Re: [Paddlewise] chine and stability

Pardon me for stepping in here - But as a rank newbie in the ranks of kayaks -
What in the heck are you all talking about?

Wayne
-----------
LedJube_at_aol.com wrote:

> Jed wrote:
> << Flatter bottomed or harder chined boats seem to
> have a very clear righting effect as they are leaned slightly.  The force to
> lean them further rises sharply as the angle of lean increases.  All this
> boils down to the perception of stability for most novices. Also most people
> understand this as primary or initial stability. >>
>
> Matt responded:
> <<Here you are confusing width below the waterline with chine. Chine is the
> snip      This contradicts Jed's assertion that hard chines are more
> initially stable.
>
> Jed's response:
>     Matt, I made an observation based on personal experience relative to the
> "feel" of one design feature versus another. Although I will never know as
> much about boat design as you have already forgotten, I do understand the
> definition of chine. My reference was to "harder chined boats" as if
> comparing two boats of similar design but with different chine features. I
> don't know if the chine is responsible for my perceptions or if it was other
> design issues that were packaged along with the hard chines, but my
> perceptions are what they are just the same.
>     In my limited experience, harder chined boats exhibit stronger initial
> stability than similarly designed and dimensioned boats with softer chines.
> All things being equal, which of course they never can be.
>
> Matt wrote:
> << snip . . . . . flared sides will have the greatest secondary stability by
> just about
> anybody's perception or "feel". This contradicts what Jed just said about
> the more rounded hull having the better secondary stability. >>
>
> Jed's response:
>     I certainly agree with your statement regarding the relative secondary
> stability of a flared hull, but that was not the issue. The original poster
> asked about chines only. My actual statement regarding secondary stability
> follows:
>     "snip . . . . A softer chined boat may seem to
>
> have less initial stability but the secondary stability will rise smoothly up
>
> the point of capsize. . . . . snip . . . . . A hard chined boat will seem
>
> to have greater initial stability but reaches it's point of capsize more
>
> abruptly and with little notice."
>
>     Again I do not attribute the effects relative to stability to the chines
> alone but rather to the boats that have hard chines versus boats that have
> softer chines. Certainly I see now, thanks to you post, that the degree of
> flare has the greatest effect on secondary stability. I do however maintain
> my perception that boats with harder chines tend to have a "notchy" feel when
> they are leaned aggressively. And that boats with softer chines tend to feel
> less "notchy".
>
> Matt wrote:
> <<I want to be clear here that I'm not trying to claim
> the opposite of what Jed wrote just pointing out that the chine is not the
> determining factor in primary or secondary stability (but it can sure help
> dynamic stability compared to a rounded hull by decreasing the sideways skid
> on the face of a steep wave--as can a V-bottomed shape). >>
>
> Jed asks:
>     Matt, is it not possible to back away from the forest a bit and make some
> generalizations about the current commercial offerings of boats with hard
> chines versus boats with softer chines? Given that we are addressing this to
> a novice curious about researching her first boat.
>     I understand that your post seeks to correct inaccuracies from my post,
> and I welcome the correction. But please remember that I was referring to
> complete boats not the chines themselves.
>
> Jed wrote:
> << Softer chined hulls tend to lack this strong initial stability but
> instead offer a smoother transition as you move from an even keel to tilting
> the boat.>>
>
> Matt wrote:
> << How would one show or detect a smoother transition? What should I look for
> on a static stability graph? All the graphs I've looked at seem to be
> relatively smooth. >>
>
> Jed responds:
>     One could easily determine the rate of change of the righting force
> relative to the change in attitude. This then could be compared relative to
> similar stability data from other designs. The combined data then would allow
> a reasonable person to make a judgment about one design having a relatively
> smooth or less smooth transition of forces as the boat is tilted off an even
> keel. Smooth or less smooth in this case would refer to the relative
> steepness of the stability curves.
>
> Jed wrote:
> << Past 10°'s or so of lean takes us into the realm of secondary stability >>
>
> Matt wrote:
> << Has this been agreed upon somewhere and I've missed it all these years?
> Please let me know your source or sources for this. >>
>
> Jed responds:
>     John Winters, in his essay on "Stability and Seaworthiness" offer a
> definition for a metacentric height. As part of that definition he refers to
> initial stability as stability at small angles of heel. He later refers to a
> small angle of heel as usually less than ten degrees.
>     I used tranductive reasoning to (incorrectly) arrive at the definition of
> Initial stability as being limited to angles of heel less than 10°. I
> apologize to all involved for my incorrect interpretation of Mr Winter's
> writings. Certainly there is some range of heel that we can agree to refer to
> as the realm of initial stability and another range that we can agree to
> refer to as in the realm of secondary stability. Please tell me what these
> ranges are so I will not misspeak in the future.
>
> Jed
>
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--
Wayne Smith           http://www.waynesmith.net/weight
07 October 1999 - 315 lb. - Dr Rumbaut - Monterrey, Mexico
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