Now that I had the Car Float the next thing to add was the Transfer Bridge that connects the car floats to the terminal.
The transfer bridge I’ll model is the replacement thru truss bridge that was put in place in 1920. As its predecessor, it is made of timber and consists of three framed Howe trusses. The available plans give a good idea of its size (approximately 104′ length and 40′ width) and the few photos document on a sufficiently detail level (at least for N scale) the way it is built.
I could not find any model that would come close so it was a no brainer to scratch-build the model and to stay as close to its prototype as possible. I had never before worked with laser cut wood structures so I gave it a try. I designed the structure with a vector graphics design tool (Inkscape). I would leave it up to the laser cutting service to deal with the intricate cutting. Following are the rough specifications of the transfer bridge project:
- Laser cut 1/16″ bass wood, three layers for the two lateral trusses, two layers for the middle truss. Each truss layer is laser cut in one piece with the diagonal wooden members about 1/16 thick. Each truss consists of 16 asymmetric segments plus two symmetric X-shaped segments on the southern end.
- Trusses have either their members oriented towards the center or towards their end which creates a pattern of interleaved diagonal members.
- Floor beams and flying buttresses made of basswood strips 1/8″ x 1/8″.
- Deck made of strips of 1/16″ Styrene sheet
- Vertical tension rods made of 0.016″ Spring Temper Brass Wire (from Clover House).
With half of the turnout of track 18 on the transfer bridge, I had to cheat and shorten the trusses while keeping the base and deck in the prototypical length so that cars could roll onto the curved ramp of the car float without touching the trusses.
One of the really neat things of the bridge is the split Wye turnout with half of its components on the bridge and the other half on the float. Having hand-built a few turnouts by now, it did not present any specific challenges. I still haven’t found an easy way to operate the turnout and I’m considering several options, including using a servo mounted under the layout.
To attach the trusses to the base plate I glued the outer most layer of the trusses to square basswood dowels 1/8″x1/8″ that carry the base plate. To paint the trusses I used a relatively dark oil-based wood stain. In all of the known photos, the transfer bridge kept its dark color over time – a result of the the creosote treatment that protects the wood from the effects of weathering. The results convinced me more than some of the tests I did using India ink for staining the wood. The finished bridge connects well to both the car float and the access tracks. By using rail joiners to tie the car float to the bridge I’m now able to navigate the locos onto the barge without using idler cars.