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  #3951  
Old 04-17-2013
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Modern boat design and Computer Fluid Dynamics (CFD)

This is an old movie: in what regards to computers and programs 5 years is a long time. We can see here the importance of computer and tank testing in what regards evaluating (and modifying) a design to make it sail better regarding the conditions in what he is going to perform.

Here they are developing a offshore fast sailboat. This was made by students, not really professionals that I believe will have another debt in what regards hydrodynamic studies.


" a 12-m length, 4.5m beam mono-hull sailboat, ready for navigating storms and enjoying extreme sea conditions. A project carried out by members of D-Tank and Rücker Ibérica, in collaboration with the Elisava Superior School of Design"



and some more:









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Boreal shipyard

I have been posting a lot about Allures, not only because they have a new boat but because we can find on line great movies, boat tests and nice movies. We cannot find almost anything about the Boreal. The movies on line are very bad they don't offer the boat to magazines for testing they did not even post on the internet decent pictures.

The owner of the company thinks that is not needed and that they will sell boats to the ones that know what they want and trust in their quality. Maybe, but I don't believe they will grow that way and not growing will make their boats more expensive than the ones produced in bigger number due to scale economy. All this because Boreal posted a movie on line. not a great one, they could have hired a professional, does not include any images of the boats sailing, it is in French and has no sub titles but at least we can see how the boats are made and the seriousness of their approach.

Here it is:

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  #3953  
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Unhappy Re: Advanced keels

Quote:
Originally Posted by PCP View Post

I saw the keels on that study you mention and then went to the conclusions to see if there were some surprises, but no. What he found confirms what is common knowledge regarding keel performance and shape.
My conclusions from the three Chalmers investigations are:
The first conclusion is that maximum thickness of the bulb must be placed well back from maximum thickness of the fin. Otherwise an extended lowpressure area is generated on the suction side (with contributions from both the bulb and the fin) that causes flow separation. Loss of lift is obtained and a really bad keel from the hydrodynamic point of view is obtained. Two T-keel designs were investigated, one with coinciding maximum thicknesses of the bulb and fin and one with maximum bulb thickness behind the rear end of the fin. The results clearly showed that the second one was best.

The second conclusion is the a flat bottom with sharp edges (chines) of the bulb is not a competitive design. A optimization was peformed where the shape of the bulb was allowed to vary from flat bottom (with sharp edges) to rounded. Rounded showed higher performance.

The Chalmers investigations were performed about 2 years ago, the results are public and should be known by serious designers (especially as Lars Larsson was the supervisor). Fixed keel design for recent custom yachts do not show an impact of this and my personal conclusion is that keel design is an ad hoc thing.
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Re: Advanced keels

Quote:
Originally Posted by Anders B View Post
My conclusions from the three Chalmers investigations are:
The first conclusion is that maximum thickness of the bulb must be placed well back from maximum thickness of the fin. Otherwise an extended lowpressure area is generated on the suction side (with contributions from both the bulb and the fin) that causes flow separation. Loss of lift is obtained and a really bad keel from the hydrodynamic point of view is obtained. Two T-keel designs were investigated, one with coinciding maximum thicknesses of the bulb and fin and one with maximum bulb thickness behind the rear end of the fin. The results clearly showed that the second one was best.

The second conclusion is the a flat bottom with sharp edges (chines) of the bulb is not a competitive design. A optimization was peformed where the shape of the bulb was allowed to vary from flat bottom (with sharp edges) to rounded. Rounded showed higher performance.

The Chalmers investigations were performed about 2 years ago, the results are public and should be known by serious designers (especially as Lars Larsson was the supervisor). Fixed keel design for recent custom yachts do not show an impact of this and my personal conclusion is that keel design is an ad hoc thing.
I am not sure If I understand what you want to say. There were 4 keels on that study :



and the conclusions are:



As can be seen in the graph, of the bulb keels, keel 4 has lowest drag at zero angle of attack. It increases faster than keel 3, which means that at 4° angle of attack keel 3 and 4 have equally large drag forces. Keel 1 was as expected best performing, but it was only evaluated as reference.

Figure 50 describes the most important behaviour and performance of the keels: the relationship between lift and drag forces. From the graph any given lift can be set, and a corresponding drag can be read. It can clearly be found that keel 4 is the better performing one of the bulb keels; especially at
small angles of attack. At larger angles of attack the trends from this curve, and more specifically from .. keel 3 is the best performing keel. This however only for very large angles of attack, for more reasonable angles of attack keel 4 is the best performing bulb keel. It is quite clear that keel 2 is inferior to the others at all lift coefficients measured.


On the evaluation of performance even if the differences are very small the results confirm the drag and lift conclusions. They have considered 16K of wind but I believe that if they had considered a much smaller wind speed the differences would be bigger.

As can be seen in Table 7 the results between the keels are very even. Keel 1 has no bulb and that makes it not comparable to the keels with bulbs. During the VPP keel 1 has only been used as a reference. Between the bulb keels, keel 4 is the winner; it has a higher velocity at all wind directions than both keel 2 and keel 3. The Keel with the worst performance is keel 2; but it is very close between the last two bulb keels.


The keels were also evaluated against each other on a race....
The times for completing the race are extremely similar. Keel 4 has the lowest lap time for the different true wind speeds. What’s most interesting is that at low true wind speeds keel 4 is even faster that keel 1.


http://publications.lib.chalmers.se/...ext/148387.pdf

Those are the conclusions of the study and those are common knowledge.

What he has done regarding CFD in the keels is what all NA, at least the ones that design race or performance sailboats do when they design the boats. They do that for the hull, for the keel and for the rudder(s).

Regards

Paulo
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Solaris 48

and after that rather technical stuff about keels, something much more beautiful, the Solaris 48 on a test by the Dutch magazine Zeilen.

I guess that with the exception of Eric, we all understand about the same regarding what the guy say about the boat but I am quite sure he is saying nice things and the images talk by themselves. It is a beautiful boat and that garage is just huge for a 48ft boat. I bet my dinghy fits there and I would like very much to have one of those on my boat.

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Re: Solaris 48

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Originally Posted by PCP View Post
and after that rather technical stuff about keels, something much more beautiful, the Solaris 48 on a test by the Dutch magazine Zeilen.

I guess that with the exception of Eric, we all understand about the same regarding what the guy say about the boat but I am quite sure he is saying nice things and the images talk by themselves. It is a beautiful boat and that garage is just huge for a 48ft boat. I bet my dinghy fits there and I would like very much to have one of those on my boat.

Beautiful boat, and imagine that: The NA is from Norwalk , CT...
Sadly we have no builders here commissioning these type of boats. I assume the market is larger in EU?!
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Bill Tripp

Italians love beautiful boats and contrary to Americans many rich guys prefer sailboats to motorboats. A sailboat gives more status, it has more class. Any doubt about that?

Regarding Bill Trip, the son of another great NA with the same name, he designs very beautiful boats and several European boat builders use their services and talent, among them Solaris.

I find absolutely disgraceful mass productio American sailboats like Hunter or Catalina being designed by minor NA while great American NA work for European brands. I believe that the bigger difference in quality between American mass produced sailboat and European ones has to do mainly because European brands have their boats designed by the best world NA while American ones are designed "in the house".

Some beautiful Bill Trip designed sailboats:

SY Sarissa - Vitters Shipyard from Vitters Shipyard on Vimeo.







Regards

Paulo
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Old 04-18-2013
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Aluwind 56





A beauty isn't it?. That is also a sad story. There was once an aluminum boat builder in Italy, Aluwind. They started with a bad idea, a Bill Dixon 44 old design, have it modified by Zerbinati and then when they commissioned this nice one to Zerbinati something went wrong, or the owner of the boat back off or they were making it without being already sold and went out of money, I don't know.... they bankrupted and a nice hull and cabin is for sell.

I have to say that the design of the interior they were proposing was quite ugly and that can have contributed to the disaster. If it is not already sold, there are a very nice hull, built by a firm specialized in aluminum boat building in Italy, probably at a very nice price ready to be finished.

Maybe that ends up to be somebody's luck

I like the classic style and the dimensions. You can see the dimensions and the real boat here:

NEW CLASSIC 56
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Old 04-18-2013
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Iy 10.98

The IY 10.98 (Italia yachts) is one of the 36ft that I like more. It is light, it is fast, it has a great cruising interior and a classical look. Well to be true the classical look is the thing I like less, I mean I like a classical touch but here it is too... uninspired? Anyway I am being picky. Personally I would take this one easily over the Dufour 36 performance (a very different boat).

If you want to see how this baby takes nasty weather have a look;



and have a better look here, I think you will be impressed (I was):



Some movies that give a pretty good idea how the boat sail in light weather and show an high quality interior and I mean really high:







and now have another look:






I guess they agree with me regarding the previous version being too uninspired because they changed it and this one is just perfect: What a beautiful boat, what a great boat!!!!!

You will be only able to understand my enthusiasm if you visit the boat and look at the quality of everything but you will be able to understand half of it if you look at the boat dimensions:



Get it?

ITALIA YACHTS » IY10.98 » Technical specifications

This is a Mauricio Cossutti design and can be made on two versions, one with a bigger draft, carbon mast and all that will make it a high performance racer in handicap racing (not losing its cruise ability) and other less pointed to racing, with a smaller draft and eventually a bigger water tankage.

Regarding performance at high level, the boat made 5th on the 2011 World ORCI championship (they claim first among standard boats) they didn't race on the 2012 (far away in Finland) and I am very curious about the performance on the 2013 World Championship that it will be in Italy, were several boats will race for sure.

A gem this one

...
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NM 38, the ORCI world Champion (B class)

And since we are talking about the IY 10.98, Mauricio Cossutti and this year ORCI world championship, he have to talk about the Champion on that size of boats, the NM 38 and surprise surprise, another Mauricio Cossuti design

The boats look very distinct but the hull is not very different even if the NM38 is more narrow and the IY 10.98 has a slightly bigger B/D ratio. This means that the NM38 is all about small drag and finesse...and it seems it works

I have already posted about it:

Quote:
Originally Posted by PCP View Post

New boat and nothing less than the actual Italian champion:

http://www.campionatoitalianoaltura2...triestewev.pdf

Another 38ft performance cruiser, an Italian one and as most of the Italian sailboats, a beauty: the NM 38.





















The boat looks great and those interiors seem very nice, especially the more modern (less wood) unfortunately they look a bit less impressive in reality:



They say about the boat:

The hull and deck are constructed under a vacuum, using female moulds and are made in PVC "sandwich" style with unidirectional and biaxial fibers glass and laminated with epoxy resin (with a lifetime guarantee against osmosis).

The carbon fibers used to reinforce the hull bottom gives a greater structural rigidity. Hull and deck are subjected to a post-treatment cycle for maximum performance of mechanical rigidity.

The structure grid is made of carbon and support the loads of the keel, mast and chain-plates, making the entire craft highly secure, even in extreme conditions.

Bulkheads are of marine plywood which are attached to the hull and fixed on the deck. The anti-collision bulkheads forward and aft are made with the same techniques like the hull and deck, so the stern and the bow of the boat are lighter and passing the wave is more comfortable.


It seems great. It is a pity that this boat has a mot very high D/B ratio, 0.309 for a 1.95m draft with a relativelly narrow hull. A crew seated on the side would not be indispensable but I bet this boat will reef rely soon without it and will have its performance noticeably handicapped. That and an interior a bit impersonal seem to me the only drawbacks for a boat that don't seem very expensive for its quality: 168 000€ without taxes.

About more 38 500€ more than the salona 38, but for having a boat with similar specs (vacuum infused and epoxy resins) the difference would be only 18 300€. However the Salona interiors seems a lot better to me.


Technical specifications
EC Certification: cat. A
Width overall: 11.40 mt
Length water line: 10.15 mt
Full beam: 3.58 mt
Draught: 1.97 / 2.30 mt
Displacement: 5.500 Kg
Ballast: 1.700 Kg
Berths: 2 / 3
Sail Area: 78 mq
Mainsail: 44 mq
Jib 105%: 34.5 mq
Spinnaker area (ORC): 100 mq




















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Last edited by PCP; 04-18-2013 at 09:13 PM.
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