Local knowledge, Duwamish 1st Ave bridge?

[twistedtree]

I see conflicting overhead clearance info for the Duwamish 1st Ave South bridge (in Seattle). Both the Raster and Vector NOAA charts list it as 39' at center span, yet the coast pilot lists it as 32'. For me that's the difference between fitting under and making a mess of my mast. And to further complicate matters, last time I went under it, the posted sign lists the clearance based off MLW or MLLW, which is unusual. Unfortunately I didn't pay enough attention, or take a picture at the time.


Anyone know what's accurate, or know why the reported clearances might be different? I have to go under it later today (PDT), and will have to wait for 3hrs while they are closed for rush hour if I can't get under it.

 

[Ken E.]

If you come up empty, call the Delta boatyard, which is close to there on the Duwamish. They build big boats and would know the heights.

 

[tiltrider1]

MLW and MLLW are big differences up here in Seattle. Current tide is going to make a big difference as well. All of this I am sure you are aware of. What I don’t know is if bridge maintenance is occurring affecting the height.

You can also reach out to Foss, Tote, or Crawley to see if they have any scheduled sailings that will open the bridge or any insight into true height.

I agree call Delta first.

 

[twistedtree]

Thanks! We are at Delta. They have been going by the charts which say 39', but noted that nearly every boat that comes in requires an opening, so they don't really pay much attention to it. He also said that because the bridges are staggered and cross at an angle, it can be tricky to stay center span.



I'm going to go with 39', and assume the Coast Pilot is out of date. There is no construction, and a couple month ago I came under it, but don't recall the exact tide at the time. That's also when I noticed that the posted sign quoted the clearance based off one of the low tide levels rather than MHW which is normal. My recollection is that I thought, Oh, I get now, but of course I've forgotten the details and always try to reconfirm something like this.


Anyway, the tide will be about 1.5' below MHW, and my air draft is 37.7', so I should clear just fine. And if I don't, my highest 2-3' are just antennas which should just slap around. Much lower and we will hit meat and bone.


Stay tuned.....

 

[twistedtree]

Made it. No drama.


The posted clearance is 48' above MLLW, or zero tide. The 39' clearance shown on the charts would suggest MHW is 9', But from what I can find, MHW is 10.5, not 9'. So now there are three contradicting clearances.

 

[South of Heaven]

Damn, that's frustrating that these WiFi based nav aids are still so slow to be updated. Too bad it's not Google based especially since you're in the Google's back yard.

 

[OldDan1943]

So you successfully clear the bridge going out on a low tide, what about when you want to come back in?

 

[Bradenvlp]

He was in the yard at Delta Marine.

 

[twistedtree]

So you successfully clear the bridge going out on a low tide, what about when you want to come back in?

We were at about 7.5' on a rising tide, with a high expected of 9.5' as I recall. My wife thought we had about 3' of clearance above the antennas, but I think there is typically more clearance than it appears in a situation like that. But she's usually really accurate with stuff like that.


Anyway, even at MHT, we would fit through.

 

[OldDan1943]

Twistedtree, when the tide comes in you have less height for your boat to clear the bridge.

 

[twistedtree]

Twistedtree, when the tide comes in you have less height for your boat to clear the bridge.

Yup, go it. But not getting the point you are making.

 

[OldDan1943]

Yup, go it. But not getting the point you are making.

So you may clear the bridge departing at low tide but, unable to clear the bridge at a high tide.