Boo2
Well-Known Member
Why don't they do them like they do depths with a subscript character for the 10ths instead of a decimal point between the characters ?
Stoopid...
Boo2
Stoopid...
Boo2
Stupid bridge height indicators on charts
- Thread starter Boo2
- Start date
Lady Campanula
N/A
Can anyone suggest a reason for this quite deliberate 'disambiguation'....?
And can anyone suggest a reason for 'Boo2's outrage?
And can anyone suggest a reason for 'Boo2's outrage?
Boo2
Well-Known Member
No, I am sober.And can anyone suggest a reason for 'Boo2's outrage?
I just happened to be browsing the potential moorings I've applied for in Offshore Navigator and got sidetracked into exploring the Solent. It's surprisingly hard to tell the difference between say 4.2m and 42m for a bridge height and it makes a big difference to how good your day will turn out...
Boo2
penfold
Well-Known Member
No, I am sober.
I just happened to be browsing the potential moorings I've applied for in Offshore Navigator and got sidetracked into exploring the Solent. It's surprisingly hard to tell the difference between say 4.2m and 42m for a bridge height and it makes a big difference to how good your day will turn out...
Boo2
If you can't visually discern the difference between 4.2m and 42m before hitting the parapet it's time to relinquish the pilotage duties...
ffiill
Well-Known Member
An interesting one carrys the main road to Skye over Loch Long at Dornie next to Eilean Donan Castle.
Historically up to ww2 there was a ferry ;then until the 1970s when the road was rebuilt a low level swing bridge.
Loch Long is a nice sheltered sea Loch and would make a lovely winter mooring.
I intend to measure the low water clearance from the bridge as I suspect my mast may well just clear the bridge at low water so long as the chanel can clear my 4 foot draft.
As my mast is currently down I can accurately measure mast.
Thought about this some years ago but mast height was a guestimate.
Historically up to ww2 there was a ferry ;then until the 1970s when the road was rebuilt a low level swing bridge.
Loch Long is a nice sheltered sea Loch and would make a lovely winter mooring.
I intend to measure the low water clearance from the bridge as I suspect my mast may well just clear the bridge at low water so long as the chanel can clear my 4 foot draft.
As my mast is currently down I can accurately measure mast.
Thought about this some years ago but mast height was a guestimate.
electrosys
Well-Known Member
Should 'ave gone to Specsavers ...
CelebrityScandel
Well-Known Member
I don't know the formal answer for this but I suspect that it is done for clarity because depths are against the chart datum and heights (not only bridges, etc but rocks also) are against the chart's height datum.
So not as "Stoopid..." as you thought.
Boo2
Well-Known Member
That doesn't really change anything ? There's no way the the height figures for a bridge can be mistaken for anything else because of the "height figure for a bridge" symbol which contains them, the only issue is that it is extremely easy to miss the dot between the units and tenths figures. There's no reason not to have heights and depths to different datums represented in the same way, especially since heights other than bridge heights are (?almost?) never encountered with a decimal anyway...
I still think it is stupid.
Boo2
CelebrityScandel
Well-Known Member
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 suggest up around +5 dioptre spec's will do the job.
Boo2
Well-Known Member
You're a little short on explainations though CelebrityScandel, that's generally a sign of someone who doesn't really understand the point s/he's making.
You don't know anything about my eysight or my navigational experience, how come the ad-hominem ?
Boo2
CelebrityScandel
Well-Known Member
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.
So it would seem to me that you are being the "Stoopid" one and are insisting on continuing to displaying that is so rather than listening to those who have far more experience than yourself.
Woodlouse
Well-Known Member
Depths are measured off the lowest astronomical tide, heights are measured off the highest astronomical tide. A difference in the methods of showing the data can make things clearer when you have both a bridge hight and a channel depth in the same little bit of chart.
onesea
Well-Known Member
Can I suggest before posting you read the OP's and other subsequent posts?
It would then be possible for you to see that the difference between Drying heights and charted depths had already been pointed out. Making your post at best arrogant, patronizing, irrelevant and worse than that erroneous.
I think Boo2 has done an excellent job in highlighting that a small oversight could, as he rightly put it make "a big difference to how good your day will turn out...".
In doing this he has also shown his believe that there could be a change in the notation to make navigation easier, is that a bad thing?
Regarding "international chart symbols" as such an experienced navigator I am surprised you are not aware chart symbols can vary not insignificantly between charts of different nations and manufactures. With regard to clearance heights I do believe there is a near standard (but not identical) but in many other areas this is not the case.
May I suggest as reference "UK Chart 5011" and "US chart No 1".
Even within the publishers in the UK Admiralty and IMRAY cannot agree on the same colour scheme.
If there is a single “international chart symbols” please advise/ correct me I would be most interested.
It is natural we all make mistakes can I kindly suggest such blatant and patronizing comments and referring to people "Stoopid" is not required.
If nothing else it is that sort of attitude that gives sailing such a poor reputation.
CelebrityScandel
Well-Known Member
I will point out that I was not the first one to use the word "Stoopid" and that the original poster was dismissive, from a position of very poor knowledge, of the suggestion I gave as to why the difference in nomenclature in response to his original question.
You should also note that I did not miss seeing "that the difference between Drying heights and charted depths had already been pointed out" as if you read my post more carefully I was referring to rocks that uncover and those that do not and that they may be shown against the two different datums.
Perhaps it is you who should be reading the whole thread correctly before playing forum policeman. And perhaps the original poster should learn that it is dangerous to throw words such as "Stoopid" around in reference to a subject he plainly has little grasp of.
But others have seen the point of my original suggestion so I have no more to say on the matter.
Conachair
Guest
http://www.iho.int/srv1/
http://www.iho.int/iho_pubs/standard/S-4/S4_v4.2.0_Aug11.pdf
Have a look at the introduction of admiralty chart 5011 - "... based on the "chart specifications of the IHO.." The right hand collumn shows the number of the IHO spec for each symbol.
You may indeed.. from their website
http://www.nauticalcharts.noaa.gov/mcd/chartno1.htm
So they seem to not entirely adopt the intenational standards (nothing new there) but include them in their equivalent of 5011.
Always new stuff to learn in sailing, isn't there.
Conachair
Guest
Mr Google can't find any specific reverences but that does seem plausable. Though chart datum/height datum doesn't necessarily have to be LAT/HAT.
Interestingly, if you look at 5011 IK 11 it shows a symbol for a rock drying as decimal and not subscript, which seems to be an exception.
These chart guys have been doing their stuff for hundreds of years, there's probably a very good historical reason for the difference in writing the heights.
CelebrityScandel
Well-Known Member
That is, just as I set out as the example in my earlier post #11, because rocks that do not cover are against the height datum of the chart, just as bridges are. Rocks that do cover are against the chart datum.
So it is not an exception it is just following what I at the start suggested was the rule - things which are against the chart datum use subscripts and those that are against the height datum use decimal points.
Boo2
Well-Known Member
Why ? There is no ambiguity about the height reference for bridges as they are contained within a bridge height symbol.
I don't really agree with other posters either that the presence of depth or rock heights nearby a bridge height symbol leads to ambiguity because the bridge height symbol encloses the bridge height data. It seems to me to be far easier to discern the dropped tenths character than to see the decimal point and bridge heights would also appear to be equally as important as non-covering rock heights.
Your experience does not sufficient to present a reasoned argument about it, and some might consider that to define stupid.
Boo2
Conachair
Guest
Check 5011. It is for rocks which covers and uncovers height above chart datum, symbols on the right are in decimal.
Robin
Well-Known Member
Use electronic (vector) charts and set the units to read 'feet' that way the decimals are pretty insignificant.
