daveg45
Well-Known Member
Hi Everyone
There seems to be lots of opinion on here about the stability of modern light yachts v older heavier ones and I came across this on another forum site. I hope the author (a site moderator) doesn’t mind me quoting him but I found it to be very informative and goes a long way to answer some of the questions:-
I think that there is no one universally right answer here but a whole lot of strong opinions when it comes to keel types. If you are traditional in your view point then you would lean towards a boat with a full length keel. If you care more about performance and ease of handling then you might lean towards a fin keel.
There are good and bad offshore boats with all kinds of keels and so buying a boat with a full length keel will not guarentee that you will end up with a good offshore boat any more than buying a boat with a fin keel will guarentee a bad offshore boat. These are at best subjective decisions.
The way that I personally look at this, If your goal is to spend almost all of your time offshore and in really remote areas of the world, then a full keel boat probably makes sense. If you are going to island hop and perhaps occasionally make longer passages, and you will be traveling in places like the US, Carribean and Europe, then a properly designed and engineered fin keel boat makes more sense. BUT again that is only my opinion.
The material below is exerpted from an article that I had written for another venue but which might help you as well.
Full keels:
These were the earliest keels and they pretty much ran from the point of entry at the bow, to the aft most point of exit at the stern. Those are full keels in the fullest sense of the word.
They have some advantages; they theoretically form a long straight plane which keeps a boat on course better (greater directional or longitudinal stability). If you run aground they spread out the load over a larger area reducing the likelihood of damage. Once really planted they keep the boat from tipping over fore and aft. They are easier to haul and work on. You can spread out the ballast over a longer distance and so they can be shallower for the same stability. You have a greater length to bolt on ballast so it is a theoretically sturdier and simpler connection.
They have some disadvantages; A larger portion of the keel operates near the surface and near the intersection of the hull and keel which are both turbulent zones. They also have comparatively small leading edges, and the leading edge is the primary generator of lift preventing sideslip. Because of that they need a lot more surface area to generate the same lift. Surface area equates to drag so they need more sail area to achieve the same speed. Long keels tend to be less efficient in terms of lift to drag for other reasons as well. As a boat makes leeway water slips off of the high-pressure side of the keel to the low-pressure side of the keel and creates a turbulent swirl know as a tip vortex. This is drawn behind the boat creating drag in a number of ways. The longer the keel, the bigger the vortex, the greater the drag. So they need more sail area again to overcome this drag. To stand up to this greater sail area the boat needs more ballast and a stronger structure, which is why long keelboats are often heavier, as well. (Of course, then the spirol starts again as more sail area is needed to overcome that additional weight as well. It is the classic weight breeding more weight design cycle) Full keels tend to be much less maneuverable.
Fin keels:
By the classic definition of a fin keel any keel whise bottom is less than 50% of the length of the boat is a fin keel. Fin keels came into being in an effort to reduce drag. Cut away the forefoot or rake the stem, as well as, move the rudderpost forward and rake it sharply and pretty soon you have a fin keel. Today we assume that fin keels mean a separated rudder (skeg hung or spade) but in fact early fin keels had the rudder attached in a worst of all worlds situation. They offer all of the disadvantages of both full and fin keels, but with none of the virtues. Unknowing or unscrupulous brokers will often refer to boats with fin (or near fin) keels as full keel if they have an attached rudder.
Fin keels with separate rudders seem to be the most commonly produced keel form in the US these days. (I could be wrong, there is a resurgence of full keels these days)
Fin keels have some advantages as well. They have less drag as explained above so they typically make less leeway and go faster. You can get the ballast down lower so in theory they are more stable for their weight. They are more maneuverable. They take better advantage of the high efficiency of modern sail plans and materials.
They have some disadvantages as well, many of these have been offset or worked around by modern technology but at some level they are still accurate critiques. They have less directional stability than long keel boats so the tend to wander more under sail. On most boats under 40-50 feet, there is a tendancy for dynamic directional stability to be more critical to course holding than the directional stability that comes from the a long keels greater longitudinal moment of intertia. Since directional stability as a product of the dynamic balance between the sail plan and underbody is so important to directional stability, in practice many fin keel boats actually hold a course as well as a full keel. In general though you can expect to make more small course adjustments with a fin keel. It is sometimes argued that the lower helm loads on a fin keeler requires less energy to make each of these corrections so a fin keel may also require less energy to maintain course. This I think is a product of the individual boat and could lead to a debate harder to prove than the number of angels that can dance on the head of a pin.
Fin keels are harder to engineer to withstand a hard grounding and when aground they are more likely to flop over on their bow or stern. (Although in 37 years of sailing, I have never heard of anyone actually experiencing this.) Fins typically have deeper draft. They are easier to pivot around and get off in a simple grounding.
There seems to be lots of opinion on here about the stability of modern light yachts v older heavier ones and I came across this on another forum site. I hope the author (a site moderator) doesn’t mind me quoting him but I found it to be very informative and goes a long way to answer some of the questions:-
I think that there is no one universally right answer here but a whole lot of strong opinions when it comes to keel types. If you are traditional in your view point then you would lean towards a boat with a full length keel. If you care more about performance and ease of handling then you might lean towards a fin keel.
There are good and bad offshore boats with all kinds of keels and so buying a boat with a full length keel will not guarentee that you will end up with a good offshore boat any more than buying a boat with a fin keel will guarentee a bad offshore boat. These are at best subjective decisions.
The way that I personally look at this, If your goal is to spend almost all of your time offshore and in really remote areas of the world, then a full keel boat probably makes sense. If you are going to island hop and perhaps occasionally make longer passages, and you will be traveling in places like the US, Carribean and Europe, then a properly designed and engineered fin keel boat makes more sense. BUT again that is only my opinion.
The material below is exerpted from an article that I had written for another venue but which might help you as well.
Full keels:
These were the earliest keels and they pretty much ran from the point of entry at the bow, to the aft most point of exit at the stern. Those are full keels in the fullest sense of the word.
They have some advantages; they theoretically form a long straight plane which keeps a boat on course better (greater directional or longitudinal stability). If you run aground they spread out the load over a larger area reducing the likelihood of damage. Once really planted they keep the boat from tipping over fore and aft. They are easier to haul and work on. You can spread out the ballast over a longer distance and so they can be shallower for the same stability. You have a greater length to bolt on ballast so it is a theoretically sturdier and simpler connection.
They have some disadvantages; A larger portion of the keel operates near the surface and near the intersection of the hull and keel which are both turbulent zones. They also have comparatively small leading edges, and the leading edge is the primary generator of lift preventing sideslip. Because of that they need a lot more surface area to generate the same lift. Surface area equates to drag so they need more sail area to achieve the same speed. Long keels tend to be less efficient in terms of lift to drag for other reasons as well. As a boat makes leeway water slips off of the high-pressure side of the keel to the low-pressure side of the keel and creates a turbulent swirl know as a tip vortex. This is drawn behind the boat creating drag in a number of ways. The longer the keel, the bigger the vortex, the greater the drag. So they need more sail area again to overcome this drag. To stand up to this greater sail area the boat needs more ballast and a stronger structure, which is why long keelboats are often heavier, as well. (Of course, then the spirol starts again as more sail area is needed to overcome that additional weight as well. It is the classic weight breeding more weight design cycle) Full keels tend to be much less maneuverable.
Fin keels:
By the classic definition of a fin keel any keel whise bottom is less than 50% of the length of the boat is a fin keel. Fin keels came into being in an effort to reduce drag. Cut away the forefoot or rake the stem, as well as, move the rudderpost forward and rake it sharply and pretty soon you have a fin keel. Today we assume that fin keels mean a separated rudder (skeg hung or spade) but in fact early fin keels had the rudder attached in a worst of all worlds situation. They offer all of the disadvantages of both full and fin keels, but with none of the virtues. Unknowing or unscrupulous brokers will often refer to boats with fin (or near fin) keels as full keel if they have an attached rudder.
Fin keels with separate rudders seem to be the most commonly produced keel form in the US these days. (I could be wrong, there is a resurgence of full keels these days)
Fin keels have some advantages as well. They have less drag as explained above so they typically make less leeway and go faster. You can get the ballast down lower so in theory they are more stable for their weight. They are more maneuverable. They take better advantage of the high efficiency of modern sail plans and materials.
They have some disadvantages as well, many of these have been offset or worked around by modern technology but at some level they are still accurate critiques. They have less directional stability than long keel boats so the tend to wander more under sail. On most boats under 40-50 feet, there is a tendancy for dynamic directional stability to be more critical to course holding than the directional stability that comes from the a long keels greater longitudinal moment of intertia. Since directional stability as a product of the dynamic balance between the sail plan and underbody is so important to directional stability, in practice many fin keel boats actually hold a course as well as a full keel. In general though you can expect to make more small course adjustments with a fin keel. It is sometimes argued that the lower helm loads on a fin keeler requires less energy to make each of these corrections so a fin keel may also require less energy to maintain course. This I think is a product of the individual boat and could lead to a debate harder to prove than the number of angels that can dance on the head of a pin.
Fin keels are harder to engineer to withstand a hard grounding and when aground they are more likely to flop over on their bow or stern. (Although in 37 years of sailing, I have never heard of anyone actually experiencing this.) Fins typically have deeper draft. They are easier to pivot around and get off in a simple grounding.
