Bridgedeck centreboard why don't they work???

The father of the idea is Rodney March, and it's an excellent idea. This supremely elegant solution works pretty well on any size of catamaran, it has just to be adapted during the design stage. It's simple, rational, and has nothing to break. Surely the winner of the Occam Razor prize.
Like I said already if I want a no worries cruising catamaran with decent performances I take this solution, and I work hard on the displacement, sail plan, rigging and hardware which are the true factors of good performances on a cruising simple tech catamaran.

 

Just found this illustration I had forgotten about

 

Could not find anything in google for large catamarans with Dart skegs.
Do you have some links?

 

Dazcat.


People seem way to preoccupied with what is used for leeway control on catamarans.
Theres now heaps of data out there to peruse. From, Hobie asymmetric, to Dart keels, to early windrush canted rounded "V" and of course more conventional foils. They all work pretty darn well in the cruising environment. For most cruisers a couple of sailing lessons would improve their windward performance far more than a set of NACA high aspect daggerboards . Those that raced one design will understand this . Those that haven't will dive for the text books and want to argue.

 

All Dazcats now come with twin carbon daggerboards?
The one in your picture explains why. So much wetted surface area as the keels are very elliptical - slow unless a lot of sail is used. Probably excellent for offshore work in heavy seas and strong wind.

 

SLOW????

Compared to what?

Hardly a race boat with that amount of accomodation.

Do you actually sail/race or just hang out here and parrot what you read on the web.

 

latest Dazcats with daggerboards?
here is one not so recent, 1998 open bridgedeck

 

Shallow Draft, importance

Better post this before I loose it again....memory

 

Trailing Edge 'flaps'

I was thinking back about how the Hobie cats (with less efficient asymmetrical hull designs than the Prindle cats) use to compete with one another. Both types use to kick their spade rudder into a forward rake position and effectively utilize some of the generated force to reduce leeway.

Were they acting like 'flaps' in a aerodynamic or hydrodynamic sense? There have been a number of discussions come up under sailing aerodynamic discussions that suggest the importance that the trailing edges of the foils can have on the pointing abilities of the vessel,...in some cases labeled flaps.

And Chris White has added some hydrodynamic flaps to his mini keels I believe.

With this being the case can we make our cruising cat rudder foils a bit bigger and perhaps act like flaps for our CS hull shapes? Or how about utilizing skeg mounted rudders rather than spades. I've always favored skeg rudders for their extra protection afforded these very important steering devices.

 

doesn't this contradict your love of shallow draft lifting rudders?

 

Yes it does.

 

Brian,
Hobie 16 and 14 balanced rudders has nothing to do with flaps.
To switch lift force to the rudders (much more effective than the hulls to provide windward lift), They use big aft mast rake to generate strong weather helm (which mean the rudders need constant incidence to go straight line), so they need balanced rudders (forward rake) to manage the lift force on the rudder.

 

And does the life force on the rudder 'foils' do anything to help counteract leeway that the poorly designed asymmetrical hulls make?? Yes, according to a number of competitive sailors I use to sail with.

You see I partially agree with what you say about how those asymmetric hulls are sailed, but I also hear what a number of competitive sailors claim about the rudder foils assisting in making their windward performance better (less leeway). Being that these foils are located at the very stern of the vessel, I drew the analogy of utilizing flaps at the rear of airfoils. It was just an analogy.

 

Hobie sailors says exactly what I say (I used to sail Hobies !), the rudders takes most part of the lift needed to counter act the leeway.

 

flaps aft an aerodynamic profile ( for decent span/chord ratio ) modify the flowfield over the whole profile to increase lift. Rudders ( high span/chord ratio) behind a Hobie hull (very low span / chord ratio <<< 1) act very little on the flow and pressure along thes hulls. Wheatherhelm increase the lift on the rudders only, in fact they decrease the lift on the hulls because they decrease the angle of attack (leeway !)