another daggerboard question

[mixmkr]

If you could have ANY shape, length, etc... of the daggerboard... ignoring class measurements... what would you change? Would a longer board help, or just add more drag? I'm even thinking about a goofy wing daggerboard, that you put in from the bottomside first. Obviously the wing would be drag going down wind and you couldn't pull it all the way up. Typically the wing is just for more ballast without the depth of the keel... but some are designed to add some lift, going to weather. And basically the daggarboard does minimal for righting moment and is more for sideways slipping.

I'll have to muck around in my spare time and see what gives. But I'd take some ideas first !!

 

[fhhuber]

Only thing I'd change (ignoring class) is to add weight.

How much is a good question though.

Basic idea is drill (or use a hole saw) to cut the opening for the lead and cast it in then file it smooth.

I took this to an extreme on a Vagabond 14 (just short of 20 ft tall mast was making the boat very "tippy" just trying to get in it) and replaced the bottom 9 inches of the daggerboard with appx 30 lbs of lead.
So far its working exactly as intended.

 

[sailcraftri]

A few years back I purchased an experimental daggerboard made by Mr. White (Sunfish Bible). It is a pivoting daggerboard with control lines to allow you to reduce draft in shallow water but not take the daggerboard out of the trunk. I refinished it but have not used it yet.

 

[odegaard]

If you could have ANY shape, length, etc... of the daggerboard... ignoring class measurements... what would you change? Would a longer board help, or just add more drag? I'm even thinking about a goofy wing daggerboard, that you put in from the bottomside first. Obviously the wing would be drag going down wind and you couldn't pull it all the way up. Typically the wing is just for more ballast without the depth of the keel... but some are designed to add some lift, going to weather. And basically the daggarboard does minimal for righting moment and is more for sideways slipping.

I'll have to muck around in my spare time and see what gives. But I'd take some ideas first !!

The problem with the all of the old woodie boards is that they are too small in area. Classic hydrodynamics recommend a certain ratio of sail area to appendages (brd. + rudder areas). When the Class (Larry Cochran- Ct.) re-designed the daggerboard to go f'glass, we lengthened the board to approach the proper ratio

If you could have ANY shape, length, etc... of the daggerboard... ignoring class measurements... what would you change? Would a longer board help, or just add more drag? I'm even thinking about a goofy wing daggerboard, that you put in from the bottomside first. Obviously the wing would be drag going down wind and you couldn't pull it all the way up. Typically the wing is just for more ballast without the depth of the keel... but some are designed to add some lift, going to weather. And basically the daggarboard does minimal for righting moment and is more for sideways slipping.

I'll have to muck around in my spare time and see what gives. But I'd take some ideas first !!

The old woodie daggerboards do not have enough area and result in leeway when going to weather. Classic hydrodynamics call for a req'd ratio between sail area and appendages. When the Class re-designed (thanks Larry Cochran) the board back in the '80's we added more length. We limited the length a bit so we would not have a grounding problem. Check out the newer f'glas board design--I would add even another 6" to length and stay with a tapered NACA cross section (like aircraft wing design).

 

[Webfoot1]

Might try killing two birds with one stone and add a Skeg or two. I'd be interested to see if this helps with the terrible directional stability problem in addition to beating upwind. Factory wooden dagger boards probably had the worst airfoil shape that could be created without just using a square plank. You could duct tape a couple Leeboards as an experiment and double the area without increasing the draft.

 

[L&VW]

Might try killing two birds with one stone and add a Skeg or two. I'd be interested to see if this helps with the terrible directional stability problem in addition to beating upwind.

Directional stability doesn't seem to be a problem for my Sunfish. I've fallen asleep a minute or two, and found myself headed in the exact same direction as intended.

Factory wooden dagger boards probably had the worst airfoil shape that could be created without just using a square plank. You could duct tape a couple Leeboards as an experiment and double the area without increasing the draft.

Leeboards come with my Folbot kayak kit on Craiglist:
Complete Sailing Kit w/ rudder, boards, rigging, sail...

I had a buyer, but couldn't find the sail. The sail had been carefully stored in the attic, but too late.

Speaking of hydrodynamics, I suggest that a ¼-inch "flat" be planed (or sanded) from the trailing edge. (Suggested at this forum earlier).

I first saw this in racing Alfa automobiles, (Alfa GTZ) which effect was, back in the 1960s, named the "Kamm-back", for the designer.
http://www.tamsoldracecarsite.net/INF10039.jpg

A good explanation of the same effect, but on a Porsche 904—from a solar engineer:
My Solar Electric Cargo Bike: Bicycle bodywork (3 of 4) Body shapes

 

[fhhuber]

Might try killing two birds with one stone and add a Skeg or two. I'd be interested to see if this helps with the terrible directional stability problem in addition to beating upwind. Factory wooden dagger boards probably had the worst airfoil shape that could be created without just using a square plank. You could duct tape a couple Leeboards as an experiment and double the area without increasing the draft.

The duct tape would last maybe 5 seconds under the load of sailing. As soon as you have any load on the boards (even just forward motion) the water will peel them right off.