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  #591  
Old 02-27-2013
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Re: Full or fin keel?

Awesome thread- Been puzzling about this for last 30yrs. with more thought in last 5 as I needed to decide on my "last" boat. There are some basic physics which I don't see stressed in the posts.
Modern boats go faster. A modern racing mono hull commonly is above 10kts. Compare the wings of biplane to a jet. As speed goes up you need a flatter foil with less chord and higher aspect. For older boats moving at hull speed or below full or fin can be argued. For modern or even semi modern cruising mono hulls full keels fly in the face of basic physics. As one increases speed and decrease the horizonal length of the keel you may decrease directional stability. This may be further modified by sailing on the chine and the wide stern with little V of modern boats. This may raise the need for daggerboards and additonal complexity. Steering may require dual rudders adding yet more complexity. Many of us think we want a monohull that will take care of us not a multihull we need to take care of in a storm. That being the case many of us choose a high aspect fin with bulb and balance spade rudder of strong construction but don't go to the limits of a Boreal, class 40 or other boats requiring multiple levels of complexities to be sailed "correctly".
There also has been little discussion of the "diagonals" and other features of hull shape on comfort. I been on several boats where the wide stern may have worked under sail but at anchor were noisy, skated around and unpleasant.
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  #592  
Old 02-27-2013
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Re: Full or fin keel?

Quote:
Originally Posted by outbound View Post
.... Steering may require dual rudders adding yet more complexity. Many of us think we want a monohull that will take care of us not a multihull we need to take care of in a storm. That being the case many of us choose a high aspect fin with bulb and balance spade rudder of strong construction but don't go to the limits of a Boreal, class 40 or other boats requiring multiple levels of complexities to be sailed "correctly".
There also has been little discussion of the "diagonals" and other features of hull shape on comfort. I been on several boats where the wide stern may have worked under sail but at anchor were noisy, skated around and unpleasant.
A Boreal is very easy to sail and very seaworthy.

http://www.voiliers-boreal.com/

Dual rudders come to stay. They did not only make possible the use of much less deep rudders as also provide a bigger safety margin not only because they are smaller (and less deep) and therefore subject to less stress but also because they are two and even without one is possible to sail the boat (slowly) back home. They are not only safer as they also provide better control of the boat, specially in what regards beamy boats. It is a need on those, but even on boats with moderate beam they increase control and directional stability.

Regarding beam and safety it is better not to forget that tank testing showed that there was a relation between the beam of a boat and the breaking wave needed to roll it. That's why multihulls are much more difficult to capsize by a breaking wave than monohulls (and the opposite regarding wind).

The trick with modern boats is to increase the capsize resistance (and the boat power) without diminishing the reserve stability, providing a good AVS and an inverted stability several times smaller than the positive stability. That is, joining the good stability characteristics of multihulls with the good stability characteristics of monohulls (reserve stability and possibility to re-right the boat).

For that beamy boats have to have a very low CG. That's why you have seen on the last years, with the increase of beam a correspondent increase of draft and the proliferation of torpedo keels with all ballast at the bottom of the keel. Draft is also a way of increasing directional stability.

Of course, not all beamy boats are alike and I would suggest that before buying one a good look at the stability curve is a must, to see if the reserve stability, a good AVS and a proportional smaller inverted stability are part of the deal.

Regards

Paulo
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Last edited by PCP; 02-27-2013 at 01:50 PM.
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  #593  
Old 02-27-2013
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Re: Full or fin keel?

Marketing relies on people thinking"If I take features found on racing boat and put them on a cruising boat it will make it faster"....not sopping to think that all of those racing attributes make boats harder and more complicated to sail as well as more expensive. In a cruising boat you should look for simple efficiency. If a boat takes work and/or is tiring to the crew at sea that can be dangerous....fatigue is one of the most dangerous things at sea.

Last edited by wolfenzee; 02-27-2013 at 04:40 PM.
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Old 02-27-2013
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Re: Full or fin keel?

Still my favorite thread. Can I ask about the Contessa 32 ? A long fin keel ? Good day, Lou
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  #595  
Old 02-28-2013
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Re: Full or fin keel?

I like this thread, but it is also an example of how people generalize. My boat was designed by William Atkin, who's designs were also used in the West Sail (sometimes called a "West Snail"). Sitting side by side on the hard they look noticeably similar, but the West Snail appears "pudgy" and in comparison, my boat is downright "sexy". My boat has a transom and if the lines were continued to a double end would be the same size my 30' has a 25'lwl and the West Sail 32 has a 27'lwl, but the beam is only 80% of the West Sail.
My full keel is fast and does maneuver well. My point being that two very similar boats can be very different in performance.

Last edited by wolfenzee; 02-28-2013 at 02:10 PM.
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  #596  
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Re: Full or fin keel?

Quote:
Originally Posted by Lou452 View Post
Still my favorite thread. Can I ask about the Contessa 32 ? A long fin keel ? Good day, Lou
Contessa 32 are fantastic boats that even by today parameters have a good performance upwind, specially in bad weather.

I will reply another way:

This is Babe, a famous S&S design and a great boat:





The boat was almost a S&S icon so S&S decided to produce the boat again with the same basic dimensions:



Do you notice any difference

Regards

Paulo
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  #597  
Old 02-28-2013
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Re: Full or fin keel?

I will show how little I know in hopes of learning Yes the rudder and keel have changed a lot. the bulb on the bottom of the keel and how much deeper the rudder. Twin rudders seem to be up and comming? The full keel is less in demand. I will just assume the Contessa 32 is very good in rough seas ? Her history after the 1979 Fastnet leads me to think this way. It could be she was with a great crew.
I hear so much about sea motion and heaving-to and how a fin will not be able to. I am trying as new sailor to sort out time proven boats and look to design transition between cutting edge and traditional this is where my dollar and building skill level will bring the best return.
How does one judge skill vs the (the boat taking care of lack of skill)
It will be some time before I move up in boat size the jump this year is from a flying junior at 13' to a Catalina-22 So I have no fin/full keel experience
I so much enjoy this thread Thanks PCP and Wolf Good day, Lou
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  #598  
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Re: Full or fin keel?

As my boat was designed 75 year ago there are alot of aspects of hull and rig design that are considered to be "obsolete" "antiquated" and "ineffiecient" (they must be ineffiecent because they don't use them anymore). But even so the boat is fast, points well, handles nicely on all points of sail etc....it's just a matter of vintage (newer must be better and older must be bad)....that is not true.

Another thing people keep forgetting...the original intention of this thread was to ask about the difference in comfort between a full keel and fin keel in blue water conditions, but has evolved into a debate about performance....lumping all fin keels in one catagory and all full keels in another, which is incredibly inaccurate.

Last edited by wolfenzee; 02-28-2013 at 09:36 PM.
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  #599  
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Re: Full or fin keel?

Quote:
Originally Posted by wolfenzee View Post
...

Another thing people keep forgetting...the original intention of this thread was to ask about the difference in comfort between a full keel and fin keel in blue water conditions, but has evolved into a debate about performance.......
Where do you get that these thread was about comfort? this was the first post and the original question:

Quote:
Originally Posted by utchuckd View Post
Can somebody pro/con a full vs. fin keel for a newbie (will learn to sail on said boat) and taking it thru the Caribbean? ...
Performance in a sailboat means basically how well a sailboat sails. Speed and sailing ability are two of the most important factors. Don't you think that it is to be considered regarding the pros and cons?

Regarding motion it has essentially to do not to fin keel or full keel but with Displacement/Length. It is true that generally the full keeler are heavier but not always true. Some full keel boat are also relatively light and some fin keel boats are heavy.

Anyway regarding motion it was already well established in other threads about the subject that some prefer the slow but deep pitching of an heavy boat to the sharper but less accentuated movements of a lighter boat and vice verse.

Regards

Paulo
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Re: Full or fin keel?

so at the end of the day it's

Whatever floats your boat ( grin).


Still think the Wolf is right there are special boats that are drawn in every vintage where the magic of balancing performance,comfort, beauty and safety are achieved. Unfortunately you generally don't know if you have such a vessel until you have owned it for some time and have put through all it's paces. At that point Paulo is looking at the next major advance.
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Last edited by outbound; 02-28-2013 at 11:14 PM. Reason: content
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