## Viewing distance over water

### Viewing distance over water

A week ago I was sailing in the Gorge at a place where it is over a mile wide.
As I jibed on the far side of the river from the launch, a woman waved to me
from the water.  She had broken a mast and needed help.  She was not to far
from shore so I told her to swim her gear to shallow water and I would go and
get another mast.

I sailed back to the launch and picked up a mast.  I put it along my mast
and tied it at the top and bottom using some strechy cord.  When I started
back across I realized that I could not see her in the water.  When I got
half way across she started up the bank on the other side so I was able to
see her.  She was able to rig up the mast and sail back across the river.

Now for the question.  How close do you need to be for someone to see you in
the water?  If she had been floating with her board and her head and arms were
the only things out of the water how close would I of had to be assuming that
I am about 6 feet tall standing on my board?

People say that you can see 13 miles on the ocean but I could not see one mile
across the river.  What gives?

### Viewing distance over water

Quote:
G Hart) writes:

[ stuff deleted ]

Quote:
> People say that you can see 13 miles on the ocean but I could not see
one mile
> across the river.  What gives?

New presciption lenses. ;^)

ciao
grant

### Viewing distance over water

Quote:
> stuff deleted ...
> People say that you can see 13 miles on the ocean but I could not see one mile
> across the river.  What gives?

I've often wondered about the same thing.

From my experience lake sailing I know that on a calm day the far shore
is clearly visible from a distance of 2 or 3 miles.  But when the wind
starts blowing the far shore can all but disappear.  Maybe the
loss of visibility is from the misting of water particles when it's
windy.

So maybe you can see 13 miles on the ocean in a dead calm.

Don

### Viewing distance over water

-

- > People say that you can see 13 miles on the ocean but I could not see one mile
- > across the river.  What gives?
-
It depends on how high out of the water your eyes and the object you are
looking at are.  That is just for the curvature of the earth. Waves
will make it harder to spot a person in the water, as will any mist.

I you are exactly level with the water and the object is level with the
water You would have to be right next to it to see it.

### Viewing distance over water

Quote:

>-

>- > People say that you can see 13 miles on the ocean but I could not see one mile
>- > across the river.  What gives?
>-
>It depends on how high out of the water your eyes and the object you are
>looking at are.  That is just for the curvature of the earth. Waves
>will make it harder to spot a person in the water, as will any mist.

>I you are exactly level with the water and the object is level with the
>water You would have to be right next to it to see it.

The other thing to watch for is surface tension, this will add to the
curvature on smaller areas of water like lakes and rivers. This also
explains why its difficult to sail away from the beach (uphill) ;)
Bruce

Bruce Spedding
IDW DSIR       Ph +64 +4 569-0788
Box 31310      Fx +64 +4 569-0132

New Zealand    ========================

### Viewing distance over water

Quote:

>- > People say that you can see 13 miles on the ocean but I could not see one mile
>- > across the river.  What gives?
>-
>It depends on how high out of the water your eyes and the object you are
>looking at are.  That is just for the curvature of the earth. Waves
>will make it harder to spot a person in the water, as will any mist.

I think the problem is that when the wind blows, you have both swell and
whitecaps.  Both are moving forms, and you quickly become overwhelmed
by the sheer number of objects that are in your field of vision.

### Viewing distance over water

Quote:

>Newsgroups: rec.windsurfing
>Date: 14 Jul 92 00:51:54 GMT
[...]
>Now for the question.  How close do you need to be for someone to see you in
>the water?  If she had been floating with her board and her head and arms were
>the only things out of the water how close would I of had to be assuming that
>I am about 6 feet tall standing on my board?
>People say that you can see 13 miles on the ocean but I could not see one mile
>across the river.  What gives?

How big was the swell that day? When I'm sailing in the ocean and
keeping an eye on a buddy I'll often loose sight of them for a while if
they're in the water because of swells.
--
-------------------------------------------------------------------------------
Jack Greenbaum     | UC Santa Barbara

(805) 893-4461     | Santa Barbara, Ca. 93106, USA
-------------------------------------------------------------------------------

### Viewing distance over water

Quote:
>Now for the question.  How close do you need to be for someone to see you in
>the water?  If she had been floating with her board and her head and arms were
>the only things out of the water how close would I of had to be assuming that
>I am about 6 feet tall standing on my board?
>People say that you can see 13 miles on the ocean but I could not see one mile
>across the river.  What gives?
>How big was the swell that day? When I'm sailing in the ocean and
>keeping an eye on a buddy I'll often loose sight of them for a while if
>they're in the water because of swells.

When I headed across it was 5.5 weather and the swells were only about 2
feet high.  There were lots of white caps and after talking with
several people by email it is my opnion that the white caps provided "video
noise" which made it hard for me to pick out the woman near the other shore.

It is scary to think about how small a distance you can be from shore and
no one know that you are in trouble.  You can test this idea by watching
someone fall and waiting for the splash to go away.  Look away for
a few a little while and then look back.  Can you see the person in the water?
How close do you need to get before you can see them?

The size of the swell directly affects your ability to see as well as the
sun direction and things like liquid smoke.

---------

For those of you who are interested in the Gorge weather this year, it has
been a little wierd.  There have been lots of 5 meter days and some better
days with most of those falling during working hours.  The Gorge is full of
people and the popular sailing locations are crowded.  The total number of
days that have been sailed this year is quite high but the sail sizes have
been on the large side also.  The water is very warm and even people learning
water starts are taking off their wetsuits.

If anyone one from the Digital Equipment sailing club that was at Rock Creek on
Sunday July 19 reads this, drop me a line.