The roll acceleration: What´s the best for crossing oceans?

MCR = Disp/(0.65*(B^4/3)*(0.7*Lwl+0.3*Lh))
http://www.tedbrewer.com/yachtdesign.html

Note:
B = Bmax
Lh = Length of hull (in many places named as LOA)
All units imperial.

Cheers.

 

To Patrick:

Trust Guillermo. He´s a true professional. As far as i know the formula is as follows:

MCR = Disp / (2/3*((7/10 * LWL)+(1/3 *LOA))*Beam4/3 )

Best winds

 

Thanks Antonio, but the man to trust is Ted Brewer, the father of the MCR, not me.
Cheers.

 

Antonio, Guillermo,

Thanks a lot to you both and to Ted BREWER moreover.

So, if you agree, the dimension of MCR is d, expressed as [ft^(2/3)] i.e. d as [cubic root of square feet].

My own 35 footer is thus MCR = 21d...
I guess that's not enough to make my family as comfortable as onboard a famous Colin Archer.

Fair winds and compulsory smooth seas, then to expect.

Kindly.

Patrick

 

Calm down, Patrick, a Transpac 52 only score 16 and in my own case , (i have a Beneteau 473) my sailboat score 26.7. Be a good trimmer avoiding low pressure systems, don´t save your money in navtex,weather-fax, HF radio, global phone and try to anticipe your movements when you were sailing with family. Personally i know people wich have crossed the Atlantic or the Pacific with lower MCR than your boat. The MCR is a data, the real true data are in your brain, be strong.

Good luck

 

Good evening Antonio,

Thank you for your personal opinion.

My fundamental concern remains about the standardisation of such ratios depending upon units and considering essential ratios do not, like nondimensional Froude number, for instance.

Kindly.

Patrick

 

Some notes regarding seasickness

I just found this thread, read over all your posts, and skimmed through some of the documents posted as well (will look more thoroughly later). Some random notes:

Modern racing sailboats, due to their light weight and broad beam, are very 'snappy' compared to older, heavier displacement hulls. This is good for speed and acceleration after turning around a mark; it's rough on the sailors. From what I hear, it's a constant challenge to avoid being launched across the cockpit... Good exercise, though! This would explain why a Transpac 52 would only score a 16 (or whatever--can't recall) on the Motion Comfort Index, while even my little Catalina 27 scores about 25.

Catamarans have an odd reputation regarding seasickness--whereas a monohull boat has a relatively predictable (although large) motion in a sea, a multihull has each hull riding on different parts of the waves, and therefore has a quite unpredictable and rather disconcerting motion. I've read of several instances where experienced monohull sailors found they suffered more seasickness on a Cat, even though there was little real motion. Strange...

Finally, my wife and I visited a boat owned by two licensed captains, who told us of an herbal remedy called Motion-Ease, sold by West Marine. They insist than anyone who comes on board dab a drop or two behind each ear, and they swear that in the three years they've sailed their 42' Endeavour, they've never had a single case of seasickness aboard.

Sorry this is all hearsay--but take it for what it's worth.

 

It is worth nothing

How do you spell rubbish?

Most "modern" racing sailboats (discounting the Open boats that are beamy due to a rule) are very moderate in beam compared to boats 20-30 years ago. You must be reading the same tired crap that's been written since the 1970s.

I have sailed and raced many modern (and older) boats and have never found any "challenge to avoid being launched across the cockpit". Just what would cause this, short of the mast miraculously disappearing?

As a one time Catalina 27 National Champion I have no small experience sailing those boats, and I can tell you that modern racing boats are far more motion friendly than an old Cat 27, especially in a quartering sea. The excess displacement and horrible rudder design of the Cat 27 makes it "good excercise" compared to a modern raceboat.


This is yet another thread about the Motion Comfort Ratio, a rubbish calculation that means nothing. The fact that people use it to make any comment on a design should make Brewer hang his head in shame.

 

Good morning,

An overseas genuine and quite ancient recipe aged two centuries must be known from our community of the "third kind", according to Aristote's classification of "those who sail", using following thread http://www.passocean.com/dddeuxsieclesdhistoire/deuxsieclesdhistoire.html

It appears a beverage to sip once before letting go !

Thanks to all.

Patrick

 

How do you spell rubbish?
r-u-b-b-i-s-h

Most "modern" racing sailboats (discounting the Open boats that are beamy due to a rule) are very moderate in beam compared to boats 20-30 years ago.
Aren't the open boats modern or what? And what comes to beam it's not only the max beam instead of overall beam
You must be reading the same tired crap that's been written since the 1970s.
Why to torture yourself, just skip the crap and look elsewhere
I have sailed and raced many modern (and older) boats and have never found any "challenge to avoid being launched across the cockpit". Just what would cause this, short of the mast miraculously disappearing?
If I recall right there have been some dismastings with modern racers
This is yet another thread about the Motion Comfort Ratio, a rubbish calculation that means nothing. The fact that people use it to make any comment on a design should make Brewer hang his head in shame
a hearsay !

 

Teddy,

Dura lex, sed lex ! Nothing but the law ?

Isn't this an open discussion in the vicinity of the initial thread: "The roll acceleration: What's the best for crossing oceans" ?

I do have a deep respect for that ratios myself especially to share and improve them in our field, well known for its "rule of thumb" and intuition that anyway made so efficient and beautiful famous ocean crossing yachts.

Pleasure.

Patrick

 

We all have our own sense of something's worth...

This is a thread about roll rate and seasickness. The Motion Comfort Index isn't perfect, but it's one of the tools that's been used to discuss differences between boats. It's not a perfect tool but this isn't a black and white world; whatever isn't perfect isn't automatically rubbish. Perhaps your world, however, IS black and white?

 

No, my world is a world of facts, not repeating silly comments over and over for years, as if that makes them true.

Originally Posted by Paul B
How do you spell rubbish?

Obviously I use a different spelling than you; we seem to disagree on a lot!

Most "modern" racing sailboats (discounting the Open boats that are beamy due to a rule) are very moderate in beam compared to boats 20-30 years ago. You must be reading the same tired crap that's been written since the 1970s.


What I'm reading are magazines like Sail, discussions in the Sailing Anarchy website, postings on the C-27/C-270 message list,

(You do realize one needs no expertise to be published in sailig periodiacals or on websites and message boards)

and books like Desirable and Undesirable Characteristics of Offshore Yachts as published by the ORC. What I read are descriptions of what it's like to sail on Open boats, Transpac boats (like the Transpac 52 that was brought up in earlier posts on this forum) and what I see are pictures of boats with wide, fairly flat beams, broad aft and fine forward. And these boats are recent--not ones necessarily from 20-30 years ago.

Let's look at the TP 52, since you want to talk about it. It is fairly representative of a modern raceboat. Canting keelers and AC boats are narrower, Open boats (a very small subset of the racing boat set) are wider.

The TP52 has a B/L of 0.28. The B/DWL is the same.
The STP 65 (big sister to the TP 52) has a B/L of 0.24.
The Catalina 27 has a B/L of 0.33. The B/DWL is 0.38.
Finisterre had a B/L of 0.29. The B/DWL was 0.41.

So let's talk about the "evil, beamy" boats, shall we?

I have sailed and raced many modern (and older) boats and have never found any "challenge to avoid being launched across the cockpit". Just what would cause this, short of the mast miraculously disappearing?

[COLOR="Red"]Well, as someone else noted, there do seem to be a lot of dismasted ocean racers lately, and some that have lost keels as well. [/COLOR]

And this has exactly WHAT to do with the MCR? It was a silly statement for the other person to make, and even sillier for you to repeat.

But what I'm thinking is that a broad light hull with very high initial stability, coupled with a heavy lead bulb held very deep by a high aspect ratio keel and providing a quite-lengthy moment arm to a weight that's a high percentage of the overall displacement

None of this is part of the MCR calculation

would result in a hull that would want to snap back upright quite quickly compared to an older bluewater boat.

And what would cause it to "snap back"? There are forces that cause the heeling moment that the righting moment is working against. Are you trying to say that it suddenly, completely disappears? Not in any of the thousands of miles I've ever sailed.

I would also suggest (and in all of this I'm just echoing what more experienced boat designers and sailors have been writing) that carbon fiber rigs and high-tech sails have a much lower inertia as well, which also allows the boat to 'snap' upright, or quickly heel in a gust or beam sea, or heave in the waves.

How on earth do you think lighter rigs make a boat "quickly heel" or heave more? More BS people like you love to lap up and regurgitate.

As a one time Catalina 27 National Champion I have no small experience sailing those boats, and I can tell you that modern racing boats are far more motion friendly than an old Cat 27, especially in a quartering sea. The excess displacement and horrible rudder design of the Cat 27 makes it "good excercise" compared to a modern raceboat.

Are you talking about a modern 27-foot raceboat? For example? With all due respect to your championship, I only brought up the C-27 as a contrast to the Transpac 52--a boat twice her length has an MCI that's 2/3 of mine.


Yes, I own a modern 27 foot raceboat. It is very light (D/L <90), but narrow (B/L 0.27). It never "snaps back" with any sort amplitude or frequency that would throw anyone across the cockpit. Belive me, the TP 52 is a boat you would much rather be on in bad weather compared to your Cat 27, regardless of the meaningless ratio you so love to embrace.

 

Paul could you please list the comments which in your opinion you find so 'Silly' along with some of the immutable facts you possess so we can all learn.

There seems to be a mindset amongst some people that where the science of Naval-architecture conflicts with their belief then the science is somehow mis-informed. These tend to be the very people with no foundation in NA who are so quick to discount studies and research that challenges their ‘facts’.

For example:
You need to consider the role that well placed mass plays in damping all the motions of a vessel. Also consider all conditions the vessel will encounter and how it will respond in those conditions. Don’t just pick the ideal conditions for that particular hull-form and then extrapolate that across the board.

Contemporary racing designs can experience some very uncomfortable and jerky motions, you just have not considered when this is likely to occur.

Roll inertia certainly changes the rate at which the vessel can vary in heel angle (mass times the square of the distance from the roll axis ). Consequently even light rigs have a very significant effect along with ballast. Motion without the rig in ballasted keelboats becomes violent in a boisterous seaway for this very reason. The loss of this damping is also responsible for a dismasted vessel being rolled repeatedly despite the lowered COG (improved static stability) after losing the mast.

 

Totally unfair and of little use to compare a 52' with a 27', whatever the ratios.
MCR gives a reasonable clue on a yacht's heaving behaviour. The philosophy behind this ratio has been strongly supported by exhaustive studies other than Ted Brewer's, and I wouldn't dare to say it's rubbish. Sustaining that only shows lack of knowledge (and prudence) in my opinion. MCR is only intended for displacement speeds, not for planning ones where hydrodynamic forces are in command.
On the other hand what is important for an all-around-go-anywhere family cruiser doesn't necessarily has to apply to a racer-cruiser mainly intended for coastal waters racing for relatively short periods of time with well trained crews.
What is clear and thoroughly proven is that a beamier and lighter boat will show bigger vertical accelerations than a narrower and heavier one. Vertical accelerations may be more seasickness inducing than rolling ones in a sailboat, as these last are dampened by the wind force on sails, except in the weaker winds.
What would be very nice is to not begin again with personal disqualifications when discussing these matters. We have had enough of those already.
Cheers.