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Building Wooden Trailer Cradles

Building Wooden Thistle Cradles

by Jason Rziha

Choosing the size/position

Unlike Chris Laborde when he built his trailer and cradles from scratch, I had limited choices on where to put mine unless I wanted to weld more braces on the trailer (I didn't). Fortunately, the trailer frame had braces that were in acceptable places - basically under the stanchions and at the back of the seats. This put them under strong areas of the boat and was close to Chris's 20% rule. By moving the bolt point to either the front or back of a brace I could move the cradles a few inches-no more.

For the size I wanted them to be as wide as possible, while letting me wrap them in fiberglass. With a 50" piece of glass, I could make them just under 11" wide and go around twice. (Not that I'd recommend doing this, now that I did it)

Research

I read all I could find on the subject- Dan Winchester's page, Brad Thompson's write up on using wacky wood (search the archives of the thistles@yahoogroups.com email list) and looked over Matt Kreuzkamp's page with pictures of his wacky wood cradles (now offline).

Preparation

Marking the placement on the boat.To mold the cradles to the boat,you want it flipped over and up on blocks. Cover it with plastic to keep the epoxy you're using for glue from getting on the boat. After you've got it positioned, center and temporarily attach what you're using as spacers while bending your plywood. The spacers account for the area taken up by the padding. In this case, I just used the padding itself- new plastic doormats. They work great, but were insanely pricey for a piece of plastic with teeth. But the boat won't trap moisture between it and the cradle.

The wood

I called my lumber supplier and explained what I was after, and they had 2 options:
Bending Poplar 1/8" $37.49/sheet
Wiggle Wood 3/8" $39.99/sheet
Being cheap I went with the 3/8" wiggle wood since it would let me get by with 1 sheet. If I did it again I'd try to find 1/4" material- the 3/8" material was a little stiff and didn't bend as nicely as I'd have liked. This led to voids in the laminate I had to deal with later.

Remember when you cut the wood to keep the grain parallel to the keel of the boat. Otherwise you'll have a hard time bending it the direction you want. The back cradle is just wide enough that you might want to cut it the other direction.

Glueing it up

The cradles soaked with glueSoak the mating surfaces with epoxy, put them together, and then line the cradle up on the boat. Drive a pair of screws into the center so the pieces stay lined up. The cradles after the glue had cured Some marks on the hull with a sharpie or painter's tape help a lot here. Clamp it in place. Band clamps or ratcheting tie-downs work best, but anything heavy will help. Even with the long open time of epoxy, you want your clamps ready before you start. It seems some of my ratchet tie-downs had wandered off, which only helped add voids.


Filling the voids

Nasty voids Fixing the voidsBecause the plywood wasn't flat and didn't clamp well, the cradles had some significant voids between the layers. After I took them off the boat I spent several days working epoxy into the voids and clamping them together.

Glassing the cradles

To protect the cradles and make them a lot stiffer, I wrapped them in fiberglass. Yes, I know glassing both sides of a boat is bad. But these won't be in the water that often, and here in AZ excess moisture is rarely an issue. I used a single piece of cloth wrapped around and around the cradles. If I did this again, I'd do it in multiple passes, letting the last one get mostly cured before applying the next.

Painting

While being in AZ is good for low moisture, the high UV isn't good for fiberglass. So after the resin was good and cured I sanded it down and painted it with a couple coats of Interlux white.

Aligning to the boat .

The challenge of aligning to the boat was matching the pitch of the cradle to the boat. I started with a 2x8" board that I notched to fit the cradle, then I cut it at an angle so the cradle matched the boat (about 6° in the front, 4° in the back). Because I needed the boat on the trailer to check the angles, I used some chunks of foam (computer packing) to keep the boat from settling on the trailer.

Once I had the pitch set, I epoxied and screwed the cradle to the brace. Then I added more blocks in front and back so that any force applied to the back of the cradle didn't have a lot of leverage and rip out the screws. More epoxy and screws held it all together. When I was done the structure under the cradle was about 5" wide, leaving no more than 3.5" of overhang in front and back.

Padding

Attaching the doormats to the cradles was surprisingly challenging. I first tried liquid nails, with it merely peeling a thin layer of plastic off the bottom of the mats and making a mess. Contact cement was what finally worked.

Bolt it on

Attaching the cradles to the trailer was pretty straightforward- just bolt it to the posts.



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