# Sight distance



## Freo

Could anyone verify the sight distance at sea. Am reading a book called Blood Ransom, about Somali pirates, and in an account of being attacked, the skipper of the fishing vessel says the following. " I was fishing not far from home - about 45 nautical miles offshore, I could still see the land."
Surely this wouldn't be possible, in a small vessel with a low freeboard.


----------



## trotterdotpom

It might be possible if he was on the other side of Africa and he was looking at Mt Cameroon (as long as it wasn't raining). Otherwise I'd say he's dreaming. 

John T


----------



## tsell

Hi Freo - it's all here: 

http://www.dublerfamily.com/Activity3.html

Somebody's telling porkies!


Taff


----------



## woodend

Dug out of the memory bank somewhere: 1.15 times the square root of the height of eye in feet plus 1.15 times the square root of the height of object in feet. Answer in nautical miles. used to use it quite a lot in the dark ages before the asvent of. radar.


----------



## trotterdotpom

tsell said:


> Hi Freo - it's all here:
> 
> http://www.dublerfamily.com/Activity3.html
> 
> Somebody's telling porkies!
> 
> 
> Taff


I looked it up ... it's written by a woman, what do you expect? I think it's about two Yorkshire terriers who sneak into Australia and dig up a chest full of Spanish dubloons and take them home to South Shields where the Somalis live. Sounds like a piece of eight to me.

John T


----------



## david freeman

home spun yarn, on the spinning wheel, by Grannie


----------



## rickles23

Hi,

If memory serves,

Visible distance (in nm) = 1.17 x the square root of the height (in feet)

Regards


----------



## MikeK

Got the South Shields bit right anyway ! Result of the good old days when the British Merchant Navy was the biggest in the world !


----------



## Somerton

I remember aboard a Port Line ship in Lat 1950s the lookout was in the foremast. 
Of the coast of North Island New Zealand . I reported a ships lights on the starboard bow . When my watchmate came off watch he said the mate said the distance on the radar 22 miles . I was in the crows nest with a good view . Now lads let's have your response . My watchmate was from Ayr . We sailed together on 2 Port Line ships .
Alex C .


----------



## BobClay

Surely vision, particularly night vision of lights could be extended by atmospherics under certain cir***stances.


----------



## Wismajorvik

Sea horizon of 22miles equates to an observer's height of 375ft according to #7 above and my dusty Burtons tables.


----------



## Basil

Somerton said:


> I remember aboard a Port Line ship in Lat 1950s the lookout was in the foremast.
> Of the coast of North Island New Zealand . I reported a ships lights on the starboard bow . When my watchmate came off watch he said the mate said the distance on the radar 22 miles . I was in the crows nest with a good view . Now lads let's have your response . My watchmate was from Ayr . We sailed together on 2 Port Line ships .
> Alex C .


If you were about 100 ft above sea level and the mast light of the other ship was about the same then I'd say you could see it and, as Bob Clay says, the loom of the light can appear before you have direct line of sight.

For U/VHF quasi-optical range we used 1.2 x SQRT Ht. (Ht ft & range nm)
That gave a slightly longer range than actual line of sight.
You can also get increased radar range due atmospheric ducting. I've seen ships off the coast of East Anglia from a ground level radar scanner near Cambridge.

p.s. also agree with Wismajorvik re dist to horizon.

p.p.s. Re OP: You could probably just see an 1800' peak at 45nm.


----------



## Binnacle

To obtain a sea horizon of 45 miles it would be necessary to ascend to an eye height of 1550 feet. Source Norie's Nautical Tables. This is presumption in normal atmospheric conditions and not "ano prop".
Air pilots please confirm.


----------



## Basil

Binnacle said:


> To obtain a sea horizon of 45 miles it would be necessary to ascend to an eye height of 1550 feet. Source Norie's Nautical Tables. This is presumption in normal atmospheric conditions and not "ano prop".
> Air pilots please confirm.


I certainly defer to your professional 'distance off' figure.
Sounds well within ball park to me.
We normally used U/VHF quasi-optical range for an idea of when we could make VHF radio contact and ditch the dreaded HF - although even my wife could handle a simplex HF 'phone patch and remember to say 'over' 
Portishead and Stockholm were usually very good.


----------



## John Rogers

I was told on a good day it was 5 miles standing on the deck, 15 miles from the Bridge and 25 miles from the crows nest. Now sitting on the truck of the mast may give you some added miles,but for sure a smile on your face or a sore rear end.


----------



## Stephen J. Card

You can see ANYTHING if the height is enough. I can see the sun at 93 millions miles! ;-)

The only thing you can see for distance, and know for certain, is to know from your own height of eye. If you know the height your own deck, bridge or crow's nest. Unless you know exactly what you are looking at you must see the second it comes over your horizon, and be able to recognize it! Unlikely. Unless it is a 'lighthouse. Knowing the height of a masthead of another ship is useless unless you know that height. The masthead might be anything from a few feet to a hundred or so. Not exactly what you want to call as good navigation!


----------



## Barrie Youde

#9 and #12 

To see the loom of a powerful lighthouse-light (long before seeing the light itself) is entirely normal; but I don't recall ever seeing any loom from a ship's simple masthead lights. 

The visibility described at #9 must surely depend on the relative heights of both the observer and the ship's lights?


----------



## Alan Rawlinson

*Horizon distance*



Freo said:


> Could anyone verify the sight distance at sea. Am reading a book called Blood Ransom, about Somali pirates, and in an account of being attacked, the skipper of the fishing vessel says the following. " I was fishing not far from home - about 45 nautical miles offshore, I could still see the land."
> Surely this wouldn't be possible, in a small vessel with a low freeboard.


Function of the ' height of eye'. 7 miles if he was lucky from a fishing boat. A bit of poetic licence by the author unless he was up a very tall mast! May have meant to write 4.5 miles which would fit the plot.


----------



## Barrie Youde

#18 

Alan takes the biscuit, no doubt!

My own recollection is that from the bridge of a pilot-cutter (height of-eye, say 25 feet) coasters would be visible at 7-8 miles and big-uns at about 10 miles.

On the foulset of nights, when taking shelter in Freshwater Bay (South -East of Point Lynas) it was a most dramatic sight to see the loom of the Skerries lighthouse (the sight-line of which was completely obscured by the Isle Anglesey) across the land, in breaks between the scudding clouds! I see it now and my spine still tingles!

Is it time yet to call the watch below?


----------



## Barrie Youde

The possibilities for this thread are unlimited!

All hands on deck! There's a pretty little girl in sight! (Guy Mitchell -remember him?)

I like the sea,
I like the navy,
I like biscuits dipped in gravy,
My pretty little black-eyed Suzy,
My pretty little black-eyed Suzy,
Cross my heart, I love you best of all! 

Eight bells!


----------



## BobClay

I went out and looked for the Andromeda Galaxy tonight. That's the better part of 2 million light years away, you can't see anything further away with the unaided eye.

Even so I don't know why I bothered, dense fog, couldn't see the bottom of my garden. [=P]


----------



## Basil

> All hands on deck! There's a pretty little girl in sight!


Recollect sailing as volunteer crew asst. eng. on a TSYT brig around the Canaries, and we were kindly given a copy of local sailing directions by the Alexander von Humboldt. (She of the green sails)
A flat area of rock approaching harbour was annotated: 'Here be naked Germans.' Can't say the Germans don't have a sense of humour!

About twenty posts to get from technical aspects of navigation to naked ladies - about average, I guess


----------



## John Rogers

Barrie Youde said:


> The possibilities for this thread are unlimited!
> 
> All hands on deck! There's a pretty little girl in sight! (Guy Mitchell -remember him?)
> 
> I like the sea,
> I like the navy,
> I like biscuits dipped in gravy,
> My pretty little black-eyed Suzy,
> My pretty little black-eyed Suzy,
> Cross my heart, I love you best of all!
> 
> Eight bells!


She was one of the Roving Kind.(Thumb)


----------



## China hand

There's a table in Nories.


----------



## Barrie Youde

Oh, for the days when the words of songs were comprehensible!

Gone, alas, like our youth, too soon!


Her hair hung down, in ringlets! - what a memorable line was that! I was aged about eight at the time. I think that I knew then that some of the girls at school sported ringlets, although I didn't really know anything, then. But, oh, how the words stick in the mind!


----------



## Binnacle

Sailing without radar it was common practice to plot a position on the chart using dipping distances. especially if the old man had a copy of "Lecky's Wrinkles in Navigation" in his bookcase. In practice you had to keep a close watch on the light especially when you reached nearly the range when the light would "dip". Nipping down to the lower bridge would confirm the light had dipped, then back up to the bridge to wait for the light to dip, when it did dip then quickly up to the monkey island to taking a bearing as it dipped. On standard Empire cargo ships on that deck, IIRC, the height of eye on the upper bridge was about 40 ft. Later when the old man surveyed the chart there was a fairly accurate departure pos'n plotted for all to see and there was no blood spilt on the carpet.


----------



## Freo

Alan Rawlinson said:


> Function of the ' height of eye'. 7 miles if he was lucky from a fishing boat. A bit of poetic licence by the author unless he was up a very tall mast! May have meant to write 4.5 miles which would fit the plot.


Thanks for all the knowledgeable replies, but he also puts the metric equivalent in brackets ie ( 85 Km). As you say, a bit of poetic licence or just plain ignorance of the subject, but then he is a lawyer.


----------



## Dartskipper

Basil said:


> You can also get increased radar range due atmospheric ducting. I've seen ships off the coast of East Anglia from a ground level radar scanner near Cambridge.


That's because all the land to the North and East of Cambridge is mostly flat as the kitchen table...(Jester)


----------



## Dartskipper

BobClay said:


> I went out and looked for the Andromeda Galaxy tonight. That's the better part of 2 million light years away, you can't see anything further away with the unaided eye.
> 
> Even so I don't know why I bothered, dense fog, couldn't see the bottom of my garden. [=P]


There's a Tommy Cooper joke in there, Bob.

This fellow goes to an optician and says he has trouble seeing long distances and needs glasses. The optician takes him outside the shop and tells him to look up....

You can guess the rest..(Jester)


----------



## ninabaker

Sadly, I no longer have my Nories tables but good old Wikipedia has a whole page devoted to *equations for distance to the horizon*.
Picking up on Basil's delightful pilotage notes: the sex/gender of the naked Germans isnt specified, so I claim the right to assume they may actually be buff Junge rather than Madchen?

nina


----------



## Somerton

The ship in question was the Port Napier. At that time she was in Port Line the largest freezer capacity ship in ( Port Line ) . Thank you .
Alex C .


----------



## Farmer John

China Hand, I have just checked my Nories, it's full of tables.!


----------



## Cisco

In the Arabian Sea in the North East Monsoon you can see for miles and xxxxxxx miles... but that's the high ground ... not the coast as such.


----------



## Alan Rawlinson

*She wears red feathers*



Barrie Youde said:


> Oh, for the days when the words of songs were comprehensible!
> 
> Gone, alas, like our youth, too soon!
> 
> 
> Her hair hung down, in ringlets! - what a memorable line was that! I was aged about eight at the time. I think that I knew then that some of the girls at school sported ringlets, although I didn't really know anything, then. But, oh, how the words stick in the mind!


Me too!

Bought my first vinyl record which was played endlessly....

It was Guy Mitchell singing 'Red Feathers' with memorable chorus lines...

She wears red feathers, and a hula hula skirt 
She wears red feathers and a Hula Hula skirt,

She lives on coconuts, and fish f'rum the sea, 
with a rose in her hair, a gleam in her eye, and love in her heart for me!

Quite a catchy tune


----------



## Barrie Youde

Ah, yes, I remember it well!


----------



## Barrie Youde

I like Jane
And I like Mabel
On their backs on the chartroom table

were other wishful thoughts in the early 1960s.


----------



## Basil

ninabaker said:


> Sadly, I no longer have my Nories tables but good old Wikipedia has a whole page devoted to *equations for distance to the horizon*.
> Picking up on Basil's delightful pilotage notes: the sex/gender of the naked Germans isnt specified, so I claim the right to assume they may actually be buff Junge rather than Madchen?
> 
> nina


ISTR more frauen than madchen


----------



## Basil

Dartskipper said:


> That's because all the land to the North and East of Cambridge is mostly flat as the kitchen table...(Jester)


Oh, I know that but, even so, in non-ducting conditions the buildings, trees, little rises etc cut out ground returns more than a couple of miles away and the ground has a tendency to absorb radar microwaves rather than reflect them. It had already been discovered that radio waves could be bounced off the ionosphere although I doubt we were getting that effect.
Anyway, this was a primary search radar for aircraft direction at RAF Wyton and we thought it was 'cool' to demonstrate ducting.


----------



## Ron Stringer

In the Eastern Med on passage to/from Port Said it was not unusual to get clear, solid and identifiable radar returns of the coast of Cyprus and Crete from well in excess of 100nm, displayed on the 40-mile range of the ship's radar. I have seen them on the old Marconi _Radiolocator IV _as well as the more advanced_ Hermes/Argus_. 

It could cause the 3rd Mate (more senior guys were already aware of the phenomenon) a bit of a shock the first time they encountered ducting and its effects on radar range.


----------



## slick

Hello all,
As mentioned elsewhere in Nostalgia I bought Tamaya sextant and had it repaired at Cookes of Hull.
I live in East Anglia on the edge of the Fens and I feel that on a good day you can see fifteen miles say out at Shippea Hill (below sea level I think) that is better than some of the horizons at sea I've used....
They call Ely Cathederal the Galleon of the Fens...
I am in the process of getting a old copy of "Ocean passages of the World", all I need is a chronometer and I'll be away.
Talk about living in the past, however we just didn't appreciate what we had...


----------



## R798780

Freo said:


> Could anyone verify the sight distance at sea. Am reading a book called Blood Ransom, about Somali pirates, and in an account of being attacked, the skipper of the fishing vessel says the following. " I was fishing not far from home - about 45 nautical miles offshore, I could still see the land."
> Surely this wouldn't be possible, in a small vessel with a low freeboard.


Depends on the height-of-eye of the observer ................... gives distance to the sea horizon; and the height of the object beyond the sea horizon being observed and the distance to sea horizon from that object: The distance at which the object is visible is the sum of those two distances. As previously stated sea horizon is 1.151 root H in feet and I think I found it equated to around 2.01
root H in metres;

I know from experience that Mt Teide on Tenerife is visible at noon having been abeam at 0600 doing 15 knots with the nav bridge height of eye 42 feet (90 nautical miles if you don't have a calculator or smart phone )


----------



## Frank P

Sailing in the Pacific south of Hawaii on the M/T Hallanger (34,000 tns) from the bridge wing we could see the top of a mountain/volcano and according to the radar we were 40 miles away.......

.


----------



## BobClay

In the Red Sea under certain atmospheric conditions I've see second trace echoes coming in on the radar showing the coastline much closer than it actually is. It's the only place I've ever seen it. 
The radar waves are literally trapped inside a low altitude atmospheric waveguide created by the conditions and a returning echo from a distant point is painted up on the next trace. I only ever saw it the once.


----------



## Dartskipper

Basil said:


> Oh, I know that but, even so, in non-ducting conditions the buildings, trees, little rises etc cut out ground returns more than a couple of miles away and the ground has a tendency to absorb radar microwaves rather than reflect them. It had already been discovered that radio waves could be bounced off the ionosphere although I doubt we were getting that effect.
> Anyway, this was a primary search radar for aircraft direction at RAF Wyton and we thought it was 'cool' to demonstrate ducting.


RAF Wyton always seemed to have some kind of activity going on when I worked around that part of the World. I used to see a Canberra flying around then, which I think was something to do with the Meteoroolgy Flight? My Niece's husband was stationed there as an instructor a few years ago, but I think it may be earmarked for closure. 

Regards.


----------



## lakercapt

Seeing things on a clear night.
Sailing up the English channel someone said you can tell the difference between French and English lighthouses as the rotate in opposite directions.
I don't know if that is true!!!


----------



## Basil

Dartskipper said:


> RAF Wyton always seemed to have some kind of activity going on when I worked around that part of the World. I used to see a Canberra flying around then, which I think was something to do with the Meteoroolgy Flight? My Niece's husband was stationed there as an instructor a few years ago, but I think it may be earmarked for closure.
> 
> Regards.


It was basically a Photo Reconnaissance station with PR Canberras and Victors. Together with the USAF traffic at Alconbury it could get a bit busy.


----------



## trotterdotpom

lakercapt said:


> Seeing things on a clear night.
> Sailing up the English channel someone said you can tell the difference between French and English lighthouses as the rotate in opposite directions.
> I don't know if that is true!!!


I dunno if it's true either but you have to be pretty close to a lighthouse to register any rotation. Isn't plan A to keep clear of lighthouses?

John T


----------



## beedeesea

Bit about direction of rotation here: http://lighthousememories.ca/2013/11/04/cw-or-ccw/#.WHJuvfmLTIU

Brian


----------



## Basil

Waverley seemed to have a fatal attraction to one.
I understand her handling qualities can be less than ideal.


----------



## Dartskipper

Basil said:


> It was basically a Photo Reconnaissance station with PR Canberras and Victors. Together with the USAF traffic at Alconbury it could get a bit busy.


Many thanks Basil. 

Yes, that whole area up to the Wainfleet Range, with Holbeach Range, was a plane spotters heaven. (But that's for another forum!)

Regards,

Roy.


----------



## Dartskipper

Basil said:


> Waverley seemed to have a fatal attraction to one.
> I understand her handling qualities can be less than ideal.


She certainly had an exciting time on her first visit to Torquay in the 1980's. I think it was the only time she called.


----------



## lakercapt

trotterdotpom said:


> I dunno if it's true either but you have to be pretty close to a lighthouse to register any rotation. Isn't plan A to keep clear of lighthouses?
> 
> John T


If you are in mid channel on a clear night you can see the loom of the lights and see the rotation.


----------



## Alan Rawlinson

*Ditties*



Barrie Youde said:


> I like Jane
> And I like Mabel
> On their backs on the chartroom table
> 
> were other wishful thoughts in the early 1960s.


Must be plenty of amusing ditties out there....

My old favourite -

She was only a Sparkies daughter,
But she did dit because her Da- Da -Did -dit!


----------



## trotterdotpom

lakercapt said:


> If you are in mid channel on a clear night you can see the loom of the lights and see the rotation.


Looked it up and apparently 99% of lights rotate clockwise (if you're looking down on them). Dunno if the 1% are French. 

One way of telling the difference between English and French lights is, if you're heading east up the Channel, the Frog ones will be on the right.

John T


----------



## John Rogers

Barrie Youde said:


> Oh, for the days when the words of songs were comprehensible!
> 
> Gone, alas, like our youth, too soon!
> 
> 
> Her hair hung down, in ringlets! - what a memorable line was that! I was aged about eight at the time. I think that I knew then that some of the girls at school sported ringlets, although I didn't really know anything, then. But, oh, how the words stick in the mind!


Just dug out my CD,one of my old time favorites.


----------



## 5036

There is also terrestrial refraction which is dependent on surface pressure and temperature, it is the effect that allows you to see over the horizon on a clear day with high pressure. I showed it to a prominent marine photographer last year heading towards the Needles Channel off Gurnard, I was amazed he had never noticed it before. At home on the Clyde, Ailsa Craig often appears floating over the horizon and the Mull of Galloway appears pointing upwards of the horizon.
In my hydrographic days we used to do resections for final positions of oil and gas production platforms after sunset as it was the time for least ray bending.
It was nicely demonstrated by Omar Sharrif arriving in Lawrence of Arabia.


----------



## sidsal

November 1943 - Aden -ancient (1917 built) Maihar. Me - first trip apprentice after HMS Conway. Topmast on rear mast removed - as was usual to make it difficult for U Boats being able to see an alteration of course. Foremast steel to table where there was a lookout post. Topmast was wooden with a large barrel lashed high up and a steel wire ladder leading up to it. Sailed 24 hours before convoy for Bombay as decoy ship. Someone had to go at dawn and dusk up to the barrel with binocs and scan for any smoke or suchlike. Senior apprentice could not stand heights and other was first tripper so yours truly had to do it, Quite scary climbing the wire ladder as the ship rolled slowly in the swell made the ladder swing away from the mast. Ruined my head for heights for good.


----------



## Alan Rawlinson

*Mast climbing*



sidsal said:


> November 1943 - Aden -ancient (1917 built) Maihar. Me - first trip apprentice after HMS Conway. Topmast on rear mast removed - as was usual to make it difficult for U Boats being able to see an alteration of course. Foremast steel to table where there was a lookout post. Topmast was wooden with a large barrel lashed high up and a steel wire ladder leading up to it. Sailed 24 hours before convoy for Bombay as decoy ship. Someone had to go at dawn and dusk up to the barrel with binocs and scan for any smoke or suchlike. Senior apprentice could not stand heights and other was first tripper so yours truly had to do it, Quite scary climbing the wire ladder as the ship rolled slowly in the swell made the ladder swing away from the mast. Ruined my head for heights for good.


Interesting account!

Your story reminded me of a bizarre happening when I was at the truck of the mainmast with a pair of 7/50 binoculars looking for a poor seamen who had been knocked overboard by a sling of dunnage. 
The ship was the twin screw 1930 built Irisbank, and I was at the top of the mainmast ladder with the round truck in my lap, so to speak. Without waning, the bridge party spotted something and the engines were put in reverse. This caused the topmast to thrash the air like a flyswat, and whip backwards and forwards violently. It was all I could do to cling on and the realisation that I was helpless made it more terrifying. 

We eventually recovered the body from very rough seas but that is another story.
(All in my book called " Any Budding Sailors?")


----------



## Barrie Youde

#58 

Hell's Teeth!

With your own weight at the truck-head, I'll bet that you were worried that the topmast might break!

Terrifying indeed!


----------



## Alan Rawlinson

*Mast*



Barrie Youde said:


> #58
> 
> Hell's Teeth!
> 
> With your own weight at the truck-head, I'll bet that you were worried that the topmast might break!
> 
> Terrifying indeed!


It was a thought,now you mention it. The only reason I wasn't flicked off, was because the astern movement was stopped just in time. I don't think anyone on the bridge noticed my predicament. 

Barrie, you must have a fund of your escapades from your pilotage days you could share?


----------



## Barrie Youde

#60 

"The masts were playing like carters' whips" is a line frequently recounted in tales of pilotage and ship-handling (or mishandling!) within the dock system.

An early lesson was "How to complete a damage report". The advice given was to avoid saying "I misjudged it" and to say, instead, "Vessel failed to respond as anticipated".


----------



## slick

All,
Talking of topmasts and trucks and other derring do's at sea.
Shinning up the fore topmast to re-reeve the dummy gantline was not for the faint hearted.
As it became apparent that someone was going to have to do it after leaving the Manchester ship canal, a deck boy (first trip) stepped forward the Bosun explained what was required, with no more ado the lad set off and whipped up the topmast threaded the dummy gantline and was back on deck before you could say knife.
He also would sweep beams 'kings and queens " over an empty Lower hold with a push broom.
I understand he was Borstal Boy, we gave him the nickname "Leaper".
H&S were nowhere to be seen....



Yours aye,

slick


----------



## Michael Taylor

As I volunteer the New Bedford whaling museum with its mass of information including a half scale whale ship model (largest model in the world). These vessels had "hoops" on each masts 100 foot plus top, one each side. On a barque there may be as many as 4 lookouts on the whaling grounds. Must have been terrifying for these mostly first trip sailors.
It is of interest that the wives of whaling Masters had on occasion taken their turn in the hoops.....not sure how those hooped skirts held up!

The distance to the horizon was known as around 12 miles from these mast heads and when the the call went up and the Master questioned "where away" they could respond with a bearing in points and a distance to the whale.


----------



## 8575

Maybe 'pretty little black-eyed Suzy' was the 2nd steward!!!


----------

