I guess all those big ships with water ballast tanks are just
pretending.

Scotty


"DSK" wrote in message
. ..
Dave Doe wrote:
a) What is the *point* of your experiement? - other than to
only prove
my argument correct.


Dave, since your argument is not correct, it would be pretty
hard to prove.

Are you saying that the water ballast inside a boat hull
does not affect it's stability? That the water ballast
"weighs nothing" until it is above the waterline?

If that were true, the boat's waterline would be the same
when the ballast tank was empty as when it is full.

Does the boat's displacement increase when the ballast tank
is filled? If so, then the the water ballast "weighs"
something, regardless of where it is relative to the waterline.

If the unit conter of gravity is below what the boat's
Center of Gravity would be without the ballast, then it
increases the boat's stability, regardless of whether the
tank is above or below the waterline.

b) try this (your experiment pretty much, say 4) ...

So 3/4 full. Hold the bottle at the top and note the weight.
Slowly
lower it into the water. Note the weight changing! ??? How
can it be
getting lighter all by itself?


Try this experiment.

Float an empty bottle. Mark where the waterline is.

Now fill it however full you want, 1/4 or 3/4 or whatever.

Does the bottle sink any deeper into the water?

No?

Then it "weighs" more, the water inside the bottle must be
weighing it down.



PS: experiment not conducted, just using simple physics.
Feel free to
do it and get back to me if I'm wrong.


Yep, it's just simple physics. But a number of people have
tried to proclaim that water ballast can't possibly work
because "water doesn't weigh anything in water." But it
obviously *does* work, and the physics (when considered
correctly) show why.

Fresh Breezes- Doug King

Scotty wrote:

I guess all those big ships with water ballast tanks are just
pretending.


Of course they are. It's just a scam to irritate the
enviro-whackoes.

The Navy is in on the joke, too...
http://p2library.nfesc.navy.mil/P2_O...book/11_9.html

Notice that ship stability takes a back seat to needling
those tree-hugging pinheads: (quote from the above web site)
"Ships with water compensating fuel systems (WCFS) are not
allowed to discharge compensating ballast water overboard in
some navy ports. Navy ship destroyers (e.g., Spruance and
Kidd class) and cruisers (Ticonderoga class) are designed
with WCFS to enhance ship stability."

DSK

"Scotty" wrote in message
...
I guess all those big ships with water ballast tanks are just
pretending.

Scotty

That, and they're stealing fresh water from the Great Lakes to take back to
Europe.

Max

"Maxprop" wrote in message
ink.net...

"Scotty" wrote in message
...
I guess all those big ships with water ballast tanks are just
pretending.

Scotty

That, and they're stealing fresh water from the Great Lakes to
take back to
Europe.


Yes buy, don't they give you guys Euro mussels in exchange?

SBV

In article ,
says...
Dave Doe wrote:
a) What is the *point* of your experiement? - other than to only prove
my argument correct.


Dave, since your argument is not correct, it would be pretty
hard to prove.

Are you saying that the water ballast inside a boat hull
does not affect it's stability? That the water ballast
"weighs nothing" until it is above the waterline?

Nope, never did. I'm saying it's stability is indeed improved (more
mass to move), but question its righting ability vs lead keel - and
posed a question about that.

The problem is that water in the ballast has the same density of the
water it is in - lead is 10? times heavier.

See my reposted question - easy figures inserted, cheers.

--
Duncan

In article ,
says...

"Dave Doe" wrote in message
. nz...
In article ,
says...
OK, Duncan. here's a little experiment you can do in your
bathtub.

1. Put an empty Coke bottle in the water. Observe how it
floats.
2. Fill the Coke bottle 1/4 with water. Observe how it
floats.
3. Fill the bottle 1/2 way. Observe how it floats
4. Fill it 3/4 full. Observe how it floats
5. Is the water in the coke bottle below the tub water
surface?
6. Wash your butt last.

Scotty

a) What is the *point* of your experiement? - other than to
only prove
my argument correct.


To prove to you that water BELOW the water line can still act as
ballast.

Indeed it can and I have not questioned that, only it's effectiveness as
not just ballast, which I have stated provides a positive stability
factor - but I question its effectiveness when used as a righting
moment. And further posed the question:

How much water ballast (approx litres) does it take to equal say
200lbs of lead hanging 6' down (on say a swing keel)?

To make it easier, how about we metricate it all for ease of
calculation:

Assume Standard Temp & Pressure (STP)
How much fresh water (density: 1000kg/m3) does it take to equal 500kg of
lead (density: 7140kg/m3) hanging 2m down with the boat at 45deg? Water
ballast tank at 1m wide and the boat is in fresh water (also at STP).

Feel free to use other figures, I've adjusted from my original, using
hopefully more "average" figures and rounded to make calcs easier.

So how much water?

And... looking at say a Mac, they say they have 1150lbs of water
ballast, that's about 520kg.

You change the figures if you think mine are unrealistic - I'd just like
to see the comparision.

PS: only got to sail against a Mac 26M once out in Lytellton; my boat's
just under 25' - the Mac is 26'. We thrashed it. (They might be quite
competative in light air; 5knts or below). My boat's 23? years old, the
Mac is less than 1. It's longer.

--
Duncan

"Dave Doe" wrote in message
. nz...
In article ,
says...

"Dave Doe" wrote in message
. nz...
In article ,
says...
OK, Duncan. here's a little experiment you can do in your
bathtub.

1. Put an empty Coke bottle in the water. Observe how it
floats.
2. Fill the Coke bottle 1/4 with water. Observe how it
floats.
3. Fill the bottle 1/2 way. Observe how it floats
4. Fill it 3/4 full. Observe how it floats
5. Is the water in the coke bottle below the tub water
surface?
6. Wash your butt last.

Scotty

a) What is the *point* of your experiement? - other than to
only prove
my argument correct.


To prove to you that water BELOW the water line can still act as
ballast.

Indeed it can and I have not questioned that, only it's effectiveness as
not just ballast, which I have stated provides a positive stability
factor - but I question its effectiveness when used as a righting
moment. And further posed the question:

How much water ballast (approx litres) does it take to equal say
200lbs of lead hanging 6' down (on say a swing keel)?

To make it easier, how about we metricate it all for ease of
calculation:

Assume Standard Temp & Pressure (STP)
How much fresh water (density: 1000kg/m3) does it take to equal 500kg of
lead (density: 7140kg/m3) hanging 2m down with the boat at 45deg? Water
ballast tank at 1m wide and the boat is in fresh water (also at STP).

Feel free to use other figures, I've adjusted from my original, using
hopefully more "average" figures and rounded to make calcs easier.

So how much water?

And... looking at say a Mac, they say they have 1150lbs of water
ballast, that's about 520kg.

You change the figures if you think mine are unrealistic - I'd just like
to see the comparision.

PS: only got to sail against a Mac 26M once out in Lytellton; my boat's
just under 25' - the Mac is 26'. We thrashed it. (They might be quite
competative in light air; 5knts or below). My boat's 23? years old, the
Mac is less than 1. It's longer.

--
Duncan

My understanding is that the Macs have an optimal window of between 7-10
kts.wind, they will hardly move in light air. Tiny rig and sailplan. Have
seen a rating for the old 26X at 226, IIRC, but I'm willing to bet that it's
very tough to sail anywhere near it's rating. Anecdotal, but I was sailing
back to the marina one day, playing with the a-sail, and I passed an x that
didn't appear to be moving, my knotmeter was reading 3-4 kts, maybe around 5
kts.of wind.

John Cairns

Are you saying that the water ballast inside a boat hull
does not affect it's stability? That the water ballast
"weighs nothing" until it is above the waterline?


Dave Doe wrote:
Nope, never did. I'm saying it's stability is indeed improved (more
mass to move)

That would be an issue of inertia... dynamic stability, if
you like the term.

... but question its righting ability vs lead keel - and
posed a question about that.


Well, I don't think that anybody has claimed that water
ballast provides equal righting moment to external lead
ballast. But it can provide significant righting moment,
especially if the boat is designed from the start to utilize
water ballast effectively.


The problem is that water in the ballast has the same density of the
water it is in

Well there you go again. The water ballast is not "in water"
it is in the boat. Will no amount of repetition get this
point across? You used the example of an empty jug vs one
1/2 full of water... is the water in the jug "in water" or
is it in the jug?

Let me propose this example- a cooler full of ice & beer is
lighter than water (hence lighter than water ballast) yet
can be pretty heavy when you're carrying it down the dock.
If you put it in the lowest possible location in the boat,
right down against the hull, and tie it in securely (to the
handles, so you can still open the lid of course), will this
improve the boat's stability?

DSK

"DSK" wrote in message
. ..

Well there you go again. The water ballast is not "in water"
it is in the boat. Will no amount of repetition get this
point across? You used the example of an empty jug vs one
1/2 full of water... is the water in the jug "in water" or
is it in the jug?


Dave just doesn't get it.
And he refuses to do any experiments because he is afraid of
water.

Scotty

In article ,
says...
Are you saying that the water ballast inside a boat hull
does not affect it's stability? That the water ballast
"weighs nothing" until it is above the waterline?


Dave Doe wrote:
Nope, never did. I'm saying it's stability is indeed improved (more
mass to move)

That would be an issue of inertia... dynamic stability, if
you like the term.

... but question its righting ability vs lead keel - and
posed a question about that.


Well, I don't think that anybody has claimed that water
ballast provides equal righting moment to external lead
ballast. But it can provide significant righting moment,
especially if the boat is designed from the start to utilize
water ballast effectively.


The problem is that water in the ballast has the same density of the
water it is in

Well there you go again. The water ballast is not "in water"
it is in the boat. Will no amount of repetition get this
point across? You used the example of an empty jug vs one
1/2 full of water... is the water in the jug "in water" or
is it in the jug?

Let me propose this example- a cooler full of ice & beer is
lighter than water (hence lighter than water ballast) yet
can be pretty heavy when you're carrying it down the dock.
If you put it in the lowest possible location in the boat,
right down against the hull, and tie it in securely (to the
handles, so you can still open the lid of course), will this
improve the boat's stability?

Not a lot no. However if you use something that's heavy. You can use
feathers if you like - good luck.

--
Duncan