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  #541  
Old 10-12-2012
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Re: Full or fin keel?

Quote:
Originally Posted by PCP View Post
Just have a look at two boats, with similar types of hulls, about the same size, one with 4.5T and a substantial part of its weight down on a bulb at the end of a 3m draft, the other one with 9T with much more proportion of weight in its hull and 1.55m of draft. Both are well designed boats thetotal RM would not be very different (due to the much bigger mass of the heavier boat) and the lighter boat will be massively stiffer.

We are talking here about a 40 class racer and about an Oceanis 41.
Paulo
Just for kicks, I decided to check your original premise. Contrary to what you say, these boats have radically different hulls. Not sure why you even posted this.

And contrary to what you say, they have radically different RM diagrams. The racers RM would be considerably higher by a wide margin. Not sure why you posted this.

Is the Racer 40 stiffer. Probably, but then again nothing you said originally was true.

The racer has 50% more hull moment only due to its increased width. I would have to look closer at the mass moment. This boat has an RM quite higher than the Oceanis. Again.. where did you come up with the idea these boats had similar RMs?
Bryce

Last edited by BryceGTX; 10-12-2012 at 07:18 AM.
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  #542  
Old 10-12-2012
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Re: Full or fin keel?

Quote:
Originally Posted by BryceGTX View Post
..
And contrary to what you say, they have radically different RM diagrams. The racers RM would be considerably higher by a wide margin. ..

......This boat has an RM double what the Oceanis has. Again.. where did you come up with the idea these boats had similar RMs?
Bryce
Glad to see that you finally agree that the 40class boat is a lot stiffer.

Since it seems that we are agreeing, I have to answer to a honest question

Regarding RM the ones from the two boats would not be that different.

What would be massively different is the GZ curve, the arm length curve. For the RM curve you have to multiply those values by the displacement of the boat and as the Oceanis weights about the double that will make things more even. In the end it would not be a considerable difference.

Regards

Paulo

Last edited by PCP; 10-12-2012 at 07:35 AM.
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  #543  
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Re: Full or fin keel?

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Originally Posted by PCP View Post
Glad to see that you finally agree that the 40class boat is a lot stiffer.

Since it seems that we are agreeing, I have to answer to a honest question

Regarding RM the ones from the two boats would not be that different.

What would be massively different is the GS curve, the arm length curve. For the RM curve you have to multiply those values by the displacement of the boat and as the Oceanis weights about the double that will make things more even. In the end it would not be a considerable difference.

Regards

Paulo
LOL.. you best quit while you are no so far behind.

I did not say definitively it was stiffer, could be. You seem to be confusing RM with stiffness which I can imagine would be a common mistake. They are quite different things. If you want to convince anyone of anything, just post the RM diagrams.

But ignoring that for a moment, you are comparing two boats that are miserable in rough water. So not sure that you are making a rational point.

You are just asking which boat will be more or less miserable. Now if I had to be on one of these boats in rough water with my wife, no doubt I would pick the Oceanis. And it is possibly less stiff which supports what I said earlier. However, I would pick it because it invariably would be more comfortable on a drouge and obviously, it is a better cruising boat.
Bryce

Last edited by BryceGTX; 10-12-2012 at 07:53 AM.
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  #544  
Old 10-12-2012
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Re: Full or fin keel?

Quote:
Originally Posted by BryceGTX View Post
LOL.. you best quit while you are no so far behind.

I did not say definitively it was stiffer, could be. ...
Bryce
Quote:
Originally Posted by BryceGTX View Post
...

Is the Racer 40 stiffer. Probably,
...
Bryce
Probably means that there is a big chance to be or it is a way not to say exactly that it is

Quote:
Originally Posted by BryceGTX View Post
Stffness is invariably created by hull design.. plain and simple. ...
Bryce
So if on the same boat I would increase significantly the ballast, or put the same ballast a lot deeper (bigger draft) I would not get a more stiffer boat? and as "stiffness (is) the ability of the boat to resist the heeling force of the sails" it would not be a boat that heel less carrying the same amount of sail?

No matter how confusing your language you seem to fail to understand the most basic principles in what regards stability in what regards sailing and stiffness.

There are two ways of increasing stiffness in a sail boat: increasing beam and lowering the CG (increasing ballast or bigger draft). Increasing beam only increases stability at relatively low angles of heel, increasing CG has a lesser effect at low angles and increased effect with heel.

Best regards

Paulo

Last edited by PCP; 10-12-2012 at 09:30 AM.
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  #545  
Old 10-16-2012
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Re: Full or fin keel?

Quote:
Originally Posted by PCP View Post
40class racer is massively more stiff [B]and by your reasoning, since both boats share the same kind of hull, the Class40 should be less of a rough water boat.
Quote:
Originally Posted by PCP View Post
Probably means that there is a big chance to be or it is a way not to say exactly that it is
I asked a number of times that you post the stability diagrams for the two boats so you might immediately see otherwise. I wanted to see specifically the boats you were comparing. Obviously, one boat is a very specific boat (Oceanis). The racer represents a whole class of boats with varying RM diagrams.

However, I wil post the representative RM diagrams to see if what you say makes sense.

The red plot is the RM diagram for the oceanis. The blue diagram is the RM of the racer. As we see, the racer has a much larger RM value that the Oceanis sooner in the RM diagram. And as you say, the RM has similar amplitude.

Now as we all know, stiffness is the derivative of the RM diagram. So at the top, I show Where each boat has the higer derivative. The Oceanis clearly has a higher stiffness over more of the RM diagram that the racer.

Usually a cruiser is more stiff near zero. The racer is more stiff at some heeling angle above a few degrees up to probably about 30 to 40 degrees. Afterwards, the oceanis is more stiff. Clearly these break points are different depending on who designed the racer.

Such RM differences are typical for racers and crusier. But again I ask, why would anyone think a racer is a rough water boat??

So remind me again.. which boat is more stiff? Better yet.. Massively more stiff???
Bryce
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Full or fin keel?-stiffnessoceanisracer.jpg  

Last edited by BryceGTX; 10-16-2012 at 08:29 PM.
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  #546  
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Re: Full or fin keel?

Quote:
Originally Posted by PCP View Post
No matter how confusing your language you seem to fail to understand the most basic principles in what regards stability in what regards sailing and stiffness.
It is clear by the previous post, the Oceanis is more stiff could be even Massively more stiff than the racer over more of the RM diagram. But you say I am confusing stiffness????

Quote:
Originally Posted by PCP View Post
There are two ways of increasing stiffness in a sail boat: increasing beam and lowering the CG (increasing ballast or bigger draft). Increasing beam only increases stability at relatively low angles of heel, increasing CG has a lesser effect at low angles and increased effect with heel.
LOL.. you are mixing stiffness and RM. Careful.. you may get in trouble again.
Bryce
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  #547  
Old 10-18-2012
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Re: Full or fin keel?

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Originally Posted by PorFin View Post
+1. We've got a full keel with a barn door rudder, and I'm here to tell you backing is ALWAYS an adventure. If there is absolutely no wind and no current, I can usually know how the beast will track in reverse. Mostly it's all about using the throttle intermittently to balance prop walk with having the rudder pretty hard to starboard (the rudder imparts very little turning effort when in reverse.)

However, when conditions are not totally benign the old gal loves to make my life interesting. Doing the mental gymnastics thinking about the opposing forces keeps me on my toes, but usually I'm left with just getting her out into a fairway with enough maneuvering space to spin her until I get pointed in the right direction.

If there's a considerable cross wind or current, I've got to weigh the possibility of becoming a "bumper boat" against my desire/need to get underway.
You just described backing our Cape Dory 28 to a tee.
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Fair winds and following seas....
Becky
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  #548  
Old 12-22-2012
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German Yacht Magazine Article on Full vs. Fin Keel

The 25/26 issue of the German bi-weekly Yacht magazine has a very interesting article comparing a full keel (Vindö 40, 31ft, 1971), a moderate fin keel with skeg (Hallberg Rassy 29, 1981) and a modern fin keel boat (Sun Odyssey 30i, 2008).

They sailed the three boats together in 5 Bft wind and 3 to 5 feet waves to find out which is the most comfortable to sail under these conditions.

They had 3 crews rotating between the boats and all crews reported that the HR and the Vindö are not only more comfortable but the HR even sailed higher and faster than the Sun Odyssey.

(I'm a little disappointed, I expected a German magazine to use 3D accelerometers and data loggers and software to evaluate the boat movements and not just rely on crew opinion )

Let me cite the closing sentences of the article:

"The most common argument used to justify the uncomfortable motion of modern cruising boats is that the typical customer (young families, older couples and charter crews) won't leave the marina in winds over 4 Beaufort anyway. For that, these boats are significantly faster in light winds than they predecessors.

The latter may be true. The first, however, should probably be reversed: maybe the reason people don't sail them in rough water is that these boats are too uncomfortable for that?"


"Häufigstes Argument zur Rechtfertigung des unbequemen Seegangsverhaltens moderner Fahrtenyachten ist, dass sie von der angepeilten Klientel - jungen Familien, älteren Paaren und Chartercrews - bei Bedingungen jenseits der 4 Beaufort ohnehin nicht mehr bewegt würden. Da blieben die meisten lieber im Hafen. Dafür seien sie im unteren Windbereich deutlich schneller als ihre Vorgäger.

Letztgennantes Argument mag stimmen. Auf das andere kann jedoch auch der Umkehrschluss angewandt werden: Wird vielleicht nicht mehr bei Seegang hinausgefahren, weil die Yachten dafür zu unkomfortabel sind?"
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  #549  
Old 12-22-2012
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Re: German Yacht Magazine Article on Full vs. Fin Keel

Quote:
Originally Posted by pvajko View Post
The 25/26 issue of the German bi-weekly Yacht magazine has a very interesting article comparing a full keel (Vindö 40, 31ft, 1971), a moderate fin keel with skeg (Hallberg Rassy 29, 1981) and a modern fin keel boat (Sun Odyssey 30i, 2008).

They sailed the three boats together in 5 Bft wind and 3 to 5 feet waves to find out which is the most comfortable to sail under these conditions.

They had 3 crews rotating between the boats and all crews reported that the HR and the Vindö are not only more comfortable but the HR even sailed higher and faster than the Sun Odyssey.

(I'm a little disappointed, I expected a German magazine to use 3D accelerometers and data loggers and software to evaluate the boat movements and not just rely on crew opinion )

Let me cite the closing sentences of the article:

"The most common argument used to justify the uncomfortable motion of modern cruising boats is that the typical customer (young families, older couples and charter crews) won't leave the marina in winds over 4 Beaufort anyway. For that, these boats are significantly faster in light winds than they predecessors.

The latter may be true. The first, however, should probably be reversed: maybe the reason people don't sail them in rough water is that these boats are too uncomfortable for that?"


"Häufigstes Argument zur Rechtfertigung des unbequemen Seegangsverhaltens moderner Fahrtenyachten ist, dass sie von der angepeilten Klientel - jungen Familien, älteren Paaren und Chartercrews - bei Bedingungen jenseits der 4 Beaufort ohnehin nicht mehr bewegt würden. Da blieben die meisten lieber im Hafen. Dafür seien sie im unteren Windbereich deutlich schneller als ihre Vorgäger.

Letztgennantes Argument mag stimmen. Auf das andere kann jedoch auch der Umkehrschluss angewandt werden: Wird vielleicht nicht mehr bei Seegang hinausgefahren, weil die Yachten dafür zu unkomfortabel sind?"
Here is the Video.In der Welle: Langkieler gegen Kurzkieler - Yacht TV - Segel Videos von Europas größtem Yacht Magazin
It is definetly an interresting article, but I am not sure we can make the deductions they made purely on keel shape, because these boats are very differrent in other regards, beam, hullshape, displacement, ballast ratio, etc.. However, one propably can safely assume that the SO 30i and a lot of current production boats are built for space below, rather than sailing.
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  #550  
Old 12-22-2012
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Re: German Yacht Magazine Article on Full vs. Fin Keel

Quote:
Originally Posted by pvajko View Post
The 25/26 issue of the German bi-weekly Yacht magazine has a very interesting article comparing a full keel (Vindö 40, 31ft, 1971), a moderate fin keel with skeg (Hallberg Rassy 29, 1981) and a modern fin keel boat (Sun Odyssey 30i, 2008).

They sailed the three boats together in 5 Bft wind and 3 to 5 feet waves to find out which is the most comfortable to sail under these conditions.

They had 3 crews rotating between the boats and all crews reported that the HR and the Vindö are not only more comfortable but the HR even sailed higher and faster than the Sun Odyssey.

(I'm a little disappointed, I expected a German magazine to use 3D accelerometers and data loggers and software to evaluate the boat movements and not just rely on crew opinion )



Let me cite the closing sentences of the article:

"The most common argument used to justify the uncomfortable motion of modern cruising boats is that the typical customer (young families, older couples and charter crews) won't leave the marina in winds over 4 Beaufort anyway. For that, these boats are significantly faster in light winds than they predecessors.

The latter may be true. The first, however, should probably be reversed: maybe the reason people don't sail them in rough water is that these boats are too uncomfortable for that?"


"Häufigstes Argument zur Rechtfertigung des unbequemen Seegangsverhaltens moderner Fahrtenyachten ist, dass sie von der angepeilten Klientel - jungen Familien, älteren Paaren und Chartercrews - bei Bedingungen jenseits der 4 Beaufort ohnehin nicht mehr bewegt würden. Da blieben die meisten lieber im Hafen. Dafür seien sie im unteren Windbereich deutlich schneller als ihre Vorgäger.

Letztgennantes Argument mag stimmen. Auf das andere kann jedoch auch der Umkehrschluss angewandt werden: Wird vielleicht nicht mehr bei Seegang hinausgefahren, weil die Yachten dafür zu unkomfortabel sind?"
I have posted about that on the interesting sailboat thread.

The comparison was made on the conditions a heavy boat with a lot of rocker would be at his best and a modern boat at is worst. They also chose for the comparison a particularly tender boat. If they had chosen the slightly bigger jeanneau 33i (much more stiff) I am sure the results would be different, not regarding comfort but speed.

That different performance with lots if wind and short waves upwind is the weak point of many modern mass production cruisers like Hunter, Catalina, Oceanis or Dufour (just to mention some). To go really fast on those conditions you need a much stiffer performance cruiser like for instance a Xp or First. It would no be more comfortable, or at least it will have a completely different motion: A more ample one (pitch) on the heavier boat, a less ample but faster and less soft on the faster boat. The less comfortable motion has also to do with speed. More speed, less comfort.

Anyway that has nothing to do with the type of keel but with the type of boat: If you keep the hulls of the heavier boats and substitute the keels by modern ones, keeping the weight but increasing RM, you would have a similar motion but a faster boat and one able to go faster upwind. Off course, faster would mean also more uncomfortable (at more speed) but that is another story.

Regardimg this:

"The most common argument used to justify the uncomfortable motion of modern cruising boats is that the typical customer (young families, older couples and charter crews) won't leave the marina in winds over 4 Beaufort anyway. For that, these boats are significantly faster in light winds than they predecessors."

I guess that they forgot to mention two things, the first one is that they should have added to that sentence: "won't leave the marina in winds over 4 Beaufort to sail upwind anyway"

and like that, that's a fact.

The second one is that they should have mentioned also that the price of a boat has more to do with weight than with length (I mean normal boats made with the same materials), so boats like the HR or Vindo, even if with modern and more efficient keels, would be massively more expensive than a boat with the same lenght like the Jeanneau, as they are all the small heavy boats on the market. With that money a sailor could buy a much bigger boat that would be faster and more comfortable. Yes. That is really why the boats on the market are what they are. Neither the designers or the sailors are dumb

Regards

Paulo

Last edited by PCP; 12-22-2012 at 08:48 AM.
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