Lizzie_B
Well-Known Member
Re: ah, right
I gave the right answer!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I gave the right answer!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Tidal Height Calcs
- Thread starter cod
- Start date
snowleopard
Well-Known Member
In that case, the answer is 3.3m.
Now a question for you - list the ways of working that out.
Now a question for you - list the ways of working that out.
cod
Active Member
That is the answer I got, we must be singing from the same hymn sheet. One point is that the barometric pressure effects all the heights involved equally so no allowance needs to be made for it to do this calculation. It is just a standard secondary port calculation.
However I did slip a second question in half way through the thread. What is the actual height of tide at 0300BST?
Any offers?
MINESAPINT.
However I did slip a second question in half way through the thread. What is the actual height of tide at 0300BST?
Any offers?
MINESAPINT.
snowleopard
Well-Known Member
The height was 1.5m with low water of 0.9, i.e. 0.6 left to fall.
You are wrong about the effect of barometric pressure - it does affect the tidal height by 1 cm for every 1MB. In the calculation it can be ignored for the following reasons: If the pressure rises above 1035 the conditions will be calm as you'll be in a massive high. If it falls presaging deterioration in the weather you'll get more water.
If you want to be precise, 1035 is 20mb above the mean so the water level will be 0.2m less than predicted.
You are wrong about the effect of barometric pressure - it does affect the tidal height by 1 cm for every 1MB. In the calculation it can be ignored for the following reasons: If the pressure rises above 1035 the conditions will be calm as you'll be in a massive high. If it falls presaging deterioration in the weather you'll get more water.
If you want to be precise, 1035 is 20mb above the mean so the water level will be 0.2m less than predicted.
Talbot
Well-Known Member
[ QUOTE ]
You are wrong about the effect of barometric pressure - it does affect the tidal height by 1 cm for every 1MB.
[/ QUOTE ]
I have never and would not use a barometric input on tidal height when forecasting ahead like this, cause there could be a massive change of pressure, or no change at all
My philosophy is that if low water is above 1m, I can park anywhere outside the green bit on the chart without worrying /forums/images/graemlins/laugh.gif
If I get it wrong, out comes the scrubbing brush to give the A/F a quick assist!
You are wrong about the effect of barometric pressure - it does affect the tidal height by 1 cm for every 1MB.
[/ QUOTE ]
I have never and would not use a barometric input on tidal height when forecasting ahead like this, cause there could be a massive change of pressure, or no change at all
My philosophy is that if low water is above 1m, I can park anywhere outside the green bit on the chart without worrying /forums/images/graemlins/laugh.gif
If I get it wrong, out comes the scrubbing brush to give the A/F a quick assist!
cod
Active Member
Not sure what I said in my last post was wrong.
I have done the calcs assuming no adjustment for barometric pressure. 968Mb and just now 1035Mb I get 3.3m every time. Whatever barometric pressure is chosen the adjustment is applied to both the height of tide in this case at 0300BST and the height at the next LW. In this particular case barometric pressure is irrelevant to the calcs.
However being able to answer the question I slipped in half way through the thread depends on knowing the relevent adjustment which as has being pointed out 1cm for every 1Mb or if you are as old as me 1 foot for every 34Mb. But also the barometric pressure the tides are based on as a starting point. Finally of course applying the adjustments in the right direction. Higher pressure lowers tidal levels lower pressure allows them to rise more.
I do agree with the answer of 3.3m but do not get the same answer as Snowleopard for the height of tide at 0300.
The height of tide calculated from the tidal curve in the almanac gives a height of tide of 1.3m at 0300BST.
We are now talking barometric pressure of 1035 which is above average. This means higher pressure, more pressure pushing down on the sea surpressing the tide so it is not allowed to rise as much as normal so our calculated adjustment must be taken off the 1.3m giving an adjusted height of tide at 0300BST of 1.1m.
MINESAPINT
I have done the calcs assuming no adjustment for barometric pressure. 968Mb and just now 1035Mb I get 3.3m every time. Whatever barometric pressure is chosen the adjustment is applied to both the height of tide in this case at 0300BST and the height at the next LW. In this particular case barometric pressure is irrelevant to the calcs.
However being able to answer the question I slipped in half way through the thread depends on knowing the relevent adjustment which as has being pointed out 1cm for every 1Mb or if you are as old as me 1 foot for every 34Mb. But also the barometric pressure the tides are based on as a starting point. Finally of course applying the adjustments in the right direction. Higher pressure lowers tidal levels lower pressure allows them to rise more.
I do agree with the answer of 3.3m but do not get the same answer as Snowleopard for the height of tide at 0300.
The height of tide calculated from the tidal curve in the almanac gives a height of tide of 1.3m at 0300BST.
We are now talking barometric pressure of 1035 which is above average. This means higher pressure, more pressure pushing down on the sea surpressing the tide so it is not allowed to rise as much as normal so our calculated adjustment must be taken off the 1.3m giving an adjusted height of tide at 0300BST of 1.1m.
MINESAPINT
cod
Active Member
I cannot imagine anyone being the slightest bit interested in using adjustments based on barometric pressure in real life. Who is interested in 8 inches or so?
MINESAPINT.
MINESAPINT.
Talbot
Well-Known Member
VLCC's will definitely be interested in this as they are sometimes very "constrained by their depth"
John_N
Well-Known Member
[ QUOTE ]
or if you are as old as me 1 foot for every 34Mb. MINESAPINT
[/ QUOTE ]
If you want to talk in old money be consistent; eg. I foot for so many inches of mercury!!
or if you are as old as me 1 foot for every 34Mb. MINESAPINT
[/ QUOTE ]
If you want to talk in old money be consistent; eg. I foot for so many inches of mercury!!
Lakesailor
Well-Known Member
[ QUOTE ]
Who is interested in 8 inches or so?
[/ QUOTE ] I know several lovely young ladies who may express such an interest
Who is interested in 8 inches or so?
[/ QUOTE ] I know several lovely young ladies who may express such an interest
rhinorhino
Well-Known Member
What's the piont of this series of questions from you?
What are you trying to prove?
If they are a genuine quest for knowledge forgive me, but I really can't see how. /forums/images/graemlins/mad.gif
What are you trying to prove?
If they are a genuine quest for knowledge forgive me, but I really can't see how. /forums/images/graemlins/mad.gif
T_S
Well-Known Member
Fetch.......You forgot about fetch man! And thank god I remembered it in my passage plan doing my CS practical as our boat could have run aground at Bradwell because of wind against tide!
Secondary port calculations were out by as much as 35 mins because of this wind against a neap flood!
Secondary port calculations were out by as much as 35 mins because of this wind against a neap flood!
Lakesailor
Well-Known Member
well, my Learned Friend, he's either preparing for a pub quiz or has been sent from "Sailing Today".
snowleopard
Well-Known Member
I already asked that question and the answer i got was
<To see if anybody can answer it!!!!!!!!!!!!!>
What do you think? Piss-take? Ego trip?
Beats me.
<To see if anybody can answer it!!!!!!!!!!!!!>
What do you think? Piss-take? Ego trip?
Beats me.
Lakesailor
Well-Known Member
Piss Take
I think it's someone on the forum with a new (second) identity having a larf. It's all the rage.
I think it's someone on the forum with a new (second) identity having a larf. It's all the rage.
cod
Active Member
What's the point of the questions.
Same question could be asked about the majority of posts.
Its quite simple. I recently took my Yachtmaster Offshore (power) which I passed by the skin of my teeth. I am planning to take the same exam under sail and am studying in order to consolidate my knowledge in the hope I will pass under sail more comfortably. There are a few subjects I know I am weak on and as well as books, internet and RYA courses I have been drawing from the considerable knowledge available on this forum. It is clear that my questions are not welcome so I will dissist from posting any more.
However if anyone is aware of a forum more suited to my needs I will be glad to hear of it. With I understand in the region of 22,000 people taking RYA courses every year I am surprised there is not already a dedicated forum.
MINESAPINT.
Same question could be asked about the majority of posts.
Its quite simple. I recently took my Yachtmaster Offshore (power) which I passed by the skin of my teeth. I am planning to take the same exam under sail and am studying in order to consolidate my knowledge in the hope I will pass under sail more comfortably. There are a few subjects I know I am weak on and as well as books, internet and RYA courses I have been drawing from the considerable knowledge available on this forum. It is clear that my questions are not welcome so I will dissist from posting any more.
However if anyone is aware of a forum more suited to my needs I will be glad to hear of it. With I understand in the region of 22,000 people taking RYA courses every year I am surprised there is not already a dedicated forum.
MINESAPINT.
tcm
...
Re: dedicated rya quiz forum
good point, i suppose.
good point, i suppose.
Lakesailor
Well-Known Member
Re: dedicated rya quiz forum
So why didn't you say that when asked at the start of the thread?
So why didn't you say that when asked at the start of the thread?
tcm
...
Re: dedicated rya quiz forum
well, why didn't HE say that? Doling out rya-ish questions just for the sake of it a moment ago...but now it's cos he's got a YM exam coming up.
well, why didn't HE say that? Doling out rya-ish questions just for the sake of it a moment ago...but now it's cos he's got a YM exam coming up.
rhinorhino
Well-Known Member
I presume you mean you are going to re-do your shore-based exam?
Maybe if you prefaced your question with "I am preparing for my ..... exam. Please provide answers for me in the approved RYA manner i.e. to .1m etc etc" you might have faced less flak.
As it is I still can't see any piont to the exercise.
The RYA exam questions remain the same all year, once they were posted on the internet (with answers) they would lose all value and the whole exam structure would have to be changed.
That also ignores isssues of copyright.
Maybe if you prefaced your question with "I am preparing for my ..... exam. Please provide answers for me in the approved RYA manner i.e. to .1m etc etc" you might have faced less flak.
As it is I still can't see any piont to the exercise.
The RYA exam questions remain the same all year, once they were posted on the internet (with answers) they would lose all value and the whole exam structure would have to be changed.
That also ignores isssues of copyright.