[bolger] Re: MJ capsize
It is difficult for me to understand how a material of considerably less
volume than the tanks could be jammed in them in such a way that it would
never move. If what you say is true, than it should be reproducible, but
it would be difficult to reproduce the amount of movement and settling
experienced by the sand in the tanks over the course of time prior to the
capsize. A simple experiment would be to remove the sand and use water
for ballast, and then deliberately turn the boat past 90 degrees. You can
than be confident that the ballast cannot move. Careening the boat will
probably require weight to be placed high up on the mast. That amount of
weight and its height above the waterline will give you an idea of the
righting ability of the boat _as designed_, and thereby hint at why the
boat actually went over and stayed over. As others have noted, other boats
built to this design have been found to be self righting. What has to be
determined is why this particular vessel was not. Without empirical testing
all the discussion that has transpired is here really rather pointless.
Making further changes to the design, such as adding more ballast, will
probably exacerbate the problems already encountered or bring new problems
into play that are not foreseeable. The other alternative is to pay a real
nautical architect real money to figure out what went wrong. This may ultimately
prove cheaper than trying to fix the problem via a series of random and
ill-considered modifications,
david
david
Hwal@... wrote:
In a message dated 3/8/2000 9:25:52 AM Eastern Standard Time, galvind@...
writes:
<< Sand, however, has a volume of about
150 lbs. per cubic foot, so the ballast tanks containing the
500 lbs. of
sand is 2.4 times the volume of the sand bags, which would allow
for
considerable shifting as the boat went over, all to the detriment
of the
boat's righting arm. >>
The sand was packed in smaller bags - and packed in such a way that
did not
allow one single idota of shifting. A staw could not have been
wedged into
those tanks.
I fail to see that 500 lbs of sand instead of 500 lbs would contribute
to a
knockdown - there are also plenty of matha janes out there who have
knocked
down with water ballast as well. Steve
------------------------------------------------------------------------
MAXIMIZE YOUR CARD, MINIMIZE YOUR RATE!
Get a NextCard Visa, in 30 seconds! Get rates as low as
0.0% Intro or 9.9% Fixed APR and no hidden fees.
Apply NOW!
http://click.egroups.com/1/2122/5/_/3457/_/952537601/
-- Easily schedule meetings and events using the group calendar!
--http://www.egroups.com/cal?listname=bolger&m=1
I wonder if any long micros or black skimmers have been knocked down? Of
course the black skimmer has some flair - so that isn't a real comparison I
guess. I'll bet that flair contributes to rounding up as a boat heals while
under way - just a guess. Can a plumb sided boat round up as it heels? Or is
it competely dependant upon ballast and sail balance? Steve
course the black skimmer has some flair - so that isn't a real comparison I
guess. I'll bet that flair contributes to rounding up as a boat heals while
under way - just a guess. Can a plumb sided boat round up as it heels? Or is
it competely dependant upon ballast and sail balance? Steve
In a message dated 3/8/2000 12:56:44 PM Eastern Standard Time,Hwal@...
writes:
<< I fail to see that 500 lbs of sand instead of 500 lbs would contribute to
a
knockdown - there are also plenty of matha janes out there who have knocked
down with water ballast as well. Steve
- ( no difference)
writes:
<< I fail to see that 500 lbs of sand instead of 500 lbs would contribute to
a
knockdown - there are also plenty of matha janes out there who have knocked
down with water ballast as well. Steve
>>sorry - what I was saying here is 500 lbs of sand instead of 500 lbs of water
- ( no difference)
In a message dated 3/8/2000 9:25:52 AM Eastern Standard Time,galvind@...
writes:
<< Sand, however, has a volume of about
150 lbs. per cubic foot, so the ballast tanks containing the 500 lbs. of
sand is 2.4 times the volume of the sand bags, which would allow for
considerable shifting as the boat went over, all to the detriment of the
boat's righting arm. >>
The sand was packed in smaller bags - and packed in such a way that did not
allow one single idota of shifting. A staw could not have been wedged into
those tanks.
I fail to see that 500 lbs of sand instead of 500 lbs would contribute to a
knockdown - there are also plenty of matha janes out there who have knocked
down with water ballast as well. Steve
writes:
<< Sand, however, has a volume of about
150 lbs. per cubic foot, so the ballast tanks containing the 500 lbs. of
sand is 2.4 times the volume of the sand bags, which would allow for
considerable shifting as the boat went over, all to the detriment of the
boat's righting arm. >>
The sand was packed in smaller bags - and packed in such a way that did not
allow one single idota of shifting. A staw could not have been wedged into
those tanks.
I fail to see that 500 lbs of sand instead of 500 lbs would contribute to a
knockdown - there are also plenty of matha janes out there who have knocked
down with water ballast as well. Steve
I have read the thread concerning this event with interest and have to
point out a factor which no one has yet considered. As designed the
ballast tanks have a volume of ~ 8 cubic feet to accomodate 500 lbs. of
water at 64 lbs. per cubic foot. Sand, however, has a volume of about
150 lbs. per cubic foot, so the ballast tanks containing the 500 lbs. of
sand is 2.4 times the volume of the sand bags, which would allow for
considerable shifting as the boat went over, all to the detriment of the
boat's righting arm. I am not engineer enough to calculate the potential
or actual effect of this, but it must be noted that vessels have long
been known to turn turtle due to the effect of shifting ballast or
cargo. The effect is similar to the already noted "free surface effect"
of a hull partially full of water. It would not be observable due to the
ballast's inaccessability under the berth flats. It has already been
noted that there is room for more sand bags in the ballast compartments,
therefore it seems inevitable that the ballast shifted as the boat
approached 90 degrees. Ballast should be fixed. If the tanks had been
full of water instead of less than half full of sand, there would be no
possibility of shifting. The correction of this problem is not to
increase the ballast, but to contain the ballast in a volume equal to
that ballast, or to return to the boat as designed, with water ballast.
In the meantime, I would hesitate to evaluate the MJ based on changes in
the design that Bolger never intended and had no control over,
david
point out a factor which no one has yet considered. As designed the
ballast tanks have a volume of ~ 8 cubic feet to accomodate 500 lbs. of
water at 64 lbs. per cubic foot. Sand, however, has a volume of about
150 lbs. per cubic foot, so the ballast tanks containing the 500 lbs. of
sand is 2.4 times the volume of the sand bags, which would allow for
considerable shifting as the boat went over, all to the detriment of the
boat's righting arm. I am not engineer enough to calculate the potential
or actual effect of this, but it must be noted that vessels have long
been known to turn turtle due to the effect of shifting ballast or
cargo. The effect is similar to the already noted "free surface effect"
of a hull partially full of water. It would not be observable due to the
ballast's inaccessability under the berth flats. It has already been
noted that there is room for more sand bags in the ballast compartments,
therefore it seems inevitable that the ballast shifted as the boat
approached 90 degrees. Ballast should be fixed. If the tanks had been
full of water instead of less than half full of sand, there would be no
possibility of shifting. The correction of this problem is not to
increase the ballast, but to contain the ballast in a volume equal to
that ballast, or to return to the boat as designed, with water ballast.
In the meantime, I would hesitate to evaluate the MJ based on changes in
the design that Bolger never intended and had no control over,
david