hitting bridges.

[Jammer]

Originally Posted by rubberducky

Would something like a FLIR M332 work?

Oh I imagine it would work quite well. For $8000 it should.



The question would be whether it's worth the money. Weatherproof surveillance cameras are a high-volume commodity product and they have become quite good. Reliable, weatherproof, low power, easy to set up, good image quality, and cheap. As in, $300 each, many from which to choose. Some of them even have IR capabilities.



I'm sure the FLIR one is better. I'd rather spend the money on sails.

[acem]

Going under the bridge sideways sounds like something I would do...

Your lucky on the Mississippi, we only get 52 ft on the Arkansas River.

Thx-Ace

[barnakiel]

But you can pin a proximity sensor on the mast and read the distance. Just like cars do when parking.


b.

[Jammer]

Originally Posted by barnakiel

But you can pin a proximity sensor on the mast and read the distance. Just like cars do when parking.


b.

I would actually like to do this, because it would allow me to make accurate surveys of the bridges in my area and note the clearance in my log under the specific gauge readings at the time of the reading.


I have not been able to find ultrasonic sensors that are up to the task. Range too short and precision to poor to be useful particularly when dealing with a target of uncertain area. If you want to know whether you missed by 11 inches or 13 inches it will tell you but I don't find that to be useful information. I want to know whether I missed by 28" or 30" so that I can decide what to do when the water is 24" higher next time, and they won't tell me that.

[CarlF]

The problem with the laser is it getting it perfectly level.

From target shooting it's known that one MOA (minute of angle) misses the target by 1" at 100 yards.

A MOA is 1/60th of a degree.

So if the masthead laser was off level by just two degrees (an unnoticeable angle on the deck of boat that could happen just by filling the water tank) then at 100 yards the bridge height would be off by ten feet. At 100ft it would still be off by more than two feet.

South of Beufort NC where there is tide, the easiest way to not hit a bridge is to not go under one within two hours of high tide.

[Jammer]

Originally Posted by CarlF

South of Beufort NC where there is tide, the easiest way to not hit a bridge is to not go under one within two hours of high tide.

Bully for you. Try sailing on a river where levels vary with weather and seasonally, and waiting for lower water may take weeks or even months.


And where the commercial traffic is never over 52' high so that the occasional taller sailboat is the only test to see whether the clearances are right. And where it's hard to be absolutely sure whether the light list has been updated with the clearance of the new bridge that is very similar to the old bridge. I've been out with string and a weight in one case to perform my own survey but even that is hard to get absolutely right.


For some of us this is a real problem. Having a camera or a laser or both as a final check on the data and the arithmetic is a prudent safety measure because the sources are unreliable and inconsistent, and the arithmetic far from straightforward. Don't sell it out as a pointless inquiry just because it isn't necessary where you sail.

[CaptTom]

Interesting concept. I love technical solutions to everyday problems.

Still, I'm skeptical. I know in the construction field there are plenty of self-leveling laser levels available. Here's one for $500. You can get them for less, but the stated range is usually something like 30-40 feet. This one claims 100'. Of course, it may be less in sunlight and when the target is a complex structure like a bridge. I'd guess a lot less. Then you have the problem of turning it on and off.

I've used these, and I just don't see them working very well on a pitching and rolling masthead.

Still, that's a starting point. Instead of a gimbal mount, think of the way a compass card floats inside a dome. Mount a spinning laser on that, or if there's such a thing as an "X" pattern laser, even better.

Or go a totally different route. Think of the rangefinder marks inside some binoculars. If you had an accurate range, and could measure the apparent distance between the water and the bridge, you could triangulate to get the height of the bridge. There's a lot of this sort of thing going on for self-driving cars.

Either way, to me it's more of a thought experiment than any practical answer. Certainly possible with today's technology, but not easy.

[rslifkin]

As a thought for high current bridges where it's close and you might need to bail out: go under it backwards. Engine in forward at low power, but not enough to fight the current. Steering will be awkward, but it's possible as the boat is still moving forward through the water. Then if you need to bail, just apply a fistful of additional throttle. That'll solve the issue of bailing out with reverse thrust, as you'll have rudder control to keep the boat from turning sideways during the bailout.

[Knotical]

I like the idea, it would be better than nothing and overtime the user can learn how to use it properly and improve upon the tech. Only thing is, if all boaters start using it can you imaging the number of laser beams on the bridge at a time? And considering a lot of airports are close to water (and thus bridges) it may not be seen favorably by the authorities.