If the daggerboard is in the center fore/aft, and you have a single mast, the center of leeway resistance could be a meter or two in front of the center of effort on the rig, resulting in a weather helm.  While I personally would rather have a weather helm than a lee helm, something that's closer to balanced would be nice.  Lighter helm, less speed scrubbed by steering against the unbalance.

  Due to the long rockerless hull, the weather helm won't be extreme, but it will probably be noticeable.  Less noticeable with an easyrig than with an una rig.

---

  I'm personally not willing to build either a rudder or daggerboard into the hull.  I know of a local F-31 available for chartering that has gone through more daggerboards than I can count.  They are designed to fail, but the hull/crashbox still get damaged. 

  Yes, offering a boat like that for charter is questionable in an area with so many rocks and shoals.  But the risk of grounding is still there regardless of who owns the boat.  Even if you know what you're doing, you can still hit a submerged log, shipping container, whale, or unexpected sandbar.  Having something that kicks up would be paramount for me.

  I love the kick-up rudders and centerboard on the Dragonfly trimarans, and if I were to get a trimaran, that would be the brand.  I can't imagine spending $200,000 on a boat that doesn't have such an important safety feature. 

  But I'd rather have a proa than a trimaran, and the Dragonfly design of a centerboard in a trunk would only work in one direction.

---

  So, what to do.

  For the sake of discussion, I'll make two assumptions based on my preferences:  a) no requirement for playing with a board on each tack, and  b) no holes/crashboxes/trunks in the hull.

  That leaves four designs I'd consider;

  1) Two daggerboards that can kick up in both directions, plus two rudders for steering.  I've not seen one of these yet, but the engineering would not be hard. 

      Pro: lots of leeway resistance, resistance it against fixed boards, lighter loads on the rudder.

      Con: four foils in the water, plus the rudders will have a tough time fighting a long hull without rocker combined with two daggerboards.

  2) One kick-up daggerboard/leeboard at the center, with two rudders for steering and a big of helm balance.

      Pro: leeway resistance on a fixed board, three foils in the water instead of four, easier to steer around a centered foil.

      Con: three foils instead of two (resistance), three foils instead of two (one more to raise/lower).

  3) Long low-aspect keel in lee hull, two smaller rudders.

      Pro: no worries about kicking up, keel could be sacrificial in some ways, protecting the hull.

      Con: more resistance to steering, requiring larger rudders, less leeway resistance when compared to the same wetted surface area in a high-aspect foil.

  4) Two larger rudders.

      Pro: Minimal number of foils in the water, powerful steering when needed (at low speeds) because of two opposing rudders.

      Con: Force on the rudders is both leeway and steering.

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  I'm currently a fan of the two deeper rudders.  As long as the loads can be handled, why add additional resistance to forward motion or resistance to steering? 

  That said, my buying/building will be influenced by the new rudder design being installed on Blind Date.  I think it's a great one in theory, but it will also be nice to see it in practice.

  Actually, I might consider a fifth option.  Gardner has me thinking about his short keel.  Perhaps something just a few cm high could help protect the hull in a grounding and/or when drying out on a beach, but without adding too much resistance.

       - Mike



Gardner Pomper wrote:

 

Hi,

I am afraid that I must expose my ignorance to the list again. I thought that a leeboard/daggerboard was for lateral resistance and provided lift perpendicular to the board. Why can't it be in the middle? What would happen if it was?

Thanks

- Gardner

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