Anchoring with poor spatial awareness?

[johnalison]

If you see an eye doctor, you'll probably get diagnosed with less than perfect stereo vision, which makes it harder to judge distances and catch balls. Your brain can compensate for this, i.e. with the boat length trick working for me.

There are several other ways of judging distance other than stereo, or binocular, vision. I haven't had binocular vision for many years since my diplopia, and probably not before because I could never resolved those stereogram drawings. You can judge distance by:
Focus - the effort needed to accommodate to a near object
Size - large objects tend to be nearer
Parallax - how much an object appears to move when you do
Movement - nearer objects tend to move faster across the field of vision
Contrast - distant objects lose contrast, except in Antarctica
Colour - distant objects lose saturation.

I doubt if stereo vision is much use at the distances we are talking about. I gather that only something like 60% of people have true binocuar vision anyway, so many or most of us use other methods of judgement. I got this last information from Stephen Pinker's great book "How the Mind Works", which is currently on loan.

 

[stranded]

Had the same problem, although it got better with more practice. I've had a £80 golfing range finder in my Amazon basket for a while now, but haven't organised shipping yet. What really helped me was thinking in own boat lengths, i.e. "how many times would Songbird fit into this gap?".

Mostly I err on the side of caution and when I'm not sure, we just keep an eye on things until the tide turns and boats swing - always ready to re-anchor if need be. So far we've never hit anyone, most of the time it turns out there was plenty of room after all.

If you see an eye doctor, you'll probably get diagnosed with less than perfect stereo vision, which makes it harder to judge distances and catch balls. Your brain can compensate for this, i.e. with the boat length trick working for me.

P.S.: Where did you end up at? We've booked a winter stay in Albufeira and are doing some boat maintenance now.

Nooka’s out of the water at Sopromar in Lagos - our plans to spend a couple of weeks putting her to bed were buggered by the refusal of the Algarve autumn to arrive so our ‘just one more night’ in the anchorage at Ferraguda turned into just two more weeks, a dash back for lift out and rather too many jobs handed over to the yard! We got back to the UK yesterday.

Btw. I am planning to drive out in January loaded with supplies for next year - it’s only a VW Golf so space limited, especially once I load my year’s supply of tea bags and grapefruit squash, but if you wanted me to bring any bits out for you I am sure we could squeeze a bit more in...

 

[stranded]

Thanks for all the suggestions - I look forward to trying them all out, while using my Christmas present range finder to check their efficacy!

 

[AntarcticPilot]

There are several other ways of judging distance other than stereo, or binocular, vision. I haven't had binocular vision for many years since my diplopia, and probably not before because I could never resolved those stereogram drawings. You can judge distance by:
Focus - the effort needed to accommodate to a near object
Size - large objects tend to be nearer
Parallax - how much an object appears to move when you do
Movement - nearer objects tend to move faster across the field of vision
Contrast - distant objects lose contrast, except in Antarctica
Colour - distant objects lose saturation.

I doubt if stereo vision is much use at the distances we are talking about. I gather that only something like 60% of people have true binocuar vision anyway, so many or most of us use other methods of judgement. I got this last information from Stephen Pinker's great book "How the Mind Works", which is currently on loan.

Basically, stereoscopic vision is only useful over fairly short distances, out to around 10m. The distance between our eyes isn't great enough to provide useful stereoscopic effects much beyond that. At greater distances, we rely on things like overlap, rate of angular movement (if we're moving, more distant things appear to move more slowly than closer things) and scale estimation. People with one eye, or with little functional vision in one eye, can easily compensate for it, without significant loss of function. My Dad was effectively blind in one eye, but his estimation of distance was far better than mine! In fact, it affected him so little that I didn't know about it until my Mum mentioned it once.

 

[JumbleDuck]

Basically, stereoscopic vision is only useful over fairly short distances, out to around 10m. The distance between our eyes isn't great enough to provide useful stereoscopic effects much beyond that.

Simple answer for the OP: Get one of these https://www.ebay.com/itm/German-WWII-Artillery-5-Meter-Coastal-Rangefinder-/300584834425

 

[iLens]

Which anchor alarm app do you use?

 

[iLens]

And another thing ... how do you estimate the swinging circle in areas with multi-metre tidal ranges

 

[LittleSister]

People with one eye, or with little functional vision in one eye, can easily compensate for it, without significant loss of function.

It's a terrible shock learn that!

I've been telling myself and others for over 50 years that my being blind in one eye is the reason I'm useless at cricket and tennis, etc.

 

[webcraft]

.
The good thing about the difficulty in judging distance in anchorages is that you nearly always underestimate it, so you are safe - and can put out more scope.

Worst issue is a long row ashore when you could perhaps have got further in.

- W

 

[mjcoon]

What about an optical one? Like this on eBay item number 222696583482

Not sure how it works though

The optical rangefinder attached to my ancient folding camera has moving mirrors (a bit like a sextant). When you align the two images you can read off the distance. Of course it is less accurate for distant objects, but that is OK for focusing...

Mike.

 

[JumbleDuck]

What about an optical one? Like this on eBay item number 222696583482

Not sure how it works though

https://en.wikipedia.org/wiki/Coincidence_rangefinder

 

[AntarcticPilot]

It's a terrible shock learn that!

I've been telling myself and others for over 50 years that my being blind in one eye is the reason I'm useless at cricket and tennis, etc.

I'm only going on my knowledge of my father, who had little or no functional vision in one eye (it exempted him from overseas service during WW2!). However, of course it affects close up ability to judge distance, and my father didn't play games such as cricket etc. But his skill at judging long distances - such as this thread is dealing with - was better than the rest of the family, and he was an excellent driver, skilled in manoeuvering in tight spaces!

I think I remember reading that skill in catching or striking balls isn't to do with judgement of distance but with unconscious prediction of the trajectory of the ball using such clues as the rate of cross-track motion, time of flight etc. A bit like knowing you're on a collision course if the bearing doesn't change!

I also am useless at games involving fast moving balls, and I have good stereoscopic vision. It didn't help that I wore glasses as a child and had a healthy fear of being hit in the face by a ball! My judgement of the motion of a ball was aimed at getting out of its way, not catching, kicking or striking it.

 

[[70521]]

And another thing ... how do you estimate the swinging circle in areas with multi-metre tidal ranges

Simple, you only need the low water range everything else will be smaller.

 

[BurnitBlue]

Simple answer for the OP: Get one of these https://www.ebay.com/itm/German-WWII-Artillery-5-Meter-Coastal-Rangefinder-/300584834425

My Brother in law collected that sort of stuff. I borrowed a WW1 or WW11 artillery range finder from him. German by Carl Zeiss. The arms were spread over two meters and came in a wooden box. Carried it home on the roof rack. Amazing I played with it from an upstairs window to measure exact distances to my neighbours fence, and the local church steeple etc. I recall that it needed two windows to accommodate the width of the lens spread. Also the windows needed to be open because the optical quality of the window glass altered the distance measured quite a lot.

I could also peer straight into any window and read book titles on their shelves. Also measure the size of their living room, CIA stuff what? I forget the magnification but it was massive and quite bright.

 

[lw395]

Once upon a time, people did this kind of thing with their sextant.

But mostly we don't need to be that accurate.
If we can assure ourselves that something is further away than 'x', that's often good enough.

 

[lw395]

My Brother in law collected that sort of stuff. I borrowed a WW1 or WW11 artillery range finder from him. German by Carl Zeiss. The arms were spread over two meters and came in a wooden box. Carried it home on the roof rack. Amazing I played with it from an upstairs window to measure exact distances to my neighbours fence, and the local church steeple etc. I recall that it needed two windows to accommodate the width of the lens spread. Also the windows needed to be open because the optical quality of the window glass altered the distance measured quite a lot.

I could also peer straight into any window and read book titles on their shelves. Also measure the size of their living room, CIA stuff what? I forget the magnification but it was massive and quite bright.

A friend of a friend bought some Eastern Bloc telephoto lenses. They were stupidly powerful, but could see straight through the house over the road, despite them having net curtains front and back. Because the depth of focus was so short, the net curtains were ignored and you could focus on stuff in their backyard. He sold them to wildlife photographers.