"DSK" wrote

The first thing that Ben wanted to know was the righting moment
(stability) of the hull, because that was the ultimate determinant
of
how much rigging load could be created.


All that tells you is when you'll have to reef. You could put a 70'
mast on the boat and a 1000 square foot mainsail, if you didn't mind
tucking in your third reef in 15 knot winds.

Nope, Doug. That statement shows that you are still not getting it.

I don't have time to belabor this further but, trust me, I know what
I'm talking about. I've analyzed these dynamics for the British
Government, was founding Chairman of the American Sail Training
Association Technical Committee, did the indeterminate structural
analysis of the rig for Coast Guard approval of the rig of the ship in
"Master and Commander" and on and on and on.

Think it through some more. I know from your other posts that you are
smart enough to get the light to go on.

I'll be glad to answer questions later. It's an interesting and often
misunderstood point.

--

Roger Long

Roger Long wrote:
Nope, Doug. That statement shows that you are still not getting it.


Bull****, I've said the SAME THING that you're saying. Look
it up. Maybe you're having a bad morning and just need to
feel superior?



Think it through some more. I know from your other posts that you are
smart enough to get the light to go on.


Thanks a lot.

DSK

On Mon, 05 Jun 2006 07:12:01 -0400, DSK wrote:

.... I once
had the pleasure (or misfortune) to work with Ben Hall designing a new
rig for my old Cal-34. I wanted to increase sail area by turning it
into a fractional rig, same fore triangle, larger mainsail.


That's a great idea. Did you go ahead with it? While I have
sailed a lot of mast head rigs, I've always liked fracs more.

Yes, it was very successful. Performance to windward and in light air
was greatly improved. Another unexpected benefit was that we rarely
needed to reef the main because the additional sail control afforded
by the frac rig allowed us to flatten it a great deal when needed.

Well, if that's the case, it's a good example of what Winston
Churchill said about being divided by a common language and an apology
(from this end) is in order.

I've encountered so much confusion over the years on this point, (even
from Coast Guard officers with naval architectural degrees engaged in
writing regulations) that I'm probably primed to expect it.

Since we have managed to so thoroughly confuse each other, I'm sure
almost everyone else is lost as well. For their benefit and not to
talk down to you:

Let's look at the simplest case, a catboat with an un-stayed mast. The
hull and ballast are a given and you now want to figure out how bit to
make the mast. You determine the maximum righting moment which will be
in the 35 - 45 degree range for this kind of boat. The mast is a
simple lever and maximum material stress will be at the deck. The
bending moment will exactly equal the righting moment. Once you know
the material properties, it's a quick calculation to determine the
required diameter, with a proper safety factor applied.

Now, you decide your catboat is a little slow so you decide to double
the sail area. Do you need to make the mast bigger? No. The righting
moment, which limits the force on the mast will be the same. The only
difference is that the boat can be heeled to any particular angle in
much less wind. The force on the mast will be the same at any
particular heel angle as it was before the sail increase.

Actually, because you have added the weight of longer mast, boom, and
gaff, as well as more sail material, the center of gravity will be
slightly higher. This reduces the righting moment. This is within the
fuzzy factor of the calculations as used in the real world but, if you
were to compulsively design to exact loads, stresses, and safety
factors, you would find that the boat with the larger sail plan could
paradoxically have a slightly smaller mast.

--

Roger Long



"DSK" wrote in message
.. .
Roger Long wrote:
Nope, Doug. That statement shows that you are still not getting
it.


Bull****, I've said the SAME THING that you're saying. Look it up.
Maybe you're having a bad morning and just need to feel superior?



Think it through some more. I know from your other posts that you
are smart enough to get the light to go on.


Thanks a lot.

DSK

Roger Long wrote:
....
I'll be glad to answer questions later. It's an interesting and often
misunderstood point.


This is an interesting discussion - it reminds me a bit of the
question of whether a fuse protects the wiring or the device.

However, the original issue was sheet loading, not rig loading. I
wonder what standards are used to design sheet blocks and tracks,
winch mounts, etc. Having seen what happens when a shackle holding a
sheet block gives way, I'm not sure I'd be too quick to say that the
genny would never be carried in high wind, or that heeling would
always relieve the load.

--
Posted via a free Usenet account from http://www.teranews.com

Roger Long wrote:
Well, if that's the case, it's a good example of what Winston
Churchill said about being divided by a common language and an apology
(from this end) is in order.


Roger, I'll apologize and start all over as well.


I've encountered so much confusion over the years on this point, (even
from Coast Guard officers with naval architectural degrees engaged in
writing regulations) that I'm probably primed to expect it.


Could be... one reason why I'mn a bit frustrated is that you
don't seem to be reading my posts. For example, what Wayne B
was talking about is exactly what I meant.

Since we have managed to so thoroughly confuse each other, I'm sure
almost everyone else is lost as well. For their benefit and not to
talk down to you:

Let's look at the simplest case, a catboat with an un-stayed mast. The
hull and ballast are a given and you now want to figure out how bit to
make the mast. You determine the maximum righting moment which will be
in the 35 - 45 degree range for this kind of boat. The mast is a
simple lever and maximum material stress will be at the deck. The
bending moment will exactly equal the righting moment. Once you know
the material properties, it's a quick calculation to determine the
required diameter, with a proper safety factor applied.

Now, you decide your catboat is a little slow so you decide to double
the sail area. Do you need to make the mast bigger? No. The righting
moment, which limits the force on the mast will be the same. The only
difference is that the boat can be heeled to any particular angle in
much less wind. The force on the mast will be the same at any
particular heel angle as it was before the sail increase.


Exactly so. And the benefit to the boat's performance will
be in lighter air, and perhaps downwind (depending on a lot
of factors). The power developed by the rig has to be
counteracted by the boat's righting moment... more power
means more heeling... and once the boat is heeled past it's
most efficient sailing angle, the boat ain't goin' one lick
faster. However, it will go faster in lighter air and reach
it's maximum developed power sooner.


Actually, because you have added the weight of longer mast, boom, and
gaff, as well as more sail material, the center of gravity will be
slightly higher. This reduces the righting moment. This is within the
fuzzy factor of the calculations as used in the real world but, if you
were to compulsively design to exact loads, stresses, and safety
factors, you would find that the boat with the larger sail plan could
paradoxically have a slightly smaller mast.


heh heh reduced windage, greater efficiency... a snowball
effect... at what point can you have infinitely large sails
with no mast at all?

Fresh Breezes- Doug King

.... I once
had the pleasure (or misfortune) to work with Ben Hall designing a new
rig for my old Cal-34. I wanted to increase sail area by turning it
into a fractional rig, same fore triangle, larger mainsail.


That's a great idea. Did you go ahead with it? While I have
sailed a lot of mast head rigs, I've always liked fracs more.


Wayne.B wrote:
Yes, it was very successful. Performance to windward and in light air
was greatly improved. Another unexpected benefit was that we rarely
needed to reef the main because the additional sail control afforded
by the frac rig allowed us to flatten it a great deal when needed.


That's what I'm sayin'
Better control over the luff of the jib as well as the main
leach; there's a reason why most of the hot-shot racers have
gone to big-roach frac rigs and a dedicated crew "trimming"
the backstay (and runners & checks, if any).

The longer luff and bigger spinnaker generally tend to favor
masthead rigs for racing, but I think that's because they
don't factor in the greater controllability of the frac rig
& make SA enough bigger. For example, in the J-29s nobody
wants the frac rigs, even though they're much more fun to
sail (IMHO) because they have a slightly smaller spinnaker.
And (again IMHO) if they were raced in heavy air the frac
rigs would rule.

Fresh Breezes- Doug King

"DSK" wrote heh heh reduced windage, greater
efficiency... a snowball
effect... at what point can you have infinitely large sails with no
mast at all?

Oh, so you want to follow that progression down to the end do you?
(I'm assuming this is a joke because, if you understand this as well
as you say you do, the answer is already obvious.)

All else being equal, the mast can get smaller as the rig gets larger.
At the same time though, the amount of wind that will heel the boat to
any specific angle is getting less since the righting moment is being
decreased by the weight of the added spars and rigging. The sails
could never be infinitely large because the added weight of cloth,
booms, and gaff will eventually bring the center of gravity high
enough that stability is zero. At that point, there will be no load
on the rig from wind and the mast could be infinitely small if there
were some other way to transfer the loads from the sails to the hull.

--

Roger Long

... at what point can you have infinitely large sails with no
mast at all?


Roger Long wrote:
Oh, so you want to follow that progression down to the end do you?
(I'm assuming this is a joke because, if you understand this as well
as you say you do, the answer is already obvious.)

All else being equal, the mast can get smaller as the rig gets larger.
At the same time though, the amount of wind that will heel the boat to
any specific angle is getting less since the righting moment is being
decreased by the weight of the added spars and rigging. The sails
could never be infinitely large because the added weight of cloth,
booms, and gaff will eventually bring the center of gravity high
enough that stability is zero. At that point, there will be no load
on the rig from wind and the mast could be infinitely small if there
were some other way to transfer the loads from the sails to the hull.


We'll make the spars out of carbon nanotubes inflated with
hydrogen so that they're lighter than air, and magnetize the
sails with an electrostatic charge to transfer the "sheet"
loads.

"Any sufficiently advanced technology is indistinguishable
from magic." -Arthur C. Clarke

Another possible solution is this
http://www.kiteship.com/
which looks like it would pose less need for righting moment
but even larger need for structural analysis. I'd like to
try one of these.

A point I was trying to make earlier is that while loads on
the rig (mast & standing rigging) are limited by the boat's
righting moment, the actual force on any given piece of
rigging can be far larger because of the geometry. For
example, the tension on the shrouds can be huge because they
are opposed by the opposite shroud and the compression of
the mast. Then you have the sheet loads, vang, halyard
tension, etc etc. The aggregate (or net) of these forces
will equal the righting moment plus the force required to
drive the boat thru the water at speed, but the boat's
structure has to be capable of holding up to the sum of
these forces.

This is probably not very clearly states so I will apologize
in advance and brace for argument

Fresh Breezes- Doug King