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  #201  
Old 03-29-2012
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Re: Full or fin keel?

Mitiempo is right. Used RM boats are very hard to get. There are a lot of sailors that would like to have one and that makes the prices of the used boats high:

FORA MARINE RM 1050 - Voilier FORA MARINE RM 1050 d'occasion - Page 1

There are however a twin keel sailboat that is possible that you would like even better that the RM. It is a more classical boat and also a favorite among French sailors. It is a seaworthy and the boat is made almost without alterations for a lot of years. I am talking about the Biloup.

They are making now a new 365 that I will post on “interesting sailboats” soon but they have a 36ft and a 30ft for a long time.

Wrighton Yachts | Bi-loup 365

They are not cheap because, like the RM, there are more sailors wanting them than the boats they have available but I guess they can be older and therefore not as expensive. For instance this one for 65 000€ that sailed far for 8 years.

Bateaux autour du monde - Sail The World - L'Univers de la grande croisière en voilier - STW

site de Mareja

Or these, even less expensive.

biloup France - Bateaux France

Regarding speed and twin keels look at this Bongo. The first movie is from a Transat race with a duo crew. They have done well.




Last edited by PCP; 03-29-2012 at 10:25 PM.
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  #202  
Old 03-29-2012
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Re: Full or fin keel?

Yahhh ... but Hinckley makes a gorgeous boat. And you didn't buy Ibis to back her up, now, did you?

2011 was my first year with a proper keelboat, a Bristol 29.9 - and as much as I learned about prop-walk over a summer of backing her into my slip, I know full well that I've only scratched the surface. (Well, actually, scratched the topsides. More than once.) But I was glad to find a boat like the Bristol, with her long, shallow-draft keel and her big solid skeg-protected rudder. After two seasons with Bossa Nova, my previous MacGregor 26 (a tender centerboard boat that gives up a lot of leeway), I wanted to go to the other extreme; and the 29.9 looked right, felt right, sailed right, and she's still right for my tastes and the next couple of years' worth of my goals.

Maybe some day I'll be sailor enough for a lovely yawl like the Bermuda 40 ...

Last edited by RickWestlake; 03-29-2012 at 10:34 PM.
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  #203  
Old 03-29-2012
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Re: Full or fin keel?

I don't think anyone has mentioned the type of boat that is very popular in France, often aluminum and with a centerboard. The name most common over here is Alubat's Ovni. Not a light fast boat but a very comfortable cruiser with a good performance and a shallow draft that opens up some interesting options.
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Full or fin keel?-cruising-sailboat-aluminium-3-cabins-92145.jpg   Full or fin keel?-ovni-side-sand_1a.jpg   Full or fin keel?-ovni-bow-sand-_1a.jpg  
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  #204  
Old 03-30-2012
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Re: Full or fin keel?

Quote:
Originally Posted by GBurton View Post
I remember seeing a video of that. The boat was inverted without its rig (by using a crane) and then the crewman inside cranked the keel over to the one side by means of a hand hydraulic pump. Seems a little extreme
Would the mast help or hinder the roll-up?
I'll admit, I do not know if the rig would or would not help/hinder the roll-up. BUT, they do have to roll back up granted with the help of the canting keel to one side, but roll up they must with in this test. Not sure one could invert one with the rig on it. So from that point of view, the inverted test that they do, will have to make do until someone can figure out how to test with the rig.

They do some different things in Europe to certify boats built over their, and here to meed certain specs. One of them is literally inverting a boat and seeing if it will roll back up. OR< the architect has to show using a know formula that the boat will roll back up right. Not sure your W32 or for that matter, my 85 Jeanneau would or would not pass the test. They may roll back up, but with in the allotted time........

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  #205  
Old 03-30-2012
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Re: Full or fin keel?

Here's one of the Open 60 capsize tests.
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  #206  
Old 03-30-2012
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Re: Full or fin keel?

Paolo,

I'm still struggling with these two statements, one from you:

Quote:
Originally Posted by PCP View Post
It is not me that thinks that a a narrow deep foil keel allows a boat to move sideways or to rotate much easily than a full keel. I have learned from others including some very experience sailors and boat designers
And this one from Jeff:

Quote:
Originally Posted by Jeff_H View Post
it is easy to see that a modern fin keel boat could easily develop much higher dampening moments and so have better dampening than a full keel boat
Now, if a fin keel allows the boat to "rotate much easily" as you say, then how can it have a "much higher dampening moment" at the same time?
I feel that both can not be true. Of course, I may be wrong and these are not contradicting statements but I fail to see why, maybe you can tell.

Peter
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  #207  
Old 03-30-2012
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Re: Full or fin keel?

Quote:
Originally Posted by pvajko View Post
Paolo,

I'm still struggling with these two statements, one from you:..


Now, if a fin keel allows the boat to "rotate much easily" as you say, then how can it have a "much higher dampening moment" at the same time?..

Peter
Peter you shoud be very carefull when quaoting somebody. I believe you did not have intention but I never said that "a fin keel allows the boat to "rotate much easily"

I have said:


Quote:
Originally Posted by PCP View Post

...

Regarding inertia and roll moment of inertia, let’s consider two boats with the same positive area under the RM curve, and therefore needing the same energy to be capsized. One is a long keeler, small draft, narrow heavy weight boat the other one is a beamy light boat with a big draft and all the ballast on a bulb at the end of a fin keel.

As I had said before the dynamic behavior of these boats when hit by a breaking wave will be very different in what regards the capacity to dissipate the wave energy moving sideways, but let’s consider that the full keeler would not trip in its keel, that the extra surface would not have a damping effect on the rotational movement and that the low mass and small under water surface would not permit the lighter boat to move much more easily sideways.


Let’s consider that the same amount of energy of the wave that hits the boats results in a rotational movement for both boats. Both boats require the same energy to be capsized so in what regards the results (capsizing or not) the effect would be the same but the kind of movement due to inertia would be very different.

The heavier boat would start to roll much more slowly but because it has much more inertia once started the rolling movement it would be much harder to stop it. On the lighter boat the roll movement will be faster but will be also stopped faster because the inertia is much smaller. Both boats will roll to the same point but the duration of the roll movement (to capsize at 90º and back to its feet) will be much longer on the heavier boat.

We could say that the slower movement is a more comfortable one but the fact is that in what regards seaworthiness the heavier boat will be much more time deeply heeled, exposing its side much longer to another breaking wave that will catch him with little stability left and therefore will have potentiated effects, resulting probably in a capsize.

...
Paulo
As you can see I have said that the energy required is the same and therefore the Fin keel boat will not "rotate much easily". It will rotate faster, it will stop the rolling movement faster and will return to its feet faster, but both boats will heel to precisely the same angle of heel.

Let me point out that this has not to do with the fin or the full keel but with the types of boats that are associated with. I have said regarding the boats:

"One is a long keeler, small draft, narrow heavy weight boat the other one is a beamy light boat with a big draft and all the ballast on a bulb at the end of a fin keel".

Regards

Paulo
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  #208  
Old 03-30-2012
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Re: Full or fin keel?

Quote:
Originally Posted by mitiempo View Post
I don't think anyone has mentioned the type of boat that is very popular in France, often aluminum and with a centerboard. The name most common over here is Alubat's Ovni. Not a light fast boat but a very comfortable cruiser with a good performance and a shallow draft that opens up some interesting options.
That is the kind of boat most French would consider a voyage and a bluewater boat. They have a bit more ballast than fin keel boats but even so they are not very heavy, thanks to its aluminum construction. For instance, an OVNI 395 weights 8800kg and a Bavaria 40 weights 8680kg.

Regarding speed they do not point as well as a good fin boat but I guess the difference will not be much if any compared with a full keel boat. They sail fast downwind with the centerboard up, and I mean really fast (can reach double digit figures) and as most ocean voyages are made following the trade winds, these boats are relativelly fast voyage boats.

Have a look at the OVNI performance (several boats) on the last ARC and you will be surprised.

Regards

Paulo

Last edited by PCP; 03-30-2012 at 04:06 PM.
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  #209  
Old 03-30-2012
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Re: Full or fin keel?

Quote:
Originally Posted by GBurton View Post
...
Would the mast help or hinder the roll-up?
In a static situation without waves I don't know but recent tank testing showed that in a dynamic situation with waves the mast will help the boat to right itself up faster. Yes I know, it looks odd, but I read the paper and against facts there are no arguments...just the need to understand why

Regards

Paulo
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  #210  
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Re: Full or fin keel?

Quote:
Originally Posted by PCP View Post
Peter you shoud be very carefull when quaoting somebody. I believe you did not have intention but I never said that "a fin keel allows the boat to "rotate much easily"
Well, Paolo, I (the forum engine) quoted that from your own post, click on the little arrow in the quote box and you'll see.

But we seem to be talking about two different things. I'm talking about your tripping over the keel scenario where you seemed to say that the beamy, fin keel boat will slip sideways rather than roll over. That is, I think in contradiction with what Jeff said (today's fin keel boats have better dampening than full keels) because if a fin keel as at least as good dampening as a full keel, I can not see why would it slip more easily sideways, but again, I may be wrong here.
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