Thursday, July 30, 2009

Hood Canal Floating Bridge - 25,000 Visits

Port Townsend, today. While I realize this is promoted as a “railroad” blog, a major engineering project has just been completed in our area that I wanted to share with you.

Appointments have sent me twice from the Quimper Peninsula to the Kitsap Peninsula traveling over the new Hood Canal Floating Bridge.(Both Peninsulas are part of the greater Olympic Peninsula.) It remains the longest floating span over salt water in the world. The original Hood Canal Floating Bridge first opened to the public in August 1961. It was destroyed by an unusually strong micro storm low-pressure centre packing winds exceeding 120 miles per hour with 85 miles per hour sustained, that traversed Hood Canal from south to north in February 1979.

The “second” bridge was “reopened” in October 1982. Much of “floating bridge” technology has been learned the hard way with some tough lessons. The Hood Canal Bridge was not the only floating bridge to sink. The original Lake Washington Floating Bridge in Seattle, the first of this type, opened for traffic in July 1940, and sank in a storm in November 1990, which was broadcast on live TV!

For years, the only way to access the Olympic Peninsula from Seattle-Tacoma was a tedious, dangerous, and time-consuming journey of 120 miles around the end of Hood Canal through Shelton.

Two-lane US Highway 101 clings to the edge of the Canal with 50 miles of permanent slow orders, some down to 20 mph around torturous curves. And woe is the wary traveler unfortunate enough to end up behind a motor home! Passing lanes are rare, and narrow 1930’s bridges guarantee puckering when passing an approaching loaded log truck!

In 1936, ferry service ran from Port Gamble to Shine, eliminating the wearisome drive around the end of Hood Canal. The Port Gamble terminal was moved to Lofall in 1949, shortening the cross Canal run to a mere 10:00 minutes between South Point and Lofall. I remember as kids riding on the M/V Rhododendron, my sister and I were admonished not to go to the bathroom; it would take longer than the ferry ride!

Eventually the ferry became a choke point as development in Port Townsend, Sequim, and Port Angeles on the Kitsap, Quimper, and Olympic Peninsulas grew, with demands for a bridge across the Hood Canal.

A site for a bridge was located just north of the ferry route. Underwater topography dictated a daring bridge design, based on pontoons rather than piers. Not only was the new structure to be exposed to the winds and weather of Puget Sound country, it also had to be flexible enough to endure a tidal range of up to 16.5 feet!

And so, in August of 1961, the worlds longest floating structure spanning 7,869 feet over salt water, the Hood Canal Floating Bridge was opened, replacing the ferry run.

Being a “navigable waterway,” the bridge had to open and close for vessels, many being nuclear submarines based at Bangor Washington. Despite the fact the channel approaches 600 feet deep, subs cannot simply dive and go under the bridge due to the spider web of 3” thick steel cables anchoring the pontoons in place to massive blocks of concrete.

For smaller vessels, the west end span over water down to the bridge deck has 31.3 feet vertical clearance to the water at Mean High Higher Water (MHHW) of 7.0 feet, while the east end provides 50.7 feet of clearance.

USS Ohio in Transit Hood Canal Bridge

The “original” and rebuilt versions of the bridge had a harp shaped section (top of photo) near the east end, that permitted one of the floating sections to be pulled into harp, thus creating a navigation channel. Video is hard to find, but this clip will give you an idea as to how the old system worked.

A few weeks ago, I had to head “into the city” and was pleasantly surprised to see the new structure with less imposing access structures onto the bridge and a wider highway deck with no “bulge” or “harp” section which used to require a slow zone. It wasn’t until after my second time over the bridge that I got to wondering “how does this thing open?”

Forget Google, I spent hours looking for some explanation as to how this new structure opens. Following my time honored system of tracking down information, I emailed the Washington State Department of Transportation, and a fellow by the name Joe Irwin was kind enough to respond, with photos, and an explanation, as to how the new bridge opens for the nukes!

Hello Robert,
I've attached a PDF that shows how the draw span pontoons extend and retract into the u-shape draw span assembly.

What it doesn't show is the lift spans, of which I've attached photos.

The lift spans are basically large steel roadway sections that are raised and lowered by powerful hydraulic cylinders. There are three spans on the east half and three on the west, and each are powered independently by four cylinders.

When the steel lift spans are lowered, they serve as the roadway decking and the extended draw span pontoons close the center channel to marine traffic and create a connecting roadway across the canal.

When the lift spans are raised, the draw span pontoons can be retracted beneath them, opening the center channel to marine vessels.

Draw Span Leaves Under Construction

Six leaves, three on the east side of the navigation opening, and three on the east side, are constructed in such a way that hydraulic rams lift, pick and slide the "leaves" or bridge sections, just lift so the pontoon sections can retract underneath. The reason there are three spans on each side that lift independently is because they weigh about 100 tons each - quite a load for the hydraulic cylinders as you might imagine.

A really great - albeit simplified - way to envision how the whole thing works is to put your hands in front of you, palms down and touch your index fingers together. Your left hand represents the lift span sections, your right, the draw span pontoon. Right now, your "bridge" is in the closed position - which is somewhat confusing because it is open to motor vehicles.

To open it for a submarine or large sailing vessel, lift your left hand slightly and slide your right hand directly beneath it. The channel, which starts at your right wrist, is now open for boating. This occurs on both the east and west sides, on a much grander scale of course, to provide a 600-foot channel.


I hope this helps,
Joe Irwin
WSDOT Communications
Hood Canal Bridge Project
www.hoodcanalbridge.blogspot.com

For those of you who have an interest in “bridge cams” this camera is operated by “Wiz-dot,” the Washington State Department of Transportation. It is located near the east end of the span, looking west. In the foreground, you can make out the west end sliding decks –gratings - that make up part of the lift and slide mechanism.

For all the flack WSDOT – Wiz Dot – takes for it’s fumbling mismanagement of the Ferry System, it “done good” on the Hood Canal Bridge. It is a handsome structure. There are only four floating bridges in the US. Beside this bridge, three others are on Lake Washington in Seattle.

A fifth floating bridge, located in British Columbia, crosses beautiful Lake Okanogan at Kelowna. The last time I was in Kelowna, the family was returning to Prince Rupert from Seattle, in July 1958. The ferry was still running!

See also: Terror on a Bridge

We recently passed a notable landmark for this blog. My Sitemeter recorded the 25,000th visitor! While many of these “hits” are known as “pass-throughs,” people searching for the combination of “oil” and “electric” (looking for furnaces and other mechanical devices,) further reports available to me show that most are rail fans sent here largely through “Google” searches for specific items.

However you arrived here, I am pleased you found us. I generally stay on topic, but certain issues I just cannot avoid commenting on!

Take a moment to scan down the “Index” in the right hand column. You may just find something out of the nearly 400 articles posted here that might tickle your interest!

2 Comments - Click here:

Bill ~ {The Old Fart} said...

Fascinating post Robert, besides trains I also like to look at bridges. Floating Bridges, I heard of them before, but never could find much on them in books or the internet.

I am just wondering why a Suspension Bridge wasn't tried here. The Span is long but other places use the Suspension Bridge type with just as long a gap.

Oh, I made a post for Dad on the blog, It was just a copy and paste from the main blog, but thought I should post it on the Train Blog as well.

Oil-Electric said...

Well for openers, the bottom at the Hood Canal site – like most of the poorly flushed Hood Canal, has deep deposits of silt. Some site reports I have read indicate that at that site, the narrowest crossing, there was up to 300 feet of mud and silt before reaching bedrock.

Floating bridge design is estimated to be between 3 to 5 times less expensive than a suspension bridge.

One estimate penciled out demonstrated that a structure like the Tacoma Narrows Bridge would have to extend 810 feet high from bedrock - 500+ feet beneath the surface.

That is taller than the Columbia Tower in Seattle. Total cost would be about $4 billion –eight times the cost of the Hood Canal Bridge.

·No expensive caissons need to be built for tower structures
·No expensive towers
·No expensive anchorages for a
·Very expensive suspension system.

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