Laser range finder for measuring bridge height

[sv_pelagia]

Originally Posted by Kelkara

23m is very low for BC, we have the advantage of being able to anchor power lines halfway up mountainsides to get a bit of extra height, so 40m or 50m is more normal, which few recreational boats have to worry about. And I bet that 23m wasn't crossing a passage, but just across the entrance to an anchorage (Kakushdish Hbr? That one sure looked low even above my little mast) with alternative anchorages nearby.

Kakushdish Hbr it was indeed... those wires sure seemed to be drooping lower. Lovely anchorage once inside.

Yes, we do sail in a different place... happily [emoji6].
Attachment 279897

[Jammer]

Originally Posted by GinoDelG

Hi,
Is anyone using a laser range finder for measuring bridge height. If so, which model and how accurate is it?

I've thought about it but have never followed through.


I have an inexpensive backup camera that I bought on Amazon. I'm in the process of making a board I can use to hoist it to just above the top of the mast with a halyard -- essentially a pigstick with the added feature of having a means to keep the camera oriented forward.


The camera came with a 60' cable and monitor. I believe it will be good enough to check clearance on some of the bridges where clearance is very close.


The laser rangefinders are reportedly accurate to the foot.

[Andrew Lippman]

My friend used a laser rangefinder in Texas several years ago. Then he called the port authority and they thanked him for the accurate measurement, which they lacked. You have to be careful to get the bottom of the support beams rather than the underside of the roadbed.

[lornolsen]

You can NOT measure height with a laser range finder in the daytime. Just try measuring your mast. I have. It just doesn't work.

[Andrew Lippman]

Worked for my friend under a bridge. I guess it's a clearer or shadier target. Your mileage may vary...

[GinoDelG]

Users have reported that on the ICW bridge height on the cards isn’t always accurate.

[Andrew Lippman]

Hence my friend doing it himself...

[Nicholson58]

Originally Posted by sv_pelagia

No. USUALLY Just the bridge height on chart (at least, out west in BC).

Bridge cards should be found as noted. Also, did you look at your charts? The clearance is shown. You can also find bridge data on line.

We always check our routes and verify clearance before starting out. At 80 feet it’s especially necessary. It’s tough to get several days along and find a low one.

[Mauseye]

Leica is the best

[Andrew Lippman]

I've always marveled at how much data is on our marine charts. How and when did they manage to gather such dense depth information and rock locations? How accurate is it? I think bridge heights are obtained from the engineering spec when available for taller bridges. I suspect it is not as well tested as the depth soundings. A measurement can't hurt, and authorities can appreciate updated reporting.

[sv_pelagia]

Originally Posted by Nicholson58

Bridge cards should be found as noted. Also, did you look at your charts? The clearance is shown. You can also find bridge data on line.

We always check our routes and verify clearance before starting out. At 80 feet it’s especially necessary. It’s tough to get several days along and find a low one.

Did you not read the post? It seems you did not and are assuming my post was about USA. It was not... I was referring to Canada.

1. NO, "bridge cards" are not common here in British Columbia. And it's not only bridges, it's also an issue with power lines overhead.

2. Of course I looked at chart (as I noted in post)

"online" not always available here in BC and certainly bridge or powerline info not easily found.

[noelex 77]

Originally Posted by lornolsen

You can NOT measure height with a laser range finder in the daytime. Just try measuring your mast. I have. It just doesn't work.

There are much more accurate ways of measuring mast height, but one advantage of laser rangefinders is you can pinpoint a precise target so measuring mast height should be possible.

Most units have a minimum measuring distance. This is usually around 10m for the better units, but can be greater for the inexpensive units. If you are not able to measure the mast height it is probably because the distance is less than this minimum.

I just tried ours. It worked fine for measuring our mast height.

[Morris Wilson]

Kelkara did the right thing at the Cambie street bridge. There are a lot of scrape marks under that bridge. Approach very cautiously fotunately the currewnt there isn't usually too much.

[Morris Wilson]

Thanx Chotu. I would like to repost your picture of the bridge card to the Canadian Coast Guard (who I've found very helpful and approachable) with the suggestion. Some times you see a bridge height in Canada but I've never personally seen a bridge card. Awesome idea

[larrymac]

It takes a little planning, but I have a video camera mounted at the mast head. Aiming is not critical, just approximate straight ahead. Most bridges have multiple ‘rails’ supporting the deck. If you can see only the rail nearest you, you are not going to clear. If you can see the rail farthest from you, you will clear at the mast head - then it’s to your judgement as to if the antenna will clear!
Some chart plotters will allow you to display camera inputs. I have found it very helpful. You can tell from quite far out if you need seek a different route or time!