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  #751  
Old 03-22-2013
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Re: Full or fin keel?

Quote:
Originally Posted by BryceGTX View Post
Hello Jeff, I pretty much stopped reading after this paragraph. Damping has nothing to do with inertia. Inertia is related to the square of the distance and the force is a function of acceleration. Damping is related to area and the moment is proportional to distance. The force is a function of velocity.

Bryce
Inane mix of physics terms
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  #752  
Old 04-10-2013
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Re: Full or fin keel?

Outbound:

If you'd really like to dig into the physics of sailboat design, I'd recommend C A Marchaj's 'Sailing Theory and Practice.' The designs have changed, although not as much as some think -- you can see the same sort of hull design popular today in the 'skimming dishes' and 'sandbaggers' of a century ago. In any event the designs may change but the physics does not.
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  #753  
Old 04-10-2013
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Re: Full or fin keel?

Keforion- thank you for the suggestion. Looked at that book a while back and tasked my poor grey cells. Big difference is I think at present even many monohulls are functioning in semidisplacement or even planing a significant amount of the time. Requirements to maintain attached laminair flow in these settings is somewhat different from my limited understanding of the fluid dynamics. But as you say there is nothing new in the world. One issue to do this with a light dinghy another to a blue water vessel wth significant infill saling in unprotected waters. great suggestion thank you.
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  #754  
Old 04-18-2013
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Re: Full or fin keel?

I vote full
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  #755  
Old 05-11-2013
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Re: Full or fin keel?

Quote:
Originally Posted by Jeff_H View Post

Keels:
The earliest form of a keel was simply the backbone of the boat extending through the bottom planking. (Like a Viking ship) That works OK with running and reaching sails but when you try to point toward the wind you slip side wards at great speed. As sails and rigs were invented that allowed boats to point toward the wind the keel was extended below the boat either by planking the hull down to a deeper backbone or by adding dead wood (solid timber below the backbone. A planked down keel permitted the space between the planking to be filled with heavy material (originally stone), which served as ballast keeping the boat from heeling. After a while it was discovered that there were advantages to bolting a high-density cast metal ballast to the outside of the deadwood and interior ballast dropped out of fashion.

Jeff
Very good post. However, the Viking ship, as an example of a keel too shallow to sail upwind, was a bad choice. During the pre-Viking migration age, the Germanic tribes used longships that, to the best of our knowledge, had very shallow keels. The Anglo-saxon ship found at Sutton Hoo is a prime example. Although, in all fairness, due to the state of the find, we can't be sure it didn't have a deeper keel, like a Viking ship. It might have, but no one wants to jump to conclusions without evidence.

A modern replica ( although reduced in size ), of the vessel at Sutton Hoo, is the Sae Wylfing. This vessel will sail to wind at around 60 degrees, I think, but it's better reaching or running.

A deeper keel was the big innovation that the Vikings added to the Germanic longship design. The new, deeper keel allowed them to sail to wind, efficiently. A modern reproduction of the Gokstad ship, the Sigrid Storrada, will do 45 degrees to wind, at 5 mph, in moderate winds.

The abandonment of the longship design, in Northern Europe, was not due to performance issues. The ship that replaced them, the carrack, was easier to defend against the raiding attacks of the longships. The high sides, and even taller forecastle and poop deck, were hard to scale, if you were boarding from a low longship, and made a good platform for throwing rocks and things on the raiders.

This quirk, which made defense more important than performance, set ship design back until the 1800's, really.
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  #756  
Old 05-11-2013
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Re: Full or fin keel?

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Originally Posted by captain jack View Post
Very good post. However, the Viking ship, as an example of a keel too shallow to sail upwind, was a bad choice. During the pre-Viking migration age, the Germanic tribes used longships that, to the best of our knowledge, had very shallow keels. The Anglo-saxon ship found at Sutton Hoo is a prime example. Although, in all fairness, due to the state of the find, we can't be sure it didn't have a deeper keel, like a Viking ship. It might have, but no one wants to jump to conclusions without evidence.

A modern replica ( although reduced in size ), of the vessel at Sutton Hoo, is the Sae Wylfing. This vessel will sail to wind at around 60 degrees, I think, but it's better reaching or running.

A deeper keel was the big innovation that the Vikings added to the Germanic longship design. The new, deeper keel allowed them to sail to wind, efficiently. A modern reproduction of the Gokstad ship, the Sigrid Storrada, will do 45 degrees to wind, at 5 mph, in moderate winds.

The abandonment of the longship design, in Northern Europe, was not due to performance issues. The ship that replaced them, the carrack, was easier to defend against the raiding attacks of the longships. The high sides, and even taller forecastle and poop deck, were hard to scale, if you were boarding from a low longship, and made a good platform for throwing rocks and things on the raiders.

This quirk, which made defense more important than performance, set ship design back until the 1800's, really.
Are you saying that sailing boats did not get better in 800 years of evolution? It looks like that and it just does not make any sense. Compared with those 800 years of evolution full keels are very close in performance to fin keels

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Paulo
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  #757  
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Re: Full or fin keel?

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Originally Posted by Thunderchild View Post
Wolf and PCP thanks for the great advise. I was looking at something called "Sailtime". I can do bareboat charters on their boats and get to know the ropes as it were. I have been looking for awhile and I have narrowed my choice of manufacturer's to Ericson, Hunter or Catalina. I checked out some Island Packets also but just too pricey for my first boat. I will be looking for a boat between 34 and 38 feet for myself. I will be cruising the Chesapeake Bay for the first couple of years to get to know her and then after that, go out on some longer range voyages. Again thanks for the good advise!
If you have never sailed before, at all, you would be better served to learn on something of the 15 foot range. A bigger boat is more stable and less sensitive. If you can handle a smaller boat, a bigger boat is easier. The boat I taught myself on was a tender 10' moth-like dinghy. Later, when I got my holiday 20, it seemed as stable and steady as a rock.

But, if you learn sailing on a cruising yacht, the day you have to sail a smaller boat, like a dingy, will be a shock.
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  #758  
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Re: Full or fin keel?

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Originally Posted by PCP View Post
Are you saying that sailing boats did not get better in 800 years of evolution? It looks like that and it just does not make any sense. Compared with those 800 years of evolution full keels are very close in performance to fin keels

Regards

Paulo
What I am saying is that the Carrack was a huge step back and we didn't develop a sailing vessel as well designed as the Viking longship, again, until around the 1800's. There was a gradual change from the carrack to the brig, but it took a long time. And brigs aren't exactly models of performance.

Yes, there were some, small traditional craft, like the faering, but ship development, as a whole was set back. Imagine how things might have developed differently, if the launch point, for development, had been the longship and not the carrack.

The longship has a lot of features of modern performance sailboats: the narrow entry, the wineglass cross section, the shallow draft ( of the actual hull, not the underwater foil ) at the mid section. If you cut a longship in half, it would resemble some of the new racing boats. Definitely a better platform for sailboat design growth than the carrack.

That's what I am saying.
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  #759  
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Re: Full or fin keel?

Quote:
Originally Posted by captain jack View Post
What I am saying is that the Carrack was a huge step back and we didn't develop a sailing vessel as well designed as the Viking longship, again, until around the 1800's. There was a gradual change from the carrack to the brig, but it took a long time. And brigs aren't exactly models of performance.

Yes, there were some, small traditional craft, like the faering, but ship development, as a whole was set back. Imagine how things might have developed differently, if the launch point, for development, had been the longship and not the carrack.

The longship has a lot of features of modern performance sailboats: the narrow entry, the wineglass cross section, the shallow draft ( of the actual hull, not the underwater foil ) at the mid section. If you cut a longship in half, it would resemble some of the new racing boats. Definitely a better platform for sailboat design growth than the carrack.

That's what I am saying.
Yes I understood what you have said but you are mixing things. Carracks were merchant ships. Till 1800 there was a continuous evolution in what regards sailing boats all around the world. You are talking about this type of boat:



The evolution was huge. All these sailingboats are from 1400 to well before 1800:















Regards

Paulo
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  #760  
Old 05-11-2013
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Re: Full or fin keel?

It's really hard to ask fin or full, for two simple reasons not all boats in either category are the same and not every ones application is the same.
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