Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 18-07-2011, 15:02   #31
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 6,318
Images: 69
Re: Flipping Cats - More 'Flippable' than Monos ?

It's already been done on this thread. The righting moments of cats are in the order of 3 or more times higher than similar size mono's.

To say they are zero is absurd. How does a boat with ZERO righting moment carry any sail at all?

There have been situations where cats and mono's have been in the same storm, with several mono's repeatedly rolling and being dismasted, even sunk with loss of life, but the cats did not capsize. With ZERO righting moment?
__________________

__________________
44'cruisingcat is offline   Reply With Quote
Old 18-07-2011, 15:08   #32
Marine Service Provider
 
Factor's Avatar

Join Date: Dec 2006
Location: Brisbane Australia
Boat: Corsair Dash MKII
Posts: 3,778
Re: Flipping Cats - More 'Flippable' than Monos ?

Quote:
Originally Posted by Amgine View Post
How wonderfully polite 44'cruisingcat. Could you perhaps point to an article about catamaran righting moment which supports your conjecture?
See post 11 above - reproduced for your convenience.

Quote:
Originally Posted by Factor View Post
Cats are far far less "flippable" than monos - Far less. CJ MArchaj indicates that the comparative roll moments of inertia

If we call the average mono as a value of 1 (.65 is the rig, .15 the hull, .15 Ballast and .05 other)
then the "average" cat has a value of 2.03 rotating on centre point, and once rotating on hull a value of 3.69.

As well as demonstrating that, the work also was interesting in that it showed that the rig contributed so much to roll moment. Indeed the work demonstrated why once a mono rolls, if it self rights before it sinks, if it loses a rig in the process then it is likely to roll much easier , i.e. using the 1 as the mean a mono without rig drops to .35 - or put another way, if mono without rig is 1, then mono with rig is 3ish, cat on centre line is 6.5 and cat on one hull is 10.5.


Please dont attack me on this work, if you disagree take it up with Marchaj or the report of the US Yacht racing union and the US society of naval architects and marine engineers.

I am not saying that all monos will flip sooner than all cats, what I am saying is that the research shows a particular position and illustrates interesting data about the effect of rigging on rolling over.
__________________

__________________
Factor is online now   Reply With Quote
Old 18-07-2011, 15:09   #33
Registered User
 
Amgine's Avatar

Join Date: Dec 2004
Location: Vancouver BC
Posts: 1,384
Images: 1
Re: Flipping Cats - More 'Flippable' than Monos ?

Perhaps we read the comment differently. I read it as "righting moment from capsized." (in which case, actually, cats have negative righting moment as do many extreme monohulls.)
__________________
Amgine
Blog

On the internet, nobody knows you're a dog anchored in a coral atoll.
Amgine is offline   Reply With Quote
Old 18-07-2011, 15:21   #34
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 6,318
Images: 69
Re: Flipping Cats - More 'Flippable' than Monos ?

Monohulls are also stable inverted. Not just the extreme ones either. They are less stable inverted than upright, (as long as the keel doesn't fall off) but then they are FAR less stable upright than a cat.
__________________
44'cruisingcat is offline   Reply With Quote
Old 18-07-2011, 15:30   #35
Registered User
 
Amgine's Avatar

Join Date: Dec 2004
Location: Vancouver BC
Posts: 1,384
Images: 1
Re: Flipping Cats - More 'Flippable' than Monos ?

Monohulls are certainly less stable upright, and way too many are stable inverted (but as an owner of a traditional monohull, I consider *all* of those extreme.)

I can hardly wait until I can afford a cat. I sail what I have, fantasize about what I want, and try to be polite when people insult either my current or dream boat.
__________________
Amgine
Blog

On the internet, nobody knows you're a dog anchored in a coral atoll.
Amgine is offline   Reply With Quote
Old 18-07-2011, 15:43   #36
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 6,318
Images: 69
Re: Flipping Cats - More 'Flippable' than Monos ?

For someone to have said cats have ZERO righting moment, I'd say "delusional" was pretty polite, athough your opinion may differ. I can accept that.
__________________
44'cruisingcat is offline   Reply With Quote
Old 19-07-2011, 16:01   #37
Senior Cruiser
 
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 6,318
Images: 69
Re: Flipping Cats - More 'Flippable' than Monos ?

Besides the "cats are more easily capsized than mono's" myth, there's also the "self righting monohull" myth.

Fact is, MOST mono's have some stability inverted. Less than cats do for sure (same as right way up) but they ARE stable inverted. They need some outside force to right them - ie a wave. In the absence of that outside force they will remain inverted - as long as they stay afloat.




As far as I can see, this is not an "extreme" boat - it's a pretty normal looking production boat. And the rig is removed - which would make it less stable inverted than if it were still fitted.
__________________
44'cruisingcat is offline   Reply With Quote
Old 19-07-2011, 16:24   #38
Registered User
 
Amgine's Avatar

Join Date: Dec 2004
Location: Vancouver BC
Posts: 1,384
Images: 1
Re: Flipping Cats - More 'Flippable' than Monos ?

I cannot view the flash video, so I cannot comment on the boat being tested. However, here's the specs on my boat. The capsize screen is 1.86, not bad for a boat with 19' of waterline.
__________________

__________________
Amgine
Blog

On the internet, nobody knows you're a dog anchored in a coral atoll.
Amgine is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Finish Work on Cats Kefaa Multihull Sailboats 16 13-07-2011 02:56


Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities


Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 06:32.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.