Jeff wrote:
JimC wrote:
And the other issue is that the water ballast extends all the way
from stem to stern. This can't be helping the pitching moment at all.
Nope. Cross-sections #4 and #5 clearly show that the ballast tank has
narrowed toward the stern such that there is an insignificant volume
(and mass) toward the stern. Instead, by far the greatest volume (and
mass) is in the area near the mast. Thus, the water ballast tank, with
greatest mass located near the center of the boat, would help rather
than augment any pitching moment.
Wrong again. it extends about 2/3rds, and the front and rear
portions of the tank taper to sharp end portions and are therefore
of little mass and no real consequence re the distribution of mass.
Not according to the published diagram:
http://www.macgregor26.com/drawings/drawings.htm
Its pretty clear from this that the ballast extends all the way
forward, and that in fact a substantial amount is forward of the
mast. You should really spend some time learning about your boat, Jim.
I never questioned whether there was a substantial amount forward of the
mast. Nevertheless, since the hull, and the tank, narrows toward the
bow, and since the lever arm extending from the mast to the bow is
relatively short, water ballast at the bow would have little effect on
the distribution of mass.
Jeff, did you happen to take courses in geometry and logic in high
school or junior high? The reason I ask is that you obviously know
nothing about either subject.
Actually, I majored in Naval Architecture for two years before switching
to Physics. Then I worked for NASA for 6 years. Any more questions?
Yes, several. - If you majored in physics and Naval Architecture, why do
you seem to know so little about them. And, what did you do for NASA. -
Surely you weren't designing any boats for them, I hope. (Incidentally,
I worked for NASA for 11 years, and was recently asked to do more work
for them.)
- The fact that the water ballast tank in the Mac extends toward the
bow, forward of the mast, is not determinative of whether it extends
about 2/3rd the length of the boat.
It starts at the bow, and it ends at the stern. The diagram clearly
shows the water ballast running the entire length of the boat. If
anything, it looks that the tanks is deepest in the forward area. The
cross-section at the forward station under the hatch appears to be by
far the largest, indicting that a large portion of the water ballast is
forward.
Here's the diagram again:
http://www.macgregor26.com/drawings/drawings.htm
please tell us if there's any other way to interpret this?
The issue, of course, is whether the mass is substantially centered
or whether substantial mass exists at the bow and stern, which might
affect the distribution of mass throughout the length of the boat. Since
that's the substantive issue, why don't we concentrate on that one.
And with a 250 pound engine hanging of the stern, that's a lot of mass
in the extremities.
Nope. The hull is built to handle the weight of the motor. As well as
the weight of several adults in the cockpit.
(Remember that my statement was in response to Scotty's ridiculous
remark that the water ballast extends "all the way from stem to
stern." - Why didn't you criticize Scotty for making such a stupid
remark?)
Because I made it. And is what is your problem with it? Are you
claiming that the diagram on the Mac site is faulty, that the tank does
not run the entire length? Or are you arguing on the meaning of "stem
to stern"?
As stated, the drawings clearly show that the ballast tank has narrowed
toward the stern such that there is an insignificant volume of ballast
water (and mass) toward the stern. Instead, by far the greatest volume
(and mass) is in the area near the mast. Thus, the water ballast tank,
with greatest mass located near the center of the boat, would help
rather than augment any pitching moment.
Also, the ballast tank is tapered at the front and back such that the
volume (and mass) of water held at the front and rear portions is
substantially less then that held toward amidships.
Clearly, there seems to be little ballast in the stern, but with the
heavy engine, plus the possibility of a full cockpit, its probably not
possible. However, the largest cross-section of the tank is shown at
the station halfway between the keel and the bow at the waterline.
While the bow obviously "tapers in" (yes indeed, they did make the bow
at the pointy end) which means the ballast must be reduced in the
forward few feet, but so is the buoyancy.
Additionally, the heavier, permanent ballast is positioned amidships,
below the mast.
Just where ballast should be. Good for them.
Jeff, I've sailed many boats. The Mac 26M doesn't pitch excessively
and doesn't pitch more than most others. (Have you sailed the 26M? - No?)
I'd love to, but most of the Mac owners hardly ever go out. I have
sailed by them a number of times and they do seem to bob around more
than heavier boats.
Perhaps you need to have your eyes examined.
Jim