On Mon, 12 Mar 2001 23:38:10 GMT, Wilko wrote:

I tried wrapping the bars with string. It helped but not enough.
I'll probably end up with black pipe insulation, attached with
wire ties. I hate the looks of duct tape.

Duct tape is ok on black pipe insulation if you can find black duct tape.

I used tie wraps (brand name?) to keep foam pipe insulation on the
vertical pipes on my roofrack, that really helps keep the noise down
(well, as long as I stay under 120 mph on the Autobahn, that is... :-)).

My thought, instead of wire tie wraps (which, I think, would have to be cut
off and replaced if I need a flat rack surface), is to use nylon straps to
hold the pipe insulation in place as needed. I'm thinking of such straps
sold in camping or automotive departments...
--
cheers, Stephen

"Stephen Bird" wrote in message
...
On Mon, 12 Mar 2001 23:38:10 GMT, Wilko wrote:

I tried wrapping the bars with string. It helped but not enough.
I'll probably end up with black pipe insulation, attached with
wire ties. I hate the looks of duct tape.

Duct tape is ok on black pipe insulation if you can find black duct tape.

I used tie wraps (brand name?) to keep foam pipe insulation on the
vertical pipes on my roofrack, that really helps keep the noise down
(well, as long as I stay under 120 mph on the Autobahn, that is... :-)).

My thought, instead of wire tie wraps (which, I think, would have to be
cut
off and replaced if I need a flat rack surface), is to use nylon straps to
hold the pipe insulation in place as needed. I'm thinking of such straps
sold in camping or automotive departments...

I tried both string & foam without luck. I still got a constant pitch howl
that became louder with speed. Then a banged a bar while carrying it &
realized that it's ring was the same pitch as the howl. It was a bell &
that was it's resonant frequency. So I filled the bars with sand. They are
heavy, but the noise is gone.

Lloyd Bowles
www.madcanoeist.4ever.cc

I had a great laugh at myself after posting my message. The original thread
was started three years ago. I must have been saving the message until I
needed the information. lol

"Stephen Bird" wrote in message replying to...
On Mon, 12 Mar 2001 23:38:10 GMT, Wilko wrote:

My thought, instead of wire tie wraps (which, I think, would have to be
cut off and replaced if I need a flat rack surface), is to use nylon straps...

On Sat, 20 Mar 2004 21:50:52 -0500, "Lloyd Bowles" wrote:

Then a banged a bar while carrying it & realized that it's ring was the
same pitch as the howl. It was a bell & that was it's resonant frequency.
So I filled the bars with sand. They are heavy, but the noise is gone.

Wow... now that is what I'd call observant! :-) I wonder if foam insulation
(which is sprayed and expands on use) would work? Is the purpose of the
sand simply to fill the hollow part of the bar?
--
cheers, Stephen

....stuff deleted

I tried both string & foam without luck. I still got a constant pitch
howl
that became louder with speed. Then a banged a bar while carrying it &
realized that it's ring was the same pitch as the howl. It was a bell &
that was it's resonant frequency. So I filled the bars with sand. They
are
heavy, but the noise is gone.


You probably don't need to fill the entire bar. I'd probably try caulking
the ends first and see if that works. Jam some paper in about 3-4 inches and
fill the end of the bar with caulk. Over the years, I've lost end caps and
rather than replace them, this worked pretty nicely (and there is always
extra caulk around).

If the noise persists, I would think that the bar/mount attachment isn't
tight enough. It it is, there should be no vibration along the length of the
bar (hence, no noise).

Rick

"Rick" wrote in message
hlink.net...

that was it's resonant frequency. So I filled the bars with sand. They
are
heavy, but the noise is gone.

You probably don't need to fill the entire bar. I'd probably try caulking
the ends first and see if that works. Jam some paper in about 3-4 inches
and
fill the end of the bar with caulk. Over the years, I've lost end caps and
rather than replace them, this worked pretty nicely (and there is always
extra caulk around).

My bar still had end caps. The noise was due to the resonant frequency of
the bar as a big chunk of metal, not as an organ pipe. So just plugging the
ends would do nothing. I agree though that I probably didn't need to
totally fill them to eliminate the noise. I'd worry though about the sand
mass slamming into & removing an endcap when I do my normal abrupt turns.

If the noise persists, I would think that the bar/mount attachment isn't
tight enough. It it is, there should be no vibration along the length of
the
bar (hence, no noise).

It's tight. Or at least as tight as plastic towers allow. I like thumping
things to hear or feel them resonate & have found some solidly welded masses
that can vibrate for a long time. The big ones are at a frequency below
hearing.

Lloyd

Lloyd Bowles wrote:

"Rick" wrote in message
hlink.net...

that was it's resonant frequency. So I filled the bars with sand. They
are
heavy, but the noise is gone.

You probably don't need to fill the entire bar. I'd probably try caulking
the ends first and see if that works. Jam some paper in about 3-4 inches
and
fill the end of the bar with caulk. Over the years, I've lost end caps and
rather than replace them, this worked pretty nicely (and there is always
extra caulk around).

My bar still had end caps. The noise was due to the resonant frequency of
the bar as a big chunk of metal, not as an organ pipe. So just plugging the
ends would do nothing. I agree though that I probably didn't need to
totally fill them to eliminate the noise. I'd worry though about the sand
mass slamming into & removing an endcap when I do my normal abrupt turns.

If the noise persists, I would think that the bar/mount attachment isn't
tight enough. It it is, there should be no vibration along the length of
the
bar (hence, no noise).

It's tight. Or at least as tight as plastic towers allow. I like thumping
things to hear or feel them resonate & have found some solidly welded masses
that can vibrate for a long time. The big ones are at a frequency below
hearing.

I pity the poor guy, driving behind you, if your caps should ever come off.

Sandblasted! g

Larry

"Lawrence Glasser" wrote in message
...
Lloyd Bowles wrote:

My bar still had end caps. The noise was due to the resonant frequency
of
the bar as a big chunk of metal, not as an organ pipe. So just plugging
the
ends would do nothing. I agree though that I probably didn't need to
totally fill them to eliminate the noise. I'd worry though about the
sand
mass slamming into & removing an endcap when I do my normal abrupt
turns.

I pity the poor guy, driving behind you, if your caps should ever come
off.

I have a bigger worry for you. I didn't bother with tower locks when I got
the racks. Theft isn't very likely in my village & there was no mention of
other reasons for the locks. I drove somewhere & found that a tower was
adrift because the latch holding the tower to track adapter was open. I
thought I had missed latching it until it happened a few more times.

A little sandblasting is nothing compared to hitting a sand filled bar with
canoe attached. I have locks now, just to keep the latches from opening
themselves.

Lloyd
www.madcanoeist.4ever.cc

Lloyd Bowles wrote:

"Lawrence Glasser" wrote in message
...
Lloyd Bowles wrote:

My bar still had end caps. The noise was due to the resonant frequency
of
the bar as a big chunk of metal, not as an organ pipe. So just plugging
the
ends would do nothing. I agree though that I probably didn't need to
totally fill them to eliminate the noise. I'd worry though about the
sand
mass slamming into & removing an endcap when I do my normal abrupt
turns.

I pity the poor guy, driving behind you, if your caps should ever come
off.

I have a bigger worry for you. I didn't bother with tower locks when I got
the racks. Theft isn't very likely in my village & there was no mention of
other reasons for the locks. I drove somewhere & found that a tower was
adrift because the latch holding the tower to track adapter was open. I
thought I had missed latching it until it happened a few more times.

A little sandblasting is nothing compared to hitting a sand filled bar with
canoe attached. I have locks now, just to keep the latches from opening
themselves.

G

I'm sorry. I'm not laughing at you, I'm laughing with you.

Assuming, that is, that you're laughing!

Larry

Michael Daly wrote:

On 21-Mar-2004, Stephen Bird wrote:

Wow... now that is what I'd call observant! :-) I wonder if foam
insulation (which is sprayed and expands on use) would work? Is the
purpose of the sand simply to fill the hollow part of the bar?

If you want to kill vibration, mass and damping is the way to do it.
Sand has mass and is very inelastic, therefore it will provide some
energy absorption. Lloyd did the right thing.

Foam would be too light and would contribute almost nothing to the
bar.

Mike

The expanding foam would stick to the inside of the tube and become
rigid. This should stop the vibration. And would be much lighter then
sand.

--
Gordon Niessen
If you aren't on the bleeding edge, you are history.

You really want to dampen the vibrations you have. i.e. reduce the Q factor
of the resonator. You can do this by introducing a dissapative element
(e.g. sand) or by coupling to a resonator that is not a harmonic of what you
have. I suspect the foam might do well at reducing the Q factor. Getting the
expanding foam in to the middle of a 78 inch bar might be a bit tricky,.

I've seen contractors use expanding foam inside the hollow rungs of aluminum
ladders. (This is definitely a case where large amounts of added mass is not
an optimum solution.)

Michael Daly wrote:

On 22-Mar-2004, "Gordon Niessen" wrote:

The expanding foam would stick to the inside of the tube and become
rigid. This should stop the vibration. And would be much lighter then
sand

Take the foam's Young's modulus and calculate how much steel it is
equivalent to. Then determine how much it increases the stiffness
of the combined tube + foam. It won't do much.

You don't want to make it stiffer. You want to reduce the resonant
frequency, not increase it. That means adding mass. Check any
book on structural dynamics.

Mike