Boat Trailer Guide Modification

My friend Tom’s boat trailer was not well designed for getting the boat onto it when in the water. In the past, Tom has made a couple of devices to help guide the boat onto its proper resting place on the trailer that have enjoyed only limited success. A couple of years ago he purchased some boat guides with angled posts (made of galvanized 2” square steel tubing) that mount on the boat trailer frame and support two horizontal bunks, or pine 2x4 rails covered with indoor-outdoor carpet. However, after installing these guides per the instruction manual, it was obvious that they were not adjustable to the extent that would actually center the boat over the trailer. Even with moving the semi-vertical posts inboard as much as possible, the guides still did not come within 6 inches of the boat on either side. Perhaps with some craft that might not be a problem, but in Tom’s boat trailer, an inch is as good as a mile. That is to say, if the boat’s keel did not come to rest on the center of the boat trailer, the boat would lean to one side.

At the same time, Tom did not want a tight fit where the bunks would rub on the boat while being towed. We compromised and decided to somehow move the bunks inboard approximately 3 ½ inches on both sides.

We examined the swivel brackets that attach the bunks to the semi-vertical posts and brainstormed various methods for moving the bunks closer to the boat. Tom came up with the best solution (which is usually the simplest and most elegant). The easiest way to get the bunks closer was to extend the reach of the brackets by about 3 ½ inches on both sides of the boat. See photo above for a view of the bracket that came with the kit. It has two holes to mount it, with wood screws, to the bunk, and one larger hole to mount the bracket on the post. Inexplicably, that larger hole in the bracket is much too large for the “swivel” bolt that was supplied with the kit. And no bushing was supplied with the kit to address that discrepancy in size.

The second photo shows the extension bracket we built to move the bunks inboard by 3 1/2 inches.

I retired to my hangar-machine shop and designed a bracket extension that I would make out of 1/8 inch thick aluminum plate. The choice of material was fairly simple: steel would have been much harder to work with; we did not require the added strength of it; and the real deciding factor was that I had a nice piece of aluminum of that thickness in my salvage bin. Above is an “engineering drawing” of the proposed bracket. For the sake of authenticity and because it was the only scrap of paper I could find, I used the back of an old invoice.

The two smaller holes in the new extension bracket would be the attachment points to the post and they needed to be match-drilled to the pre-existing holes in that post. In the original configuration, those two holes in the posts were to give you a choice whether to mount the single swivel bolt on the bunk bracket either higher or lower to suit your boat. But in our arrangement, I would be using both of the holes in the post in order to mount the extension bracket rigidly onto that structure. The original bracket would still be attached to the bunk in virtually the same manner as intended, but it would now use our extension as the attachment swivel point instead of the post itself. I used a bushing to match the over-sized hole in the original bracket with the bolt supplied with the kit- an improvement over the parts supplied with the kit.

And here is a photo of the 4 brackets needed for the project. What is nice in this kind of small project is that once I made the first bracket, I could use it as a template for match-drilling all the holes in the other brackets, and as a template for cutting the brackets themselves out of the scrap aluminum plate with a band saw.

As with any metal project of this sort, in order to make these parts finger friendly, I burnished the sharp edges off the extension brackets and put a radius on (rounded off) all the corners with a belt sander.

This project escaped numerous attempts to over-engineer it and only required one trip to the local mom and pop hardware store.

The biggest lesson I hope the reader takes away from this tutorial is that many things you purchase may not be a perfect fit or may not work exactly the way you would like. Once you buy something, it is yours, and you should feel free to improve upon it. In my home and in my workshop there are dozens of appliances, tools, etc that I have modified and are much more useful because of it.