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.

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

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.

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.

"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