Sailboat design for "Ultimate Storm"

Sailboat design for "Ultimate Storm"

Post by Jim Cha » Wed, 27 Mar 1996 04:00:00


Quote:

>     b) was in serious danger of holing after losing the mast, because
>        the standing rigging was still intact, holding the spars around
>        the boat, and
>     c) (for the monohulls) suffered from vicious sea motion after losing
>        the rigging, because they lost the counterbalancing effect it had
>        to the deep fin keel.

I think these last two have been a problem since the invention of the
sailing boat! ISTR some dramatic descriptions of similar problems in
one of C.S. Forester's "Hornblower books...

Jim C

 
 
 

Sailboat design for "Ultimate Storm"

Post by Dick Parsha » Wed, 27 Mar 1996 04:00:00

I know there was some discussion in this group of the disasterous 1994
Queen's Birthday yacht race off New Zealand, but I didn't pay much
attention at the time.

I just finished reading the book "Rescue in the Pacific", about the
events of that weekend.  Perhaps it's because I'm not a blue water
cruiser, but the book described boat after boat that:

     a) couldn't be kept from lying beam-on to the seas,

     b) was in serious danger of holing after losing the mast, because
        the standing rigging was still intact, holding the spars around
        the boat, and

     c) (for the monohulls) suffered from vicious sea motion after losing
        the rigging, because they lost the counterbalancing effect it had
        to the deep fin keel.

Obviously the conditions they were facing WERE extraordinary.  However,
it seems to this inexperienced day sailor that there are some serious
design issues with regard to most modern yachts' abilities in really
severe conditions.  What sort of sailboat would you have wanted to be on
in these conditions (other than one back at the marina)?

While the book was certainly a sensational read, I thought it left
something to be desired in terms of analysis and recommendations.
What about the rest of the 60-boat fleet that was out there?  How did
they survive, and how well?  What did they do differently, and was there
anything different about the boat they were on?

Oh well, just random ramblings....

-----------------------------------------------------------
*** Parshall               IT Support, 3M Corp, Austin TX

Opinions expressed herein are my own and may not represent those of 3M.

 
 
 

Sailboat design for "Ultimate Storm"

Post by Dick Parsha » Thu, 28 Mar 1996 04:00:00

Quote:


>>     b) was in serious danger of holing after losing the mast, because
>>        the standing rigging was still intact, holding the spars around
>>        the boat, and

>>     c) (for the monohulls) suffered from vicious sea motion after losing
>>        the rigging, because they lost the counterbalancing effect it had
>>        to the deep fin keel.

>I think these last two have been a problem since the invention of the
>sailing boat! ISTR some dramatic descriptions of similar problems in
>one of C.S. Forester's "Hornblower books...

>Jim C

Would a boat with an unstayed rig, and a higher center of gravity (inside
ballast, long shallow keel with external ballast) be a better choice for
long distance cruising?  Is this getting into the old trade-off between
ability to crawl off a lee shore vs. all other aspects of performance ?

-----------------------------------------------------------
*** Parshall               IT Support, 3M Corp, Austin TX

Opinions expressed herein are my own and may not represent those of 3M.

 
 
 

Sailboat design for "Ultimate Storm"

Post by Nigel Farran » Fri, 29 Mar 1996 04:00:00

Recommended reading is  "Heavy Weather Sailing" by K Allard Coles. Each
hull design is different in the way it reacts. The main message is that
each storm is different and one needs to know the various survival
techniques that must be adopted at different times during the storm for
your particular boat. One strategy is not going to work all the time.

Fair winds

Nigel A. Farrand

 
 
 

Sailboat design for "Ultimate Storm"

Post by mark edward balco » Sat, 30 Mar 1996 04:00:00

Quote:
>Would a boat with an unstayed rig, and a higher center of gravity (inside
>ballast, long shallow keel with external ballast) be a better choice for
>long distance cruising?

Why would you want a high center of gravity? That goes against everything
that I have ever read about stability. Dont you want the center of
bouyancy to be as far above the center of gravity as possible? Doesn't
this give you the best righting moment? I don't understand.

Mark  S/V Kaiulani

 
 
 

Sailboat design for "Ultimate Storm"

Post by Dick Parsha » Sat, 30 Mar 1996 04:00:00


Quote:

>>Would a boat with an unstayed rig, and a higher center of gravity (inside
>>ballast, long shallow keel with external ballast) be a better choice for
>>long distance cruising?

>Why would you want a high center of gravity? That goes against everything
>that I have ever read about stability. Dont you want the center of
>bouyancy to be as far above the center of gravity as possible? Doesn't
>this give you the best righting moment? I don't understand.

>Mark  S/V Kaiulani

I remember an exhibit in a maritime museum somewhere:  a crossection of
a boat hull, pivoting in the middle, with a height-adjustable ballast
weight on the bottom.  With the weight all the way down (deep ballast
keel), you could feel the increased stiffness (ability to carry more
sail, and right more quickly in a knockdown), but the oscillation
frequency was relatively high, ie. quicker, more uncomfortable movement.
With a shallower ballast weight, the hull was more easily tipped (cannot
carry as much sail), but the oscillation was much slower, translating to
a more comfortable movement of the boat, with the added benefit of
shallower draft for getting into interesting, out-of-the-way places.

It's just a matter of the tradeoffs to be made, and where your priorities
are, I guess.

-----------------------------------------------------------
*** Parshall               IT Support, 3M Corp, Austin TX

Opinions expressed herein are my own and may not represent those of 3M.

 
 
 

Sailboat design for "Ultimate Storm"

Post by Stuart Wi » Sat, 30 Mar 1996 04:00:00

Quote:

> >Why would you want a high center of gravity? That goes against everything
> >that I have ever read about stability. Dont you want the center of
> >bouyancy to be as far above the center of gravity as possible? Doesn't
> >this give you the best righting moment? I don't understand.

> >Mark  S/V Kaiulani

> I remember an exhibit in a maritime museum somewhere:  a crossection of
> a boat hull, pivoting in the middle, with a height-adjustable ballast
> weight on the bottom.  With the weight all the way down (deep ballast
> keel), you could feel the increased stiffness (ability to carry more
> sail, and right more quickly in a knockdown), but the oscillation
> frequency was relatively high, ie. quicker, more uncomfortable movement.
> With a shallower ballast weight, the hull was more easily tipped (cannot
> carry as much sail), but the oscillation was much slower, translating to
> a more comfortable movement of the boat, with the added benefit of
> shallower draft for getting into interesting, out-of-the-way places.

Longer pendulums have longer periods, not shorter.

Deeper ballast will certainly have increased righting moment,
compared to the same ballast carried higher
(other than at zero heel, where all such moments are zero).

Did the demo you saw include the effect of bouyancy somehow?
Hull form has as much effect on stability as center of ballast mass.

The two extreme forms of hull stability are as follows:

narrow beam, deep hull, heavy low ballast. Type example is heavy
English "cutter" circa 1900 or earlier,
for example deep sea cruisers by Albert Strange (not his
canoe yawls). Tends to roll slowly
and stay at a fixed angle relative to gravity (downwards).
The fixed angle will be non-zero when sailing.
Drawback is that waves wash over your decks, and similar behavior.
Also heels easily at first, but not later. This type rarely
seen today, in new boats. Increased weight means increased
cost so the cut-the-cost attitude assures big heavy boats are rare.

wide beam, little deadrise. canoe hull form. Modern racer & some "cruisers".
Tends to stay flat with respect to the water surface. If the water
is big waves you are going to pitch and roll a lot, but take less
water compared to first example. Resists tipping at first more than
the first example does, but less later (greater initial righting moment).

Take your pick. Do you want to heel a good deal at first and then
stay steady, or sail flat until the waves pick up when things
begin to bounce around?

The racers have pretty much settled on version two.  Good and bad
boats can be made either way. Lots of other things matter, too.
Well-designed sharpies are good boats of the second example;
lots of classic sailing yachts follow the first.  

For the big storm?  That's a really involved question.  Everything has to
be done right, a lot more than picking a good design on paper.
Many designs have survived big storms, and some of the same
kinds disappeared. Mother Nature can cook up something too big
for any private vessel to survive, but she does it very rarely.
In WWII a destroyer when told to press ahead in a storm radioed for permission
to surface.

This question ought to go to the cruising guys.  They will really
kick up the dust over it.

 
 
 

Sailboat design for "Ultimate Storm"

Post by SailDesi » Sun, 31 Mar 1996 04:00:00

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.

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
acceleration loads.

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 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
safety..........

Cheers,


 
 
 

Sailboat design for "Ultimate Storm"

Post by Dick Parsha » Tue, 02 Apr 1996 04:00:00

Quote:

>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
>safety..........

Right.  Too "stable" and the ride can be viciously quick, scrambling your
brains; too "unstable" and the roll period is so slow that you are just
sloshing around getting queezy as well as worried that it won't come
back up from one of it's rolls.  

I remember reading about a "rule of thumb" for what is the best range,
involving the boat's beam and the timed roll through 1 cycle, which
one could do (carefully) at the dock with a bunch of friends.  I think
it was in Dave Gerr's "The Nature of Boats".

Of course, a several posters have noted, this relates to the hull form,
etc., as well as ballast placement.

-----------------------------------------------------------
*** Parshall               IT Support, 3M Corp, Austin TX

Opinions expressed herein are my own and may not represent those of 3M.

 
 
 

Sailboat design for "Ultimate Storm"

Post by Eric Blumhag » Wed, 03 Apr 1996 04:00:00

Quote:


>>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
>>safety..........

>Right.  Too "stable" and the ride can be viciously quick, scrambling your
>brains; too "unstable" and the roll period is so slow that you are just
>sloshing around getting queezy as well as worried that it won't come
>back up from one of it's rolls.  

>I remember reading about a "rule of thumb" for what is the best range,
>involving the boat's beam and the timed roll through 1 cycle, which
>one could do (carefully) at the dock with a bunch of friends.  I think
>it was in Dave Gerr's "The Nature of Boats".

There are two things involved in how the boat responds to seas. The method
described above (aka sallying ship) gives an idea of what the boat's
moment of inertia is, including the mass of the water that the boat has to
move in order to roll. The moment of inertia of the boat is almost
entirely a function of its shape, and is relatively independent of how
high you put the ballast.

Quote:

>Of course, a several posters have noted, this relates to the hull form,
>etc., as well as ballast placement.

Ballast placement will affect the righting moment of the boat at various
angles of heel. As an extreme example, think of a cylindrical ship vs a
sheet of plywood that is weighted so that it is vertical in the water. If
you play with the ballast placement, you could get it so that they have
approximately the same righting moment at every angle of heel. However,
when you consider motions, though, the plywood won't move nearly as much
as the cylinder, because it has to shove a heck of a lot more water out of
the way to move. I know that I would rather be on the plywood "boat" than
the cylinder.

The other problem is that it is pretty hard to accurately predict the
added mass of the boat (the mass of water you have to move along with the
boat) without actually building a model and testing it, which doesn't help
much when you aare trying to design a boat on paper. The empirical
formulae are really unpleasant to use, as well.

Quote:
>-----------------------------------------------------------
>Dick Parshall               IT Support, 3M Corp, Austin TX

>Opinions expressed herein are my own and may not represent those of 3M.

--Eric

--
| We have been put here on this earth    | Eric Blumhagen            |

| tell you differently.                  |                           |
|            --Kurt Vonnegut, Jr.        |                           |

 
 
 

Sailboat design for "Ultimate Storm"

Post by John Curt » Wed, 03 Apr 1996 04:00:00

Quote:

>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
        between:  

                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
        about.

Quote:
>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
>acceleration loads.

>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
        insignificant.

Quote:
>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
>safety..........

>Cheers,



--
        Jack Curtis    

        /* Design Verification - Cisco Systems - ATM Business Unit */

 
 
 

Sailboat design for "Ultimate Storm"

Post by Terry Schell;x33 » Thu, 04 Apr 1996 04:00:00

For the ultimate storm has anyone considered a submarine?  Hell, you
are going to have water over the deck most of the time, why not just
plan for it?  

You avoid excess windage (just a breather tube/mast) and you avoid almost
all of the wave action.

"Weather looks bad.  Better strike the sails and dive to 4 fathoms."

Terry Schell

 
 
 

Sailboat design for "Ultimate Storm"

Post by Dexplor » Thu, 04 Apr 1996 04:00:00

Arni--

I think your last statement is very important.  While heaving to is a
viable tactic in fairly high seas which are not breaking, any yacht is
going to subjected to enormous strains, and a probability of repeated
rolling, (with attendant rigging carnage and dire danger of holing),
if the tactic is attempted in huge breaking seas, or in storms where
rouge waves (as much as twice the hight of the average wave) are
prevalent.  Simply giving up and lying ahull is worse.  

The usual tactic is to run before such seas under bare poles.  The
boat motion is much calmer.  However, with really steap seas and large
breaking crests there is then the danger of pitchpolling, if the yacht
speed is not limited.  What happens is the yacht accelerates down a
steep wave and digs her bow under at the bottom, while the extra steep
wave is simultaneously pushing the stern forward.

The classical solution is a drogue.  Sometimes merely long warps,
probably tied together and at least 300 feet long are used, streamed
from the stern. Parachute or open weaved basket type drogues are also
used at the end of a long warp.  There is some problem with such types
from  slack and pickup as a result of wave acceleration and release.
If slack occurs at just the wrong time, pitchpoling remains possible.

Personally I think the Don Jordan  designed (he put it in the public
domain) series drogue is the best solution.  Some 100 to 200 little
cones (depending upon displacement) attached  in series along 300ft of
warp, which is attached to the stern with a bridle.  There's a 30lb
weight or so at the sea end of the drogue (e.g. anchor chain).  The
design depends upon no one or even several chutes, and picks up
increased loads during wave acceleration much more quickly -- since
there are cones starting some 75 ft. from the yacht.  The field
reports have been universally favorable from what I've heard/read.
One user rode out Hurrican Gordon a couple of years ago in the Gulf
Stream, streaming a Jordan series drogue.  (I have no connection with
the series drogue other than owning one.)

The best discussion of drogues vs. sea anchors vs. other survival
tactics I have ever seen is in the library of the Sailing Forum on
Compuserve (file drogue.thd).

        --Cheers,  Doug

Quote:

>The issue, of course, is not really one of weight in these extreme conditions.
>When the top of a large wave breaks, or 'rolls' over, there is a tremendous weight
>of water which travels downwards hitting the upper parts of the yacht. Naturally
>a yacht with a high freeboard or deckhouse is more greatly affected. At the same time,
>the underwater hull and keel is being lifted up the wave by the rotational water
>movement within the wave. The wider and longer the keel, the more it holds the water
>and defies gravity's attempts to right the boat. There is a *** rolling effect which
>can roll the yacht right over. In other words, the very performance factors which
>attract cruisers to long deep keels and high freeboard can contribute, in the wrong
>conditions, to LESS safety. Theoretically a deep NARROW keel with a bulb containing most
>of the ballast would work better on a yacht lying ahull, because gravity would have some
>chance of forcing this keel sideways through the water to right the boat.
>Another factor to consider in comparing righting moments is mast damage. It is the mast
>breaking during a 360 roll, or even a knockdown, which causes the dangerous damage,
>often by tearing open the deck. The quicker the roll, the more likely this is to happen
>as the mast is forced through the water.
>I am convinced that lying ahull should be avoided at all costs, and either stay head to wind by using a sea anchor, or run downwind towing a drogue.

 
 
 

Sailboat design for "Ultimate Storm"

Post by Matt Peders » Sat, 06 Apr 1996 04:00:00

Well, nobody has discussed it yet, but there is another tactic
besides running off and lying ahull.  Larry Pardey makes a good
case for it in a new book.

The basic theory is you heave to (jib backed, or jib/trysail,
whatever works for the boat).  It may require you to set a
parachute anchor.  You try to keep the boat at about 50 degrees
to the wind, and you want to make absolutely no headway
or sternway.  The boat will slide through the water creating
a slick, which has the property of pretty much eliminating
breaking waves from crashing down on you.

There are some advantages to this over running off. You get
some rest, you don't have to worry about getting tired and
broaching, and you don't have to worry about pitchpoling.

Matt