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  #2121  
Old 03-17-2012
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Re: Interesting Sailboats

Quote:
Originally Posted by pellot View Post
Hello,

Have you see the keel weight?
It is 1900 kg
It is heavier than a lot of competitors.
Are you sure the weight of your bavaria 36 is correct ? Is it a Bavaria wheight, or is it a real wheight?
Some yards report false wheight... Lighter than the real one

Bye
I guess you are talking about the Dufour 36 performance?

Yes I am right about the Bavaria 36, not the last model but the previous model. That one weighted about 5.5T and was a light boat with a keel with only 1500kg of ballast on the 1.65m keel draft and if I remember correctly only 1 300Kg on the optional 1.9m keel.

http://www.ayc.hr/technical/36.pdf

The actual model is a very different boat, stronger (I guess) and heavier with 7T and 2080 kg of ballast.

Bavaria Yachtbau: Technical Data

Regarding the Dufour Keel weight (1900kg) it has to be superior than the competition (for the same effect) because the boat is heavier (6.4T).

Dufour 36: Sailing Joy as Guiding Theme | Boats.com Blog

What matters is the type of keel (the Dufour has one that maximizes ballast effect), the draft and the B/D ratio (0.297) and of course, the shape of the hull.

If we compare in that matter the Dufour 36 performance with the First 35 (that has a similar keel and the same draft) we will see that the B/D ratio is bigger (0,304) even if its ballast is only of 1670kg.

Beneteau First 35 Racer/cruiser: Sailing Boats | Boats Online for Sale | Grp, Sandwich | Western Australia (WA) - Perth Wa

The difference in weight between the Dufour 36p and the First 35 is of almost a Ton, and that is a lot on a performance boat, specially on a 35/36ft boat.

Regards

Paulo

Last edited by PCP; 03-17-2012 at 04:06 PM.
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  #2122  
Old 03-17-2012
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Re: Interesting Sailboats

ORCI world championship is still an amateur championship, but among the amateur races it starts to build a solid reputation. Mostly raced by performance cruisers, it was hosted last year in Croatia and this year will be raced in Finland, in August. There are already 120 entries and the number is certainly going to rise.

Entries » Audi ORC International World Championship 2012

Some great images of last year championship:

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  #2123  
Old 03-18-2012
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On dynamic stability

On another thread about boat keels, comparing Fin keels with long keels I have made some comments that I will post here as an introduction of a post about my thoughts on boat stability:

So, taken from another thread and regarding dynamic stability: Fin keel versus fin keel:

Are you familiar with the term "tripping on the keel"?






(Regarding to what Tony Marchaj says on “Seawortiness the forgoten factor”) there are 30 years of sailboat design between that book and today and 30 years where mathematical computing models of boats and hydrodynamics and tank testing have assumed a main role to understand dynamic stability and the way a boat reacts with the sea.

But more than what those studies have shown I would say that more was learned with the pragmatical work of many Naval Architects and many thousands of designs and the assessment that was made of those designs mostly by racers, that in some cases were also the designers.

Regarding waves, breaking waves are the only real danger for a monohull and you don't find them only near shore. With a formed sea with big waves and over 35K winds the top of the waves break and if the wave is big, the top of the wave are many tons of water. On that drawing is that what is happening: it is not all the wave that is breaking (like in a beach) but just the top.

By any mean I want to say that full keels are dangerous, just showing that they have also some disadvantages in what regards seaworthiness and namely in what regards dynamic stability.



Those drawings are pages of a book written by one of the biggest sailors of all times, Eric Tabarly. He was not a theorist but you can be sure he knows what he was talking about. He raced what was then modern boats (transats, circumnavigations) and him and the guys that were behind the designs he sailed had an important role in the development of today's modern hull shapes, rudders and keels.

And I am saying that he knows about what he is talking about because he did not only sailed extensively racing boats but also its family boat (that he loved) the Pen Duick, an old and beautiful old full keeler.




Well, as Leonard da Vinci once said: "Experience is the mother of all Knowledge" and Marchaj had some but not much in what regards sailing.

On other hand, experience, with full keelers and fin keelers was a thing that Eric Tabarly had in huge amounts: “A former officer in the French navy who is often considered the father of French yachting”.


Marchaj made a notable theorist work trying to explain reality (based on 35 year old sailing boats) trough equations and mathematical calculations but let me tell you that even if static stability is a simple and forward thing, dynamic stability is a very complicated subject (the interaction of a variable sea motion with a boat and its effects on boat stability) and even today with all tank testing and mathematical computer aided models it is far from being a settled matter.

But if the science is still messing around with dynamic stability Naval Architects have been working on the model of the best boat to fast and safely cross oceans. Probably nothing as contributed as much to the knowledge of dynamic stability than the 35 years of designing small boats to solo crossing oceans, what is called the Mini class racing:


Classe]Classe Mini Mini

What was learned with these boats influenced bigger sailing boats, racing and cruising, in an extent that can be considered probably as the biggest influence on modern yacht design, and what was learned had all to do with dynamic stability.


....

Last edited by PCP; 10-10-2013 at 06:19 AM.
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  #2124  
Old 03-18-2012
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Re: Interesting Sailboats

A break here, to report that Abu Dhabi is back in Port with a bulkhead that pop out of place in big waves and lot's of wind. The fleet is heading to huge seas and upwind 40k of wind so they decide to enter for a quick repair.

Volvo Ocean Race 2011-2012 | Abu Dhabi safely back in Auckland to carry out repairs



Sanya managed to be first out of Port but some hours later is Camper that is leading with a short lead over Puma while Telefonica is playing another game.

Things are going to be hot on the next days.

Volvo Ocean Race 2011-2012 | Race Data Center

Last edited by PCP; 03-18-2012 at 02:49 PM.
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  #2125  
Old 03-19-2012
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Re: Interesting Sailboats

Back to boat stability:

Ten years ago I had already an interest in boat design and particularly in boat stability and seaworthiness. I had read already a lot about stability and had left behind the nonsense of the capsize ratio and had a good understanding of the static stability. Had already seen a lot of GZ curves (arm length curve) and understood the importance of weight on the RM curve ( you obtain a RM curve multiplying each point of the GZ curve by the boat displacement).

The area behind the positive part of the GZ curve represents the energy needed to capsize a boat and because you obtain the RM curve multiplying the GZ curve by the boat displacement, weight is an important factor in static stability.

I was trying to find some answers about that here, a lot of years ago:

How heavy is too heavy II ?

At that time I was asking myself what the right weight should an offshore boat have and made a lot of comparisons with the RM stability curve of the boat I had with stability curves of boats that I would like to have (bigger boats) to establish a minimum AVS and a minimum RM area, regarding what I wanted for my next boat.





And then my attention was focused in two facts:

1 - The OVNI 43 (and 435) had a lousy static stability curve with a relatively low AVS but it was justly considered as one of the best offshore and voyage boat, a seaworthy boat that sailed everywhere without any problem.

That was the boat that Jimmy Cornell had chosen for himself after several circumnavigations in heavy boats, and a boat that deserved from him the biggest praises in what regards seaworthiness: A light aluminum centerboarder, the type of boat he still consider as ideal for offshore voyaging and circumnavigation.

2 - Add the minis, an incredible small and light boat (26ft and about 1T) obviously with a small RM curve (big GZ curve but small RM curve because the boat is very light), a boat that needs a small amount of energy to be capsized and that had crossed the Atlantic racing , year after year, sometimes with bad weather, in huge number (each race has about 70 boats), without any significant problem. One of them has even circumnavigated non-stop.

So, there is something wrong with basing the stability and the seaworthiness in what regards stability only on the Static stability.

Obviously the Dynamic stability counts for much in the capacity a boat has to resist capsizing and contrary to a very popular opinion I don’t think it has nothing to do with the roll moment of inertia, or the boat mass. If it had, the Miniclass racers or the light OVNI (with little inertia) would be boats that would be easily capsized.

It has all to do with the way a boat dissipates the energy of a breaking wave:

if the boat transform all that energy in a rolling movement (tripping on the keel) the chances are that the boat will capsize. If the boat can dissipate the energy of the wave in a kinetic movement (sliding laterally) the chances are that the boat can resist capsizing.

A heavy boat needs objectively much more energy to be capsized but if most of the wave energy is transformed in a rolling movement tank testing shows that it does not matter much. Any breaking wave over 1/3 of the LOA of the boat can capsize it (no matter the weight) if the boat does not transform the wave energy in kinetic movement.
The energy of a breaking wave is so big that to have a bit more or a bit less RM does not matter much.

So, in what regards dynamic stability what counts most is all that facilitates the dissipation of the wave energy trough kinetic movement (instead of a rolling movement):

Low mass, small underwater appendices (keel and rudder), low freeboard, beam and of course a proportionally high RM (that will not be big in absolute value because the boat has a low mass).

As you probably have already noticed this description suits well in a Mini class racer, or a 40class racer or in an Open 60, that are boats whose hull shape has been developed for transatlantic and circumnavigation solo racing, where ease of use and stability are paramount.

And because NAs are not stupid this tendency is also a marked tendency on modern cruising boats, I mean small appendices, low mass and beam even if low freeboard is hard to get giving the needs of interior space.

Dynamic stability is very important but that does not mean that Static stability is meaningless. I would say that there are still some very important points to consider:

The RM force the boat is making to right itself up at 90ş is probably the most important, others are the AVS point, the downflooding point and the proportion between the positive and negative part of the curve.

The Max RM is also important but that is not an absolute value and it is proportional to the weight of the boat and the sail area it needs to sail. I would say that a GZ max value gives a better picture here, becuase it is a comparable value with boats with diferent mass, if the LOA is not very different.

However Static stability it is not definitively the only thing to look at when considering the implications of stability on boat seaworthiness even if it is a lot more meaningful than the old capsize ratio.

These are basically my thoughts about boat stability. I am sure that I know more than some years back, but probably I will know more in the future, so please don't consider this as a finnished subject.

It is not closed for me and even less for the ones that know more than me and that design sailingboats. Regarding those, you can bet they will use what they know for building better and faster boats, so you have just to look at what they are doing, especially in what concerns offshore racing where stability is not only fundamental to safety but also to carry more sail and to have faster boats.

With time that knowledge will be used to make better, faster and safer cruising sailboats.


....
nemier, mitiempo, daviid and 2 others like this.

Last edited by PCP; 03-19-2012 at 03:42 PM.
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  #2126  
Old 03-19-2012
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Re: Interesting Sailboats

Quote:
Take a look at a different boat, a wooden and a popular one. Ok it has epoxy on the marine plywood but it is still basically a wooden boat.
LOL. "Wooden boat", to me, as a concept, has wooden timbers and a planked hull. Plywood is made with wood, but the concept is really that of composites.
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  #2127  
Old 03-19-2012
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Re: Interesting Sailboats

Well it is not a fiberglass boat and is made of wood or plywood if you want.

Not many boats are built like that and RM is the only boat builder with a significant production that make the boats that way. Lots of smaller French boat builders use plywood but mostly for smaller sailing boats.

Another nice image:



Regards

Paulo

Last edited by PCP; 03-19-2012 at 10:23 PM.
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  #2128  
Old 03-19-2012
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Re: Interesting Sailboats

I have said that things in the VOR promised to be interesting. Well, look at this:


Strong gale force winds in excess of 45 knots have joined forces with six metre waves in a gang-attack against the fleet that has left sailors and boats reeling in pain.

But the fleet has remained defiant said CAMPER skipper Chris Nicholson who is amazed by the punishment the Volvo Open 70s are enduring.
...
Nicholson admitted some surprise to have survived the battering unscathed up to this point. “So far we haven’t broken anything which is almost surprising given how hard we have been coming off these waves,” he said.

“When we get 45 knots, above 35 knots, we are slowing the boat down a bit to get through it. It should stay at 25 to 30 knots (of wind) tonight and then slowly ease back into the low twenties. So we have to just get through tonight with everything in one piece.”

Despite the tough conditions Nicholson said the CAMPER crew had made few concessions and were pushing hard whenever possible despite the almost impossible environment on deck.
..
(On deck) you can’t stand up. If you move anywhere you are crawling around on your hands and knees clipped on. Every little job that we take for granted normally is now a bit of a procedure.

“Everything has a high level of difficulty with it. Just to go over to the leeward side of the boat to ease a sheet the driver has to ease up a little bit otherwise that person gets washed down the deck.”


Volvo Ocean Race 2011-2012 | Defiant fleet on their knees, but battling on




Back on the race Telefonica due to that brilliant move (I confess that it did only seem odd to me at the time) is leading, Camper is following, Groupama is recovering and overtake Puma and they are all pushing hard.

The ice limit was moved up and that is a pity because the big downwind winds are now off limits

Volvo Ocean Race 2011-2012 | Race Data Center

Last edited by PCP; 01-13-2014 at 06:24 AM.
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  #2129  
Old 03-20-2012
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Re: Interesting Sailboats

This one goes to the category: What the hell are they doing?



And this one to the category :



and this one to the category: Nice boats, nice sailing


Last edited by PCP; 03-20-2012 at 01:12 PM.
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Old 03-20-2012
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Re: Interesting Sailboats

The ones that find that some of the sailboats I post here looks like spaceships will be right regarding this one. This one does not like to a sailboat at all and probably that has to do with being designed by aerospace engineers.

Take a look:














Even the name seems more appropriated for a fighter jet than to a sail boat: V-44 Albatros

They say about the "boat":

v-44 Albatross has ‘three axis control’ similar to a conventional fixed wing aircraft. At high speed, the boat is effectively flown at very low altitude using active control in all three axis.

The three axis are:

1. yaw from foot rudder pedals controlling the rudder;
2. roll from control stick left / right movement, similar to ailerons on conventional aircraft. The aerodynamic design enables roll control without lift cross coupling;
3. height above surface from control stick fore / aft movement controlling overall lift / power of wing-sails.

There is no other sailing boat which has this degree of active control. The benefit of this approach is to give prolonged periods of the hulls remaining completely free from the surface of water, minimising a major drag component.

The boat can sail on both port and starboard tack; the wing-sails and keels roll through 90 degrees as the v-44 turns through the wind.

The maximum speed of the boat is the cavitation speed of the keel. This is maximized by using a cambered keel section and transposing between two keels as the boat tacks.

The skipper is able to actively maintain a boat speed just under the cavitation speed of the keel across a range of sailing conditions.

Max velocity: 70K


...
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