Richard Ferguson wrote:

Sounds like you guys have made up your mind that CG is the issue, and
that adding weight to a boat can't possibly make it unstable, and that I
don't know what I am talking about, so I think I am wasting my
breath/typing.

Richard, if you're sincere in your desire to understand this (and I
believe that you are), you can't allow yourself to get frustrated when
you get answers that you don't understand or don't agree with.

Let me make one last try to support my position.

1. My friend, who is kind of a skinny guy, but is about the same height,
had no problem with the kayak. He is not an expert kayaker. We later
went out offshore into some waves in the Pacific ocean, he in that kayak
and me paddling a windsurfer hull, neither of us had problems, we went
snorkeling, and then climbed back on and paddled back in. This was not
an ultra-narrow high performance narrow sit on top, it was a cheap
recreational type of sit on top, which one would expect to be pretty
stable.

Fine.

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. But maybe you guys think that I am not only incorrect,
but an incompetent paddler. That is probably the only way you can
logically defend your position.

There is no need to get defensive. There is a difference between being
competent and being comfortable in a specific boat. When I first started
paddling, I did so in a fairly wide boat (24" beam). I learned a lot of
skills and felt that I was reasonably competent. When I switched to a
narrower (22") boat with a rounder hull profile, it was like having to
learn all over again. It took months before I was as comfortable in it
as in my wider boat. I now paddle boats that are narrower and
considerably less stable comfortably and that old 22" feels like
paddling a sofa.

It's not a matter of competence. It's a matter of getting used to a
particular boat. If you're used to a wider and/or more stable boat, your
body is used to making relatively coarse movements and large weight
shifts in the course of paddling. Those same movements and weight shifts
in a less stable boat will cause greater movement of the boat, making it
feel unstable. Once you get used to the finer movements necessary in the
less stable boat, it will feel comfortable. It's simply a matter of
adjustment. If you were to paddle a less stable boat for a while then
get back into your old one, it will feel like a barge.

3. He warned me before I tried it that I would probably have trouble
with the boat, that I was too heavy for the boat. He said that his
daughter usually used the boat, and the boat was probably sized more for
her than 200 pound men.

Perhaps so, but if you didn't sink it, that's not what made it feel less
stable. It's probably simply a less stable boat that you're not used to.

The only way to settle this issue scientifically would be to take that
boat with a medium weight paddler, and gradually add weight to the boat
to make the total weight (paddler plus dead weight) equal to around 200
pounds, and see how the boat performed. Obviously I think the boat
would become unstable, and you guys think that the boat would not become
unstable. Since you have never seen a boat become unstable with heavy
loads, you think it can't happen, but it happened to me.

You're simply misinterpreting your experience Richard.

I have loaded my camping boat until it had less than 1" of freeboard
(distance from the gunwale to the water) and it became more stable. I
have 2" or less of freeboard in all of my boats and they're quite
stable. It's a common recommendation for owner of high volume touring
boats to add weight to them to increase stability when they're not
loaded with gear.

How many more examples do you need?

As I said, you guys are not going to listen to me, so I will shut up. ;-)

Open-mindedness goes both ways. If you're not willing to listen to the
answers you receive, why even bother to ask a question? If all you want
is validation of your opinion, you won't find it here, since it's
incorrect. We're trying to help you understand what you experienced. If
anyone should listen, it should be you, don't you think?

You have a choice. You an cling to your belief or you can listen to the
information that's being offered to you. What you do is entirely up to
you. Just remember that you cannot make something true simply by
refusing to believe that it's not.

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

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

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

On 18-Jun-2004, Wright wrote:

Given two identical
touring kayaks and two people of equal abilities, if one weighs 125 lbs and
the other weighs 190 lbs what would be the differences, if any, on stability
and performance?

If you made it through the nonsense that followed, Brian's answer is correct.
Low-placed weight increases stability, high-placed weight decreases it. Hence
women and shorter men tend to see more stability than tall, big people. Adding
weight (gear) up to a reasonable load limit tends to increase stability.

If you pick up a copy of Sea Kayaker magazine, you'll find that they include
a graph of stability (righting moment vs angle of heel) with every review of
kayaks. I recently posted about this and can add that they plot four curves.
There are curves for light and heavy paddlers both with and without gear.
A light paddler with gear always shows the greatest stability, while the
heavy paddler without gear always shows the least stability.

Mike

On 6/21/04 1:51 PM, in article , "Michael
Daly" wrote:

On 18-Jun-2004, Wright wrote:

Given two identical
touring kayaks and two people of equal abilities, if one weighs 125 lbs and
the other weighs 190 lbs what would be the differences, if any, on stability
and performance?

If you made it through the nonsense that followed, Brian's answer is correct.
Low-placed weight increases stability, high-placed weight decreases it. Hence
women and shorter men tend to see more stability than tall, big people.
Adding
weight (gear) up to a reasonable load limit tends to increase stability.

If you pick up a copy of Sea Kayaker magazine, you'll find that they include
a graph of stability (righting moment vs angle of heel) with every review of
kayaks. I recently posted about this and can add that they plot four curves.
There are curves for light and heavy paddlers both with and without gear.
A light paddler with gear always shows the greatest stability, while the
heavy paddler without gear always shows the least stability.

Mike
Thanks for the reply. It certainly makes sense that more gear weight (up to
a point) low in the boat would make it more stable. The heavy keel on a
sailboat would be an extreme example of that. Here is the part I don't quite
follow. I have seen the reviews in Sea Kayaker magazine and they assume, if
I am understanding them correctly, that the center of gravity for both the
lighter and the heavier paddler is 10 inches from the low point of the seat.
In other words the center of gravity is at exactly the same place for both
paddlers (without any gear). Yet the curve for the lighter paddler
indicates more stability. Is this because weight below the center of
gravity and weight above the center of gravity are not created equal? That
is, the 50% of the weight of the heavier paddler that is above the center of
gravity must cause somewhat more instability than the 50% of the weight of
the lighter paddler? Is that correct, or am I misreading the graphs?
Chuck

On 21-Jun-2004, Wright wrote:

I have seen the reviews in Sea Kayaker magazine and they assume, if
I am understanding them correctly, that the center of gravity for both the
lighter and the heavier paddler is 10 inches from the low point of the seat.
In other words the center of gravity is at exactly the same place for both
paddlers (without any gear). Yet the curve for the lighter paddler
indicates more stability.

Interesting - I never noticed that comment about CG position in the reviews.
Since these are static and not dynamic stability calculations, the mass at
the CG is all that matters. If both the heavy and light paddlers have their
mass at the same point, then the only difference is the quantity and the
stability curves do not reflect the difference in distribution.

Since that CG (10" up and 10" forward) is above the center of bouyancy, any
heeling will have it contribute to the overturning moment. The heavier
paddler will still have the lesser stability at a given angle of heel. If
the CG was determined for real paddlers, taking into account different CG
positions, the moments calculated would be slightly different.

Don't forget that these figures still ignore the fact that a real paddler
will tend to keep his/her body roughly vertical if the kayak heels. This
greatly changes the overturning moments.

Mike

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

Actually, a heavier person will be less stable on a sit-on-top and more
stable in a traditional kayak. Since a person sits above the waterline
on a sit-on-top kayak, the kayak is more top-heavy and subject to sway
from side to side. In a traditional kayak, your weight is below the
waterline, and thus provides ballast to the kayak. The heavier, the more
stable.

Brian Nystrom wrote:
Richard Ferguson wrote:

Every boat has a designed load range and an optimum load range, which
is the engineering view of the world. I have a personal story.

I one time tried to use a friend's sit-on-top kayak. Now I am a big
guy, around 200 pounds, and heavier than he is. I found that if I
took my feet out of the water and put them on the deck, I went over
almost instantly, in calm water. With my feet and lower legs in the
water, the boat sat higher in the water, and was reasonably stable.
However much my legs weighed, maybe 30 pounds (15 kg), it was the
difference between stability and instability. After swimming a few
times, and failing to get far from the dock, I gave him back his kayak.


Your issue was not likely one of absolute weight, but center of gravity.
The only way one can be too heavy for a kayak is if you literally push
it under water. However, the higher your center of gravity, the less
stable the boat will be. Also, the heavier you are, the more effect you
will have when you shift your weight or lean. People who are tall and
heavy will find a given boat to be much less stable than a person who's
short and light.

I think that the extra weight took away the initial stability that the
kayak was intended to have. My guess is that the boat was designed for
smaller people, but usable for medium sized people. My weight was
outside the operating range of that design, making the boat unusable
by me.


That's highly unlikely. With most kayaks, the stability increases as you
push the boat deeper into the water, up to the point that the gunwales
submerge.

I would make a guess that overloading a boat is generally much more
detrimental than underloading a boat. A large boat paddled by a small
person probably will be slower and more subject to wind and wave than
a smaller boat paddled by the same person, but probably still safe and
usable.


Actually, the opposite is true. A heavier person pushes a boat down
farther in the water, increasing the length of the waterline. While this
adds more surface friction, it also increases the theoretical hull speed
of the boat, making it possible to paddle it faster before "hitting the
wall", so to speak.

I paddle low volume boats and am at the upper end of the recommended
weight range for all of them. I also build skin-on-frame boats that are
even lower in volume. All of my boats perform well and have the added
benefits of a better fit and less windage.

On 21-Jun-2004, lcopps wrote:

Since a person sits above the waterline
on a sit-on-top kayak, the kayak is more top-heavy and subject to sway
from side to side. In a traditional kayak, your weight is below the
waterline,

This is not completely correct. There are SOTs that have a paddler in
pretty much the same position as a conventional kayak and it isn't
likely that your CG is below the water line in a conventional kayak.
Picking the recent Nordkapp H20 review as an example, the waterline
is 6" above the bottom for a 200lb paddler with 100lb of gear. That
paddler's CG is likely close to the 10" height that SK assumes in their
calculations. Hence, his CG is about 4" above the waterline.

Mike