Tuesday, April 7, 2015

Final SR 520 pontoons floating through Seattle this Thursday

By Nicholas Mirra

This week marks the last chance to witness a tugboat pushing an enormous concrete pontoon through Seattle's Lake Washington Ship Canal en route to Lake Washington. Pontoon construction for the new SR 520 floating bridge is complete, and the final three pontoons – numbers 75, 76 and 77 – will slip through the city's boat channel on Thursday, April 9.

A tugboat pulls one of the final three pontoons for the new SR 520 floating bridge out of WSDOT's Aberdeen casting basin on March 10. The trio of pontoons are scheduled to complete their ocean voyage to Seattle on Thursday, April 9.

The first of the new bridge's pontoons arrived in Seattle back on Aug. 11, 2012. Since then, small packs of pontoons (Anyone know what a group of pontoons is called? We hope it's something cool, like a Council or a Ziggurat.) have been towed through the locks as our construction sites in Tacoma and Aberdeen turned them out. The final three pontoons are longitudinal pontoons, the largest type of pontoon used in the new floating bridge. At 360 feet long, 28 feet tall and 11,000 tons, they make for a tight squeeze through the Hiram M. Chittenden Locks in Ballard.

It takes about three days for these pontoons to complete the 260-nautical-mile, open-sea voyage from Aberdeen, around Cape Flattery, and through the Puget Sound to Seattle. On Thursday they will be brought one at a time through the locks, the trailing two waiting their turn in Shilshole Bay like kids queuing at the top of a water slide.

A pontoon coming through the Hiram M. Chittenden Locks on May 4, 2014.

This means that if you're in Seattle on Thursday, you'll have three chances to see the pontoons float through the locks, past Gas Works Park and the Arboretum, on their way to Lake Washington. Bring a camera because we are holding a photo contest for great pontoon photos. See the full contest rules here (pdf 317 kb). Submit your photos via Twitter with the #520pontoon hashtag. The deadline is noon Monday, April 13. Send us a great shot and you could win a guided tour of the new floating bridge construction site for you and a friend!

The SR 520 website's pontoon-tracking page will provide more information, as available, on the precise time the pontoons are expected to arrive at the locks in Ballard. The webpage also has links that show the exact location of the three pontoon-towing tugboats – the Western Ranger, Arthur Brusco and Nancy M – as they navigate to Seattle. A map of suggested viewing locations (pdf 2.5 mb) in Seattle for taking photos is on the webpage too.

With pontoon construction complete, what comes next for the new floating bridge? These final three longitudinal pontoons will be joined to the 15 already at the construction site. Later this year, all the pontoons will be joined together. Construction is on track to open the new floating bridge in 2016.

Pontoon tidbits
Pontoon construction broke ground in Aberdeen in February 2011 and in Tacoma in January 2012.

Pontoons were towed to Lake Washington one at a time for assembly on the lake, sort of like that third-floor apartment you furnished by carrying Ikea furniture up the stairs in boxes, knowing once the furniture is assembled it won't fit back down the stairs.

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