Adapting a trailer for a sailbaot

Building a Sailboat Trailer

Since Belle did not come with a trailer, much of why she was so inexpensive, we had to source a trailer to put under her to make her useful to us. Buying a custom trailer was going to be in the $3000 range, 10X what we paid for Belle. Adapting a used trailer was going to be the only affordable. So this is how we set about building a sailboat trailer.

So how does one go about building a sailboat trailer? The easy way is to start with an existing trailer. We need some fairly detailed knowledge about the boat we intend to trailer. We need a trailer that is long enough and strong enough to support the load so we need to know where the center of gravity of the boat is, how far forward and aft the bow and stern are from this point, how much the boat weighs, how far from centerline the reasonably flat/horizontal hull areas extend, and how far these areas are vertically from the bottom of the keel.

Notes taken during survey
Here’s a copy of the notes I took during my survey

Measure It Up

When building a trailer for a sailboat, getting sizes and dimensions right is crucial. I took some critical dimensions during my survey of the boat (yes, I felt comfortable doing my own survey) and while shopping for the trailer. You can see those above. I used these to source my parts for the trailer refit. Our sailboat, an O’Day 23-2 comes in at a max displacement of about 3500lbs. That is equal to the maximum weight of the boat. So I knew I had to find a trailer that could hold 3500lbs. I also knew the shoal keel was going to cause the boat to trailer rather high off the ground and from my father’s experiences I knew I wanted the boat as low as possible and as long a tongue as possible to give us the most flexibility in launch ramp choices. The higher your boat sits on the trailer, the deeper and steeper the ramp you are going to need to launch and recover the boat.

Adapting Trailer for Sailboat
The trailer as we bought it

We located our trailer at KM Boat Salvage in Plaistow, NH. Keith had about 30 trailers to choose from. While there were some tandem axle trailers suitable, I decided to go with a heavy single axle Escort brand trailer for a few reasons.

  • A single axle is more maneuverable, less tire drag in tight turns.
  • This trailer was all galvanized and had hydraulic surge brakes (working or not?)
  • The price was half that of the tandem axle trailers ($650)

Looking at the wheels/hubs, I could see they were 6 lugs with 2.5″ caps. And counting the leaf springs, I could see there were 5 leaves. This suggests fairly clearly that the trailer has a ~5000lb class axle. That gives us plenty of room for the weight of the trailer itself once we subtract the weight of the boat. (1500lbs allowance for the weight of the trailer).

Tear It Down, Start With Lights

Once we had the trailer home, we stripped the old bunks and brackets off and removed the broken/old lights. We also removed the bow rest and winch post as they would need to be reconfigured to support the mich higher bow than what the trailer had been set up for.

Building a sailboat trailer
Bending the Light Brackets

I made up some new light brackets as the old ones had rusted too much. I found some galvanized tie plates at Lowesdepot and bent them at 90 degrees in my bench vise. I then enlarged two of the holes that lined up with the mounting posts from the trailer lights I bought. These brackets are then secured to the frame by pinching them behind the u-bolts for the rearmost bunk brackets.

Building a sailboat trailer
New Brackets Installed

The old wiring was stripped off the trailer and the new wiring from the new light kit was strung out on the frame. Rather than use the wire nuts that came with the kit, I preferred to make the connections more permanent and reliable by soldering the wires together and covering the joints with shrink wrap. You can also dab some dielectric grease over the solder joint before you slide the shrink wrap down for even more protection but its the steel in the cheap nuts that rots rather than the copper wire.

Soldering new trailer wire harness
Soldering New Wires

The ground wire that comes with these kits is always pathetically short. I’ve never had a vehicle with the trailer plug close enough to the tongue to use such a short wire. So, I harvested some white wire from the “car side” harness and soldered it to the trailer harness. I then used some dielectric grease in an attempt to protect the trailer frame from salt (fool’s errand) and a stainless self -drilling screw to bond it.

New Bunks and Brackets for the Trailer

Using the measurements I had taken and the construction of our new trailer, I set about trying to find bunk brackets for adapting the trailer to the sailboat. The dropped axle of the trailer is ideal letting the keel go as low as possible. Measuring up from the keel I needed bunk brackets in the 20-24″ range given we have a 4″ tube section. This tube section, and the lack of horizontal cross members severely limited our choices for off-the-shelf bracketry. Most brackets are designed for 3″X3″ tube cross members. The cross members on the Escort are “L” channel and not suitable for u-bolts. I also refuse to drill new holes in the galvanized trailer frame as these would expose bare steel and rust quickly.

Eastern Marine Trailer Parts Super Store had only one solution for our trailer situation. And I could find no solution elsewhere. The Tiedown 24″ bunk bolster brackets would have to do. However, these are set up to have a swivel top bracket bolted directly to the top with a short bolt. If the brackets were attached to cross members, this would be fine as they would allow the bunks to pivot to the slope of the hull. However, we had to attach to the longitudinal frame members so the bunks would want to pivot forward and back rather than side to side. The solution I came up with was to use bunk stiffening bracket weldments that had a tab welded to a tube. By bolting this to the bunk bracket and using two swivel top brackets to either side of the weldment I could change the pivot direction by 90 degrees.

Building a sailboat trailer
The only solution we could find to fit 3″X4″ tube section
Building a sailboat trailer
We used these to change the pivot angle of the bunks
Building a sailboat trailer
We had to use two of these on each bunk to bolt to the weldments

We then had to set about the bunk boards. I had seen a lot of boat trailers with long bunk boards strung between the brackets. It seems to me most of the board area in these cases does nothing but prohibit you from servicing the hull while on the trailer and rubbing bottom paint off. No weight is being carried more than a few inches from the brackets as the boards will simply bend away. I had also seen many trailers using round or square bunks atop the brackets and this seemed more ideal, I originally ordered only four brackets to save money, but once in hand, I realize we had too little margin for error and ordered another two.

Making New bunks
Epoxy gluing bunk layers together
Completed bunk with bracket but no carpet
Completed but no carpet

I had to replace the wood on the engine mount as well, so I bought a sheet of 3/4″ hardwood plywood. Did not splurge for marine plywood ($$$$) so it has lots of voids in it. I also wanted to reduce the chances of point contact with the hull. The bunk carpet will only disperse a minute amount of load. I chose to cut 1/8″ luan into “inverse circles” to raise the edges of the bunk pads in hopes that they would spread the load more effectively to the edges of the bunk boards. I laminated two layers of 3/4″ plywood and then the 1/8″ luan, sanded edges round, waterproofed with deck and fence sealer (two wet coats) and then Diana stapled bunk carpet to the bunks with stainless steel staples.

Time to Get the Boat on the Trailer

Trailer ready for boat
Ready to set the boat on it and make final changes

With the bunks fitted to the trailer casually, we were ready to go fetch the boat as they would have to be adjusted for height and angle while setting the boat on the trailer in order to complete building a sailboat trailer. Check out the next post to see the process we came up with for transferring the boat from the jack stands to the new trailer!

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