Stupid bridge height indicators on charts

[VicS]

A quick glance at US Chart No 1 suggest the same notation is used as on UK Admiralty charts

Metres and decimetres, with the decimetres as a subscript, for depths and drying heights above chart datum

Metres and decimal for heights of features that do not cover and bridge clearances ( topography that's the word!)

Gob-smacked though to discover than US charts are metric!


Now wondering why depths and drying heights are given in metres and (subscripted) decimeters while heights of non covering features are given in decimal metres ???
Hang-over from the days when depths were in fathoms and subscripted feet perhaps ????

 

[CelebrityScandel]

Now wondering why depths and drying heights are given in metres and (subscripted) decimeters while heights of non covering features are given in decimal metres ???
Hang-over from the days when depths were in fathoms and subscripted feet perhaps ????

Hi VicS, as I have said I do not have access to UKHO charts to check on them at the moment for myself but along the lines I have set out I suspect the non covering features on the chart are against the Height Datum, not against the Chart Datum. Whereas the depths and drying heights (drying heights inferring that they cover) are against the Chart Datum. So subscripts for those against the Chart datum and pointed decimals for those against the Height Datum.

I would welcome your feedback as to if that is what seems so on the UKHO charts.

 

[CelebrityScandel]

Quote from Celebrity Scandal post #14
"But others have seen the point of my original suggestion so I have no more to say on the matter."
Do you wish to retract that statement?????

No I don't. The entry of a sensible and open minded poster with very interesting observations has encouraged me to persevere.

 

[Elessar]

You are still missing the point.

Maybe.

To me it seemed your point was to belittle someone.

As you begin to gain some experience as a navigator you will come to learn the merits of there being a difference.

In the meantime do as others have suggested and get some glasses for close up work - if your eyesight is as poor as your navigation experience then I up around +5 dioptre spec's will do the job.

then to try and demonstrate your superior knowledge

Let me help you out with one very simple example which I would have expected any navigator would realise or have taken what from I said as a lead to follow up for themselves.

For rocks that cover and uncover the depth can be given in brackets and with a subscript for the decimal. For rocks that do not cover the height is given in brackets and as a decimal for the fraction; the difference avoiding confusion.

One is against the chart datum and the other is against the height datum (I trust that you know the difference). Have a look at the international chart symbols and you will see what I mean. No one is going to make an exception for bridges.

Unfortunately, whilst trying to show off even in this "simple" example you are wrong - rocks which cover and uncover have a drying height, not a depth.
Rocks which don't ever cover are land features.

You then go on to demonstrate a lack of understanding of the height datum in the erroneous statement

heights (not only bridges, etc but rocks also) are against the chart's height datum.

because bridges and land feature have different datum points.

But also in your attempt to belittle Boo2 your logic is completely flawed.
You said the merit of the decimal for heights is that it is easy to distinguish them from depths.

Why is this flawed?

Because many heights and depths are integer only. So I hope you don't rely on this little "fact" of yours.
But also you state that rocks which cover and uncover have a depth not a height.

In reality you need to see and understand all the depths and drying heights where you are sailing, and clearance heights. Other heights are usually just a nice to know.

BTW of course I understand that boats travel internationally, I have sailed in the waters of 14 countries this year. But that is beside the point.
And yes there are dredged depths as decimals on the Itchen chart as discussed in my post above. I think this is different to a depth because it is not claimed to be current, but I don't know and don't claim to.

So in summary:

Boos 2 made a point about decimals in clearance heights. It was an opinion, and and VicS has demonstrated he has a point. Either way it was just an opinion.

You then claimed he was stupid and myopic. And in the process demonstrated that you are not only bloody rude but have worrying gaps in your knowledge.

And that sort if irritated me if that didn't show.

 

[VicS]

Hi VicS, as I have said I do not have access to UKHO charts to check on them at the moment for myself but along the lines I have set out I suspect the non covering features on the chart are against the Height Datum, not against the Chart Datum. Whereas the depths and drying heights (drying heights inferring that they cover) are against the Chart Datum. So subscripts for those against the Chart datum and pointed decimals for those against the Height Datum.

I would welcome your feedback as to if that is what seems so on the UKHO charts.

Yes I think that is so but I don't have the latest edition of Admiralty chart 5011, the equivalent of US chart no1 .
The edition I have and the charts I copied the extracts from earlier seem to follow the same rules as US Chart no1. Not been through either with a fine toothed comb though.

The whole argument that Boo started is rather lost on me. You read a chart, you read it carefully and if you understand the nomenclature you know what its all about.

You should try reading some of the old black and white fathoms charts in the dim light above a chart table .... much much finer detail and thick with soundings.
We had some old French ones ... they were even more difficult to read than the UK ones!

 

[Elessar]

A quick glance at US Chart No 1 suggest the same notation is used as on UK Admiralty charts

Metres and decimetres, with the decimetres as a subscript, for depths and drying heights above chart datum

Metres and decimal for heights of features that do not cover and bridge clearances ( topography that's the word!)

Gob-smacked though to discover than US charts are metric!


Now wondering why depths and drying heights are given in metres and (subscripted) decimeters while heights of non covering features are given in decimal metres ???
Hang-over from the days when depths were in fathoms and subscripted feet perhaps ????

Could be. Even more odd is the decimal for dredged depth. What were heights in fathom days - yards or feet?

 

[Seajet]

At the first International Festival Of The Sea, I was lucky enough to row an old gig past & chat with a crew-member of a replica 18th century Frigate; he was a bit displeased they had lost a few feet of main topmast, courtesy of a bridge on the way up to Bristol.

I don't know the skipper, but I'm sure he's a better navigator than I'll ever be; we all c**k it up sometimes, it's the ones in public that hurt !

 

[VicS]

Could be. Even more odd is the decimal for dredged depth. What were heights in fathom days - yards or feet?

Feet!

 

[CelebrityScandel]

And that sort if irritated me if that didn't show.

It did show. And you have let it get in the way (and are still doing so) of correctly interpreting what I have suggested about depths/heights/whatever in response to the original question and how their presentation either as a pointed decimal or a subscripted one depends on whether the depth/height/whatever is against the Chart Datum or the Height Datum (appears to, I did say at the outset that I do not know the formal reason and I have to say I don't go around checking all the charts of the world as to whether they all handle them the same way as I have never had a problem with pointed decimals being used).

Just chill out. I am as interested as anyone as to whether my suggestion stacks up or not else I would not be wasting time here with all the angry ones around. But so far very few have had any go at checking and only VicS coming up with interesting comprehensive information. If you can make some knowledgable and reasoned observations along similar lines then I am all ears but you seem too angry to do so.

 

[Abestea]

Just a thought that came to me as i read through this. Since depths have subscripts, why don't heights then have superscripts? It would eliminate the small decimal point which may be lost, but if you instantly look at a figure and saw it has either a subscript or superscript then you would know exactly what it means.

I suppose the only drawback is that someone may misread it whereas the decimal point makes it blatantly obvious that it is a height compared to the subscript for depth.

 

[CelebrityScandel]

Yes I think that is so but I don't have the latest edition of Admiralty chart 5011, the equivalent of US chart no1 .
The edition I have and the charts I copied the extracts from earlier seem to follow the same rules as US Chart no1. Not been through either with a fine toothed comb though...

...You read a chart, you read it carefully and if you understand the nomenclature you know what its all about.

You should try reading some of the old black and white fathoms charts in the dim light above a chart table .... much much finer detail and thick with soundings.
We had some old French ones ... they were even more difficult to read than the UK ones!

Thanks for checking.

We always have both paper and electronic copies of the Symbols, Abbreviations, etc requirements at the nav station and they do get used as one cannot remember everything.

Regarding the old charts I too have been around long enough (have broken the 6 decades - whoops, shouldn't mention that as I can see the "crotchety old man" claims coming from some already )

But I have been known to miss things on modern charts too, very, very rarely though.

 

[Seajet]

Hazards on charts

Perhaps the suggestion we're coming to here is that, as Professional sea-goers sadly dwindle in numbers, charts - paper or electronic - should be more user friendly ?

I'm not saying for an instant that people should be less trained, quite the opposite; but take another example going the other way, the submarine barrier between Southsea and Horse Sand Fort in the Solent, appallingly marked on charts ( or to eyesight even in daylight ) and the claimer of many victims...

Saying "you should have been trained to pro' standards" is no excuse for not having big red lines and clear figures - clear to the uninitiated - on charts, and in these days a hazard proximity warning alarm.

 

[VicS]

Just a thought that came to me as i read through this

No thinking allowed ... to dangerous!

Perhaps because

32 is a drying height of 3.2m​

32 is a depth of 3.2m​

3.2 is a height of a feature above the height datum of 3.2m​

3² is 3 squared!​

noticed by the way that soundings and drying heights are (normally) italicised

Anyway enough for tonight. Take 5011 to bed... we will have a test tomorrow!

 

[Seajet]

VicS,

you and I both know this, but a death or damage sentence is harsh these days for a novice on their first trips ?!

I'm sure things could be made clearer.

 

[caiman]

Any chance of the uk government(no capital letters intended)giving out a free,online,electronic version of 'syms&abbs' like wot our American bretheren get from theirs?
Yeah ,right.
Have a look at the survey date on your most commonly used chart.
1800's surveys at (soon to be) 2012 prices.=Rip Off.And we are mug enough to pay!!
The UK chart symbol for a 'Flying Pig' is?
Cheers

 

[Conachair]

I believe we are on the same wavelength Conachair.

....

So the rule I suggested is that if the object (rock, bridge, etc) is against the chart's height datum then the decimal part is shown as a decimal. If the object is against the chart datum then the decimal part is shown as a subscript.

Not the same wave length at all. My point was that in 5011 ed2 there is an example showing covering/uncovering rocks measured from chart datum shown as a decimal, not subscript. IK 11. Digging deeper into the small print this is no longer used but there will be admiralty charts out there with this style of decimal unit.

So you are wrong, there are exceptions.

Who gives a sh!t, you tick too many of the troll boxes to be taken seriously.

 

[VicS]

Not the same wave length at all. My point was that in 5011 ed2 there is an example showing covering/uncovering rocks measured from chart datum shown as a decimal, not subscript. IK 11. Digging deeper into the small print this is no longer used but there will be admiralty charts out there with this style of decimal unit.

So you are wrong, there are exceptions.

Who gives a sh!t, you tick too many of the troll boxes to be taken seriously.

As you say there is, but obsolescent. Also note printed as Dries 1.6m or Dr 1.6m not just as a numerical value so quite unambiguous.

.

 

[Conachair]

As you say there is, but obsolescent. Also note printed as Dries 1.6m or Dr 1.6m not just as a numerical value so quite unambiguous.

.

Absolutely.

But sometimes when someone comes in with the "I know it all" it can get just a bit to tempting to point out that they don't.

In broader terms with navigation I find it best to treat every last piece of info with a fair degree of caution. Even Mk1 eyeball is not to be trusted.

 

[onesea]

Absolutely.

But sometimes when someone comes in with the "I know it all" it can get just a bit to tempting to point out that they don't.

In broader terms with navigation I find it best to treat every last piece of info with a fair degree of caution. Even Mk1 eyeball is not to be trusted.

+1 You can do all the homework you want but there is still plenty of space for things to go wrong, its part of the fun of playing boats...

Certainly looking at this and certain other threads there are people who I would think, you are not the crew/ skipper for me

 

[Elessar]

noticed by the way that soundings and drying heights are (normally) italicised

this is one of the differences between US and UK charts.

In the US
upright = feet or old/unreliable metric data
italicised = metric or old/unreliable feet data

In the UK the upright just means old/unreliable.

since you can get italicised data on early 1900s lead line source data, gawd knows what the definition of old is.