Centerboard/Daggerboard Size Help?

[fishmonger]

I have read that a centerboard or daggerboard needs to be 4% of sail area.

Does this matter regardless of angle of heel--or in other words, does 4% of the sail area (board) need to be immersed at all times?

If I only need 4% total, then why do so many boats have such large centerboards/daggerboards in relation to their sail area?

Background: I'm almost finished with the hull of my 12' sailing skiff. The design is supposed to use a leeboard. . . but they are just so ugly I decided to change to a daggerboard or a centerboard. A daggerboard will take up the least space, but if I really only need 4% of the sail area, then I could easily get away with a tiny centerboard (I only have approx. 70 sq. ft. of sail). But if I need to have 4% immersed at all times, then I'm going to have to stick with a daggerboard so I don't loose all my internal space. Any help would be appreciated. I got wonderful answers from my last post months ago. Thanks!

[tspeer]

There are lots of other deisgn options that have the advantages of your leeboards without being ugly. For one, you could build in twin daggerboard boxes just inside the topsides - think of them as leeboards that are just inside the skin instead of being just outside the skin.

Another time-honored solution is bilge boards. These are twin boxes, just like centerboard boxes, but are built into the sides of the cockpit. Here is a picture of an M-16 scow. The bilgeboard slots can be seen each side of the forward cockpit and the handle of board is visible in the picture.
Notice how the bilgeboards open up the cockpit - there is no obstruction.

The boards are canted out 15 degrees to match the heel of the boat when going to windward


Structurally, the boards form a shear web that strengthens the boat, and the trunk, side deck, and bottom form a closed tube that is very stiff in torsion.

You can also locate bilge boards along the inside face of the seat on a dinghy, forming an unrestricted footwell.

Like a leeboard, only the leeward bilge board is used at a time. You put the windward board down just before tacking, perform the tack with twice the board area which helps to prevent stalling, and then retract the new windward board after the crew gets the jib sheeted in and comes to the high side to hike.

[duluthboats]

[Raggi_Thor]

Remember that the lift from a foil grows with the square of the speed. So if you double the boat speed, you can have 1/4 the area, theorethically.

[mackid068]

Stick with the leeboard, it's unique!

[Andy P]

The optimist ( ~ 4m² sail area ) has a larger area daggerboard than a B14 ( ~ 16m² sail area )
The difference comes from the short hull, low speed of oppie vs longer, higher speed B14.
But the B14 board area is a bit on the small side - it's not so good in very light winds, and you have to be careful not to stall it after tacking etc.

[fishmonger]

2 mini pivoting bilgeboards on either side of the seat! I'll get enough area, the middle of the boat will be left open, it will be unique, and I won't have to worry as much about rocks!

Now how big do I have to make the 2 bilge boards?

Thanks everyone for your help!