Monday, December 7, 2015

Verifying Bridge Heights

We tried something new on this year's trip south. Due to significant rainfall this year in the Carolinas, the water at many bridges along the ICW was higher than normal. We avoided most of the high water by waiting until the end of October to head south. But there were still a couple of surprises. The first was at the Atlantic Beach Bridge at Morehead City. The air draft boards read 62ft and we were at high tide. Dave on Fifth Quarter was traveling along with us so we both anchored off the side of the channel to wait for the water to recede.

GoPole with Camera
I eventually got bored and decided to experiment with an idea that I had a while back. I taped my GoPro + GoPole to the top of our boat hook, tied it onto the spin halyard, enabled WiFi to my iPad, and sent it aloft to look at the bridge. The boat hook is one of those three extension models and is about 12 ft long when fully extended. I used two clove hitches in the spin halyard, one at the bottom handle and another at the middle of the boathook. With the GoPole, that gave me about 7ft of extension above the spinnaker halyard block, which is 6ft below the masthead instruments. The first time it went up the camera was facing the wrong direction. I noted the amount that it needed to turn, bought it down, corrected it, and raised it again. It sat about 2 inches above the wind instruments, which I could see in the bottom of the camera's view.

I knew that we were clear as long as I could see the underside of each support beam. If we came to a beam where I couldn't see the bottom, then the camera wouldn't clear it. The bridge beams are wide, so it is easy to check. We go very, very slow. Inches per second. Good boat handling skills are required to stay centered under the bridge and go slowly enough to back out if we're not going to clear. If there is much current running with us, this can be a real challenge. We also wait until any vessel wakes have subsided and make sure that there is no one coming up behind us. It helps to have one person looking at the camera display and one person driving.

With WiFi control, I was able to record the approach. To keep it interesting, I increased the video speed at the beginning and end. The transit of the spans is at actual speed, so that gives you an idea of the boat speed. The GoPro has a fish-eye lens, which creates some interesting visual effects on objects that are far away, like the initial view of the span where it looks like it dips in the middle. Only when we were within a couple of feet of the bridge could we clearly see the bottom of the supports. It looks like the camera cleared the supports by an inch or two. There is no audio for the first minute that is run in fast forward. Audio is included in the real-time video section. The vibration is the movement of the camera back and forth, because I didn't have a good way to keep it stabilized in the wind.

Link: Atlantic Beach Bridge 640x360.