Team Lalou's new Multi 50 trimaran

Hi Doug, please have a look at www.madership.com (more coming soon). You will find a CFD pic showing a hull in a hydrofield. There is lift in 1/3 from bow (cwl) and at the stern - at the end of the hollow section. If you like, take a spoon in a water flow. You will find suction at the convex side and lift at the concave.
If you are interested, I will show you more tomorrow - it is now ten past midnight. Regards Manfred

 

Thanks, Manfred-I'm interested in any information on the hollow theory. I clicked on the link but didn't see anything-it was in German so I may have missd something.

 

Hope, I can do it with my poor English. Hollows are not new. Aeroplane wings have them and boats - for instance Atkin motor boats - following the law of Bernoulli.

On the first pic you can see a model of a 27m Motoryacht. When you look at the bottom you can see the hollow section in the last 1/3. It is only a "slight" hollow or dimple (german: Delle).

I was lucky to watch tanktesting (of madership.com) over some days at Duisburg University years ago on Christmas, when nobody needed the tank. The model performed extraordinary well, no stern suction, small stern wave, even run and so on.

The second pic shows the CFD result (same hull, same University). You can see the lift from the first 1/3, then the suction area (convex part of the hull) and at the last 1/3 (concave) the dynamic lift (Dynamisch erzeugter Auftrieb).

The problem is to have the right balance/distribution of pressure on the whole hull. If the distribution of lift and suction is well balanced there are a lot of benefits from more speed with less power to more stability (plus no yawing, rolling etc) in waves.

It took a long time and a lot of tests to develop the final hull, which performed well from fn 0.4 (displacing) up to fn 1.2 (planing) at high Reynolds numbers.

 

Thank you, Manfred. Seems like testing would be real important with such a design where the characteristics are different for every hull?

 

The man behind madership.com got it patented and has developed a formula for different hulls. First he was successful with his sailboats ( f.i. "Zoom 900") and Motorboats. Now he is concentrating on RoRo Ships.

But the central idea is well spread. Surely you have heard of "Kiribati Dimple" ? http://harmenhielkema.blogspot.de/2009/04/hull-asymmetry.html

 

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No, never heard of it under that name. Are you suggesting the hollow in the new tri is similar to the "Kiribati dimple"? I have heard the same story about the aerodynamic mods in a different context: it has been explained to me that that is why you sometimes see a recess(dimple?) in way of the attachment of a fin keel.

 

Hmmmm?

 

In his blogspot Harmen Hielkema:

Doug, I think you are right. There might be similar aspects.

 

Don`t know the intentions of the designer. Seems to me as a retractable stern wedge to avoid stern suction to get an even run at high speed. The ILLBRUCK (John Kostecki) was clocked with nearly fourty knots: http://www.speedsailing.de/DE/_schiffe/illbruck.php
Hmmmmm?

 

Is the use of the flap similar to the use of a trim tab on power boats.

I understand several open 60's had the flap under the transom.

 

It seems to be so. Trim tabs, wedges, retractable wedges or bulb bows, fins and so on in my opinion (as far as an amateur like me is able to judge about this) are substitute for a design that is not sufficient. If a boat does not deliver the demanded characteristics they shall improve the design.

The problem is, that tank tests are extremely expensive. If tank tests are possible mostly only the choosen design is tested, not an alternative with different charactersitics or dimensions. CFD or CAD alone often are not sufficient.

Madership were lucky to get financial support for extensive tests in Hamburg and Berlin.
The result was to be heard and raed with lectures like this:

Experimental research into the dynamic stability of maderform hulls in different sea conditions

Dr. ...., .... ,..... GmbH, Duisburg

The presentation focuses on five hulls of vastly different dimensions and displacements that have been tank tested in a wave simulator. The results confirm that maderform hulls show very small rolling and pitching movements even while sailing in critical sea states (wavelength of 1.0 - 1.5 LWL) - in both head and rear longitudinal seas. These hulls which are based on the principles of the flying wing are self-stabilizing in longitudinal as well as in lateral direction when sailing in longitudinal seas by the force of the water flow around them. The shape of the hull causes a continuous direct flow at the stern which in turn prevents rear slamming and all its undesirable consequences such as the surfacing of propeller or rudder. maderform hulls distinguish themselves by their exceptionally high yaw stability - which in concordance with their aforementioned qualities enables them to sail directionally stable even in rear seas. The tests prove that it is possible to design hulls in such a way that they - by themselves - show all the qualities usually obtained through the use of auxiliary devices such as anti-rolling tanks or stabilizing fins - but without the detrimental effects of said devices.



In the test series a typical RORO with bulbbow was tested under the same conditions and it capsiced.

 

Team Lalou's new Multi50 "Arkema" came in second overall behind the recently revamped Maitre Jacques in the Multi50 class in the recent Grand Prix Guyader. A pretty impressive debut with strong competition.

A video has been put up which features an interview with Lalou and includes some shots of the multis in action at the event. Sailing segment starts at about 4.00 in the video.

http://www.tebeotv.fr/emission/jt.html

 

^^^

I'm very happy to see that Lalou has both a new sponsor and sharp new trimaran!
It has been a year or so since I was following the 50's closely, but Lalou's previous boat was put together from affordable bits and never the most competitive. His 3rd place with that boat among the Multihulls in the Route du Rhum (and he was also leading Lemonchoix for a while if I recall) owed something to the problems which beset the three 50's favorites.
I knew Lalou back in the days when he was the boat captain on Lege Cap Ferret, am quite amazed to see him soldiering on. And I wish him luck!

 

Lalou, Fabienne and the whole team involved with the project are a great bunch of people I'm pleased to see them rewarded for their efforts through the build with a competitive Multi 50. Lalou mentioned in one of the interviews that the sail wardrobe was still not complete so on certain angles they are at a disadvantage. The sails are on order they just were not ready for the recent racing as they tune up the boat it should become even more competitive.

 

The latest Seahorse magazine features an article on this new Multi50 trimaran design.