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Twin daggerboards for a Spindrift N11

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Hey everyone,

I've just joined this great community of BandB fans! After extensive research the Spindrift N11 suits my requirements perfectly and I'm now in possession of the plans and have asked for the plywood and epoxy for Christmas - although my wife knows if she arranges this with Santa she won't see me until Spring!

Anyway, before I get underway I wondered what everyone's thoughts were on a double daggerboard set up - much like the black hulled yacht in this clip -

https://m.youtube.com/watch?v=lbBtybMan-4

If the daggerboards are wing shaped they should provide significant lift to windward when close hauled. So I'll be able to sail on a close reach, flatter, dryer and still make the same COG as a harder pressed single daggerboard boat?

The only cons I can see so far are the extra weight of the second centreboard case and daggerboard (and obviously the extra cost and build time).

Wing shaped daggerboards are used regularly on cats. But do they really work?

What do you think?

Thanks in advance,

Jim

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Hi Jim,

 

Welcome to the CS clan.

 

Here's my $0.02 on your double daggerboard idea.

 

Sail flatter?   Probably not.  Heel will be determined by the athwartships (take that, spell checker!) force from the sail and where the mass is in the boat.  In order to sail a steady  course the upwind lifting force generated by the foils will exactly balance the force on the sail.   You might make slightly less leeway with the double-board setup, but heel will be the same.

 

Drier?  I think that would mostly depend on the heel.  If you're heeled over, the windward gunnel might give you more protection.  Flatter might even be wetter.

 

Certainly if you have a foil that's too small, you'll get blown off course to leeward.  No good.  On the other hand, if you have too much foil area under the boat, you might be slowed down by the drag caused by moving a lot of extra surface area through the water.  That's no good either.  So, maybe your idea would produce a small performance increase, maybe it would slow you down.   Tragically, you may never know the difference unless you sail the two types side by side.

 

Whatever the configuration, all of the foils should have that wing shape (round in front, tapered in back) to give lots of sideways "lift" force while minimizing drag.

 

The double daggerboard setup is needed on cats because either hull can be lifted out of the water when they heel.  You need to keep a foil in the water.  Not a problem for the dinghy.

 

For a single hull, I think the only real advantage would be a comfort advantage just having less structure in the cockpit, and in the Spindrift, the cockpit is already clean & simple with the daggerboard almost under the center thwart.  There's not much to gain there.

 

My opinion is that it would be a shame to complicate such a simple and clean setup.  One sheet, one tiller.  Left hand right hand.  I like the math.   That said, it's your party. Make boat, be happy.  I would suggest going as far as you can in the build without committing one way or the other, and then see how you feel about it.

 

Cheers!

Bob

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Unless you make asymmetrical daggerboards I don't see them doing anything at all and nothing you describe except lift.  And the lift you would get from asymmetrical boards would seem hardly worth it in a dinghy.  The biggest issue I see sailing would be the raised board fouling the vang and getting in the way.  11 feet is a small boat.

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Can't tell from the videos, but curious if those daggerboards have a camber in the chord (say 2412 vs 0012 NACA foil shape), to give them additional lift in one direction, with the opposite in the other?  Also......are they mounted parallel to the centerline or at an angle to give additional lift?

 

Second, is there some mechanical mechanism to raise and lower these boards when tacking? Automatically, or does the skipper / crew also have to raise and lower the boards in addition to working the jib sheets when tacking?

 

Don't know if the boats have been built to test it, but what would matter would be the best of these two boats matched against an identical boat with only one board (ooxx naca foil) on the centerline. But if there was an advantage, would racing rules allow its use? If not, what would you be left with? A recreational boat that would point a few degrees higher? Is that worth the effort?

 

Also curious that on two otherwise similar boats, a normal main and the fathead seem to be sailing the same. If so, so much for that hype.

 

On a Spindrift, if she was not sailing flat enough, I'd think it easier to hike out. And BTW, doesn't this only matter when pointing to the max?

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Now that I think about it a bit more......is this not a case of "back to the future"?

 

Are those not unlike leeboards in function? Didn't they invent the CB to get rid of leeboards?

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Thanks for all your replies. I think Hiri is right - simpler is better (unless complicated looks really cool).

The double daggerboard is a feature of the Redfox -

http://sailboatdata.com/viewrecord.asp?class_id=4648

They have a curved cross section so that they create lift, essentially driving the boat to windward, rather than just providing lateral resistance.

But I guess, as Bob rightly points out, the primary advantage of this set up is it takes the centreboard case off the centre line and frees up living space. Not an issue in an N11...

Anyway, I'm really pleased to have had such quick and comprehensive replies, reassuring to know I'll be able to seek help here in the future.

I'll stick to the N11 plan that Graham conceived rather than tweaking it with my own America's Cup ideas. Bermuda, 2017 here I come :)

Jim

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I got to see those nasty beasts on the bay last go round. I am OUT on any sailing I must wear a crash helmet for. Watching one of those things get out of the water and foil on away is mind boggling. You rarely see motor boats struggle to keep pace with a sailboat race!

It is truly amazing how fast those crazy foiling multis go.

I'm also a fan of those foiling Moths.

Except for me to use. I'm all about just sitting there giggling because I'm not doing ANYTHING, but the boat is moving. Slow boats are just fine with me. Well, non foiling slow, not unsailable slow. A little surfing or planing can be nice. :)

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One board trunk is already in the way. Two would be worse. Great boat that sails awesome just the way it is. IMHO. I do encourage experimentation.

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This place is magic. So many interesting posts. A guy sails a moth out of Port Edgar, my local marina. It looks a lot of fun. But I'll need more home comforts.

I've read every detail about Chick's CS17 - she looks amazing. And I'd like to go the same route as Steve, try out skills with the N11 and then maybe, if all the tools I own aren't epoxied together, a slightly larger daysailer.

I live in South Queensferry, Scotland on the Firth of Forth - hence ForthBridge - a shallow draft CS17 would be perfect for exploring.

I am now explaining the cost of my wife's expenditure to her in terms of plywood sheets. Slowly but surely... It's cold here in Scotland so it might have to be a living room build :-) Once the Christmas tree is down of course

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Jim,

Everyone fancies themselves a little bit of a naval architect.  That is plain to see by the wide variety of postings on this forum.  We all want to put our own little tweak into the boats we build.  It's human nature.  But I'll tell you something-- in the two years that I've been acquainted with these boats, I have been very impressed with the simplicity, efficiency and speed that Graham designs into them.  They are darned near perfect.  It will be very rare for someone to actually improve on his work.  So, as we say here in the States,  "If it ain't broke, don't fix it!"

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