I've noticed something strange. I had suspected it for sometime but just
a little while ago my suspicion was confirmed. We had sailed to a small
island and moored in the only cove. Chart indicated no hazards, just
sand with small shell bottom. Dropped the anchor (Sarka) in about 4m of
water and laid out about 6:1 rode as per usual. The depth under the keel
indicated 5m. Went to bed. During the night I woke up with a strange
feeling of uncertainty. Perhaps the boat's motion had changed but
nothing obvious. Peering into the blackness, the loom against the stars
indicated we had not moved. Nevertheless, the feeling did not go away. I
flipped on the depth sounder and it read 4m but then started to chnage
-then 3.5 then 3.0 then 2.5 and that is when I reached for the engine
key. But it stopped rising at 2.3 and we need 1.8m. With little tide
left all would be well. As I watched it slowly increased again. I
deduced that we were ever so slowly swinging over an uncharted rock.
Intrigued I snorkeled out in the morning (Brrrrrr) and saw the rock. We
had laid just enough rode to place out keel right over the center of a
2-3 m wide rock platform with sand and deep water all around it.

Now why did we just end up over a rock? My suspicion is that boats seek
out rocks -is this possible? If so, why do boats seek them out?

Did I wake up because the small swell was accentuated as we swung over
the rock and I sensed it in my sleep?

Any similar experiences?

Cheers

It's obvious you went over a seamount or a rock.

Just as helicopters and planes can go into ground effect you went into
shallow water effect.

Back when I was a bubblehead, one relied on this sense greatly.

BC

"Navigator" wrote in message
...
I've noticed something strange. I had suspected it for sometime but just
a little while ago my suspicion was confirmed. We had sailed to a small
island and moored in the only cove. Chart indicated no hazards, just
sand with small shell bottom. Dropped the anchor (Sarka) in about 4m of
water and laid out about 6:1 rode as per usual. The depth under the keel
indicated 5m. Went to bed. During the night I woke up with a strange
feeling of uncertainty. Perhaps the boat's motion had changed but
nothing obvious. Peering into the blackness, the loom against the stars
indicated we had not moved. Nevertheless, the feeling did not go away. I
flipped on the depth sounder and it read 4m but then started to chnage
-then 3.5 then 3.0 then 2.5 and that is when I reached for the engine
key. But it stopped rising at 2.3 and we need 1.8m. With little tide
left all would be well. As I watched it slowly increased again. I
deduced that we were ever so slowly swinging over an uncharted rock.
Intrigued I snorkeled out in the morning (Brrrrrr) and saw the rock. We
had laid just enough rode to place out keel right over the center of a
2-3 m wide rock platform with sand and deep water all around it.

Now why did we just end up over a rock? My suspicion is that boats seek
out rocks -is this possible? If so, why do boats seek them out?

Did I wake up because the small swell was accentuated as we swung over
the rock and I sensed it in my sleep?

Any similar experiences?

Cheers

Fiberglass and wood boats are magnetically attracted to buoys, pilings,
and rocks.

--
"j" ganz @@
www.sailnow.com

"Navigator" wrote in message
...
I've noticed something strange. I had suspected it for sometime but just
a little while ago my suspicion was confirmed. We had sailed to a small
island and moored in the only cove. Chart indicated no hazards, just
sand with small shell bottom. Dropped the anchor (Sarka) in about 4m of
water and laid out about 6:1 rode as per usual. The depth under the keel
indicated 5m. Went to bed. During the night I woke up with a strange
feeling of uncertainty. Perhaps the boat's motion had changed but
nothing obvious. Peering into the blackness, the loom against the stars
indicated we had not moved. Nevertheless, the feeling did not go away. I
flipped on the depth sounder and it read 4m but then started to chnage
-then 3.5 then 3.0 then 2.5 and that is when I reached for the engine
key. But it stopped rising at 2.3 and we need 1.8m. With little tide
left all would be well. As I watched it slowly increased again. I
deduced that we were ever so slowly swinging over an uncharted rock.
Intrigued I snorkeled out in the morning (Brrrrrr) and saw the rock. We
had laid just enough rode to place out keel right over the center of a
2-3 m wide rock platform with sand and deep water all around it.

Now why did we just end up over a rock? My suspicion is that boats seek
out rocks -is this possible? If so, why do boats seek them out?

Did I wake up because the small swell was accentuated as we swung over
the rock and I sensed it in my sleep?

Any similar experiences?

Cheers

Navigator wrote:
I've noticed something strange. I had suspected it for sometime but just
a little while ago my suspicion was confirmed. We had sailed to a small
island and moored in the only cove. Chart indicated no hazards, just
sand with small shell bottom. Dropped the anchor (Sarka) in about 4m of
water and laid out about 6:1 rode as per usual.

Is "sarka" a type of anchor? How much scope do you let out to set the
anchor?

.. The depth under the keel
indicated 5m. Went to bed. During the night I woke up with a strange
feeling of uncertainty. Perhaps the boat's motion had changed but
nothing obvious. Peering into the blackness, the loom against the stars
indicated we had not moved.

??? Dang you're good, doing celestial navigation to within a couple of
meters by eyeball through the port.

Why didn't you take a bearing, or better a transit, on some fixed
objects on shore? That way you can really tell for sure if you've moved
outside your swing circle.


... Nevertheless, the feeling did not go away. I
flipped on the depth sounder and it read 4m but then started to chnage
-then 3.5 then 3.0 then 2.5 and that is when I reached for the engine
key. But it stopped rising at 2.3 and we need 1.8m.

I thought you said your depth sounder indicated depth under the keel?

... With little tide
left all would be well. As I watched it slowly increased again. I
deduced that we were ever so slowly swinging over an uncharted rock.
Intrigued I snorkeled out in the morning (Brrrrrr) and saw the rock. We
had laid just enough rode to place out keel right over the center of a
2-3 m wide rock platform with sand and deep water all around it.

Now why did we just end up over a rock? My suspicion is that boats seek
out rocks -is this possible? If so, why do boats seek them out?

The Finagle Factor: perversity of the universe trends towards a maximum.

Same reason why boats sitting around a start line in no wind tend to
magnetically drift together.


Did I wake up because the small swell was accentuated as we swung over
the rock and I sensed it in my sleep?

It's possible.


Any similar experiences?

Mostly, I've awakened at some change that I *thought* meant we were
dragging, but turned out to be harmless. Or fishermen putt-putting by in
the wee hours. Most recently, I woke up about 2 minutes before the turn
of the tide when we were anchored in a channel and swinging to the
current. I watched the boat swing around and settle down peacefully,
dozed lightly in the pilothouse for about an hour waking up every few
minutes, then went back to bed when it was obvious that nothing was
going to happen. This kind of thing is a sailors instinct and almost
everybody who cruises much developes it in some degree.



OzOne wrote:
We seem to become ultra sensitive when hanging off a hook.

Alternately, I was tied alongside a jetty a few years back, dropped
off to sleep and woke to find that I was neatly tied off ON THE OTHER
SIDE of the jetty.
I asked a local about it and he said that fishing boats sometimes use
that wharf to unload. He had helped them quietly move us around the
end and onto the other side without waking us.

Those guys were slick all right. They must unload pretty quietly too!

No mean feat with a 46' yacht.

OK, now you're bragging...

Fresh Breezes- Doug King

Actually, the rise and fall of water over a shallow plug or area does cause
a "suction" effect and will pull you toward it.

See for yourself, just watch the water over a shallowly submerged boarding
ladder, piling or rock. The structure truncates the wave structure
underneath the surface and only allows higher frequency components of the
wave to exist above the shallow, hence the faster waveforms in the water in
the decaying response waveform and the lower frequency components in the
forcing function. In other words, the water drains faster than it fills (or
has a different waveform) and a relative "vacuum" is formed.

BC


"Navigator" wrote in message
...
I've noticed something strange. I had suspected it for sometime but just
a little while ago my suspicion was confirmed. We had sailed to a small
island and moored in the only cove. Chart indicated no hazards, just
sand with small shell bottom. Dropped the anchor (Sarka) in about 4m of
water and laid out about 6:1 rode as per usual. The depth under the keel
indicated 5m. Went to bed. During the night I woke up with a strange
feeling of uncertainty. Perhaps the boat's motion had changed but
nothing obvious. Peering into the blackness, the loom against the stars
indicated we had not moved. Nevertheless, the feeling did not go away. I
flipped on the depth sounder and it read 4m but then started to chnage
-then 3.5 then 3.0 then 2.5 and that is when I reached for the engine
key. But it stopped rising at 2.3 and we need 1.8m. With little tide
left all would be well. As I watched it slowly increased again. I
deduced that we were ever so slowly swinging over an uncharted rock.
Intrigued I snorkeled out in the morning (Brrrrrr) and saw the rock. We
had laid just enough rode to place out keel right over the center of a
2-3 m wide rock platform with sand and deep water all around it.

Now why did we just end up over a rock? My suspicion is that boats seek
out rocks -is this possible? If so, why do boats seek them out?

Did I wake up because the small swell was accentuated as we swung over
the rock and I sensed it in my sleep?

Any similar experiences?

Cheers

It's all explained he

http://www.soest.hawaii.edu/PubServi...fs/Eriksen.pdf

BC

Rocks in your head, MC....actually, it was probably gravimetrical
changes...every time the boat wallowed over the rock, your center of gravity
changed and your inner perceptions, so finely tuned, registered the effect
and awakened you...this would not have happened to a lesser man, say...Doug?
But then, he probably doesn't have a propensity for finding every rock in
the ocean like you do....

--
katysails
s/v Chanteuse
Kirie Elite 32
http://katysails.tripod.com

"Women and cats will do as they please, and men and dogs should relax
and get used to the idea." - Robert A. Heinlein

DSK wrote:

Navigator wrote:

I've noticed something strange. I had suspected it for sometime but
just a little while ago my suspicion was confirmed. We had sailed to a
small island and moored in the only cove. Chart indicated no hazards,
just sand with small shell bottom. Dropped the anchor (Sarka) in about
4m of water and laid out about 6:1 rode as per usual.


Is "sarka" a type of anchor?

Yes it is.

How much scope do you let out to set the
anchor?


Well, it depends on the depth. My rule is not less than 4:1. Often use
6:1 and if it's going to blow let out more still (combination rode).


.. The depth under the keel indicated 5m. Went to bed. During the
night I woke up with a strange feeling of uncertainty. Perhaps the
boat's motion had changed but nothing obvious. Peering into the
blackness, the loom against the stars indicated we had not moved.


??? Dang you're good, doing celestial navigation to within a couple of
meters by eyeball through the port.

Why didn't you take a bearing, or better a transit, on some fixed
objects on shore? That way you can really tell for sure if you've moved
outside your swing circle.


... Nevertheless, the feeling did not go away. I flipped on the depth
sounder and it read 4m but then started to chnage -then 3.5 then 3.0
then 2.5 and that is when I reached for the engine key. But it stopped
rising at 2.3 and we need 1.8m.


I thought you said your depth sounder indicated depth under the keel?


Typo -it's always reading depth under transducer.

Cheers

Interesting idea. What if the wavelength is much longer than the
structure -does that have an effect?

Cheers

Bob Crantz wrote:

Actually, the rise and fall of water over a shallow plug or area does cause
a "suction" effect and will pull you toward it.

See for yourself, just watch the water over a shallowly submerged boarding
ladder, piling or rock. The structure truncates the wave structure
underneath the surface and only allows higher frequency components of the
wave to exist above the shallow, hence the faster waveforms in the water in
the decaying response waveform and the lower frequency components in the
forcing function. In other words, the water drains faster than it fills (or
has a different waveform) and a relative "vacuum" is formed.

BC

katysails wrote:

Rocks in your head, MC....actually, it was probably gravimetrical
changes...every time the boat wallowed over the rock, your center of gravity
changed and your inner perceptions, so finely tuned, registered the effect
and awakened you...this would not have happened to a lesser man, say...Doug?
But then, he probably doesn't have a propensity for finding every rock in
the ocean like you do....

So are you saying I rock?

Cheers