>The effects of a shorter ballast arm are NOT linked to pendulum theory, as
>Stuart Weir would hope. The longer keel with ballast fuirther down is
>decidedly more stable, and has greater power to carry sail, but we are
>talking here about survival in not only wind, but waves.
I think that you are too quick to discount the "pendulum" effect.
Pendulum theory is important, but it is certainly not simple.
Let's call it a complex interaction
1. the swing moment of inertia of the hull, which is
important in both pitch and roll directions. (different
along both axis, too).
2. the location of buoyancy, also important in both
pitch and roll, is the source of form stability.
3. wave action (which is, admittedly, not easily modeled)
A sailboat without a mast (lower moment of inertia) will both
pitch and roll at a faster rate, than the same hull form with
a mast. Now the mast adds instability, but decreases the
"roll rate". Racing sailors keep weight out of the ends of the
boat, as they don't carry about how uncomfortable the action is,
but do care about "hobby horsing", which is essentially pitching
in resonance with the waves, slowing the boat down.
I recall a series of tank tests published in one of the cruising
magazines, in which the swing moment of inertia made quite a
difference when models were struck by breaking waves abeam.
Faster rolling boats tended to roll further and trip over their
gunwale. Slower rolling boats tended to fair better.
Pretty complex area. No wonder there is lots to argue
>Consider a VERY stable boat in waves, with both buoyant and Ballast
>stability. As the wave profile moves across the boat, it is stable
>enough, and with a shorter period of roll, for the boat to react quickly
>to the wave and hence roll with it (assume no sail due to high winds).
>Thus the motion will be fast and uncomfortable, leading to higher
>Now think of an almost unstable boat in similar conditions. The wave
>profile will not affect the boat half so much, due to the fact that the
>righting moment from the angle of the wave face will be much lower.
I think that your points above are valid, however you
are talking form stability here, my contention is that it is
a complex dynamic, and the moments of inertia are not
>I know that some of this sounds contradictory, but the theory holds up to
>practical testing, and has done so for many years. The trick is in
>judging just how unstabel you can make the boat to achieve comfort witth
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