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  #3581  
Old 02-14-2013
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Re: Interesting Sailboats

Quote:
Originally Posted by olianta View Post
"There is not a single drawing for any of the boats - not for the interior, nor for the hull or anything. Mat uses a plastic material to build a model. He starts by
cutting the view from above. He shapes the plastic into a sailboat and test it in his bathtub, adding weights and obviously finding the centre of gravity. Once complete the first yacht in the line is constructed based on the model. Then the boat is entered in the summer racing circuit in the Swedish archipelago near Stockholm to test it sailing. Afterward, the design is fine-tuned and improvements are incorporated in the line"
.

How does it sound?
It sounds good

He is one of the last NA from the old school before computers. There are some good ones still doing great boats....and the performance on the race track speaks about design quality, whatever the methods that are used.

There are several Nordic ones on the same category among them Oluf Jřrgensen the designer off Luffe yacht (that also races them), Niels Peter Faurby, the designer of Faurby yachts (also a racer) is another. I think they use design but not CAD and I bet that they start with models. That was the way boats were designed in old days. First it was made half hull and then the lines were taken from there.



On the South of Europe there are not many examples that I know off, except one that counts a lot by the great performance of his boats, I am talking about Jacques Valer a guy from the old generation that I don't believe uses the computer except for the final images of his boats. I saw paper designs from him not long ago. He designs the boats for JPK and JPK boats win everywhere:

JPK

Anyway a generation that will end up in some years, I am sure. Today everybody uses CAD for design. However they are also part of a generation of NA that continue strong, the ones that race their boats or had an active past as racers. Many of those are today main NA, specially in France.

Regards

Paulo
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  #3582  
Old 02-14-2013
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What an wonderful boat: Black Maggy

Incredible 32fter, not only beautiful but also ultra high-tech:






Don't miss this video:

Kompositrakete aus Hooksiel - Yacht TV - Segel Videos von Europas größtem Yacht Magazin


Here you can see how it was built:

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  #3583  
Old 02-15-2013
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On multihull stability

I had posted this on another thread about multihulls. I think that it would be interesting to post it here as well since it contains interesting data and links:

Quote:
Originally Posted by PCP View Post
mdi posted a link with interesting information about multihulls, including stability on another thread. I think it is useful to have it here also. The link:

Multihull Dynamics, Inc. - Account Login

and my comments:

Quote:
Originally Posted by PCP
Thanks, interesting stuff.

But in what regards stability the ratios they use are a bit limited. Both take into account the sail area but in extreme situations one does sail in bare poles or with very little sail area so in fact those ratios don't tell about the absolute stability of a boat but about the stability for the max sail area the cat can carry (you can always reef).

Multihull Dynamics, Inc. - News Article

Looking at the formulas they attribute the same importance to three factors: Length, beam and weight. That seems a bit arbitrary to me.

I remember some years ago of some huge racing multihulls (60ft) that were capsized on a huge storm, carrying no sail, just for the windage on the mast. If I remember rightly 70 to 80K winds.

A good way of having an idea of an absolute static stability measure on a multihull would be to know what the intensity of wind would be necessary to capsize the cat only with the wingage over the mast and cabin. I don't understand why that is not used. It is not difficult to computer predict that and surely If I sailed a cat I would know more about that than about a relative stability regarding Stability/sail area. I can always reef or go to bare poles.




Interesting that the stability ratio used by the designer of Tom cats multihulls is not the same:

"The stability formula gives a result which is the wind speed (in Knots) required to just lift the windward hull (the point at which, in a cruising boat, not a beach cat, you scream "Let go the sheets!", or better still "Let's put a reef in her").

Stability = 13.7 sqrt(Wt * 1/2Bm/SA * HCE)"


Welcome to TomCat Boats

As you can see they are different:



Multihull Dynamics, Inc. - News Article

Anyway on this times of CAD design, with powerful programs I don't understand the need of approximated ratios when it would be easy for the designer to calculate for each boat (taking into consideration all boat's dimensions) this value and most of all the force of wind needed to capsize the boat on bare poles. This could be a king of AVS point for multihulls, not related to heeling but with wind force. If those values were mandatory we could have a pretty good idea of the stability of each cat.

Anyway, as we cam all see, Beam, length and weight are all determinant factors in a multihull stability and that's why I had made some personal reserves to the use of small light cats for offshore work.

...
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  #3584  
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Re: Interesting Sailboats

Speaking about JPK: What about the 38FC with double keel: Will there be a big lack in speed oder stability?
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Twin keels

Quote:
Originally Posted by robelz View Post
Speaking about JPK: What about the 38FC with double keel: Will there be a big lack in speed oder stability?
No, the stability is almost for sure the same. They normally calculate the need in ballast to have an identical stability curve. The difference in speed is marginal and will only matter to competition.

If you look, somewhere in this thread is a comparative between a RM with a mono keel and another with a twin keel, made by RM yachts. The differences are small, some tenth's of a knot.

The boat will have a better mass distribution and without sails the boat will roll less, not to mention the advantage of a smaller draft and the possibility to beach the boat for repairs or anti-fouling.

There is a good reason why lots of French performance cruisers that are used mostly for cruising use twin keels. The advantages are many and if well designed the inconvenients are not significant, just a small loss in performance.

This is a good article about twin keels, a bit partial towards them, but a good one anyway:

And from France we have what I consider to be some of the most innovative and technologically advanced Twin Keel boats ever seen, although not particularly offering shoal draft capability.
The RM range of Twin keel sailing yachts... Marc Lombard, a prolific and talented designer with Open 50 and 60 ocean racing machines to his credit, has designed the most recent boats in this range....

On many large cruising yachts it is obvious that as soon as they heel, the wide body of the hull pivots the short fin keel into a position where it is presenting no lateral resistance to the water and thus the whole boat slips away to leeward.

Indeed it could be argued that Twin Keels are the obvious choice for the
modern voluminous hull shape providing excellent accommodation for today’s
sailor who still requires good pointing ability and straight tracking....


http://www.wrightonyachts.com/wp-con...ftwinkeels.pdf

Here another slightly partial article on Twin keels.

Bray Yacht Design and Research Ltd. - The Advantages of Twin Keels

Don't let they foll you: regarding performance the only thing better than a deep draft torpedo keel is a deep draft canting torpedo keel (even if they require foils).

But when draft becomes part of the question it is well possible that the same medium draft twin keel is more efficient than a medium draft monokeel and with smaller drafts, the advantage of the twin keel becomes bigger. At least is what the French think and they have a lot of experience on the subject.

For example, regarding the RM 10.60, the two keels proposed are monokeel with 1.95m and twinkeel with 1.65m. They say that the difference in performance between both keels is marginal, even if the monokeel has a better performance but if they used both keels with 1,65m I doubt very much the monokeel would be a match. That's their point and that's why they offer mostly and recommend twin-keels for cruising.

Performance cruisers like the JPK 38, RM or Bongo they made the boats with twin and mono keels and they will provide you with all the information regarding the advantages of both systems. All of those twin keels are high performance keels.

Regards

Paulo
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Last edited by PCP; 02-15-2013 at 02:26 PM.
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  #3586  
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Randonneur 980

Never talked here about amateur boat building but since we are talking about twin keels I remember having seen this Canadian home built Randonneur 980(Montreal) and since it is a nice one and one of those twin keels way ahead of its time, here are the pictures:



















This is not the same boat, but just to show the keels and ruders:



The Canadian one was built in 2008 and the one on the last photo in 2006 but the design is older...older but still very modern. They are still being built:

CONSTRUCTION AMATEUR D’UN RANDONNEUR 980 | Newswinch

That is a Marc Lombard project and in fact very close to the ones he had designed for RM.

When they solve the problems with the site you can have more information here:

http://www.marclombard.com/

What makes them popular is, besides performance, that they are easy to build. Marine plywood impregnated with resin and then kevlar or other less expensive fiber. 3000 hours of work is what it takes.

Here you have lots of photos of that Canadian one being built (on the left):

Artaban, le randonneur canadien. - La construction amateur d'un randonneur 980, voilier en CP époxy
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New solo Atlantic Record by Francis Joyon

This guy is incredible...with 56 years of age he beats his own old 2008 SOLO record (with the same boat) by MORE THAN A DAY

There are some guys that become better with age, like the wine. His time is really incredible: 8 days, 16 hours, 7 minutes and 5 seconds.

The absolute record belongs to Franc Cammas with a full team in the huge Groupama tri with 7 days and almost 11 hours.

We are talking about the central Atlantic record, the same route that Colombo did. Colombo took about 40days

The solo monohull record belongs to Giovanni Soldini on the VOR 70 Maserati with more 2 days and 8 hours.

Chapeau to Joyon. Now to finish is career with all records he only needs to beat the North Atlantic Record and win the Route du Rhum. Some tough competition for the last one, I am sure, maybe even Cammas.



Even the British are enthusiastic about the man:

One of the greatest seaman of our times has set a new record: the incomparable Francis Joyon yesterday knocked 1 day and 4 hours off the course record for the Columbus Route between Cadiz and San Salvador.
....

Typical of Joyon, he had no help to do this. In nearly all of the outright records sailors have the benefit of extensive weather and routeing information researched and sent from ashore. Not Joyon. He is the ultimate single-hander, preferring complete self-reliance.

He is a truly remarkable man, one of our time's most modest, skilful, seamanlike sailors, a real pleasure to meet in person and quite shy. He is a great hero of mine - if you don't know his whole history, do read my detailed profile of him here, he's an absolute giant of the sport.

Joyon record | Yachting World

Read it, it is interesting:

http://www.yachtingworld.com/blogs/e...fastest-seaman


....
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  #3588  
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Re: Interesting Sailboats

As you know, Javier “Bubi” Sansó’s IMOCA 60’ Acciona 100% EcoPowered capsized almost a month ago in the end stage of the Vendée Globe race, and the skipper was airlifted sound and well 300 NM away from the Azores by the Portugese coastguards .

Here are some amazing images of the capsized yacht before it was righted and towed to Ponta Delgada.

Remember it was the keel that failed, there was nothing wrong with the mast and rig until the boat turned over…





Best regards,

Eric
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  #3589  
Old 02-16-2013
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Re: Interesting Sailboats

Paulo, if you are cruising in the Med, you cannot take advantage of the ability to beach with a twin keel. Therefore, in my opinion the issue is whether you want a boat with a smaller draft, in which case as you say it is better to choose a twin keel than a shoal mono keel as offered as an option by many boat yards. Do you think for a crusing yacht the tween keel option makes sense as a precaution against losing the mono keel if you hit an UFO. And vice versa if you run aground with a tween keel yacht wouldn't it be more difficult to refloat it? Last concern about the tween keel - does it increase drag?
Regards
Rumen
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Old 02-16-2013
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Twin keels

Quote:
Originally Posted by olianta View Post
Paulo, if you are cruising in the Med, you cannot take advantage of the ability to beach with a twin keel. Therefore, in my opinion the issue is whether you want a boat with a smaller draft, in which case as you say it is better to choose a twin keel than a shoal mono keel as offered as an option by many boat yards. Do you think for a crusing yacht the tween keel option makes sense as a precaution against losing the mono keel if you hit an UFO. And vice versa if you run aground with a tween keel yacht wouldn't it be more difficult to refloat it? Last concern about the tween keel - does it increase drag?
Regards
Rumen
Yes it increases drag but in a way that will only matter if you race. Yes it will make more difficult to refloat a boat aground and I don´t think that losing a keel in a modern cruising boat is a concern.

However I find the two rudder option very interesting in what regards that. Rudders are a lot less fragile than keels and today mono rudders are almost as deep as keels while with two rudders you have not only two but much less deep rudders.

I confess I am not worried to touch the ground at slow speed with the keel but I am worried to do that with the rudder and that can happen when you moor Mediterranean style on some small harbor (anchor first and then backwards to the quay). I guess I am going to mount a forward looking sonar to have first a look at the quay deep before going backwards

Everything comes with vantages and disadvantages and the twin rudders make a boat very hard to maneuver.

Back to twin keels, their advantage is more efficiency with less draft and the possibility to beach the boat. The disadvantages are a marginally worse performance with a deeper draft boat. Your pick

Regards

Paulo
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