Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 20-06-2011, 07:22   #1
Registered User

Join Date: Apr 2011
Posts: 7
Ovni AVS?

hi guys , dum quetion for you , if a onvi has a AVS of only 110 degrees ,
what happerns if you go passed 110 ?

i know this is not a tank tested avs and is done on a computer and is theory , but in theory what happens at say 140 , 160 ,180 ?



cheers
__________________

__________________
jbeam is offline   Reply With Quote
Old 20-06-2011, 17:09   #2
Registered User
 
Cormorant's Avatar

Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,074
re: Ovni AVS?

Once it's inverted, it will be much less stable than in the upright position. So even though on a flat calm sea, it might actually stay upside down once you go past 110, in the sort of sea that would roll you, the next big wave should easily roll you back upright. Not a fun ride, but good to know you'll see daylight again.
__________________

__________________
Cormorant is offline   Reply With Quote
Old 20-06-2011, 17:19   #3
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
re: Ovni AVS?

Quote:
Once it's inverted, it will be much less stable than in the upright position.
Only asking, how do you know that, have you seen the elusive stability curve, since OVnis have their ballast in the hull rather then the kneel, I wonder how much of the stability curve is "below the line", which is the only way to judge the recovery situation.

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-06-2011, 17:34   #4
Registered User
 
Cormorant's Avatar

Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,074
re: Ovni AVS?

Sorry -- I should have prefaced that by saying it was an intuitive guess rather than a scientific analysis. I haven't seen the stability curve. Just going on the assumption that the boat's lower half (when upright) is heavier than its upper half; that even without a deep lead keel, CG is still down low. If it can self-right from 109 degrees, you just have to wonder how much force it would take to shove it from 180 to 109. Again just a guess, it it seems unlikely that it needs as much force as it took to roll it from 0 to 110. Hmm. . . . I don't sound very convincing. . . .
__________________
Cormorant is offline   Reply With Quote
Old 20-06-2011, 18:04   #5
Registered User
 
Cormorant's Avatar

Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,074
re: Ovni AVS?

I didn't realize there was so much history to this sort of question. Here's one relevant CF thread from a couple years back:
Any Ovni Owners / Sailors Out There ?

And Jimmy Cornell has a lot to say about Ovnis and their suitability as blue-water cruisers. Though he is a bit fuzzy on the math / stability curves as well. . . .
__________________
Cormorant is offline   Reply With Quote
Old 20-06-2011, 19:01   #6
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
re: Ovni AVS?

Oh I know about the debate and Cornels Views, I just thought that you had some ( new) info

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 20-06-2011, 19:20   #7
Registered User
 
Cormorant's Avatar

Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,074
re: Ovni AVS?

Yes, I had a feeling that you've followed this for a while. . . . The link and the Cornell reference were really more for the OP's benefit, in case he hasn't Googled it to death already. . . . Interesting stuff. I think I'll go Google it a bit more.
__________________
Cormorant is offline   Reply With Quote
Old 21-06-2011, 08:12   #8
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,596
Images: 240
re: Ovni AVS?

Boat Stability is the resistance to capsizing; and the Angle of Vanishing Stability (AVS) is the degree the boat can heel, and still right itself.
Boats which have a stability angle of less than 140 degrees, may be left floating upside down once capsized. Boats with a higher angle will usually right themselves.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 21-06-2011, 09:17   #9
Registered User

Join Date: Apr 2011
Location: Hood River Or
Boat: Boereal 44
Posts: 189
re: Ovni AVS?

I don't think you can use conventional stability math for these boats. They function completely differently in all types of seas. Can they roll? You bet they can but it is not easy, most likely a steep wave, pitch pole situation. If seas are that big she will right again. Remember these boats slide sideways if caught beam too in a breaking wave, even better than a fin keel will.
As a new buyer in a Boreal, I have many nights staying awake picturing myself at the helm in 5 to 7 meter storm driven waves and wondering how she will handle. My images feel and look pretty good, better than my images of our Mason 44 in those seas. By the way the Mason sailed well in storm seas but you always had the feeling there could be instant disaster in steep big seas.
I'm looking forward to the day crossing the Bay of Biscay in the new boat and seeing what she does but until then it will be a test drive once in awhile when we go visit the factory every 5 or 6 months and the rest of the time my imagination.
__________________
stevewrye is offline   Reply With Quote
Old 21-06-2011, 09:27   #10
Registered User
 
Cormorant's Avatar

Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,074
re: Ovni AVS?

The one Ovni capsize I saw mentioned (off the coast of Norway) came back up in 3-5 seconds. I'm sure it was the longest 3-5 seconds ever recorded, but still nice to know it righted itself.
__________________
Cormorant is offline   Reply With Quote
Old 21-06-2011, 10:03   #11
cruiser

Join Date: May 2010
Location: SF Bay Area; Former Annapolis and MA Liveaboard.
Boat: Looking and saving for my next...mid-atlantic coast
Posts: 6,197
re: Ovni AVS?

You also have to take into consideration the coach house shape in righting, as well as the beam. A flat deck is going to FX righting.
__________________
SaltyMonkey is offline   Reply With Quote
Old 21-06-2011, 17:06   #12
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Quote:
Originally Posted by stevewrye
I don't think you can use conventional stability math for these boats. They function completely differently in all types of seas. Can they roll? You bet they can but it is not easy, most likely a steep wave, pitch pole situation. If seas are that big she will right again. Remember these boats slide sideways if caught beam too in a breaking wave, even better than a fin keel will.
As a new buyer in a Boreal, I have many nights staying awake picturing myself at the helm in 5 to 7 meter storm driven waves and wondering how she will handle. My images feel and look pretty good, better than my images of our Mason 44 in those seas. By the way the Mason sailed well in storm seas but you always had the feeling there could be instant disaster in steep big seas.
I'm looking forward to the day crossing the Bay of Biscay in the new boat and seeing what she does but until then it will be a test drive once in awhile when we go visit the factory every 5 or 6 months and the rest of the time my imagination.
I see nothing in an ovni that suggests she's exempt from the normal stability curves, nor any particular reason why she may side slip any more or less then any similar cross sectional fin Boat.

It has always been strange that Ovni have declined to release stability figures. The calculated ones by others suggest an AVS of 100 degrees. By contrast , Southerly who put all the ballast in the drop keel, are very forthcoming with their numbers.

Most boats even with a 100 degree AVs will quite happily role back , because the conditions in which the role occurred tend to also cause the easier role back.

I'm sure that you'll be delighted crossing biscay. Just avoid it from end of sept on.

bTW surely the European STIX figure had to be available for the Ovni. It would provide a reasonable comparison

Dave
__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Old 22-06-2011, 00:21   #13
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,619
Re: Ovni AVS?

This is only stability curve of an Ovni that I have seen (from Yachting monthly)

It looks a bit scary. The stability inverted is the same as the right way up. if this graph is correct if it inverts I think you would be waiting for a similar magnitude event to the one that capsized it in first place before it rights itself. I would think it would sink first.

In practice Ovnis are very capable offshore boats with many having made long voyages.
Attached Thumbnails
Click image for larger version

Name:	Stability ovni 385.jpg
Views:	1496
Size:	111.8 KB
ID:	28844  
__________________
noelex 77 is offline   Reply With Quote
Old 22-06-2011, 01:13   #14
Registered User
 
Doodles's Avatar

Join Date: Nov 2009
Location: Virginia, USA & Krabi, Thailand
Boat: Wauquiez Pretorien 35; Nordica 16
Posts: 2,810
Images: 1
Re: Ovni AVS?

Quote:
Originally Posted by noelex 77 View Post
This is only stability curve of an Ovni that I have seen (from Yachting monthly)

It looks a bit scary. The stability inverted is the same as the right way up. if this graph is correct if it inverts I think you would be waiting for a similar magnitude event to the one that capsized it in first place before it rights itself. I would think it would sink first.

In practice Ovnis are very capable offshore boats with many having made long voyages.
Anyone know or care to venture a guess as to how this would compare to a Southerly or Feeling (swing keels) where the ballast is in the keel versus the hull of the Ovni?
__________________
Mundis Ex Igne Factus Est
Doodles is offline   Reply With Quote
Old 22-06-2011, 05:07   #15
Nearly an old salt
 
goboatingnow's Avatar

Cruisers Forum Supporter

Join Date: Jun 2009
Posts: 13,649
Images: 3
Re: Ovni AVS?

a quote from YBW in 2004

"the choice is between a french ovni and a british southerly, and what is worrying me is the stability curves. the ovni has an avs of 107 degrees and a max righting moment of 3.5 tonne meters at 50deg. stix 30.8 By contrast, the southerly claims an avs of 160deg, a max righting moment of 6.5 tonne meters at 67deg and a stix of 57. "

this is due to teh 7 foot drop keel and the ballast in it.



( the whole web page is on stability of southerys)http://www.troldand.dk/en/?The_Yacht:Stability
Dave
__________________

__________________
Check out my new blog on smart boat technology, networking and gadgets for the connected sailor! - http://smartboats.tumblr.com
goboatingnow is offline   Reply With Quote
Reply

Tags
ovni

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
Any Ovni Owners / Sailors Out There ? neelie Monohull Sailboats 83 14-10-2016 19:38
Used Ovni Yacht freetime General Sailing Forum 3 30-01-2010 16:35
The Boat of Cruising Dreams - Ovni ribbony Monohull Sailboats 29 17-09-2009 06:14
OVNI/Alubat information? gbanker Monohull Sailboats 1 01-10-2006 19:36



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:19.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.