Paddler's Weight vs. Stability and Performance?
 

Actually, I did address this, though somewhat briefly. Regardless, this
is a good point.

MikeSoja wrote:

On Sat, 19 Jun 2004 21:44:50 GMT, Richard Ferguson
posted:

snips

1. My friend, who is kind of a skinny guy, but is about the same height,
had no problem with the kayak.


[...]


2. If the center of gravity is the issue, how come my buddy had no
problem with the boat, and I could not keep it upright for 10 seconds in
flat water, once I lifted my legs out of the water? I am not that bad a
paddler, and since he is the same height, his center of gravity would be
about the same.


According to the responses I've seen, the deduction above has not
been specifically addressed.

The center of gravity of the *paddler* has nothing to do with the
center of gravity of the combined *boat and paddler*. Paddlers of
similar centers of gravity but different mass, upon entering any
boat, will change the center of gravity of the "at rest" boat they
enter in proportion to their mass.

If you stand a five foot high piece of balsa wood in the cockpit of
a kayak, not much is going to happen. But stick a five foot tall
piece of oak, with the same outer dimensions as the balsa piece, in
the boat and the thing will tip over. Both the balsa piece, and the
oak piece, individually, have similar centers of gravity, but when
joined to the boat, their different masses will move the center of
gravity of the boat differently. Two people of similar height, but
different weight, will also differently affect the way a boat heels
and rights (ignoring factors such as whether the boat is inherently
more stable sitting lower in the water or not.)

The above is just a dramatization, and an extreme one, so don't try
it at the lake without adult or female supervision.

Mike Soja

Paddler's Weight vs. Stability and Performance?
 

Define "wide". In my previous posts, I was referring to boats in the
typical touring width range, which is ~20"-24".

Richard Ferguson wrote:

Sorry to be a little cranky on this thread. After messing around in
boats for 35 years or so, I know what boat behavior is normal and what
is not.

Let me ask a question of Brian and Marsh: If not overloading, what
could cause an ordinary (not narrow) recreational sit on top kayak to
become extremely unstable? I know that narrow boats are unstable, which
just makes common sense, but this was not a narrow boat. In some
private email, Marsh mentioned 17 inch wide boats; 17 inches seems very
extreme to me, and I would expect to swim often if I was in such a boat.
So tell me, how can one make a wide boat unstable, if not by
overloading or standing up?

I agree that in most circumstances, weight makes a boat more stable. I
am currently in the process of learning to pole my canoe, which means I
stand up in my canoe. I started out with a little extra weight in my
canoe, and swam once the first day. The second day, I added more
weight, securely tied town, and the boat felt a lot more stable.

Richard



Richard Ferguson wrote:

Mike explained my situation better than I could. With the sot close
to sinking, which it appeared to be, the stability situation changes a
lot. I can easily imagine that this might not be typical, even for an
sot, which I suppose is why people are having trouble with my
experience and analysis.

This was not a narrow high performance type of sit on top, just
looking at it, you could see that it was an inexpensive recreational
type of kayak. I know a narrow boat when I see one, and this was not
a narrow boat. Brian and Marsh have basically ignored my statement
that this was not a narrow high performance boat that could logically
be expected to be inherently unstable for an inexperienced user, but a
wider recreational boat that should have been very stable, but was
very unstable for me. Mike at least is listening to me.

Richard



Michael Daly wrote:

On 19-Jun-2004, Brian Nystrom wrote:


(THS in MPH = 1.34 x the square root of the waterline
length).




Minor nit - that formula's for knots, not mph.

By the way , the guy did say he practically sank the sot. In that
case, stability would be limited and lifting his legs _might_ have
done the trick regardless of the CG change. His comment about the
elliptical section suggests that the sot has a bit of tumblehome.
That would mean that if he's significantly close to sinking, he
has no righting moment increase on heel. Any reduction in
stabilization ("sponson" effects, roll damping from his legs, CG
position etc) can undo everything.

While your argument is completely correct for the typical situation,
I think his explanation is a bit vague/difficult to envision - hence
he might be partially correct without being able to express it in
standard terms. The bigger problem is that he's viewing the general
characteristics of kayaks from his single, possibly atypical,
experience.

Mike

Paddler's Weight vs. Stability and Performance?
 

Michael Daly wrote:

On 19-Jun-2004, Brian Nystrom wrote:


(THS in MPH = 1.34 x the square root of the waterline
length).


Minor nit - that formula's for knots, not mph.

Thanks for correcting that, Mike.

Paddler's Weight vs. Stability and Performance?
 

30 inches or more wide.

Richard


Brian Nystrom wrote:
Define "wide". In my previous posts, I was referring to boats in the
typical touring width range, which is ~20"-24".

Richard Ferguson wrote:

Sorry to be a little cranky on this thread. After messing around in
boats for 35 years or so, I know what boat behavior is normal and what
is not.

Let me ask a question of Brian and Marsh: If not overloading, what
could cause an ordinary (not narrow) recreational sit on top kayak to
become extremely unstable? I know that narrow boats are unstable,
which just makes common sense, but this was not a narrow boat. In
some private email, Marsh mentioned 17 inch wide boats; 17 inches
seems very extreme to me, and I would expect to swim often if I was in
such a boat. So tell me, how can one make a wide boat unstable, if
not by overloading or standing up?

I agree that in most circumstances, weight makes a boat more stable.
I am currently in the process of learning to pole my canoe, which
means I stand up in my canoe. I started out with a little extra
weight in my canoe, and swam once the first day. The second day, I
added more weight, securely tied town, and the boat felt a lot more
stable.

Richard



Richard Ferguson wrote:

Mike explained my situation better than I could. With the sot close
to sinking, which it appeared to be, the stability situation changes
a lot. I can easily imagine that this might not be typical, even for
an sot, which I suppose is why people are having trouble with my
experience and analysis.

This was not a narrow high performance type of sit on top, just
looking at it, you could see that it was an inexpensive recreational
type of kayak. I know a narrow boat when I see one, and this was
not a narrow boat. Brian and Marsh have basically ignored my
statement that this was not a narrow high performance boat that could
logically be expected to be inherently unstable for an inexperienced
user, but a wider recreational boat that should have been very
stable, but was very unstable for me. Mike at least is listening to me.

Richard



Michael Daly wrote:

On 19-Jun-2004, Brian Nystrom wrote:


(THS in MPH = 1.34 x the square root of the waterline
length).





Minor nit - that formula's for knots, not mph.

By the way , the guy did say he practically sank the sot. In that
case, stability would be limited and lifting his legs _might_ have
done the trick regardless of the CG change. His comment about the
elliptical section suggests that the sot has a bit of tumblehome.
That would mean that if he's significantly close to sinking, he
has no righting moment increase on heel. Any reduction in
stabilization ("sponson" effects, roll damping from his legs, CG
position etc) can undo everything.

While your argument is completely correct for the typical situation,
I think his explanation is a bit vague/difficult to envision - hence
he might be partially correct without being able to express it in
standard terms. The bigger problem is that he's viewing the general
characteristics of kayaks from his single, possibly atypical,
experience.

Mike

Paddler's Weight vs. Stability and Performance?
 

Richard Ferguson wrote:

30 inches or more wide.

That's really wide to the point of not even being a kayak any longer. I
cannot imagine a 30" wide boat that's unstable regardless of the weight
placed in/on it. Also, I have yet to see a boat that wide that couldn't
handle at least 300 pounds, regardless of what the manufacturer's weight
rating is. Even little 10' x 27" - 3" puddle boats can handle a large
load and are all rated to at least 225#.