Bridge Clearance_How little is too little.... - Page 2 - SailNet Community
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post #11 of Old 04-25-2014
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Re: Bridge Clearance_How little is too little....

40m ultra maxi under a 9m bridge...


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Re: Bridge Clearance_How little is too little....

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Originally Posted by capecodda View Post
Ever notice that no matter how high a bridge is, when you look up just before passing under it seems like you're gonna hit

Seriously, I'd probably go but my first trip under would probably be at 1/2 tide or less.

Put a notch in a piling at your home marina before you go under, if you make it, keep pushing the notch a little higher

(are you talking about the new Sakonnet River bridge)
You are correct... The bridge I am talking about is the Sakonnet River bridge. It's not exactly new, but new enough that it's vertical clearance is not marked on the chart or the notice to mariners. I found online that it was designed and built with a minimum of 65' of clearance. I used to go under it with my old boat but as mentioned above it always looks wicked close and the new boat is slightly taller.

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post #13 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

I never trust chart marks. There is a bridge here in New Orleans that is marked at 62' but the center span is 60. Luckily a side span is actually higher (though not as wide). If you are this close I recommend scouting it first.

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post #14 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

Put a camera at the top pointed forward. As you get closer, you ought to be able to see the bottom of the bridge. If not, then stop.

The camera and home made boat-balls are on my list. I've bought a few 31 gallon plastic garbage cans. With external marine ply disk on the outside to reinforce the bottom, they ought to work. It's part curiousity and part wanting some ICW possibilities. Our air draft is 66' plus vhf antenna.

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post #15 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

My boat has an air draft of 60' to the top of the mast, 61-1/2' to the top of the expensive parts, and just over 63' to the tip of the VHF antenna.

Anything lower than the Verrazanno Narrows Bridge makes me nervous, but 65' and 64-1/2' bridges have been fine. When the VHF antenna tings on the low steel the bridge isn't high enough.

I've measured a number of masts and found them different heights than the owner thought. Surprise!

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post #16 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

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You are correct... The bridge I am talking about is the Sakonnet River bridge. It's not exactly new, but new enough that it's vertical clearance is not marked on the chart or the notice to mariners. I found online that it was designed and built with a minimum of 65' of clearance. I used to go under it with my old boat but as mentioned above it always looks wicked close and the new boat is slightly taller.
When we had a LH, we couldn't go under that one (77 ft)...except one time without a mast on the way to Bristol for a paint job (long story). The previous owner took the boat through the Annisquam (cape ann), under a bridge that was way too low. How do I know, the bread crumb trail on the chart plotter. Must of been an low, low tide

I remember there were high tension lines at Sakonnet, I don't know if they are still there. Just to add to the paranoia, I've always wondered when they specify a clearance how far from the power lines do they keep you to avoid arc over.

Even going down the cape cod canal, those high bridges look close on any boat.

Bridge-o-phobic, yep looks like we've got it this one. Don't know if there's a cure
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post #17 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

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Obviously when you hit... its to little. There was a newly constructed bridge just up river from where I keep my new boat (Mount Hope Bay which is on the MA/RI border). It has a bridge clearance of 65 feet at average high tide, I calculated the total height from the water height and got 61 feet which includes the wind instrument/antennas aloft.

What is your comfort level?
To answer your question, it would depend a lot on the tidal differences in the area. Also, silting and dredging can alter the actual water depth if a strong wind is blowing it in or out of river, as can rainfall. I'd be uncomfortable with 4" feet of clearance, but if I was positive of the figures, then I would do it consistently. If I had the tiniest bit uncertainty in the figures, then no way. Of course, the vhf antenna should work somewhat, bent over parallel to the water.

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post #18 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

Think of the VHF whip as a "feeler gauge."
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post #19 of Old 04-26-2014
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Re: Bridge Clearance_How little is too little....

Don't calculate, MEASURE! Otherwise, you don't know if you have the stock stick.

(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")

"Well, I just climb up to them."

by Joe Brown, English rock climber




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