Bridgedeck centreboard why don't they work???

Whale Fins, nature's answer

Let me throw a curve ball at you fellows.

A long time ago there were some discussions of the shapes that mother nature provided us. One such discussion referred to the shapes of the leading edges of whale fins.


Here just one reference I found real quick. I'm sure there are more.
http://newatlas.com/bumpy-whale-fins-set-to-spark-a-revolution-in-aerodynamics/9020/

What if our centerboards, daggerboards had some sort of scalloped leading edge :?: (maybe not as radical as this image)

.....a few more references....
https://www.technologyreview.com/s/409710/whale-inspired-wind-turbines/

https://www.scientificamerican.com/podcast/episode/005E4190-9DE4-32A2-015B43F0702189EA/

https://en.wikipedia.org/wiki/Tubercle_effect

 

I like it Brian. I like it a lot, and probably very tolerant of changes in angle.

I've seen this before, interesting concept, could be just the ticket, going to make fabrication interesting.
Im thinking you would not have to go further down than perhaps the top 1/3 - 1/2

 

Um, no. It would be easy to incorporate the rod as part of the nose foil section, think internal rod. Then it can be controlled from the top of the board. Same with the trailing edge one, you don't want gaps or levers that can hit waves.

 

I like it too Brian, an interesting thought, Natures fences?

 

Maybe they could help supercavitating foils but at those speeds I'd think smaller or a texture would be better.

I'll read more when I'm not trying to build a bike wheel.

 

well, there is difference in philosophy.
external - liable to damage but easy to maintain and repair
internal - relative protected but difficult to maintain/repair?

Would have to see how it would be implemented.

 

re the whale fins

more useful on the rudder as its a more direct analog of the whale fin -- would be a floating trash magnet of course
for the center board, may be switch to a high performance laminar flow foil and add the protuberances with ribblets to make the foil more resistant to stall?
So the foil is significantly thinner but not as sensitive to attack angles?

 

The issue with tubercles and fences is they will not really be compatible with one of the major benefits of a pivoting centreboard. IE they will serve to create drag and ventilation at all besides one pivot angle.

 

SNAP

Of course movable fences are exempt
probably more practical to design for 5% forward rake in normal operation condition to suppress ventilation, no fences-ribs whatever, and accept some loss at other settings.

 

I haven't caught right up on the thread yet

I did see you had a few ideas. I will take a look later

 

For goodness sake Guys. This whole thread has produced a whole mess of complicated ideas.
I would like to hark back to solving the problem of the Gordian Knot, where the whole message is that the most simple answer always turns out to be the best.

We are talking about a Cruising Catamaran, and a centrally positioned, pivotting and surface piercing board will be OK for that purpose, providing it is properly designed and supported.
I merely said (and I don't retract) that it would not be as efficient as a daggerboard or fixed fin. Admittedly pivotting centerboards, retractable daggers and fixed fins all have their own problems, but their efficiency as leeway resisting foils is better than a surface piercing board, as has been proven.

 

You have provided zero evidence for any of that. I believe the upwind performance will suffer compared to proper daggers but have no reason to believe it will be worse than lar keels. Since this is a cruising boat where upwind matters far less than downwind the lar keels will be much worse and the CB will not have slot drag. So for the overall SOR that we are actually talking it may well be more efficient, which is the whole point. And it has been proven (because I said so )

I agree fancy moving fences etc are probably an over complication.

 

It has not been proven by me,------but by many other much more qualified
sailing researchers than me.

 

More assertions, no evidence. Please provide some. Particularly compared to LAR keels. And keep it on topic to the SOR which is a cruising cat, not a racing cat where downwind speed matters more than small gains in upwind VMG. Remember the total SOR matters.

It has been proven by many other much more qualified sailing researchers than me that no slots or LAR keels is much more efficient downwind.

Also you asked me to explain my theory why higher aspect boards would work better. No comment on my answer? I took the effort to reply. Daiquiri later on said pretty much the same thing.