How to Adjust Boat Trailer Rollers
Like a boat trailer bunk, rollers are there to make the job of loading and unloading your boat easier. Rollers move as your boat is moved. This reduces overall friction and makes it possible to get a boat, which in some cases can weigh thousands of pounds like a good size sailboat, on and off pretty easily. But rollers won’t do a very good job if they are not correctly aligned. You want them working with you and not against you. Let’s check out how to align those boat trailer rollers to make your job easier.
How to Adjust Boat Trailer Rollers
If you have new rollers or even old rollers, it doesn’t hurt to test and make sure they’re working well. You should be able to make the roller turn with nothing but a length of fishing line. If the roller is too stiff, you may need to replace it.
There are a few ways to adjust rollers to the right position. One of the more complicated ways involves taking measurements and doing it mathematically. There’s nothing wrong with this way. In fact, it will give you the best results. It also takes longer and I don’t think it’s entirely necessary. You can adjust them by eye with a level just as easily and save some time.
To start with your adjustments, you’ll want to use a spirit level at the rear of the boat above the transom near the motor. You’ll also need a couple of people to keep the boat balanced so it will sit and rest securely while you do these adjustments.
Remove the fasteners holding your rollers and roller arms in place. If there are any bunks, those need to go too. This is where your partners come in handy as they can keep the boat steady. DO NOT remove the rollers under the keel. We’ll keep those in place until later.
Placing the Rollers
With your rollers loose and out of the way, your two helpers have to keep the boat even. This is why you have that spirit level in place. Get them to get the boat completely even and then pick a side to adjust the rollers first. Get the roller arms and rollers adjusted to the correct height in order to maintain your boat evenly and level.
Adjust the bolts and secure the rollers in place so they are supporting your boat. Work your way down the line from stern to bow, ignoring the keel roller which you’ll work on last.
You can use a line to help you set the angle. Run a string from the front of the boat to the back. Measure from the second roller, not the keel roller. This is just because the shape of your boat may have a greater or lesser angle. You’re looking for a slight angle of about 5 degrees to help facilitate the boat on and off the trailer.
Once one side of the boat is adjusted, double check that you’re still level. If all looks good, repeat the process down the other side of the boat. Keep an eye on the spirit level to make sure it’s all perfectly even. If not, make adjustments as necessary.
Adjusting the Keel Roller
Your keel roller is not supposed to be even with the other rollers. Remember, you want that boat to get on and off the trailer easily. You want a very slight angle and that is achieved by having keel rollers slightly lower than the others. Ideally you’re looking for about a 5 degree angle here. Slight, but enough to help the boat roll on and off when you move.
All rollers should be touching the hull evenly on all sides now. You should be able to adjust the keel rollers now to ensure you have that proper angle you want. Try maybe ¼ to ½ a turn on the height adjustment with an adjustable wrench.
Test the Alignment
You can hook up your tow vehicle and drive the boat down the road for a few blocks to give it a chance to settle and for everything to fall into place. One you’ve done so, check your levels again and make sure all rollers are still holding the hull evenly.
Adjust your keel rollers so they’re taking the weight of the boat. Make sure self-centering rollers and the bow roller are all properly adjusted and aligned. If all has gone to plan the entire boat should be evenly balanced between strakes and the keel with no shifting or leaning to one side or another. If anything is off, whether balance or angle, go back and make adjustments as necessary.
Things to Remember
We’ve recommended rollers in another article and it’s good to ensure you have the right kind. There are a lot of options for boat trailer rollers, and some are better quality than others. Remember that black rubber rollers are often really cheap but may potentially leave marks on your hull. Blue poly or red poly rollers are good choices but they can cost a little more. Red poly is best for fiberglass hull boats. Blue poly is better suited for aluminium boats. If you see yellow poly out there, which is becoming more and more common, know that those are often very similar to red and best suited for fiberglass hulls. Always check what the manufacturer says to be sure, however.
If you prefer the method of measuring, you can do this with your boat on the trailer just at first. You’ll need to either make a sketch or take some notes as you go so you know where everything is and where it needs to be.
In this case, measure from the centerline of your boat to each strake. Aim for the center of the roller arm to get the most accuracy. You can then measure each bracket and roller arm to determine how much they need to be moved inboard and outboard. Now drop your boat down the boat ramp and into water and finish the job.
Use the same process as above and use a string to set keel roller height, but keep the angle to about 5 degrees. Lower your wobble rollers maybe 10 to 15 mm and bring the boat back into the trailer, keeping it centered on the keel rollers.
Raise the wobble rollers from back to front until they’re just touching the hull and proceed as mentioned above with even adjustments and tweaking the keel rollers.
The Bottom Line
Once you get the hang of adjusting rollers on boat trailers, the job doesn’t have to be too hard or take too much time. Don’t be frustrated if your first attempt takes a few tries to get right as it happens to the best of us. As always, stay safe and have fun.