Bridgedeck centreboard why don't they work???

False. the apex begins just after the bow, it's a sine qua non requisite for an efficient Dart shape. Look at a Dart pic...
An apex does not need to be thick, it's a plate separating the flows. It doesn't need to be deep, just enough to get the vortex well aligned. The small angle is a absolute requisite.
It works by generating vortexes not laminar lift and downwind it's a stabilizer plate.
The total volume can be very low. The "big" radiuses are the consequence of the mode of fabrication in one piece with the hulls in molds, not an hydrodynamic necessity. A good archi can use this building necessity for damping the horse hobbying.
The is no problem to place the CP at its place, to get a good block coefficient, a good prismatic coefficient and to obtain the good Bonjean curves for nice extremities which give good damping qualities. Ie a boat that does not bury its bow nor its stern and doesn't not balance on a perturbation like a 1965 Cadillac with worn shock absorbers.

Look with attention at the SL 16 pics post #373 page 25. A lot of information, learn to detail a pic. The cat is good enough to be an international serie. Daggerboards are part of the SOR of an Extreme 40 which is not a cruising boat nor a simple beach cat. Read my post about the good use of a Dart shape, you take a solution after making a serious SOR, so the same NA can use different solutions for different boats and that doesn't mean that one is intrinsically inferior or superior to the other, simply it's more adapted for the goals. There is not universal solution written in the Naval Architecture for Dummies book.
To update about Loday (who I know and appreciate) http://www.sirena-voile.com/v3/en/sirena-voile/yves-loday-architecte.html, If you have better credentials in the same domain...He knows his job.

 

Thank you for explaining why Dazcat used to make dart/delta keels but no longer does. Showing a two man beachcat up on one hull is enough to convince any cruiser of their lack of appeal. http://www.boatdesign.net/forums/at...board-why-dont-they-work-sl16-catamaran-y.jpg

 

aren't that a cruiser's preferences ? Together with the advantages of the dart keels under light performance cruisers, especially sufficient performance , better than stub keels, .....
Why not ?




What compromise do we need, do we want ?
do we ever had the dart keel on our list ?


A small camper cruiser w. dart keels. Under the trailing edges of the keels one can mount wheels for easier beaching/trailering, or pulling up a strand. A clever boat.

http://www.google.de/search? http...VOKywKHagUDcUQ7AkIKA&biw=1024&bih=644#imgrc=_








pogo

 

please recheck your that. it now returns " Le document que vous cherchez n'existe pas." Seems as if the boat is no longer in production?

 

Sorry,
post 41.

http://www.boatdesign.net/forums/multihulls/my-folding-catamaran-41857-3.html

Or
http://www.google.de/search?q=twist...VOKywKHagUDcUQ7AkIKA&biw=1024&bih=644#imgrc=_



pogo

 

It's why I explained that the Dart apex is a solution of limited domain and very good on a cruising cat inside a precise SOR. It's the destiny of most technical solutions of a problem. All depends on what will be the use of the final product

I said that the dart solution was an elegant one to solve efficiently the problem created by suppressing the daggerboard while keeping good enough performances is a primordial requisite. The results were excellent and the Dart met all its goals, and was sold by thousands.

Other thousands of beach cats used the same solution with good results far from being ridiculous when racing with similar sized cats.
The Dart has never been intented to beat a Tornado, or to be the ultimate racer but in 1976 it appeared to be a very good sport catamaran for couples. The performances in the absolute were far of being ridiculous.

If you want to go very fast use daggerboards, extremely fast foils etc. If you want to go fast enough without an excruciating penalty because not using daggerboards for several reasons on a cruising cat, the dart solution is an interesting one. Same on a beach cat.

It's not an under apreciated underrated miracle solution drowned by the maffia of the boat builders and designers, it's simply because these people have to eat and thus must follow the trends of the market.
And one of the trends is the imitation of the racers, as we saw with the cruising monohulls made with the IOR hulls of the last One Half Cup 30 years ago. That eliminates automatically all the solutions that do not fit in that trend. Daggerboards are in the trend even when useless nuisances, dart keels are not in the trend even when useful.

 

DART KEELS ARE NOT IN THE TREND, EVEN WHEN USEFUL.

Thanks.
"In my stomach" i had this answer,
with other words , i felt these facts.

O.k. , a little background is useful...



Thanks .

pogo

 

"Showing a two man beachcat up on one hull is enough to convince any cruiser of their lack of appeal" ????? Please explain this cryptic sentence.

 

not a problem. hint, if you right click on the post number at the top right of the message frame (#41 in this case), you can copy the link location and then paste the link to that exact post in your message.

 

I appretiate it,
but,
i'm not a digitale native..
With other words, i 'm too old.
mea culpa

pogo

P.S.
English -- an additional problem .

 

if you want to convince people to buy or build something "different" it would help to have a reference boat that has the same SOR or close enough, and demonstrates the advantages offered. Cruisers intend to fly a hull? What would be your reference boat for cruisers with dart/delta keels?

 

Phhhh.
The above shown pretty heavy Benetau Blue II , a cruiser, is aible to run up to 18 knots. She's pointing high , biut has disadvantages in lighter airs ( bruce nr. and more wetted surface)
See the big Dazcat , a fast boat.
So what ?
I guess that you don' t accept any "cruising compromise", less draught, better grounding,....a.s.o., see above.
Of course, for a high performing boat ( your bot, your next boat ) daggerboards are the best solution.
i think that it it is necessary to realize that other skippers need other solutions, other, better, compromises.

For me, a Forum is for figuring out, for learning. for putting together individual knowledges...not for insisting on an own level.

c u

pogo

 

actually my preference is for LAR minikeels on 10.4 m open bridgedeck. But I could be convinced otherwise.
What did I say ? here http://www.boatdesign.net/forums/mu...d-why-dont-they-work-57051-26.html#post798875
"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." which pretty much agrees with your "disadvantaged in light airs"

 

Help me out here. The Dazcat shown here http://www.boatdesign.net/forums/mu...d-why-dont-they-work-57051-26.html#post798874 is a 1395 Dazcat built as kit. What is its draft? The only collateral info I can find is here https://equipmentsalesworld.com/dazcat-southern-ocean-47/ for a Dazcat Southern Ocean 47 (45ft 11" so 14m) they quote draft of 7 foot 3 inches. Something is wrong with this figure?
The Dazcat 1495 (14.75m) has published draft of 6 ft 3".
BAHIA 46 has draft of 4ft 3"
LEOPARD 45 draft 5ft but disp 32,000lb
edit: the video appears to show that the Dazcat 1395 has daggerboards.

 

I'm not sure what you mean by a "Dart " keel.
Would the LAR keel on a Crowther International 23 be one. ?
If so, it's a no brainer.
The one I had, "Silent Runner", slaughtered the whole fleet in the "Round the Island " trailer boat race in Melbourne 1979.