Wednesday, February 24, 2010

Destination: Hood Canal Floating Bridge

If you arrived here by searching for a chart, please see this page.

The Hood Canal floating bridge is an amazing piece of engineering. It is a huge concrete structure carrying Washington State Route 104 across the Hood Canal, connecting the Olympic and Kitsap peninsulas. Those 7,869 feet in the span save more than 100 miles of driving around the entire Hood Canal (which is not actually a canal, but a long, narrow natural waterway).

The bridge is floating because the water depth is too great for pilings to be a usable support solution. Although it looks like it is two layers, it is not. What you are seeing is the roadway carried on pillars above the concrete pontoons. The ends of the floating span connect to fixed structures, but the span itself rises and falls with the tides - more than 16 feet. Tricky anchoring. Tricky engineering.

The center 600 feet of the bridge can be opened for marine traffic by withdrawing sections into wide spots in the non-moving portions. And marine traffic there is - the Bangor Naval base is located on the Hood Canal, below the bridge.

In a 1979 winter storm with sustained winds of 85 mph and gusts to 120 mph (hurricane, anyone?), the western drawspan and the pontoons of the western half broke loose and sank. It is thought that blown-open hatches allowed flooding of the pontoons, causing the sinking.

In 2005, we transited the bridge aboard Eolian. Opening the span requires at least an hour's notice (contact the bridge on VHF channel 13). When you are arriving at the bridge for your scheduled opening, you should hail the bridge again to let them know.

The actual opening of the span is quite an involved affair. This is a big machine! The operation takes 30 minutes or so and involves a lot of driving here and there by the bridge operators on top of the pontoons (below the road surface). Eventually, one of the draw spans begins to move, and a gap slowly opens, and you are signaled to pass.

Because this is no small deal, and because the opening and re-closing of the bridge causes such long delays for the automotive traffic on the bridge, the bridge operators attempt to "bunch" up the marine traffic. When we transited in 2005, we shared an opening with a US Naval warship. We let them go first.

In this last picture, we have cleared the bridge and are looking back at it. To help give some scale, if you look closely, you can see one of the bridge tenders' pickup trucks parked on the pontoon.

It's an interesting place. After all, where else are you likely to see a submarine on your way to work?

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