourself as best as possible under your trailer to visualize that your boat is resting on all the keel rollers. If they are; Great! If not, you will need to climb under and use the appropriate adjustable wrench to loosen your boat trailer roller brackets and move them up so the keel roller is resting on your boats hull. Start at the front of your trailer and work your way to the rear.

Note: If you cant get under your boat while its on the trailer, you will need to launch or remove your boat and then make the adjustments of the rollers higher. Just make note of how much space there is and how much to raise your brackets. 

As a general guide, the rollers at the front of your trailer will be slightly higher than the rear rollers. This should follow the shape of your boats keel and allow for an easier launch when at the boat ramp.

Step 2 – Adjusting Your Boat Trailer Bunks

Plastic-boat-trailer-bunks-18Once you are happy that your boats keel is resting on your boat trailers keel rollers, it is time to make the adjustments to your boat trailer bunk brackets and hardware. With your boat resting on your keel rollers, you should be able to make changes to your boat trailer bunks without removing the boat from your trailer.

Your boats bunks will vary by boat manufacture as to were the trailer bunk guides will be resting. However, as a general guide, your trailer bunks will be resting approximately 1/3 up from the bottom of your boats hull.

Just like your keel rollers, we want to start with the front of your boat trailer. Loosen your adjustable boat trailer bunk brackets so they are free to raise. Raise your brackets so that your bunks are resting on your boats hull. Once the front of your boat is resting on your bunk guide, repeat the same process with the rear bunk bracket.

Once you have finished the first side of your boat you decided to adjust, repeat the same process with the opposite side.

When done correctly, your boat should not be ‘tipsy’ and should be resting firmly on both boat trailer bunks as well as your keel rollers. If your boat is still not sitting correctly, go over your boat trailer from step 1, and see which part of your boat trailer is not sitting correctly with your boat. Adjust your brackets as required, so that all boat trailer parts are resting correctly with your boat. 

Tools You May Need

  • Adjustable Wrench.
  • Torque Wrench.
  • Screwdriver.


Check the stability of your boat trailer bunks after each time you launch and retrieve your boat. With constant use, its not uncommon for your brackets to shift slightly. If this happens, adjust them accordingly back to their original resting position.



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