Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:

"robert childers" wrote in message
...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it does
an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full stop in
110 meters, but what happens to the 900 people on board?

This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and 240
cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046" with
three engines in service, as they were the night of the collision, to determine
the crash stop distance of the vessel. This was done by taking her to a preset
speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111 m, in
about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45 seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback" (i.e.,
coming to a dead stop) from 46 knots in just a third of a mile. This is amazing
for a vessel of this size, especially compared to a modern aircraft carrier that
requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of which
could be walking around, I'm sure they would end up with more than one lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...
Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:

"robert childers" wrote in message
...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it
does
an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full
stop in
110 meters, but what happens to the 900 people on board?

Good lord. Do they really think that full astern the best way to slow a
fast vessel? Do you think they felt the extreme cavitation?

Cheers MC

Jeff Morris wrote:

This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and 240
cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046" with
three engines in service, as they were the night of the collision, to determine
the crash stop distance of the vessel. This was done by taking her to a preset
speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111 m, in
about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45 seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback" (i.e.,
coming to a dead stop) from 46 knots in just a third of a mile. This is amazing
for a vessel of this size, especially compared to a modern aircraft carrier that
requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of which
could be walking around, I'm sure they would end up with more than one lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...

Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:


"robert childers" wrote in message
...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it

does

an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full

stop in

110 meters, but what happens to the 900 people on board?

I don't know ... do water jet propulsors cavitate in full reverse?

Or is it possible that this system adjusts the throttle automatically for
maximum thrust?


"MC" wrote in message
...
Good lord. Do they really think that full astern the best way to slow a
fast vessel? Do you think they felt the extreme cavitation?

Cheers MC

Jeff Morris wrote:

This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and
240
cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046"
with
three engines in service, as they were the night of the collision, to
determine
the crash stop distance of the vessel. This was done by taking her to a
preset
speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111
m, in
about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45
seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback"
(i.e.,
coming to a dead stop) from 46 knots in just a third of a mile. This is
amazing
for a vessel of this size, especially compared to a modern aircraft carrier
that
requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of
which
could be walking around, I'm sure they would end up with more than one
lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...

Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:


"robert childers" wrote in message
...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it

does

an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full

stop in

110 meters, but what happens to the 900 people on board?

A water jet vessel is not put in astern by running the engine astern.

Cheers MC

Jeff Morris wrote:

I don't know ... do water jet propulsors cavitate in full reverse?

Or is it possible that this system adjusts the throttle automatically for
maximum thrust?


"MC" wrote in message
...

Good lord. Do they really think that full astern the best way to slow a
fast vessel? Do you think they felt the extreme cavitation?

Cheers MC

Jeff Morris wrote:


This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and

240

cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046"

with

three engines in service, as they were the night of the collision, to

determine

the crash stop distance of the vessel. This was done by taking her to a

preset

speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111

m, in

about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45

seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback"

(i.e.,

coming to a dead stop) from 46 knots in just a third of a mile. This is

amazing

for a vessel of this size, especially compared to a modern aircraft carrier

that

requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of

which

could be walking around, I'm sure they would end up with more than one

lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...


Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:



"robert childers" wrote in message
om...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it

does


an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full

stop in


110 meters, but what happens to the 900 people on board?

I've not seen a system that adjusts for full thrust in reverse or ahead.
But, the 10s crash stop is hardly impressive. Imagine taking 10s to slow
from a gentle run to a stop! Then again, the big water jet cats I've
ridden on here seem to have little power astern. I've also noted that
they power up ahead quite gently and if the throttle is opened
agressively the pump seems to make caviation type noises. It might be
that the water jet intake is optimised for power ahead?

Cheers MC

Jeff Morris wrote:

I don't know ... do water jet propulsors cavitate in full reverse?

Or is it possible that this system adjusts the throttle automatically for
maximum thrust?


"MC" wrote in message
...

Good lord. Do they really think that full astern the best way to slow a
fast vessel? Do you think they felt the extreme cavitation?

Cheers MC

Jeff Morris wrote:


This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and

240

cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046"

with

three engines in service, as they were the night of the collision, to

determine

the crash stop distance of the vessel. This was done by taking her to a

preset

speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111

m, in

about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45

seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback"

(i.e.,

coming to a dead stop) from 46 knots in just a third of a mile. This is

amazing

for a vessel of this size, especially compared to a modern aircraft carrier

that

requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of

which

could be walking around, I'm sure they would end up with more than one

lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...


Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:



"robert childers" wrote in message
om...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and it

does


an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full

stop in


110 meters, but what happens to the 900 people on board?

Frankly, don't know - this is way outside my experience. However, I'm a bit
impressed that a large ship can stop from 10 knots in little over a boat length.
Is this typical for traditional displacement ferries?


"MC" wrote in message
...
I've not seen a system that adjusts for full thrust in reverse or ahead.
But, the 10s crash stop is hardly impressive. Imagine taking 10s to slow
from a gentle run to a stop! Then again, the big water jet cats I've
ridden on here seem to have little power astern. I've also noted that
they power up ahead quite gently and if the throttle is opened
agressively the pump seems to make caviation type noises. It might be
that the water jet intake is optimised for power ahead?

Cheers MC

Jeff Morris wrote:

I don't know ... do water jet propulsors cavitate in full reverse?

Or is it possible that this system adjusts the throttle automatically for
maximum thrust?


"MC" wrote in message
...

Good lord. Do they really think that full astern the best way to slow a
fast vessel? Do you think they felt the extreme cavitation?

Cheers MC

Jeff Morris wrote:


This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and

240

cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046"

with

three engines in service, as they were the night of the collision, to

determine

the crash stop distance of the vessel. This was done by taking her to a

preset

speed and then setting the engine control to 100 per cent power astern. At
a
speed of 10 knots the ferry was able to come to a complete stop within 111

m, in

about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45

seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback"

(i.e.,

coming to a dead stop) from 46 knots in just a third of a mile. This is

amazing

for a vessel of this size, especially compared to a modern aircraft carrier

that

requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of

which

could be walking around, I'm sure they would end up with more than one

lawsuit.

BTW, this was originally built for the Bass Strait run.


"MC" wrote in message
...


Do you really mean 10 knots to full stop in 110 meters? If so, that's a
fairly gentle stop from a slow 'fast cat'.

Cheers MC

Jeff Morris wrote:



"robert childers" wrote in message
om...
IMHO a kayak would not be an impediment to a large vessel in any of
the cases you are citing. They'd scarcely know there were bits of
fiberglass in their wake.

You're quite correct - but what if the vessel is a high speed ferry and
it

does


an emergency stop? The Bar Harbor Fast Cat can go from 10 knots to full

stop in


110 meters, but what happens to the 900 people on board?

I've been on a Fast Cat (@35k) during a crash stop, as a demonstration.
Stopping distance was within a boat length (this was one of the larger
cats) The maneuver doesn't involve changing engine speeds, just the
direction of the waterjet thrust, and was well within the bounds of most
people to easily stay upright (G though grabbing something was a good
idea).
I've also done this maneuver on Z-drive tugs .... same results ....
fact, we sometimes use this maneuver for pilot boarding. .... come down
the side of ship on opposite heading at about 5-6 k, crash stop and go
astern,in the opposite direction at 6-8k while coming alongside (ship
maintains 7-8 k).... (eg scares the bejeebers out of the first time
onlookers).

otn

Jeff Morris wrote:
This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and 240
cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046" with
three engines in service, as they were the night of the collision, to determine
the crash stop distance of the vessel. This was done by taking her to a preset
speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111 m, in
about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45 seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback" (i.e.,
coming to a dead stop) from 46 knots in just a third of a mile. This is amazing
for a vessel of this size, especially compared to a modern aircraft carrier that
requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of which
could be walking around, I'm sure they would end up with more than one lawsuit.

BTW, this was originally built for the Bass Strait run.

So when you say "well within the bounds of most people to easily stay upright"
does that mean that out of 900 tourists given no warning, a number would land on
their butt?

How quickly does the thrust get reversed? 35 knots is 60 feet/second - if it
takes several seconds to do the reverse, that leaves well under a boatlength for
the serious deceleration.

This reminds me of another question I've had for a "pro." How quickly do you
figure a helmsman would react to a hazard in the water, especially given no
warning. For combat situations, I've heard it varies between a second or two
for the pro, to about 6 seconds for the civilian. From my own experience, I
feel like I respond pretty quickly if an event is something that I'm
anticipating, but the last I had a "close encounter" in the I was disappointed
that I felt like 2 or 3 seconds passed before I reacted. However, I was able
to do a crash stop before things got hairy, the T-boat that would have hit me
never flinched.

-jeff


"otnmbrd" wrote in message
...
I've been on a Fast Cat (@35k) during a crash stop, as a demonstration.
Stopping distance was within a boat length (this was one of the larger
cats) The maneuver doesn't involve changing engine speeds, just the
direction of the waterjet thrust, and was well within the bounds of most
people to easily stay upright (G though grabbing something was a good
idea).
I've also done this maneuver on Z-drive tugs .... same results ....
fact, we sometimes use this maneuver for pilot boarding. .... come down
the side of ship on opposite heading at about 5-6 k, crash stop and go
astern,in the opposite direction at 6-8k while coming alongside (ship
maintains 7-8 k).... (eg scares the bejeebers out of the first time
onlookers).

otn

Jeff Morris wrote:
This is for a vessel 91 meters long, d5617 tons, carrying 900 passenges and
240
cars.

From the accident report:
"After the collision, a speed trial was performed on board the "INCAT 046"
with
three engines in service, as they were the night of the collision, to
determine
the crash stop distance of the vessel. This was done by taking her to a
preset
speed and then setting the engine control to 100 per cent power astern. At a
speed of 10 knots the ferry was able to come to a complete stop within 111
m, in
about 30 seconds. The speed was then increased to 14 knots and the test
performed again. The ferry was able to stop within 163 m, in about 45
seconds."

From a Navy evaluation:
"In addition, it demonstrated the capability of performing a "crashback"
(i.e.,
coming to a dead stop) from 46 knots in just a third of a mile. This is
amazing
for a vessel of this size, especially compared to a modern aircraft carrier
that
requires approximately 2 miles to stop."
http://www.tea.army.mil/pubs/nr/depl...HSSarticle.pdf

I admit this isn't pulling that many G's, but out of 900 people, many of
which
could be walking around, I'm sure they would end up with more than one
lawsuit.

BTW, this was originally built for the Bass Strait run.

Jeff Morris wrote:
So when you say "well within the bounds of most people to easily stay upright"
does that mean that out of 900 tourists given no warning, a number would land on
their butt?

Possibly, but I didn't consider the sensation to be all that greater
than correcting for normal seaway motion when moving .... just longer in
duration.

How quickly does the thrust get reversed? 35 knots is 60 feet/second - if it
takes several seconds to do the reverse, that leaves well under a boatlength for
the serious deceleration.

I couldn't give you numbers, but the maneuver consist of moving a "pot"
over the "jet" thrust to redirect flow and I'd put it in the 2-3 second
category.

This reminds me of another question I've had for a "pro." How quickly do you
figure a helmsman would react to a hazard in the water, especially given no
warning. For combat situations, I've heard it varies between a second or two
for the pro, to about 6 seconds for the civilian. From my own experience, I
feel like I respond pretty quickly if an event is something that I'm
anticipating, but the last I had a "close encounter" in the I was disappointed
that I felt like 2 or 3 seconds passed before I reacted. However, I was able
to do a crash stop before things got hairy, the T-boat that would have hit me
never flinched.

-jeff

Tough to say and would depend on many factors, not the least of which is
the particular helmsman (pro or civilian). One big factor will be
experience level .... to see, assess, understand, and react, based on
past experience with similar situations. The attention level of the
particular helmsman (either pro or civilian) at the right moment will be
another factor.

otn