Desirable and Undesirable Characteristics of Offshore Yachts

[CapDave]

Marc seems to be suggesting substituting a different trade-off - adding more mass, more inertia.  And yes, that is another worthwhile thing to consider, but it is still a 'fixed' trade-off.

Ted Hood drew a lot of fast centerboard boats with this design approach - heavy, shallow draft, board only heavy enough to go down. No idea on numerical RM or AVS. I sailed his LH53 design about 5K miles in a wide variety of East Coast conditions (no breaking waves, though close once) and it was a great boat to sail. I sailed the 78' (87' LOA, see pictures below) version about 2K miles - 80 tons, drew 7', with a dagger in the rudder, and trim board right in front of the rudder, and a 10' centerboard - yes, we drew 17' board down. Both boats could carry a lot, a lot, of sail. Approaching Hatteras once in the LH53 we had near-breaking waves on a broad reach in heavy winds, and she was a little squirrelly but still very controllable.

Of course Dodge Morgan (3rd nonstop solo circumnavigator in 1986) sailed a 60' "whale bottom" centerboard Ted Hood design around in 150 days smashing the record and holding it for four years.

 

[Panoramix]

That article looks a bit a sales pitch, for his designs (like the UFO 445) over the more successful ovni.

Marc Lombard is the current designer for OVNI, the 385 was designed by Marc Briand and they moved away from these low AVA designs from the 90s.  

 

[estarzinger]

Marc Lombard is the current designer for OVNI, the 385 was designed by Marc Briand and they moved away from these low AVA designs from the 90s.  

Out of curiosity show me a current Ovni curve please.  And still none of this refutes the empirical fact that those Ovni's had/have a very good offshore record in some of the toughest parts of the world. There is no evidence for the 'frankly dangerous' comment - I could be wrong but I dont believe they ever lost a boat nor a crew (at sea - I seem to remember someone fell into a Crevasse while ashore) in the high latitudes.

from their web site current line: 395 Architect : Philippe BRIAND / 400 Architect : MORTAIN & MAVRIKIOS / 445/450 Architect : Marc LOMBARD - looks like rather a mix.

And please remember that I am STILL not arguing about/that high rm and avs is generally nice to have - to deal with the wide range of conditions that a yacht could face.  As I said above I picked that corner of the design space for my own yacht.  Please remember the discussion is about the trade-offs in the narrow niche of running - where arguably RM is less important, especially when/if you have stopped 'racing'.   And the fact that the Pogo design gives you a choice, with its own trade-off of somewhat more complexity. Which I would not have wanted in a high latitude expedition boat, but is fine for other purposes.  We are discussing whether there is a place to use that flexibility when running or not.

 

[estarzinger]

Ted Hood drew a lot of fast centerboard boats with this design approach - heavy, shallow draft, board only heavy enough to go down. 

Of course Dodge Morgan (3rd nonstop solo circumnavigator in 1986) sailed a 60' "whale bottom" centerboard Ted Hood design around in 150 days smashing the record and holding it for four years.

yea, Ted's boats are certainly a 'player' in this whole discussion.  

Dodge's boat is big enough that the inertia scale would be tipped way in its favor - but it did and has done quite well.

Size is probably the single biggest lever you can pull for capsize resistance. One of the few simple things that seems true across almost all the design spectrum corners (including even multi hulls).

 

[Jud - s/v Sputnik]

Of course Dodge Morgan (3rd nonstop solo circumnavigator in 1986) sailed a 60' "whale bottom" centerboard Ted Hood design around in 150 days smashing the record and holding it for four years.

Not to argue who was third  nonstop solo around (b/c it’s pointless - pointless to argue, and the actual undertaking itself is pointless, if very cool  ) but: http://covarimail.com/IACH/solo_nonstop.lasso

(What’s remarkable to me is how utterly different some of these boats were - Dodge Morgan’s custom Ted Hood 60’er in 1986, and the relatively little known Peter Freeman on a self-built 32 foot ferrocement boat, a year earlier, in 1985.)

 

[estarzinger]

(What’s remarkable to me is how utterly different some of these boats were 

The same is true of the CCA Blue Water Medal winners - astonishing variety of vessels: I love going back and looking at the early winners and what they accomplished

https://www.cruisingclub.org/award/blue-water  (look down the right hand side bar)

 

[Jud - s/v Sputnik]

The same is true of the CCA Blue Water Medal winners - astonishing variety of vessels: I love going back and looking at the early winners and what they accomplished

https://www.cruisingclub.org/award/blue-water  (look down the right hand side bar)

Which makes one wonder how Yoh Aoki could’ve been overlooked for a Bluewater Medal...I’d have chosen him over E. Newbold Smith in 1976.... Hella more impressive story and voyage (Japan-Japan via the Horn).  And a tiny homemade 21 ft plywood boat!!

https://www.aoki.us/zen24/histry/47/

 

[DDW]

Not sure how easy to get there, but the stability curve on that Ovni 385 makes it look like if it did go over, it might well stay there awhile. Area under the curves about equal and maybe a little more stable upside down than right side up. My own boat the righting arm upright is about 2.5x that upside down, and the ratio of areas about 6:1. And it wasn't designed for the Southern Ocean. So whatever is going on with those keeping them upright, it is probably fortuitous. 

 

[Knut Grotzki]

May be a few "Dériveur intégral" had a 100º AVS but there was recently an article in Voiles et Voiliers where Marc Lombard said specifically that you need to make these boats heavy to get an acceptable AVS : https://voilesetvoiliers.ouest-france.fr/industrie-nautique/chantier/architecture-navale/architecture-navale-marc-lombard-et-la-recette-du-deriveur-integral-1f3adbfc-4808-11ea-a27e-33e04757e9a2

These boats lift their centreboard which completely retract inside the hull so the dynamics are very different from a swinging keel which stays outside. Also whether the centreboard is in or out, the AVS is about the same whether for a swinging keel boat lifting the keel reduces the boat stiffness and AVS. Finally some French centeboard have capsized (remember TAO ?) and the modern trend is to have an AVS of more than 110º, that's the Boreal 47 in a worts case scenario (fully loaded with empty tanks as the tanks help with stability)



I can't find the AVS of the Pogo 12.5 keel up but my guess is that it is less than that.

Why is ... "and the modern trend is to have an AVS of more than 110º, that's the Boreal 47 in a worts case scenario (fully loaded with empty tanks as the tanks help with stability)"? When I read the specs the tanks seem to pretty low in the hull.



Thanks!

 

[Panoramix]

Why is ... "and the modern trend is to have an AVS of more than 110º, that's the Boreal 47 in a worts case scenario (fully loaded with empty tanks as the tanks help with stability)"? When I read the specs the tanks seem to pretty low in the hull.

The tanks are below the centre of gravity thus when you fill them the boat becomes safer, the opposite of storing fuel on deck! So when you compute the stability curve, to be on the safe side you assume that they are empty (worst case scenarion)

@estarzinger there is a stability curve of a newer OVNI in the article I linked to above.

 

[MFH125]

We then get to a different discussion about AVS, and a class of designs I think you already referred to. . . the line leading from damien 2 to the OVNI and Garcia's.  Which all have quite low AVS (like 100-110) but also have very good experience in high latitude exploration.   Why their record is 'good' could would be difficult to answer - perhaps 130 AVS is actually not needed even for full time life in the south, or perhaps these yachts have other traits than 'make up for' low AVS, or several other possible explanations. 

A couple thoughts on this:

1. What does a good record mean here?  How many boats?  How many cruising full time?  How many hours in breaking seas?  How many knockdowns or capsizes recovered from?  Can we really pull useful statistics from this?
   
   The conditions where AVS really comes into play are very rare in cruising life, even in high latitudes.  Side impact airbags are clearly a life saver in cars in the right conditions: I know someone who walked away from an accident in which he pulled out in front of a semi that was going 50mph due to side-impact airbags.  But would statistics tell you they were a good idea if you only tracked ~500 cars? 
   
   These strict AVS "requirements" are arbitrary.  A boat with an AVS of 121 degrees is not radically more suited to offshore cruising than her sister with an AVS of 119 degrees.  The difference isn't a cliff it's a balance of probabilities: what percentage of capsizes will the boat remain inverted.  If an AVS of 110 means that in the relatively rare event of a full inversion you have a 35% chance (I'm pulling numbers from air, here) of the boat remaining inverted vs. a 20% chance on a boat with AVS=120 deg, it would take a lot of knockdowns and thus a lot of boats cruising to get enough data to make a statistical distinction.
   
    
   
2. Most cruising boats probably sail with an AVS significantly lower (5-10 degrees, maybe) than reported by the builder.  Cruisers have a habbit of accumulating stuff that gets stored relatively high up: arches, dinghies on davits, jerry cans on deck, etc.  Even most storage in cabins is usually above the VCG.  Are those OVNI and Garcia really sailing at their designed loading conditions? Their "as sailed" AVS may be even lower -- maybe not, depends on how thoughtful the designers were and how aggressive the marketing departments are in trying to lower the reported values.
   
    
   
3. Is this really a trade-off that one needs to make?  If the benefit of these centerboard boats and swing keel boats is that they can shift the center of lateral resistance aft, then there are surely other ways to accomplish that which do not compromise AVS.  Those aft daggerboards on the Boreals would work fine on a deep keel boat.  This reminds me that Dave Gerr's BOC racer from the early 90's, HOLGER DANSKE, had a centerboard well aft, presumably to improve the helm when running.  I don't think the boat was ultimately built with the centerboard, but the idea would be applicable to a cruising boat.
   
   
   

 

[olaf hart]

Why is ... "and the modern trend is to have an AVS of more than 110º, that's the Boreal 47 in a worts case scenario (fully loaded with empty tanks as the tanks help with stability)"? When I read the specs the tanks seem to pretty low in the hull.

View attachment 442092

Thanks!

Thats a pretty small amount of ballast for a 47 footer, especially one with a board..

 

[Upp3]

Thats a pretty small amount of ballast for a 47 footer, especially one with a board..

Depends how heavy boat you have. Board though makes the mass less effective.

 

[estarzinger]

A couple thoughts on this:

1. What does a good record mean here?  How many boats?  How many cruising full time?  How many hours in breaking seas?  How many knockdowns or capsizes recovered from?  Can we really pull useful statistics from this? Well something like 600 boats.  Jimmy Cornel says only one is known to have capsized (>90 degrees - off norway) and it came back up in less than 5 seconds.  Hours in breaking seas we cannot know for any design series - but these and the garcia were viewed as more 'expedition purpose' than most and you see them quite commonly in remote and difficult places - they would have 'as much as any'.  From a statistical point of view - if you wanted to test the hypothesis these boats are 'Frankly Dangerous' you would get zero confidence - there is zero empirical evidence to support that.  My statement 'they have a good record' would get high confidence - it is just simply factually true - but I would not claim that in any way statistically 'proves' that 100-115 avs is satisfactory for running in breaking waves - it merely raises the question whether that it may well be satisfactory when running.  
   
2. Most cruising boats probably sail with an AVS significantly lower (5-10 degrees, maybe) than reported by the builder.  Yea, sure. The calculated AVS is merely a theoretical number and most boats would be worse.  This is like a 'noise factor' that effects all boats - not sure how it moves the conversation forward, except it would seem to make the ovni/garcia style boats 'good results' even more indicative. (as a side note, our own boat was one of the few which would have been significantly better than design RM/AVS because she was deigned for thick/heavy teak decks which we did not put on, instead putting some of that weight into the bulb and some other of it into structure)
   
3. Is this really a trade-off that one needs to make? Those aft daggerboards on the Boreals would work fine on a deep keel boat.  but the idea would be applicable to a cruising boat. This started as a discussion about the pogo specifically.  I was curious how it specifically was best handled. And its design specifically raises the possibility of this trade-off. It would be fascinating to see some analysis of big wave running directional stability and helm balance, etc with and without aft daggerboards, with the keel in various positions . . . but as we discussed above that is an opaque issue. On my own boat I rejected the aft dagger board idea as added complications (not desirable on a boat spending most of its time in very remote places) and taking up space.
   
   I think perhaps this horse has been beat enough. I would just add a final comment - that there is a significant difference between racing usage and cruising usage - in cruising, if you know your boat and are an intelligent seaman, you can adapt to its design.  If (just for example) you get cresting waves on the beam, you can change course to put them behind the beam.  As a racer, there is a fastest routing and sail configuration and you are likely to push that string further than a cruiser would.
   

 

[estarzinger]

Which makes one wonder how Yoh Aoki could’ve been overlooked for a Bluewater Medal...I’d have chosen him over E. Newbold Smith in 1976.... Hella more impressive story and voyage (Japan-Japan via the Horn).  And a tiny homemade 21 ft plywood boat!!

https://www.aoki.us/zen24/histry/47/

There was a long period when the CCA considered single handing unseamanlike.

 

[estarzinger]

@estarzinger there is a stability curve of a newer OVNI in the article I linked to above.

oh, so 110. hmmm . . ok  (when I read the article I thought you would have considered that part of your " '90's too low " school)

Thanks for the discussion.  I appreciate your bringing information to the table.

 

[MFH125]

I think we're more or less in agreement, Evans.

My statement 'they have a good record' would get high confidence - it is just simply factually true - but I would not claim that in any way statistically 'proves' that 100-115 avs is satisfactory for running in breaking waves - it merely raises the question whether that it may well be satisfactory when running. 

This was my point.  I don't doubt that they are successful cruising boats, but I'm suspicious that one can infer all that much from their success about acceptable AVS one way or the other.  A single knockdown in 600 boats illustrates that even expedition boats are only rarely in conditions which test their ultimate stability.

I agree that the fact that most boats sail with AVS's lower than "as advertised" is a point in favor of the Garcias, etc.  It's just one more reason to consider dogmatic opinions about 120 degrees (or any other standard) as ipse dixit.

 

[Panoramix]

oh, so 110. hmmm . . ok  (when I read the article I thought you would have considered that part of your " '90's too low " school)

Thanks for the discussion.  I appreciate your bringing information to the table.

110º is certainly not huge. TBH, I would prefer sailing the POGO with the keel down in gnarly conditions but I think that part of the reason for that is that I've learnt to sail proactively in breezy conditions and I would feel more at ease on a boat that needs to be handled like this.

 

[shaggybaxter]

Did I mention how good this thread is? Just wanted to say thanks to all of you chaps, its enjoyable, stimulating and thought provoking just listening.  

 

[Jud - s/v Sputnik]

Did I mention how good this thread is? Just wanted to say thanks to all of you chaps, its enjoyable, stimulating and thought provoking just listening.  

I hope someone who’s familiar with “Desirable and Undesirable Characteristics of Offshore Yachts” —i.e., the actual book— can tell me (us) if the stability/hull design concepts that have been discussed lately - specifically AVS, RM, etc— are touched on in this book?  It’s a topic I know little about, and a marine/hydrodynamic engineering treatise on it would be over my head - but a gentle introduction —and, critically— application— of said concepts, somewhat in depth, would be nice...