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  #351  
Old 04-11-2012
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Re: Full or fin keel?

That is pretty funny. You have to love the internet. Those are badly editted versions of old articles of mine.
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  #352  
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Re: Full or fin keel?

very interesting read from one of those luxury builders (Gozzard) that build bluewater boats for ages regarding their keel choice and their evolution from full keel to a modified fin keel:

We have a unique perspective when it comes to keel design (philosophy) by having had many years of practical experience with a full keel, a modified full keel with a "Brewer Bite" and our current configuration; a modified fin keel with fully skeg protected rudder ...

Prior to 1980 all Ted's designs were based on the traditional full keel. By the mid 80's our keels evolved into a modified full keel by employing the Brewer Bit (first designed by Ted Brewer). Essentially it was a full keel design with a large section cut away in front of the rudder. ...

In 1999 we modified the keel again (along with a complete redress of the hull structure). This time we further decreased the wetted surface and used a real 64 Series NACA foil section. The new keel was a little shorter (fore and aft), taller and far more defined. Still too large to be called a fin keel but at the same time it could not really be called a modified full keel either.

The results were very positive. The biggest improvement is in performance without any noticeable loss of sea keeping ability. In fact the new design is easier to control, lighter on the helm and obviously faster in all points of sail.

Why do we like a Modified Fin over a Full or a true Fin Keel?

A typical fin keel used on your average club racer/cruiser has a significant performance advantage over your typical full keel - of this there is no question. A fin keel sails far better (especially to weather) and affords superior maneuverability both under sail and power (especially in reverse).

There is also no question that full keels have some advantages over a narrow fin and they include better tracking (especially in quartering seas), being obviously more durable structurally by simply having far more contact area with the bottom of the hull and allowing lower CG (center of gravity) storage capacity (which would make the boat more stable).

For the modern cruiser concerned with safety and comfort, obviously the requirements should more closely favor the full keel characteristics at the expense of the higher performance fin... right? Well, not so fast ... .

Full keel designs have very limited directional stability in reverse as they have a tendency to either go straight or walk in the direction of the prop rotation.

They will not steer in reverse unless you have enough speed over the rudder to counter the massive lateral plain of the keel. This means you have to have water flow (and a good deal of it) over the rudder before you will gain any ability to control direction... this often means you are going way too fast for the situation. Any one who tells you any differently is either trying to sell you a full keel boat or has never experienced anything else. ...

For many this fear is real and far worse than getting caught out in any bad storm. You will often find these owners are very reluctant to take their boats into unknown situations which limits their freedom and ability to use the boat.

Full keels do not turn very well... while full keels do have the advantage of a lot of lateral resistance on some points of sail, they generally sail very poorly to weather. It is not that the boat can't point to weather; it is the fact that the leeway is so bad you will find it is much faster (Velocity Made Good or VMG) to crack off and build speed to allow the keel to work with its lateral surface.

Unlike a full keel, a fin keel can create lift to offset the leeway (to a degree). It does this by utilizing an airfoil shape similar to that of a jet's wing which is designed to work at high speeds and, as it turns out, water has very similar hydrodynamic properties at low speed to air at high speed. All the various foil sections have been developed and tested and the simple fact is that there is a relationship between the shape of the foil and the length of the cord compared to the width. ... To try and claim a full keel can create lift is misleading at best as any lift it can create is offset negatively (if not completely) by the increased wetted surface of the keel itself.

Wetted Surface - As a vessel passes through the water it physically moves the water around the boat and this creates friction. The more wetted surface the water has contact with, the more effort is required to move the boat. Obviously a full keel has far more wetted surface than a smaller keel.

....




The Gozzard is a very very conservative boat builder and it is not an example of a modern bluewater boat. Brands like Malo, Oyster, Najad, Halberg-rassy Moody, Morris have also done that way, I mean from full keel, to modified full keel, to modified fin keel. The difference is that all these have already passed from a modified fin keel to a fin keel and I guess Gozzard will do that one day, if it does not bankrupt first.

Regards

Paulo
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Last edited by PCP; 04-11-2012 at 03:40 PM.
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Re: Full or fin keel?

Quote:
Originally Posted by PCP View Post
very interesting read from one of those luxury builders (Gozzard) that build bluewater boats for ages regarding their keel choice and their evolution from full keel to a modified fin keel:

We have a unique perspective when it comes to keel design (philosophy) by having had many years of practical experience with a full keel, a modified full keel with a "Brewer Bite" and our current configuration; a modified fin keel with fully skeg protected rudder ...

Prior to 1980 all Ted's designs were based on the traditional full keel. By the mid 80's our keels evolved into a modified full keel by employing the Brewer Bit (first designed by Ted Brewer). Essentially it was a full keel design with a large section cut away in front of the rudder. ...

In 1999 we modified the keel again (along with a complete redress of the hull structure). This time we further decreased the wetted surface and used a real 64 Series NACA foil section. The new keel was a little shorter (fore and aft), taller and far more defined. Still too large to be called a fin keel but at the same time it could not really be called a modified full keel either.

The results were very positive. The biggest improvement is in performance without any noticeable loss of sea keeping ability. In fact the new design is easier to control, lighter on the helm and obviously faster in all points of sail.

Why do we like a Modified Fin over a Full or a true Fin Keel?

A typical fin keel used on your average club racer/cruiser has a significant performance advantage over your typical full keel - of this there is no question. A fin keel sails far better (especially to weather) and affords superior maneuverability both under sail and power (especially in reverse).

There is also no question that full keels have some advantages over a narrow fin and they include better tracking (especially in quartering seas), being obviously more durable structurally by simply having far more contact area with the bottom of the hull and allowing lower CG (center of gravity) storage capacity (which would make the boat more stable).

For the modern cruiser concerned with safety and comfort, obviously the requirements should more closely favor the full keel characteristics at the expense of the higher performance fin... right? Well, not so fast ... .

Full keel designs have very limited directional stability in reverse as they have a tendency to either go straight or walk in the direction of the prop rotation.

They will not steer in reverse unless you have enough speed over the rudder to counter the massive lateral plain of the keel. This means you have to have water flow (and a good deal of it) over the rudder before you will gain any ability to control direction... this often means you are going way too fast for the situation. Any one who tells you any differently is either trying to sell you a full keel boat or has never experienced anything else. ...

For many this fear is real and far worse than getting caught out in any bad storm. You will often find these owners are very reluctant to take their boats into unknown situations which limits their freedom and ability to use the boat.

Full keels do not turn very well... while full keels do have the advantage of a lot of lateral resistance on some points of sail, they generally sail very poorly to weather. It is not that the boat can't point to weather; it is the fact that the leeway is so bad you will find it is much faster (Velocity Made Good or VMG) to crack off and build speed to allow the keel to work with its lateral surface.

Unlike a full keel, a fin keel can create lift to offset the leeway (to a degree). It does this by utilizing an airfoil shape similar to that of a jet's wing which is designed to work at high speeds and, as it turns out, water has very similar hydrodynamic properties at low speed to air at high speed. All the various foil sections have been developed and tested and the simple fact is that there is a relationship between the shape of the foil and the length of the cord compared to the width. ... To try and claim a full keel can create lift is misleading at best as any lift it can create is offset negatively (if not completely) by the increased wetted surface of the keel itself.

Wetted Surface - As a vessel passes through the water it physically moves the water around the boat and this creates friction. The more wetted surface the water has contact with, the more effort is required to move the boat. Obviously a full keel has far more wetted surface than a smaller keel.

....




The Gozzard is a very very conservative boat builder and it is not an example of a modern bluewater boat. Brands like Malo, Oyster, Najad, Halberg-rassy Moody, Morris have also done that way, I mean from full keel, to modified full keel, to modified fin keel. The difference is that all these have already passed from a modified fin keel to a fin keel and I guess Gozzard will do that one day, if it does not bankrupt first.

Regards

Paulo
Nothing new in your argument here Paulo. Except that its funny that the manufacturers first reason of why not to buy a full keel boat is because they don't back up under power well..... and people are more afraid of docking than they are of an offshore storm. Really?

They forgot to mention that the fin keel boat is cheaper to manufacture as well. I wonder why?
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Re: Full or fin keel?

Best I could do Jeff. Gotta love the internet, especially all your good posts here.
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Full or fin keel and a dozen other marginally related topics

This thread sure has taken a tortuous track from the original question about the merits of Fin vs Full keels. Coming back to the thread, I find myself thinking; Are you still here? [IMG]Are you still here?[/IMG]

But in its wild path, the thread has opened a whole slew of issues with various folks seemingly talking past each other, rather than having a productive and vaguely linear dialogue on the original topic of keel types.

It seems to me that much of this non-linearity has been caused by the sheer broad range of the topics being used, and the points diffused the loose association between the responsed and the topic being bandied about, and the sometimes dubious assumptions about the implicit connection between these various design factors. To me, in many cases, the connection between many of the indivdual comment and the responses to the point being raised, at best comes off as a real stretch and at worst, comes off as, 'I don't know nothing about art, nor understand your point, but I know what flavor ice cream I like' type non-sequitors. It would seem as if this discussion would be a lot more productive if the topics were treated separated rather being discussed with the assumption that they are a lot more linked than I would respectfully suggest that they are.

To try to help clarify this point, I would suggest that a brief index of the discussion topics contained within this thread might include:
• The merits and limitations of fin keels versus full keels.
• Boats operating as a system rather than as individual components discussed in abstract
• How most people who sail use their boats (day sailing and coastal cruising) and what those people need out of their boats, vs. more specialized uses such as offshore-distance cruising, performance passage makers, high level racers, and racer-cruisers.
• The impact of marketing vs. science in the selection of a boat by the general boat buying public.
• The impact of marketing vs. science in the selection of a boat by the offshore cruising boat buying public.
• Why Island Packets are not a good example of either traditional full keeled cruising boats nor of modern design principle, but somehow seem to be able to market themselves as both.
• The impact of cost on selection if the goal is one of these specialized uses.
• The merits and limitations of boats which are short or long for their displacement.
• The merits and limitations of various hull forms, and the impact of modeling on the success of a design of any general type.
• The merits of simplicity vs. sophistication vs. targeted sophistication.

I am sure that I am missing other topics that reared their ugly little heads, but it seems to me it would be a lot more useful, if people tried to make thier arguments based on points that were actually being made, and with the topic it was being mentioned in. Instead, it appears that many of the participants respond with an answer that only relates to a completely different topic relative to the point being contested and/or which at best perhaps assumes some association to the point raised.

For example, the thread starts with a very broad general discussion of keel types. The counter to some point in that discussion is an argument that boats that are longer or shorter for their weight make better offshore cruisers. To which the response is that the hull forms popular on coastal cruisers are less comfortable for offshore use. To which, the response is that coastal cruiser hull forms perform better. To which the response is that full fledged, grand prix level race boats are fragile. And so on. It sure makes for a confusing, and less useful thread, that taken at face value is not even all that accurate. But at least it has been mostly been civil…

Jeff
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Last edited by Jeff_H; 04-11-2012 at 06:03 PM.
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  #356  
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Re: Full or fin keel?

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Best I could do Jeff. Gotta love the internet, especially all your good posts here.
No problem. Thanks for the kind words. If you would like I would be glad to send you cleaner versions of those discussions electronically. They appeared to have been selected from edited versions and then further edited.
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  #357  
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Re: Full or fin keel?

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Originally Posted by GBurton View Post
Nothing new in your argument here Paulo. Except that its funny that the manufacturers first reason of why not to buy a full keel boat is because they don't back up under power well..... and people are more afraid of docking than they are of an offshore storm. Really?

They forgot to mention that the fin keel boat is cheaper to manufacture as well. I wonder why?

On Gozzard, after trying both types of keels on basically the same boat they say:

The biggest improvement is in performance without any noticeable loss of sea keeping ability. In fact the new design is easier to control, lighter on the helm and obviously faster in all points of sail.....

Full keels do not turn very well... while full keels do have the advantage of a lot of lateral resistance on some points of sail, they generally sail very poorly to weather. It is not that the boat can't point to weather; it is the fact that the leeway is so bad you will find it is much faster (Velocity Made Good or VMG) to crack off and build speed to allow the keel to work with its lateral surface.


Directionality backwards it’s an advantage but it is not the more important. The more important is that they get a better sailboat without "any noticeable loss of sea keeping ability". That is the reason why all boat manufacturers changed to fin keel, not only Gozzard.

A modified fin keel like the one on the Gozzard is not less expensive than a full keel. Gozzard is an heavy boat, now as before and heavy boats are expensive.

Regards

Paulo

Last edited by PCP; 04-11-2012 at 05:46 PM.
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Re: Full or fin keel?

Jeff H
You have a wealth of knowledge of boats. Could you tell me how you gained this knowledge?
Regards
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Re: Full or fin keel?

And for the record since this does relate to the original topic, at least when I was associated with the boat building, a well engineered fin keel boat is actually quite a bit more expensive to build than a full keel. The requirement of a precision ballast casting, more sophisicated framing, the requirer higher strength keel bolts and backing plates all add to the cost of building a fin keel boat.

Inexpensive boats typically had longer keels with encapsulated non-cast ballast until coastal sailors came to expect more performance out of their boats.
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Another topic

Quote:
Originally Posted by casey1999 View Post
Jeff H
You have a wealth of knowledge of boats. Could you tell me how you gained this knowledge?
Regards
Thank you for the kind words. I wrote this for someone else who asked a similar question so I apolize that it is pretty long. Growing up I wanted to be a yacht designer. Like some kids study and memorize batting averages, I studied and memorized boats. I have some training as a yacht designer and have designed and built a few boats, and worked for naval architects and yacht designers at different times in my life, BUT I do not consider myself a professional yacht designer. I have also worked in boat yards and as a consultant to boatyard owners, designing repairs and alterations to yachts. My mother had two companies that built and imported boats from Taiwan, which gave me a lot of insights into the boat building industry. I still attend yacht design symposia in an effort to remain current in yacht design theory.

I first started sailing in 1961 and more or less have sailed ever since. I enjoy most types of sailing. I currently sail on the Chesapeake Bay but have sailed on much of the U.S. Atlantic coast. In a given year, I typically will daysail, race (both my own boat and other people’s boats), and cruise (both my own boat and other people’s boats) and can be out on the water as many as 100 days a year. I do a lot of single-handing. While I have cruised offshore and made a number of offshore passage, I strongly prefer coastal cruising. While I have raced dinghies and very high performance boats, I prefer racing 22 to 40foot keelboats. I have owned wooden boats and enjoy sailing on traditional watercraft. These days I prefer to own modern performance cruisers.

In a general sense, I have strong preferences for boats that perform well, and that offer a wide range of sailing abilities in a wide range of conditions. I really am no longer a fan of ‘heavy weight offshore boats’. I currently own a Farr 38 (Farr 11.6) which I daysail, singlehand and cruise. The Farr 11.6 are hard to classify boats and not exactly your normal off-the-rack cruising boat or racing boat. They were built as fast offshore cruisers but have had a very successful racing record. They also have a remarkable record as short-handed offshore passage makers. For example, my boat was single-handed into the States from Cape Town, South Africa

In my life, I have owned over a dozen boats with family members owning over several dozen more. I typically race on a variety of boats over the course of the year and sometimes help out with deliveries, or help a new owner ‘sort out’ a boat that is new to them. I also like sailing up to boats from astern and observing their sailing abilities, meaning relative speed, stability and motion. All of that combined gives me a relative sense of how many different boats are built and how they sail. I have also been a consultant to people who are restoring boats or making tricky repairs which has given me the chance to crawl around the back corners of many boats over the years and I have a pretty good memory of the details which I have seen.

Many of my friends are yacht designers, sailmakers, and marine researchers and surveyors who collectively also give me an inside track when I am researching a topic. (I think that Bruce Farr cringes when he sees me coming up the aisles at the grocery store.)

My comments are predominantly based on my own experiences and research. I see my comments as being simply my opinion, but I also see them as reasonably well informed comments based on comparasons of the boats I have known, either through sailing on or repairing, and the information gained by reading, lectures or discussions with design professionals.

Anyway, that is who I am.
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