Design of 16' foot beach catamaran

"As patzefran mentioned - I think in many cases negative rocker is used because it's trendy nowadays. But to perform some numerical test would a doublebody configuration be okay to just have a look at the pressure distribution around the hull to check which design is better or would you suggest to use free surface simulation including dynamic trim and sinkage? When I know about the pressure around the hull - how can I continue to optimise my design to find the right position and depth of the rocker. Should I just test some different variations to see which is best or can I get some keys from the results to know about in which direction I have to go?"
The most successful I`ve read last time about hollow lines is from Dr. Paul Mader (maderform): Segeljolle ZOOM 585 mit maderform Rumpfkonzept | SegelReporter http://segelreporter.com/pressemitteilungen/segeljolle-zoom-585-mit-maderform-rumpfkonzept/. The pics: Segeljolle ZOOM 585 – Fotos vom maderform Rumpfkonzept | SegelReporter http://segelreporter.com/pressemitteilungen/segeljolle-zoom-585-fotos-vom-maderform-rumpfkonzept/
I `ve been lucky to watch some tests at Duisburg University testank in 1993 and took some fotos.





You will find more about the designs of Dr. Paul Mader in "Jahrbuch der Schiffbautechnischen Gesellschaft". If I remember correct there are two articles. Dr. Mader claims that he will need at least 200 pages to describe his hulls fully.

 

Wow this is realy interesting ... can you please tell me in which edition of the STG yearbook this was published?

 

Nico, I've been around the F16 world for as long as its been around, they are designed with lots of parameters that are a bit wide specification to really get an ideal shape, principally the weight of the crew ranges from about 70kgs to nearly 180kgs, that's a big difference in flotation and hull size values. Certainly the early designs had too little buoyancy and designs such as the Blade were superseded by the Stealth and Viper pretty quickly. Also negative rocker has long been forgotten as it makes the short boats almost impossible to tack at low speed and sluggish to say the least on general handling.

Where they are now is probably the Nacra F16 which has a relatively flat stern section but is a big boat on F16 standards. The one thing that seems a must though with these big flat hulls which seem to just skim over the water, is long high aspect dagger boards and large deep rudders.

The hulls you can build at home quite easy using various methods but the daggerboards are a bit more difficult as if you don't get them just right, they can make the boat a dog or break.

What I'm trying to say is design the boat for easy construction that has more normal dagger boards. Doing it this way the weight comes down and the costs reduced significantly for not much of a slower boat. Perhaps find yourself a copy of the Blade F16 plans and put a bit of width in it at the bottom and you wouldn't be far off a pretty good boat.

 

1. Experimentelle Untersuchungen zur dynamischen Stabilität von maderform Rümpfen im Seegang
   Dr. Paul Mader, Mader HYCOM GmbH, Duisburg
   (Sprechtag "Seeverhalten von Schiffen" - 27. September 2012)
   Band 106, Seite 42
2. Widerstands- und Seegangsverhalten von alternativen Liniendesigns - ein Untersuchungsbericht
   P. Mader
   Band 99, Seite 162, 2005

Experimental research into the dynamic stability of maderform hulls in different sea conditions
Dr. Paul Mader, Mader HYCOM 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.


Experimentelle Untersuchungen zur dynamischen Stabilität von maderform Rümpfen im Seegang
Dr. Paul Mader, Mader HYCOM GmbH, Duisburg

Insgesamt sind fünf in den Hauptabmessungen und der Verdrängung sehr unterschiedliche Rümpfe im Seegang untersucht worden. Die Ergebnisse belegen, dass gerade in den kritischen Wellen (Länge der Welle 1,0 bis 1, 5*LWL) sehr schwache Roll- und Stampfbewegungen in längslaufenden Wellen sowohl bei der Fahrt gegenan als in achterlicher See auftreten. Die auf dem Nurflügelprinzip beruhenden Rumpfformen stabilisieren sich im längslaufendem Seegang durch die bei der Umströmung auftretenden Kräfte, sowohl in Längs- als auch Querrichtung selbst. Eine durch die Rumpfform bedingte permanente Anströmung des Hecks verhindert Heckslamming und damit dessen unangenehme Folgen, wie Austauchen von Schraube und Ruder. Die Rümpfe zeichnen sich durch eine sehr hohe Gierstabilität aus, welche in Verbindung mit der vorgenannten Eigenschaft eine richtungsstabile Fahrt in achterlicher See möglich macht. Die Versuche belegen die Möglichkeit Schiffsrümpfe so zu konstruieren, dass sie die Aufgaben der bekannten Hilfseinrichtungen wie Antirolltanks und Stabilisierungsflossen ohne deren Nachteile übernehmen.

Faster than TORNADO

 

Does this also permit good inherent tacking performance w/o LAR keels or daggerboards?

edit: of course the resistance only appears at some fwd speed.
umm, may be yaw resistance = slow to tack

 

As I´ve not sailed a maderform SAIL design I had to read all the tests I could get of his boats (Zoom 495, 585, 605, 805, 919). They are all monohulls.
There are no complaints about tacking abilities. All competitions they have been involved were won by them.

 

Thanks for the video
the really flat aft section would appear to generate too much skin friction but maybe the pronounced waisting triggers/prolongs air ingestion.
Interesting.
Could be overthinking this. Shifting displacement from the center line to sides of the hull would stiffen the boat up.

 

Sorry, UpOnStands, it is not easy for me to tell you in English what happens with a "maderform" hull moving through the surface of water. The resistance of this hull is remarkably lower than all other hulls of the same lenght and beam. To understand this you need the physical law of Bernoulli and the "Impulssatz" of Newton (conservation of momentum ). Maderform hulls deliver minimal waves in a flow, hydrodynamical lift which raise the hulls and reduce wave and skin friction resistance. Please have a look at the last pic of my posting 16. The red area on the last third part (red colour) of the hull is an area of high lift which reduces skin friction remarkably. Maderform hulls are patented. I add a CFD sheet of a "normal" convex hull for you to compare the areas of lift and suction.



A simple sketch may show the difference of a displacement, a planing and a maderform hull.



Other designers have tried the same configuration:





Two times accelleration and slow down of waterflow to get lift:

 

You are right, it seems an extremely complex interaction.
One point, the English abstract of Dr. Maders paper (Experimentelle Untersuchungen zur dynamischen Stabilität von maderform Rümpfen im Seegang : 27.09.2012 Seeverhalten von Schiffen : Sprechtage : Archiv : STG-Veranstaltungen : Schiffbautechnische Gesellschaft e.V. : Experimentelle Untersuchungen zur dynamischen Stabilität von maderform Rümpfen im Seegang : 27.09.2012 Seeverhalten von Schiffen : Sprechtage : Archiv : STG-Veranstaltungen : Schiffbautechnische Gesellschaft e https://www.stg-online.org/veranstaltungen/Sprechtag_Seeverhalten_von_Schiffen_/1340266550.html)
makes no mention of reduced resistance. Yaw stability is emphasized (dynamic stability in the title) but nothing on resistance.

 

First try to sell, what sells best. And then read this: Posting 19
2.) Widerstands- und Seegangsverhalten von alternativen Liniendesigns - ein Untersuchungsbericht
P. Mader
Band 99, Seite 162, 2005

Widerstand = resistance

 

Nico, found a description that might help you: https://www.segeln-magazin.de/sites/default/files/boats/brochures/00000212.pdf

 

sorry but do you have a link?
tried searching for it but found nothing

 

Yes, it is not so easy to find anything about maderform. Dr. Mader had a wharf and gave lectures (university) but did not like discussions with people who did not understand Bernoulli, Newton and modern hydrodynamics. Therefore not much is left.

May be you can find this:
But you can not get access. It is only for members, especially academic.

I have found an article of german "YACHT" from January 1988 which is very informative because it was written by Dr. Burkhard Müller-Graf who has conducted the tank tests in Berlin. May be you can find what you are looking for. If you have further questions - don`t hesitate to ask. I will try to help - as far as I am able to.

 

Many thanks, will have to spend some time with the article but the first thing that strikes me is that the resistance curves cross at 10 knots.

 

Very interesting, the Mader hull design could possibly explain why both my sit on kayaks have this feature at both ends of the hull to reduce yaw as well as offer a lower pitching moment. Not suitable for a beach cat though as you need a hull that can offer dynamic lift as speeds increase, just like the F16 does. I guess it's down to what performance envelope you are designing for?

Here in the western approaches in the UK most of the summer consists of sea breezes and light airs, in the autumn it tends to Be very mixed but generally windy and in the winter we just leave well alone as the sea states are often dangerous. My old Hurricane 5.9 was great in most conditions, but compared to a modern cat it probably would lack that extra performance jump while blasting off wind with the kite up.