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  #801  
Old 05-16-2013
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Re: Full or fin keel?

Paulo, your last picture looks like a boat designed to beat a rating system weighted against LOA.
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  #802  
Old 05-17-2013
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Re: Full or fin keel?

Quote:
Originally Posted by killarney_sailor View Post
Paulo, your last picture looks like a boat designed to beat a rating system weighted against LOA.
Sorry Killarney I don't know what you are talking about. The last boats I posted where historical boats.

Regards

Paulo
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  #803  
Old 05-17-2013
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Re: Full or fin keel?

Quote:
Originally Posted by wolfenzee View Post
Even living at the dock and not taking my boat out I still exercise my engine.

The MacGregors with enough power can get up and plane to get you back to the marina in time so you don't miss cocktail hour. As much as I dislike them, I have noticed one thing about MacGregors.....the owners do tend to use them a lot more, and that what it's all about right.
It is possible for me to get my boat over 20kts....but that would involve putting it on a container ship.
I described my Mac 26X, Bossa Nova, as a 26-foot, sleep-aboard sailing dinghy, that can also serve as a funny-shaped travel trailer. It's a very good first boat, for someone who hasn't decided between sailing or power-boating, or who wants to take it on a camping vacation to some big lake or bay, or other sheltered waters; and I know a few people who have taken their MacGregors to the Bahamas, and had a great trip of it.

But you can only do so much with a Mac.

I don't regret putting my Mac up for sale and buying my current Bristol 29.9, even if I'm paying several times as much to keep Halcyon in a slip as I was paying to keep Bossa Nova on her trailer at the same marina.
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  #804  
Old 05-17-2013
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Re: Full or fin keel?

There are also cut away and modified keels. Much of the choice depends on your sailing preferences: fast vs comfortable (sea kindly); deep water ocean cruising (deeper keel) vs Bahamas bank or wanting to pull into shallow harbors (shoal keel); etc. As mentioned above, having the rudder be shorter than the keel and protected (hung or skeg) is import for cruising. We have a heavy boat with a 5.5’ draft. She’s not fast but she’s comfortable (aka civilized) and sea worthy. With the 5.5’ draft there are a number of hurricane holes here in the Bahamas that I can not get into and harbors that I have to wait for high tide to enter. I’m ok with these trade offs.

As all the sailboat cruising and boat buying books would say, there are always trade-off when aquiring a boat.

Julia
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Mariner 39 (NH built, cruising version)
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  #805  
Old 05-17-2013
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Re: Full or fin keel?

Everything is a compromise of some sort or another...it's just more obvious in boats
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  #806  
Old 05-17-2013
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Re: Full or fin keel?

Quote:
Originally Posted by outbound View Post
Still, there have been modifications applied to full keel boats that improved function such as those using Henry Sheel's work or the keels with a gap in the middle which I recall were done by an englishman who's name escapes me. ..
the Scheel keel that I know is a kind of previous bulbed keel but with a lot of drag.

I guess you are talking about tandem keels? Those are a lot more interesting specially in what regards low draft solutions even if they have been used (without much success) even in top race boats.













Regards

Paulo
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  #807  
Old 05-17-2013
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Re: Full or fin keel?

The gap distance between the two fins is critical Look at it on the AC boat. Most more mundane boats do not have the bulb length to accomodate the required gap distance.
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  #808  
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Re: Full or fin keel?

Yes, I know but has some major Na have been using them (I believe Farr had designed one for the shoal version of the Bavaria vision) I believe they can design them in an effective way otherwise they would not be using them. I am quite sure they design them using CFD.
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Old 05-17-2013
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Re: Full or fin keel?

"I believe they can design them in an effective way otherwise they would not be using them."

What a novel thought. I wonder how many design features have been tried over the years that have proven less than effective but initiated with that same optimism? The "split keel" has been around for quite a long time.

Maybe in time it will join some other "breakthrough" keels like theScheel keel, Reijo Salminen wing keel, eliptical planform keels, to name three.
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Last edited by bobperry; 05-17-2013 at 11:27 PM.
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  #810  
Old 05-18-2013
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Re: Full or fin keel?

Quote:
Originally Posted by bobperry View Post
"I believe they can design them in an effective way otherwise they would not be using them."

What a novel thought. I wonder how many design features have been tried over the years that have proven less than effective but initiated with that same optimism? The "split keel" has been around for quite a long time.

....
Sorry, I guess I was not been clear. They are around as you say for a long time, from the time CFD studies were not the norm to study keel, hull and rudder efficiency, but things were done by try and error, experience and a good eye.

They survived till today were they are designed not by trial and error but by seeing their comparative performance with other types of keels in CFD studies. If they are still used by major NAs it is because they are a valid alternative to other options, specially in what regards low draft options.

For instance, Mortain&Mavrikios, the designers of the line of Harmony, Etap, Lockwind, Passoa, Nautitech Feeling and some Dufour said about tandem keels regarding their use on the Harmony:

“Those looking for small draughts will be delighted to know that cast-iron tandem keels …offer almost the same sail stiffness and the same ability to go close winded as lead keels with far deeper bulbs”.

http://www.mortain-mavrikios.com/MMC%20Brochure.pdf

And Etap said some years ago regarding the use of tandem Keels on the Etap 30i:

"After thorough investigation and numerous tests, ETAP Yachting N.V. is pleased to introduce its ETAP tandem keel. The most important advantages of this keel are the excellent sailing qualities at a considerably reduced draft. This new design is the result of a co-operation with the architects' bureau Mortain-Mavrikios.

The two most important features to reduce drift, are the size of the lateral plan and its efficiency. The efficiency is defined by the proportion between the depth of the keel and the length. Also a wing section is a classic aid to improve the efficiency.

For a strong reduction of the draft neither a wing keel or a bulb keel were sufficient. The solution was found in placing two shorter keels behind one another, linked by a wing-bulb profile : the ETAP tandem keel.

The ETAP tandem keel gives a better aspect ratio, thus generating more lift.
In addition to increased stability, the wing-bulb also provides better hydrodynamic characteristics. "


Tandem keels are also used by J&J yacht design in several Bavarias.

http://greenlinehybrid.com/J-and-J-design

Regards

Paulo
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Last edited by PCP; 05-18-2013 at 01:56 PM.
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