Roll Pitch & Comfort
 

There was a thread back a ways that was about roll rate and comfort Vs.
safety. Just thought if anyone was interested there are two lists on the
boatdesign.net/forums that show Ted Brewer's " motion comfort ratio" of
quite a few different sailboats. May be useful as a comparison chart for
anyone looking at buying a boat. First list is of boats with a
comparatively high MC ratio, and the second list is of boats with lower
ratios.

http://www.boatdesign.net/forums/showthread.php?t=20655
Scroll down to find the lists in two posts.

Red

Roll Pitch & Comfort
 

Red wrote:
There was a thread back a ways that was about roll rate and comfort Vs.
safety. Just thought if anyone was interested there are two lists on the
boatdesign.net/forums that show Ted Brewer's " motion comfort ratio" of
quite a few different sailboats. May be useful as a comparison chart for
anyone looking at buying a boat. First list is of boats with a
comparatively high MC ratio, and the second list is of boats with lower
ratios.

http://www.boatdesign.net/forums/showthread.php?t=20655
Scroll down to find the lists in two posts.

Red

More
http://www.mahina.com/boats.html
http://www.tedbrewer.com/yachtdesign.html
http://www.image-ination.com/sailcalc.html
and the best
http://www.johnsboatstuff.com/technica.htm
G

Roll Pitch & Comfort
 

IMO, Ted Brewer's motion comfort ratio is BS. Brewer is an interested
party and he admits that the "ratio" was made up as a kind of joke.
There is absolutely no evidence that it works. As a general theory is
is indefensible. On any given day I'd bet you'll be a lot more
comfortable in a Catalina 30 than you will be in a 5.5 meter both in
terms of motion comfort and amenities but you certainly will not learn
that from the "comfort" ratio. Any comfort motion rating system that
says that the Colin Archer ketch is the pinnacle of comfortable is
just plain cr@p. I'd rate the "comfort ratio" as significantly less
important than the color of the mast step in my boat comparison list.
Of course, TB has a different view. You can see his rational he
http://www.tedbrewer.com/yachtdesign.html.

-- Tom.

Roll Pitch & Comfort
 

On 2008-02-27 02:01:49 -0500, " said:

IMO, Ted Brewer's motion comfort ratio is BS. Brewer is an interested
party and he admits that the "ratio" was made up as a kind of joke.
There is absolutely no evidence that it works. As a general theory is
is indefensible. On any given day I'd bet you'll be a lot more
comfortable in a Catalina 30 than you will be in a 5.5 meter both in
terms of motion comfort and amenities but you certainly will not learn
that from the "comfort" ratio. Any comfort motion rating system that
says that the Colin Archer ketch is the pinnacle of comfortable is
just plain cr@p. I'd rate the "comfort ratio" as significantly less
important than the color of the mast step in my boat comparison list.
Of course, TB has a different view. You can see his rational he
http://www.tedbrewer.com/yachtdesign.html.

-- Tom.

I'd be a bit less inflammatory if I wrote on the subject, but I have to
say that I agree for the most part.

Then again, if we're heeling between 15 and 25 degrees, my lovely lady
knows not to complain as that's normal for our lovely
lady/beast/vessel. If she were longer and heavier, the acceptable heel
numbers would be a bit lower.

--
Jere Lull
Tanzer 28 #4 out of Tolchester, MD
Xan's pages: http://web.mac.com/jerelull/iWeb/Xan/
Our BVI trips & tips: http://homepage.mac.com/jerelull/BVI/

Roll Pitch & Comfort
 

Red wrote:
There was a thread back a ways that was about roll rate and comfort
Vs. safety. Just thought if anyone was interested there are two lists
on the boatdesign.net/forums that show Ted Brewer's " motion comfort
ratio" of quite a few different sailboats. May be useful as a
comparison chart for anyone looking at buying a boat. First list is
of boats with a comparatively high MC ratio, and the second list is
of boats with lower ratios.

http://www.boatdesign.net/forums/showthread.php?t=20655
Scroll down to find the lists in two posts.

Red

Best way to reduce roll is to put some sails up!

Dennis.

Roll Pitch & Comfort
 

On Wed, 27 Feb 2008 10:55:51 GMT, Jere Lull wrote:

On 2008-02-27 02:01:49 -0500, " said:

IMO, Ted Brewer's motion comfort ratio is BS. Brewer is an interested
party and he admits that the "ratio" was made up as a kind of joke.
There is absolutely no evidence that it works. As a general theory is
is indefensible. On any given day I'd bet you'll be a lot more
comfortable in a Catalina 30 than you will be in a 5.5 meter both in
terms of motion comfort and amenities but you certainly will not learn
that from the "comfort" ratio. Any comfort motion rating system that
says that the Colin Archer ketch is the pinnacle of comfortable is
just plain cr@p. I'd rate the "comfort ratio" as significantly less
important than the color of the mast step in my boat comparison list.
Of course, TB has a different view. You can see his rational he
http://www.tedbrewer.com/yachtdesign.html.

-- Tom.

I'd be a bit less inflammatory if I wrote on the subject, but I have to
say that I agree for the most part.

Then again, if we're heeling between 15 and 25 degrees, my lovely lady
knows not to complain as that's normal for our lovely
lady/beast/vessel. If she were longer and heavier, the acceptable heel
numbers would be a bit lower.

It is somewhat interesting that the antiroll fins on a cruise ship
will kill the roll completely, but the ship still pitches noticably in
one foot waves.

Casady

Roll Pitch & Comfort
 

" said:
IMO, Ted Brewer's motion comfort ratio is BS. Brewer is an interested
party and he admits that the "ratio" was made up as a kind of joke.
There is absolutely no evidence that it works. As a general theory is
is indefensible.

No, it's defensible on several grounds. It was invented by a
knowledgeable NA, it does model
that "bigger + heavier = more comfort" which is true, and it is widely
quoted.

None of that makes it a valuable quantity for comparing boats IMHO.
For example, if you take two boats of very similar dimension &
displacement, the one with longer
overhangs will have a higher "Motion Comfort Index." Why? Because old
salty prejudices favor boats
with long overhangs. Long overhangs were fashionable in the early
1900s but they don't make a boat
more comfortable at sea, if anything they make it wetter, slower, and
less "comfortable" by most
definitions of the word.

.... On any given day I'd bet you'll be a lot more
comfortable in a Catalina 30 than you will be in a 5.5 meter both in
terms of motion comfort and amenities but you certainly will not learn
that from the "comfort" ratio.

And you'd be more comfortable yet in a cheap hotel. Where does this
fit into the ratio?
;)


... Any comfort motion rating system that
says that the Colin Archer ketch is the pinnacle of comfortable is
just plain cr@p. I'd rate the "comfort ratio" as significantly less
important than the color of the mast step in my boat comparison list.
Of course, TB has a different view. You can see his rational he
http://www.tedbrewer.com/yachtdesign.html.



Jere Lull wrote:
I'd be a bit less inflammatory if I wrote on the subject,

Yeah, but where's the fun in that?


Then again, if we're heeling between 15 and 25 degrees, my lovely lady
knows not to complain as that's normal for our lovely
lady/beast/vessel. If she were longer and heavier, the acceptable heel
numbers would be a bit lower.


And most likely, slower in lighter air.
95% (or more) of all sailing is done in winds of less than 15 knots.
Therefor, any boat
which does *not* have to reef or reduce sail in 15 ~ 18 knot winds is
a *less* capable
vessel. But again, old salty prejudices lean the other way....

Fresh Breezes- Doug King

Roll Pitch & Comfort
 

"Red" wrote in message
...
There was a thread back a ways that was about roll rate and comfort Vs.
safety. Just thought if anyone was interested there are two lists on the
boatdesign.net/forums that show Ted Brewer's " motion comfort ratio" of
quite a few different sailboats. May be useful as a comparison chart for
anyone looking at buying a boat. First list is of boats with a
comparatively high MC ratio, and the second list is of boats with lower
ratios.

http://www.boatdesign.net/forums/showthread.php?t=20655
Scroll down to find the lists in two posts.

Red

There is a degree of subjectivity in that. The two largest factors affecting
comfort are the condition of the person's inner ear and their body
morphology. The inner ear obviously is the source of balance but body
morphology is interesting. These boat studies tend to be old and don't
account for obesity and the roll pitch comfort of the human body itself as a
result of mechanical displacements of large amounts of fat tissue. A thin
person may be quite comfortable in those old fashioned vibrating belt
machines but an obese one would experience extreme discomfort as they fly
about all over the place. An obese person's fat tissues can couple into the
motion of the boat in a positive sympathetic mode, increasing the motion of
the boat and also of the person itself. This mechanical regime would
increase until non linearities in the adipose tissue or transient boat
displacements introduced harmonics and dampened the overall response. The
concepts of comfort with regard to boat motion are indeed true, but the
specifics, namely rates and axis should be reconsidered due to the ever
increasing size and elasticity of boat passengers. This is exceedingly true
in the States, where eating has become full time sport.

Nigel

Roll Pitch & Comfort
 

On Wed, 27 Feb 2008 07:29:41 -0800 (PST), wrote:

No, it's defensible on several grounds. It was invented by a
knowledgeable NA, it does model
that "bigger + heavier = more comfort" which is true, and it is widely
quoted.

It also assigns a very low comfort number to the Frers 41 which jibes
very closely with my experience. It has a quick squirrelly motion
offshore and is a bit of a vomit comet.

Roll Pitch & Comfort
 

On Feb 27, 5:29 am, wrote:
" said:
IMO, Ted Brewer's motion comfort ratio is BS. ...

No, it's defensible on several grounds. It was invented by a
knowledgeable NA, it does model
that "bigger + heavier = more comfort" which is true, and it is widely
quoted.

No, the ratio does not say that "bigger" is more comfortable. Just
the opposite. It penalizes length (70% waterline + 30% overall) and
beam to the 1/3. The results of this can be silly. The idea that an
Alberg 30 is vastly more "comfortable" than a Transpac 52 is absurd.

I want to be clear that I'm not disparaging Brewer. He has drawn some
beautiful boats and written at least one very good book. It's just
his "CR" that's bogus. Brewer claims that heave and pitch response
will be slower on a boat with a heavily loaded water plane and low ppi
all else being equal. That's true for heave and probably reasonably
indicative for pitch. He also asserts that roll response will be
slower on heavy narrow boats. That may be true, but misses some major
factors. The problem is that he goes on to assert that boats with
slow initial pitch and roll and heave responses are "more
comfortable". This completely ignores major factors like period,
amplitude and damping. And, of course, begs the questions of what is
comfort is and what conditions we are talking about. Down wind boats
with high "CR" will be slow and have a tendency to roll
uncontrollably. Upwind they will be slow but wet; if you don't rise
to meet a wave you must go through it. Indeed, a high "CR" pretty
much assures slowness. It is true that slower is generally more
comfortable. It is also true that you can sail a fast boat slowly but
you can't make a slow boat fast... Theres more, but my work is
calling.

--Tom.

Roll Pitch & Comfort
 

On Feb 27, 4:08 pm, " wrote:
On Feb 27, 5:29 am, wrote:

" said:
IMO, Ted Brewer's motion comfort ratio is BS. ...

No, it's defensible on several grounds. It was invented by a
knowledgeable NA, it does model
that "bigger + heavier = more comfort" which is true, and it is widely
quoted.

No, the ratio does not say that "bigger" is more comfortable.

Yes it does.
Look at the math.

Increase displacement, "Comfort Ratio" goes up. Increase LOA but not
LWL, the ratio goes up. The funny thing is that if you take the same
LOA and Disp, and reduce LWL, the ratio goes up. If you keep
everything the same and decrease beam, the ratio goes up.

The assumption is that the heavier a footprint a boat has, the higher
load per waterplane area, will give a boat more comfortable motion in
a seaway. There is some real-life justification for that, but to
assume that narrow heavy boats with long overhangs are the ultimate in
seagoing comfort is absurd.

.... Just
the opposite. It penalizes length (70% waterline + 30% overall) and
beam to the 1/3. The results of this can be silly. The idea that an
Alberg 30 is vastly more "comfortable" than a Transpac 52 is absurd.


In this case, "comfort" is defined only by the boat's motion in a
seaway.


I want to be clear that I'm not disparaging Brewer. He has drawn some
beautiful boats and written at least one very good book.

Many moons ago, my family owned a Brewer design. It was a good boat.

It's just
his "CR" that's bogus. Brewer claims that heave and pitch response
will be slower on a boat with a heavily loaded water plane and low ppi
all else being equal. That's true for heave and probably reasonably
indicative for pitch. He also asserts that roll response will be
slower on heavy narrow boats. That may be true, but misses some major
factors. The problem is that he goes on to assert that boats with
slow initial pitch and roll and heave responses are "more
comfortable". This completely ignores major factors like period,
amplitude and damping.

Agreed.
But those can't be reasonably quantified with the very simple
dimensions commonly available.


.... And, of course, begs the questions of what is
comfort is and what conditions we are talking about. Down wind boats
with high "CR" will be slow and have a tendency to roll
uncontrollably. Upwind they will be slow but wet; if you don't rise
to meet a wave you must go through it. Indeed, a high "CR" pretty
much assures slowness. It is true that slower is generally more
comfortable. It is also true that you can sail a fast boat slowly but
you can't make a slow boat fast...

Agreed


Theres more, but my work is
calling.


I'd say your work here is done ;)

DSK

Roll Pitch & Comfort
 

On Feb 27, 2:51 pm, wrote:
... No, the ratio does not say that "bigger" is more comfortable.

Yes it does.
Look at the math.

Increase displacement, "Comfort Ratio" goes up. Increase LOA but not
LWL, the ratio goes up. The funny thing is that if you take the same
LOA and Disp, and reduce LWL, the ratio goes up. If you keep
everything the same and decrease beam, the ratio goes up. ...

Help me out Doug. The formula is:

C = D/(.65(.7Lwl+.3Loa)*B^1.33

Where C is the "Comfort Ratio", D is displacement, Lwl is the length
on the load waterline, Loa is the overall length and B is the beam.

Now, if you fix the displacement but make the boat bigger in any
dimension the ratio goes down. All of the dimensions are in the
denominator. Thus, it seems to me that making the boat "bigger" makes
it score less well on the CR. I don't follow how you can say that if
you increase the LOA but not LWL the ratio goes up. Are we looking at
the same formula?

-- Tom.

Roll Pitch & Comfort
 

tsmw wrote:
C = D/(.65(.7Lwl+.3Loa)*B^1.33

Where C is the "Comfort Ratio", D is displacement, Lwl is the length
on the load waterline, Loa is the overall length and B is the beam.

Now, if you fix the displacement but make the boat bigger in any
dimension the ratio goes down. All of the dimensions are in the
denominator. Thus, it seems to me that making the boat "bigger" makes
it score less well on the CR. I don't follow how you can say that if
you increase the LOA but not LWL the ratio goes up. Are we looking at
the same formula?

-- Tom.

Try it in excel. I think the multiplier of less than one has an
effect.
If you keep everything else constant and increase the LOA, the "Motion
Comfort Ratio" goes up slightly.
That's making the boat bigger, nyet?
If you keep everything else constant and decrease the LWL, the "Motion
Comfort Ratio" goes up by a greater amount than above. Ditto for
decrease in Beam. This isn't increasing size, but decreasing LWL while
holding everything else constant is increasing the overhangs, which
does not really improve seakindliness.
The greatest increase in the ratio is of course had by increasing
Displacement, which is again increasing size.
Disp & LOA are the largest factors in a boats size IMHO ;)

DSK

Roll Pitch & Comfort
 

Tom wrote:
IMO, Ted Brewer's motion comfort ratio is BS. Brewer is an interested
party and he admits that the "ratio" was made up as a kind of joke.
There is absolutely no evidence that it works. As a general theory is
is indefensible. On any given day I'd bet you'll be a lot more
comfortable in a Catalina 30 than you will be in a 5.5 meter both in
terms of motion comfort and amenities but you certainly will not learn
that from the "comfort" ratio. Any comfort motion rating system that
says that the Colin Archer ketch is the pinnacle of comfortable is
just plain cr@p. I'd rate the "comfort ratio" as significantly less
important than the color of the mast step in my boat comparison list.
Of course, TB has a different view. You can see his rational he
http://www.tedbrewer.com/yachtdesign.html.

-- Tom.

Hi Tom,
While I have no experience in yacht design whatsoever, I can see what
Brewer was trying to accomplish. The following is a partial copy of his
description from his website:

"COMFORT RATIO (CR): This is a ratio that I dreamed up, tongue-in-cheek,
as a measure of motion comfort but it has been widely accepted and,
indeed, does provide a reasonable comparison between yachts of similar
type. It is based on the fact that the faster the motion the more
upsetting it is to the average person. Given a wave of X height, the
speed of the upward motion depends on the displacement of the yacht and
the amount of waterline area that is acted upon. Greater displacement,
or lesser WL area, gives a slower motion and more comfort for any given
sea state.

...The intention is to provide a means to compare the motion comfort
of vessels of similar type and size, not to compare that of a Lightning
class sloop with that of a husky 50 foot ketch."

So while I agree that there may, or may not be, hard "science" behind it
(and I admit I wouldn't know), it seems useful as a comparison when
looking at similar type boats for a given usage. And it seems to agree
with the descriptions and discussions that were put forth in that
earlier thread by Roger Long and others.

Red

Roll Pitch & Comfort
 

On Feb 28, 4:50 pm, wrote:
Try it in excel. I think the multiplier of less than one has an
effect. ...

I don't do excel but since I have it I put in: =D2/
(0.65*((0.7*B2)+(0.3*A2))*(C2^1.33)) and if you increase any dimension
the CR goes down. Remember the mathematical operators have an order
of precedence that not all programming languages enforce so you might
need the extra parans to get the formula to work as Brewer intended.

-- Tom.

Roll Pitch & Comfort
 

On Feb 28, 5:05 pm, Red wrote:
Hi Tom,
...So while I agree that there may, or may not be, hard "science" behind it
(and I admit I wouldn't know), it seems useful as a comparison when
looking at similar type boats for a given usage. And it seems to agree
with the descriptions and discussions that were put forth in that
earlier thread by Roger Long and others. ...

Hi Red,

Sorry I went ballistic over all this. It is great to be talking boats
again in the group and I appreciate your post. Obviously, I don't
think the CR has any value at all, but I'm certainly not an expert
either. I'll Let Roger speak for himself, but he's selling boats that
would rate miserably on the Brewer CR (because they have lightly
loaded water planes) and has written a paper on their seakindliness.
Do keep in mind that Brewer is selling boats designs that are more
expensive to build, slower and have less usable interior space than
they typical mass market boats. It happens that the only generally
used metric that they rate well on is the one he made up... And, while
I actually like many of his designs a lot I'm waiting to see some
empirical support for his CR before I give it any weight at all...

-- Tom.

Roll Pitch & Comfort
 

Tom wrote:
Sorry I went ballistic over all this.

Ha! Going ballistic seems to be something most of us here do at least
once in awhile (I'm guilty), so no prob.

It is great to be talking boats
again in the group and I appreciate your post. Obviously, I don't
think the CR has any value at all, but I'm certainly not an expert
either. I'll Let Roger speak for himself, but he's selling boats that
would rate miserably on the Brewer CR

I would welcome Roger's further enlightenment on this subject.

Do keep in mind that Brewer is selling boats designs that are more
expensive to build, slower and have less usable interior space than
they typical mass market boats. It happens that the only generally
used metric that they rate well on is the one he made up... And, while
I actually like many of his designs a lot I'm waiting to see some
empirical support for his CR before I give it any weight at all...

-- Tom.

I understand. What I have seen though, are ratings that Brwewer himself
has done on numerous boat designs other than his own, and he still finds
the CR to be useful for comparison in those cases - not comparisons
*against his own designs*, but against similar boats for similar usage
regardless of who designed either of them.

Red

Roll Pitch & Comfort
 

On Feb 28, 6:29 pm, Red wrote:
...What I have seen though, are ratings that Brwewer himself
has done on numerous boat designs other than his own...

I have not seen these. Do you have a link? However, what I want to
see is experimental evidence that people actually experience less
discomfort on boats with high CRs. I think the physics of the CR is
so simplified that there is little reason to believe there will be
much correlation between high CRs and more comfortable boats or even
boats with slower rates or smaller magnitudes of heave, pitch and
roll. The argument that it only works for very similar boats seems to
suggest it is broken, too. Very similar boats will behave so
similarly that it may be the only way to tell if you're more
comfortable is to calculate the CR...

Sigh, since the horse is dead it won't mind me beating on it. I think
Brewer's basic premise is wrong. One more reason I think the CR is
bogus is that it assumes that the sails can always provide roll
damping. This is often not the case underway and is seldom if ever
the case at anchor. A boat with a high CR will almost certainly be
unlivable at anchor if there is even a suggestion of a ground swell.
It is axiomatic that cruisers spend 90% of their time at anchor. So,
even if Brewer is, by some ineffable chance, right about the CR
underway you're still likely to gain a whole bunch more "comforts" on
a low CR boat at anchor than you will lose underway.

-- Tom.

Roll Pitch & Comfort
 

Brewers' designs are known to be sea kindly. Maybe he is on to something?
Gordon

Roll Pitch & Comfort
 

On Feb 28, 6:29 pm, Red wrote:

...What I have seen though, are ratings that Brwewer himself
has done on numerous boat designs other than his own...

Tom replied:
I have not seen these. Do you have a link?

No Tom, I have seen these comparisons in magazines he writes articles
for. If I can dig one up I'll send you the info.

Red

Roll Pitch & Comfort
 

On Mar 1, 3:22 pm, Red wrote:
On Feb 28, 6:29 pm, Red wrote:

...What I have seen though, are ratings that Brwewer himself
has done on numerous boat designs other than his own...

Tom replied:
I have not seen these. Do you have a link?

No Tom, I have seen these comparisons in magazines he writes articles
for. If I can dig one up I'll send you the info.

Red

Thanks. It'd be interesting to see the citations, but don't panic
over it.

Cheers,

-- Tom.