In article ,
says...
.... 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?



Well?
How about an answer on this one?

It's in the jug. Where's the jug? What's the overall effect of 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?


Dave Doe wrote:
Not a lot no.

Which means yes.

Correct, never denied (2nd or 3rd or 4th time I've had to say that?).
The righting factor is almost purely *density* related though. Hint:
think about what you're 'in' and what you 'are' and what you 'have' to
provide righting moment.

Clearly - any material not exceeding the density of what you are 'in' is
going to be poor. Given 'ideal' (no mass boat) - it's extremely poor.
Add the mass of the boat itself, it's even worse performance wise.

Ah good, so now we've gone from "Water cannot be ballast
because it doesn't weigh anything when below the waterline"
to admitting that something that is in fact lighter than
water *can* function as ballast below the water line,
although not as efficently as denser material.

Sorry if you're a pedantic ******* - my argument simply asks to
compare the effectiveness of water ballast righting ability vs lead
keel. PS: I think you've misquoted me - indeed I think you have taken
the ol' poetic licence thingie and just made up my "quote" - if so, yer
a *******. If not, sorry, but water (or any mass) is a ballast that has
inertia (perhaps I've confused folk with stability when I mean momentum
or inertia) - however that does *not* go hand in hand with righting
ability. Again, sorry for any confusion there, I take 1/2
responsibility.

I've posted the comparison question. Send your answers to D. Conners.


Think it over some more. I compliment you on your ability to
gradually recognize facts contrary to your prejudices. Most
people can't ever take this first small step.

Hmmm, I think you're comment quite pretentious. How about we keep to
fact not fiction. My initial reply to the OP was stability in terms of
momentum or inertia (due mass) - and not stabilty in terms of righting
ability (due density). I hope that is clear.

--
Duncan

.... 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 Doe wrote:
It's in the jug. Where's the jug? What's the overall effect of the jug?

It is lower in the water because of its increased weight.
Hence, increased displacement.... it should be very obvious
that the water in the jug has weight.



Not a lot no.

Which means yes.


Correct, never denied (2nd or 3rd or 4th time I've had to say that?).

Like 2nd or 3rd or 4th time you've "had" to say that 'water
doesn't weigh anything in water.'


The righting factor is almost purely *density* related though.

No, it isn't.

It is related to weight (pushing down on mass) and bouyancy
(pushing up on volume).

... Hint:
think about what you're 'in' and what you 'are' and what you 'have' to
provide righting moment.


I am explaining exactly that. Density has nothing to do with
the basics of how stability is achieved.


Clearly - any material not exceeding the density of what you are 'in' is
going to be poor.

Wrong.



Sorry if you're a pedantic *******

Trying to clear up your prejudices & misconceptions makes me
a pedantic *******?

Thanks.

DSK

"Dave Doe" wrote in message
. nz...

You clearly have no idea what MASS and DENSITY are about.


Yes I do, I have a lot of MASS and you are DENSE.

SBV

"Dave Doe" wrote in message
. nz...

Can you sink a 'positive buoyancy' boat with water? Can you
sink it with
lead? You've proven my own point.



What do submarines fill their ballast tanks with?

Jax?




"Dave Doe" wrote in message
. nz...
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.

ie stability.

... 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.

Provide some evidence.

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.

Where is 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?

What is your point? Put feathers in the bottom of your boat?
Or put
water? Or go deeper 1and put lead? I think you need to
consider the
basics when considering a sailing vessel; water on or about the
centerline is a waste of potential that is even more easily
achieved
otherwise. It is the same density of the stuff you're moving
through -
it's a very major factor, as you're floating on it. Consider
the
obvious. When the boat is on an angle the only force the water
can
exert is on the air below it and not the water (it exerts no
effective
force on the water if you can get your head around that). And
that is
only because it is held there in it's ballast tank and not
allowed to
'seek it's natural place at the bottom' (it's heavier than the
surrounding air - but please don't dissregard the whole
equation - what
the boat is in).

Consider the absurd, a boat of no mass other than its water
ballast. It
will sit in the water, level with the ballast waterline. If you
are to
heel it - well you work it out. The maths is easy, consider
the water
ballast as a "solid" (as it cannot move).

Then consider the same mass many times denser at a point well
beyond the
fulcrum point the water ballast is on.

Also think of boat speed and drag (wetted area).

Short of moving magically moving the water ballast from one
side to the
other - same as the tack - water ballast is a crock.

It's a lot heavier than air, but look at "what you're doing"
and the
alternatives.

Come on - do my maths (example question posed already, no
answers yet)

--
Duncan

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

"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.

Is the water in a plastic floating in the ocean:
a) in the plastic bag?
b) in the water?

Well technically, it's in the plastic bag. Is the plastic bag
a factor?
No.


So now plastic is weightless too? Oh, the fact that you can see
through it is fooling you.

Scotty

In theory, if you sealed your mast and filled it with helium,
would that decrease 'weight aloft'?

Help with stability?

SBV



"DSK" wrote in message
t...
.... You used the example of an empty jug vs one

In article ,
says...
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.


Dave Doe wrote:
ie stability.


There is a difference between static stability ei righting
moment, and dynamic stability or roll resistance. The first
is relatively simple, the latter vastly complex and
influenced by underwater foils, distribution of mass,
distribution of hull volume & reserve bouyancy, etc etc.

Correct me if I'm wrong, Dave: you started out by saying
that water ballast cannot generate righting moment.

No I said it provides stability - which you have accurately identified
above as intertial/momnentum type stability vs righting moment.

Righting moment - for us yachties - is, to me, very questionable vs
traditional keel weighted systems.

This is a yachting NG not a ship NG. Performance is foremost. I've
posted a comparison question. And indeed continue to question the
effectiveness (or lack of) of water ballasted sailing vessels. As said:
what you are 'in', what you 'are, and what your 'ballast is' - are
"relatively" important in terms of *density*.

Here's a comparison in air:
To fly a plane two important calculations have to be done:
1. must be below MAUW (maximum all up weight). This equates to having a
boat that is denser than water - yer sink. (OK, not really, safety
margin involved but any folk that "know" can see by your takeoff if
you're overloaded - sticks out like a sore thumb).
2. must be within center of gravity limits (stated 'arms' for postions
on the plane: rear seats, front seats, wings (fuel), calc moments for
those based on masses in those positions, add 'em up - is it 'in the
envelope'?). In a *yacht* - the very opposite applies, the COG (or arm
or leverage point) needs to be as displaced as possible - this is
maxmised by mass/density and leverage (arm (distance "away")).

You have yet to convince me how a water ballasted yacht does a good job
of that given it fails on both counts: mass due density/volume and
leverage.

... 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.


Provide some evidence.


That lots & lots of water ballast boats are out there
sailing? That I've personally sailed about a dozen boats
with water ballast, and found them to have no significant
difference in the way they sail compared to lead ballasted
boats?

For example, we owned & sailed a 19' water ballasted sloop
for eleven years. Many times at club get-togethers, people
would say "Is a water ballast boat stable enough"? I would
say, "Step on the gun'l and see." People would always
conclude, after this very real test, that our boat was just
as stable as 21 foot & 22 foot boats with lead ballasted
swing keels & keel/centerboards. It's a question of how the
boat is designed, not the material used for ballast.

It has everything to do with the ballast material - specifically the
density of. If the ballast was not at least the density of water, it
would not right if it was flooded with water, would it? Indeed it would
turn the boat upside down. Isn't that why poly and other 'lighter than
water' materials are put in at or near the topsides of boats - to keep
them upright and in some cases floating when "sunk"? (they are of
lesser density than water).

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.


Where is the boat?


Floating.

In? Density of that stuff? Relativity is important here. Density of
water is 1000kg/m3 at STP. Consider any boat; it's volume, it's mass -
and therefore its density. *ANY* boat with a density less than
1000kg/m3 will therefore float (better be pedantically correct: fresh
water: STP). So long as the 'boat' has itself, a displaced center of
gravity (feathers as some would like) then it will have righting force -
albiet your sailboat, not mine. For yachting, that is a *very*
important factor. We're not just using righting force against a
possible capsize - we're sailing. So "maximise the righting moment" is
a designer's goal surely.


AGAIN-
If the water ballast did not "weigh anything" then the boat
would not get lower in the water when the ballast tank is
filled.

100kg of anything will displace 100liters of fresh water at STP - right.

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?


What is your point?

That water ballast works just fine.


... I think you need to consider the
basics when considering a sailing vessel;

We have done exactly that, Dave.

.... water on or about the
centerline is a waste of potential that is even more easily achieved
otherwise.

Really? Like what?

Everything denser than water. If as a keel, it will have less wetted
area and provide leverage. If 'in the boat' it will occupy less space
and so be closer to the centerline in terms of height and width however
it will provide little leverage (but still be better than anything less
dense in the same place).

.... It is the same density of the stuff you're moving through -
it's a very major factor, as you're floating on it.

Actually, it's not a factor at all. Water is heavy. Put it
down low in the boat, and it functions as ballast.

"Water is heavy" is a meaningless statement. Indeed in the perspective
it should be viewed: the boat, the ballast and the water - it's heavier
than much of the boat (it won't work otherwise).

Water is as heavy as it is - specifically 1000kg/m3 (I guess I need to
spell it out: fresh water, STP). So we have a density factor. That's
what we are floating IN.

You have admitted a lead keel is a lot better yerself. OK, yer comments
above re your water ballasted yachting days noted; digested and now laid
to rest in the most private room in the house - um... you sail in a
traditional lead type keel fined boat now?

You're racing tomorrow - it's gonna be close. You have a full holding
tank and water tank. Both lower GOG. Gonna leave 'em that way?


.... Consider the
obvious. When the boat is on an angle the only force the water can
exert is on the air below it and not the water (it exerts no effective
force on the water if you can get your head around that).

Wrong, wrong, and wrong.

Does the force of gravity have some sort of sixth sense that
the water ballast is "exerting force on the air below it"?

No, gravity pulls downward equally on the water ballast at
all times, just as it does on the hull, the crew, the beer,
and for that matter, the water that the boat is floating in.

Sorry for my rough physics - however my argument is - in essence the
same thing... do I need to explain? - I guess so... the air 'below' the
water is the air that is just that - below and to one side of the water
(the boat is say at 45 deg). Gravity will exert a greater force,
effectively, on one side of the boat, due the water being more on that
side, and the air more on the other. The effective force itself - will
be the "water on one side over the air on the other".

Consider the absurd, a boat of no mass other than its water ballast. It
will sit in the water, level with the ballast waterline. If you are to
heel it - well you work it out. The maths is easy, consider the water
ballast as a "solid" (as it cannot move).

The ballast lowers the center of gravity of the boat. As the
boat heels, the center of bouyancy shifts to the low side.
The center of bouyancy pushes up, the center of gravity
pushes down, when the boat is level they are in alignment.
When the boat is heeled, there is a lever arm between the
forces which is the force we call "righting moment."

A given displacement & a given lever arm will give the same
righting moment, whether the ballast is lead or feathers. It
is true that lead can be placed lower in the boat, but that
doesn't change the basic physics of stability.

I wouldn't agree with that at all. You correctly state COG - nice to
see you are getting it. Lead is heavier than water, it can therefore
increase righting moment: acting a) as a heavier and denser mass and b)
at beyond the centerline of the boat, greatly increasing leverage or
arm. Anything less dense will result in decreased arm if mass is held
constant. This applies to water ballasts.

Short of moving magically moving the water ballast from one side to the
other - same as the tack - water ballast is a crock.


Wrong. Just look at the plain facts.

It's a lot heavier than air, but look at "what you're doing" and the
alternatives.

Come on - do my maths (example question posed already, no answers yet)


I have given you many sensible answers, and tried to explain
the physics in easy terms. I thought you were getting the
point, but no you reply that 'it's a crock.' So good bye, Dave.

No probs, I've got my books nearly done - so won't be back to read
anymore crocks for another day - you're off the hook for 12 hours.


--
Duncan

In article ,
says...

"Dave Doe" wrote in message
. nz...

Can you sink a 'positive buoyancy' boat with water? Can you
sink it with
lead? You've proven my own point.



What do submarines fill their ballast tanks with?

positive bouyancy boat submarine - EVER.

--
Duncan

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

"Dave Doe" wrote in message
. nz...

Can you sink a 'positive buoyancy' boat with water? Can you
sink it with
lead? You've proven my own point.



What do submarines fill their ballast tanks with?

positive bouyancy boat submarine - EVER.


Bzzzt...Oh, I'm sorry, the correct answer is ''WATER'' .

Thanks for playing.

SBV