otnmbrd wrote:
snip
course, this doesn't address the surfacing sub issue.......

Nor does being awake and looking, when it comes from underneath...

Andy.

New Conservative wrote:
Hi all,

I haven't actually sailed a boat yet but plan to later this year. I am
therefore still a bit green when it comes to the intricacies of the
subject.
Say I'm keen to visit the West Indies and I'm leaving from say
Southampton, England. I'm on my own and will need to sleep every day,
even if only for a few hours. Is it safe to let a boat 'sail herself'
while I catch some shut-eye, or is this a no-no?

Is it safe - not really because of the risk of a larger vessel turning
your boat into smaller pieces. I had an acquaintance who was single
handing who was bashed into by a cruise ship. He swore he was just
below for 15 minutes having a cup of tea and updating the chart
position.

Ships can come over the horizon in about 10 minutes to your position
if moving at say 22 knots. They seldom keep a good lookout at sea in
my experiences, and a small boats lights at night are only visible 2
miles away. At 22 knots that's a pretty short time to notice a
contact and alter course for the big ship. Big ships often have their
radar off during the day too.

Can it be done safely
or would I have to drop all sail and just bob around in the dark for a
while until I've awoken?

Dropping sail just makes you a stationary target rather than a moving
one and increases your exposure time.

Obviously it'd make for a shorter passage if
I could somehow keep going 24/7. And ideas? Thanks.

1. Consider taking a crew member just for the offshore passage from
England to the West Indies. Crew fatigue is probably one of the
biggest causes of accidents on offshore trips

2. If you're determined to do it solo, invest in a Radar with a
"guard zone"; a radar detector like a CARD, and carry life insurance.
Get a timer that wakes you every fifteen minutes to look around.

3. The most dangerous times are within a few hundred miles of the
coast but that is probably 48 hours of sailing for a typical cruising
boat so you need to be alert for that time period. That's a long time
to be alert after an ocean passage.

In short it's not a good idea, although people do it.

Evan Gatehouse

Evan Gatehouse wrote:

Ships can come over the horizon in about 10 minutes to your position
if moving at say 22 knots.

AFAIK the horizon is 22 odd miles away. A ship moving at 22kts would
therefore take about an hour to get to you.

Dan wrote:
Evan Gatehouse wrote:

Ships can come over the horizon in about 10 minutes to your
position
if moving at say 22 knots.

AFAIK the horizon is 22 odd miles away. A ship moving at 22kts would
therefore take about an hour to get to you.


Sort of. A bunch of common misconceptions revolve around the "horizon".
Your horizon, the water perimeter you see will be around 2-3 miles
depending on your height. The ship on the other hand being much higher,
and with lights high up at night, will have much longer horizon of its
own. Couple those to get the distance at which you see it, and you are
looking at 15+ miles.

On the other hand, take one of those bloody cross channel cats at 40
Knots and it get s a bit more interesting.

PyroJames

The horizon depends on the height of your eye - the dipping distance
tables in the almanac give the distance off for height. You will see
objects above sea level 'over the horizon' according to their height so
as the ship approaches, you will see more of it.

It is all in the yachtmaster shorebased course - possibly day skipper too!

Nick

Dan wrote:
Evan Gatehouse wrote:


Ships can come over the horizon in about 10 minutes to your position
if moving at say 22 knots.


AFAIK the horizon is 22 odd miles away. A ship moving at 22kts would
therefore take about an hour to get to you.

Nick wrote:
The horizon depends on the height of your eye - the dipping distance
tables in the almanac give the distance off for height. You will see

objects above sea level 'over the horizon' according to their height
so
as the ship approaches, you will see more of it.

70 foot high ship viewed from 3 metres high. I can't be arsed to do the
maths but I bet it isn't *far* off 22 miles.

What would you estimate?

Dan wrote:
Nick wrote:

The horizon depends on the height of your eye - the dipping distance
tables in the almanac give the distance off for height. You will see


objects above sea level 'over the horizon' according to their height

so

as the ship approaches, you will see more of it.


70 foot high ship viewed from 3 metres high. I can't be arsed to do the
maths but I bet it isn't *far* off 22 miles.

What would you estimate?


Not quite that far. Dipping distance(nm) is 2.08 * SQRT(height in
metres). 3 metres gives a horizon at 3.6 nm. The 21 metre ship has a
dipping distance of 9.5 nm. So at 13.1 nm you will see the tops of the
masts and at 3.6 nm you will see the hull down to waterline.

On 1 Mar 2005 01:24:24 -0800, "Dan"
wrote:

AFAIK the horizon is 22 odd miles away. A ship moving at 22kts would
therefore take about an hour to get to you.

=========================================

That's way optimistic, even for a good radar. Good sized boats
disappear from view on my flybridge at around 8 miles, small boats at
2 to 4 miles.

Ships can come over the horizon in about 10 minutes to your position if
moving at say 22 knots. They seldom keep a good lookout at sea in my
experiences, and a small boats lights at night are only visible 2 miles
away. At 22 knots that's a pretty short time to notice a contact and
alter course for the big ship. Big ships often have their radar off
during the day too.

Let me try to clear up some serious misconceptions:

First, your "visible horizon" depends on two things: height of eye and
your atmospheric visibility. With a height of eye of 8 feet (rough
guess of your height of eye on a small yacht) your visible horizon in
clear conditions is roughly 3 miles. To calculate how far you might see
a "big ship", you'd add the distance of the horizon for the ship's
superstructure (say 9 miles for a 60 foot high ship). So in this case,
the furthest you'd be able to see this ship is roughly 12 miles, and
quite possibly alot less than that. If you don't believe me, look it up
in Bowditch.

Second, what speed ships operate at runs the gammut, but what I consider
to be the "big guys": super containerships, tankers and cruise ships,
normally run around 32-36 knots.

So best case scenario: you're sailing (at 6 knots) towards a ship
(steaming at 32 knots) that's on a reciprocal course, so you're closing
at roughtly 42 knots. So time from first visible at 12 miles to
collision is roughly 17 minutes. Remember, that's a "best case"
scenario with an "alert" lookout.

Third, it's been my experience (30+ years at sea) that almost every
merchant vessel at sea maintains a -very good- watch and lookout. There
are exceptions though, and a few particular flags (China and N. Korea
come to mind) have a reputation for not responding to hails. It's been
my experience, both as an officer in the merchant marines and a fellow
cruiser, that it's our fellow cruising community that most frequently
fails to maintain a proper lookout.

The problem for merchant ships is that small sailing vessels are just
hard to see. VERY hard to see. They usually present a poor RADAR
target and have dim or no navigation lights.

Fourth, by law all ocean going merchant ships are required to be fitted
with and operate their RADARs. If a ship has a RADAR failure, they are
required by law to head directly to port and not get underway until it's
been fixed (there's more to it than this over simplification, but I'll
spare you the details). I know of no ship's master that would risk
his/her license and livelyhood by allowing their RADARs to be secured
while operating at sea. Your comment to the contrary is complete nonsense.

On the otherhand, I'd bet at least 90% of the cruising yachts out there
(based on what I've seen) only use their RADAR in fog, and rarely in
open ocean.

Over the years I've met a great number of cruisers that:

- all hands sleep below at night, no lookouts at night;
- turn off navigation lights at night to "conserve power";
- never operate their RADAR, except near shore in fog;
- never monitor VHF hailing frequencies;
- have little or no knowledge of the Nautical Rules of the Road.

.... all very "unseamanlike" and fool-hardy practices IMHO.

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So best case scenario: you're sailing (at 6 knots) towards a ship
(steaming at 32 knots) that's on a reciprocal course, so you're closing
at roughtly 42 knots.

OOPS, I mean't to use a ship at 36 knots in this example.

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