Full or fin keel? - Page 52 - SailNet Community
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post #511 of 847 Old 10-03-2012
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Re: Full or fin keel?

people can yap all they want to about different keels and styles o boat. it is going to be a huge investment--time, money and lifestyle--why dont you take a sail on each kind of boat that interests you--as opb cruising or racing--see what YOU like best an buy that????
in order to know what YOU like to sail, you have to sail it .....have fun--is the most funnest part of boat purchasing--research!!!!

btw--we dont need no stinkin numbers--when passion hits, BUY.
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post #512 of 847 Old 10-03-2012
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Re: Full or fin keel?

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btw--we dont need no stinkin numbers--when passion hits, BUY.
Well said!! Love your attitude!

Much as I like science and understanding - art, music and passion are really what matters to me! I've never tried a boat before I bought it, probably because I buy cheap wrecks for a song that need work before launching. Always it's the older traditional styles that grab me when I see them sitting beside the road. But this year I bought a Hunter 23 (a wreck). Partly because of this thread, and partly because it was there. A super ugly stubby wing keeled boat, which I hate to look at and always think "toy boat". I must admit, it sails surprisingly well. And, when I'm on it, I can't see how ugly it looks, I just sail around the beautiful traditional boats and look at them. With a theoretical hull speed of something like 5.9 knots, I was surprised when my new (tiny, pocket sized hiking style) first GPS showed I was doing 6.2 MPH (not knots) going against the tide while tacking into the wind. Recently I found that it recorded tracks of where I went, and showed my top speed to be 8.3 MPH. I can only think I must have been surfing down some monster waves going with the wind and tide. (Week long sail/anchor.) Of course, when I'm ripping along, I don't bother changing screens on the GPS to see my speed, too busy sailing! So I've enjoyed my first "modern" boat more than I expected. Except looking at it.
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post #513 of 847 Old 10-03-2012
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Re: Full or fin keel?

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One of the LAST boats I would want to be on is an IP in higher winds......but that is me.
Marty
200 years of yacht Architects would vehemently disagree with you. The IP is not as wide as most big cruisers, and coupled with the full keel tends to make the hull less stiff. As we all know the lower the stiffness, the better the rough water capability.

The huge keel mass coupled with the heavy hull results in a quite low CG further enhancing its rough water capability. And as everyone knows the IP is extremely respected in its rough water capability.

Bryce
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post #514 of 847 Old 10-03-2012
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Re: Full or fin keel?

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Originally Posted by BryceGTX View Post
200 years of yacht Architects would vehemently disagree with you. ... As we all know the lower the stiffness, the better the rough water capability.

...
Bryce
Yes of course, all naval architects now that a tender boat is safer than a stiff boat on rough water, I mean sailing...

Regards

Paulo

Last edited by PCP; 10-03-2012 at 08:06 PM.
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post #515 of 847 Old 10-03-2012
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Re: Full or fin keel?

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BryceGTX must have missed my point. We all make tradeoffs to suit our needs.
Your boat was designed entirely as a performance shallow water boat. That means at all costs, even salon room was compromised to performance. That huge divider running directly down the center line of the boat from the steps to the forward bulkhead, from deck to ceiling, over a foot wide is a serious compromise.

So now you have a shallow water boat. Lets compare the shallow water performance to the IP. A particular IP has a draft of 4 feet. To put your boat in the same shallow water requires you to place your keel only half down. So now you keel is at 4 feet.

Problem is, only half of your keel is in the water. This means, only half of your lee resistance is provided. And of course only half of your keel weight is where is suppose to be. The other half of the weight is inside your salon uselessly creating a heeling moment.

The IP owner would have to remove his keel and place it on his salon floor to get the same effect as your boat in this configuration. So clearly, when we compare the performance of your boat in the same shalllow water you are at a serious disadvantage.

You complained that the IP is hard to tack because of its dual headsail configuration. However, its inner jib is invariably a self tacking jib. In situations where constant tacks are required why use the outer jib? In that case the IP owner has it all over your boat. He just turns his wheel.

My argument with you is not that your boat does not head to wind just fine. But you thoughtfully left out all the other advantages of the IP over your boat.

Bryce
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post #516 of 847 Old 10-03-2012
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Re: Full or fin keel?

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Yes of course, all naval architects now that a tender boat is safer than a stiff boat on rough water, I mean sailing...

Regards

Paulo
Glad you are continuing to learn something from me. As we all know, a stiff boat follows the waves due to its significant hull moment, creating poor movement. Perhaps you need to review and learn from my previous posts. But to quote a book written 150 years ago:

A manual of Naval Architechture, 1877

"A stiff ship is... A steady ship on the contrary when exposed to the action of waves keeps nearly upright. the stiffest ships are the least steady."

Paulo.. I have pointed this out before. The characteristics of a rough water boat is it reamains vertical in the presence of waves. This is the characteristic of the IP.
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post #517 of 847 Old 10-03-2012
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Re: Full or fin keel?

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Originally Posted by BryceGTX View Post
Glad you are continuing to learn something from me. ... But to quote a book written 150 years ago:

A manual of Naval Architechture, 1877

"A stiff ship is... A steady ship on the contrary when exposed to the action of waves keeps nearly upright. the stiffest ships are the least steady."

...
Bryce
I hope you start reading more recent books, you need it. XXI century sailboats boats have little in common with XIX century boats

Regards

Paulo

Last edited by PCP; 10-03-2012 at 08:46 PM.
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post #518 of 847 Old 10-03-2012
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Re: Full or fin keel?

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Mitigating against the harshness of the motion, dampening from the keel and rig can greatly improve rotational motion comfort, slowing changes in direction without adding the kind of inertia, which tends to make the boat more dramatically over shoot the wave face and so experience grater impact forces.

And this is where the specifics of the design come into play. Too much form stability and the boat will throw its occupants around mercilessly. Too little form stability and the boat will roll and pitch the occupants to death. Which is why I personally advocate a more moderate design philosophy than seems to be the case with the more extreme current design practices.

Coming back to the Full keel vs Fin topic, this another area where the specifics of the design come into play. A full keel would tend to have a comparatively large area which helps to increase dampening force thereby slowing roll rates, but full keels a shallower draft which works against creating as large a dampening moment. So depending on the design, a deep fin, although generating less sideforce, may in fact generate an equal or greater dampening force.

Jeff
Jeff, you are thinking way too simplistically. We had a short discussion earlier in this thread. A significant problem with the long keel is that the force generated by movement of the keel stops being a damping component, but instead changes the dynamic center.

So you cannot say that the damping increases as some power, because at some point it is no longer damping. In large waves, the long keel on a boat with large hull moment can actually cause the boat to heel more because the dynamic center may drop below the CG of the boat.

So invariably, the shallow long keel often provides the better damping for a heavy boat. When I create my thread this will become clear.

There is no boat with wide beam and long keel will result in a good rough water boat. This has been pounded into yacht designers since time begin. Unless you put a coresponding heavy ballast to counteract the hull moment. But then it simply changes the mass moment to hull moment ratio which is what I suggest using as a rough water indicator; for lack of a better term, Bryces rough water coefficient.

Bryce

Last edited by BryceGTX; 10-03-2012 at 11:20 PM.
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Re: Full or fin keel?

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Originally Posted by PCP View Post
I hope you start reading more recent books, you need it. XXI century sailboats boats have little in common with XIX century boats

Regards

Paulo
If that were true, perhaps you can provide a quote from a newer book refuting my statement. My newer books support my statement. However for those that want to understand the mechanics, it is much more clearly explained in the older books.

The other point I wish to pound into peoples minds is that everything we are discussing has been discussed for centries. Even moveable balllast (which current racers think is so cool except they uselessly place it on the keel) was used in every racing boat prior to 1850 when it was outlawed by racing rules.

Bryce

Last edited by BryceGTX; 10-03-2012 at 09:09 PM.
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Re: Full or fin keel?

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Originally Posted by BryceGTX View Post
If that were true, perhaps you can provide a quote from a newer book refuting my statement. My newer books support my statement. However for those that want to understand the mechanics, it is much more clearly explained in the older books.

The other point I wish to pound into peoples minds is that everything we are discussing has been discussed for centries. Even moveable balllast (which current racers think is so cool except they uselessly place it on the keel) was used in every racing boat prior to 1850 when it was outlawed by racing rules.

Bryce
Like in other subjects your opinions are so twisted that I refuse to discuss them with you and I wonder how many people really believe you know what you are talking about.

It is common knowledge that a stiff boat is safer in bad weather and this is not only a subject NA knows about, any good sailor with experience with stiff and tender boats in bad weather will know that.

A sailboat is not a motorboat that bobs around in waves and in bad weather will be strongly “tied” to a side by the force of wind on its sails. A stiffer boat will have more stability and a superior RM than a tender boat, can carry more sail in bad weather and will be “tied” much strongly to one side than a tender boat that will tend to bob around with the waves.

You don’t need a book to know this; you have only to experience it.

Regards

Paulo
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