On Sun, 20 Mar 2005 16:52:00 -0500, Marley wrote:

Short Wave Sportfishing wrote:

On Sun, 20 Mar 2005 15:36:54 -0500, Marley wrote:


Izmack wrote:

Hi Everyone,

We are looking at at late 80's Trojan F32 with very high moisture
readings in the hull, but zero signs of blistering either currently or
in the past. Our surveyor, who was VERY thorough, said the following:

"Bottom was found in above average condition, having no signs of
blistering,crazing or delamination. High moisture levels were noted,
ranging between 80-100 and some crusty deposits were noted, indicating
laminate hydrolysis. Recommendation to dry store vessel each winter off
season to maintain current good condition. If vessel is left overboard,
some blistering or delamination could be expected over time."

I know I'm asking for a barrage of opinions, but, considering it's a 16
year old boat and the fact we are first time boat buyers and that the
rest of the survey was above average, what do you all think? And -
will future buyers balk at resale?


You need to better understand moisture meters and readings.

Moisture meters have to be calibrated very carefully.

For example they are used extensively in determining the amount of
moisture in lumber when it is being or has been cut or kiln dried. In
order to make that determination the user first sets the calibration of
the meter against a known standard. In other words, using a piece of
identical lumber of a specific known moisture content that is kept in a
controlled environment.

In the case of a boat, that is not easily accomplished. In fact is
impossible. You don't have a standard upon which to calibrate the
meter. Bottom line, the actual NUMBER read is completely meaningless. I
repeat, it is MEANINGLESS.


~~ snippage happens ~~

The fact is that you can't calibrate a meter if you don't know were
zero is. I can only conceive of one way that a meter measure would be
invalid and that is if zero wasn't zero - as in your illustration.
Why somebody would use a meter that wasn't zero is beyond me.

Your wood sampling example is not calibration, but comparative
measurement. You have a zero meter, you measure the standard, then
measure the test piece and make the evaluation. You just can't walk
up to the standard and test it without having a baseline - which is
zero.

For straight measurement, it is most certainly accurate and it's done
all the time to determine set times for aggregate mixes, core moisture
in building roofs, materials density and many other types of
structural conditions. You walk in with a zero meter, take your
measurement and make your recommendation. What you are measuring, by
what ever method from doppler to resistance, zero has to be zero for
any measurement to be valid.

It is most certainly not meaningless.

I hope you'll take the time to reflect upon this in a logical manner.
If not, well... at least I tried. Last post on the subject from me though.

Obviously you are much smarter than I am and have it figured
perfectly.

But as you seem to have so much more knowledge of the subject than I
do, allow me to ask a couple of questions which I'm unclear on.

1 - What is the meter baseline and how to you set it?

2 - How can you make a content analysis of any material without first
starting at a reference point? If that reference point isn't zero,
then was is it?

3 - If the baseline is not zero, how do you determine what zero is?

I am very interested in your response - I wish to be enlightened.

Later,

Tom

"Short Wave Sportfishing" wrote in message
...


2 - How can you make a content analysis of any material without first
starting at a reference point? If that reference point isn't zero,
then was is it?

3 - If the baseline is not zero, how do you determine what zero is?

I am very interested in your response - I wish to be enlightened.

Later,

Tom

Howdy Tom,

I was following this thread with casual interest until I realized that
moisture meter is, as the other poster suggested, really a density meter. I
am curious if it is really a ultrasonic density measuring system. I recall
that they are calibrated using calibration blocks of a material with a know
and certified density.

Eisboch

On Sun, 20 Mar 2005 19:01:50 -0500, "Eisboch"
wrote:


"Short Wave Sportfishing" wrote in message
.. .


2 - How can you make a content analysis of any material without first
starting at a reference point? If that reference point isn't zero,
then was is it?

3 - If the baseline is not zero, how do you determine what zero is?

I am very interested in your response - I wish to be enlightened.

Later,

Tom

Howdy Tom,

I was following this thread with casual interest until I realized that
moisture meter is, as the other poster suggested, really a density meter. I
am curious if it is really a ultrasonic density measuring system. I recall
that they are calibrated using calibration blocks of a material with a know
and certified density.

Howdy Sir - how's the weather?

It depends on your definition of density. Using a standard definition
of density like the mass per unit volume of a substance under
specified conditions of pressure and temperature, then no, a moisture
can't measure density in that sense.

You measure density by specific gravity - that is weighing the
material in question or determining it's relative hardness (density)
by deforming the surface or the shape of the material in some manner
and measuring the force needed to do so. Then applying some
mathematics, you have density.

As I understand it, and have demonstrated to myself by playing with
the one I have, moisture meters measure resistance. They do this by
using a 1 KHz modulated signal anywhere from 5 to 40 KHz in frequency
across a predetermined distance (centers of the probes or pads).

The presence of water would necessarily mean that there was lower
resistance, but it doesn't mean that the material is less dense.
We're not dealing with a solid block of something - this is woven and
porous fiber. The density of the fiberglass and resins isn't the
issue - it's the water in, through and surrounding the fibers and it's
penetration through the resins.

Think of it this way. If you fill a ceramic bowl with water and put
the meter pads in it, what are you measuring? The amount of water in
the bowl or the density of the bowl?

Yes/No?

Later,

Tom

"Short Wave Sportfishing" wrote in message
...

It depends on your definition of density. Using a standard definition
of density like the mass per unit volume of a substance under
specified conditions of pressure and temperature, then no, a moisture
can't measure density in that sense.

You measure density by specific gravity - that is weighing the
material in question or determining it's relative hardness (density)
by deforming the surface or the shape of the material in some manner
and measuring the force needed to do so. Then applying some
mathematics, you have density.

As I understand it, and have demonstrated to myself by playing with
the one I have, moisture meters measure resistance. They do this by
using a 1 KHz modulated signal anywhere from 5 to 40 KHz in frequency
across a predetermined distance (centers of the probes or pads).

The presence of water would necessarily mean that there was lower
resistance, but it doesn't mean that the material is less dense.
We're not dealing with a solid block of something - this is woven and
porous fiber. The density of the fiberglass and resins isn't the
issue - it's the water in, through and surrounding the fibers and it's
penetration through the resins.

Think of it this way. If you fill a ceramic bowl with water and put
the meter pads in it, what are you measuring? The amount of water in
the bowl or the density of the bowl?

Yes/No?

Later,

Tom

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may (or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law and
others) although we delt with the refractive index of a material rather than
it's density. I donno ... just a thought.

Eisboch

On Mon, 21 Mar 2005 04:38:53 -0500, "Eisboch"
wrote:

~~ snippage ~~

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may (or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law and
others) although we delt with the refractive index of a material rather than
it's density. I donno ... just a thought.

Just so that I'm not missing something (which is possible - I'm not
the brightest bulb in the drawer), allow me to explain my thought
process here.

For one thing, water is relatively transparent to ultrasound under
normal conditions. It will reflect hard returns like thermoclines for
example and that is a density change I admit, but the distance from
the surface or transducer, the water is transparent. So in one sense,
yes, it does measure density.

However, when you are dealing with the presence of internal water in a
dense material, how to you measure it? To strain the bowl analogy a
little, what are you measuring for - the presence of a bowl or the
presence of water? If you reflect ultrasound into the bowl and get a
hard return, does that indicate that the entire bowl is solid or that
there is a hard bottom indicating the presence of a bowl?

To my simple mind, to test for the presence of water in any material
you start by measuring resistance to electrical signals (and the
argument can be made about density there also, but there is a subtle
difference). The more water, the less resistance and vice versa.

If you take a uncompromised piece of fiberglass as a base line, flip a
signal through it and use that as zero or base line, any changes have
to be due to decreased resistance to the signal.

Right?

Later,

Tom

"Short Wave Sportfishing" wrote in message
...
On Mon, 21 Mar 2005 04:38:53 -0500, "Eisboch"
wrote:

~~ snippage ~~

Whatever floats your boat. Actually, I was trying to recall what limited
knowledge I have with ultrasonic nondestructive testing and how it may
(or
may not) apply in the moisture testing. Ultrasonics are used to test for
flaws or inclusions in welds, but can also be used for other materials to
measure thickness and changes in the density of the material. My bag was
thin films for optics and we but used many of the same laws (Snell's law
and
others) although we delt with the refractive index of a material rather
than
it's density. I donno ... just a thought.

Just so that I'm not missing something (which is possible - I'm not
the brightest bulb in the drawer), allow me to explain my thought
process here.

For one thing, water is relatively transparent to ultrasound under
normal conditions. It will reflect hard returns like thermoclines for
example and that is a density change I admit, but the distance from
the surface or transducer, the water is transparent. So in one sense,
yes, it does measure density.

However, when you are dealing with the presence of internal water in a
dense material, how to you measure it? To strain the bowl analogy a
little, what are you measuring for - the presence of a bowl or the
presence of water? If you reflect ultrasound into the bowl and get a
hard return, does that indicate that the entire bowl is solid or that
there is a hard bottom indicating the presence of a bowl?

To my simple mind, to test for the presence of water in any material
you start by measuring resistance to electrical signals (and the
argument can be made about density there also, but there is a subtle
difference). The more water, the less resistance and vice versa.

If you take a uncompromised piece of fiberglass as a base line, flip a
signal through it and use that as zero or base line, any changes have
to be due to decreased resistance to the signal.

Right?

Later,

Tom



No, actually I consider myself a middle of the road .... oh .... sorry ... I
forgot we were actually talking boats here.
Seriously - I don't know. I just never stopped to think about how a
non-invasive "moisture" meter worked.

Eisboch