NE dory centerboard mod

Just a question. I am wondering if the centerboard could be a more specific foil shape  typically found on performance dingys? should the trunk be about a quarter inch wider to fit a wider board foil?  I know foils are important performance factors. Or  would it not make any difference on this boat


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RE: NE dory centerboard mod

I remember reading something from John H saying he is "famously fussy" about foils yet is pleased with foils like those in the plans. Having made NACA foils and this type, I can tell you it is much easier to make this type.

I suspect foil shape does matter, just not as much as on a competitive/racing speed demon where every ounce of drag matters. Maybe you want to beat your mate; might matter then.

RE: NE dory centerboard mod

A daggerboard with a thicker chord and with a full NACA foil shape would improve performance, but in a boat like this the difference would be incremental.  

The improvement would be noticeable only on a race course, between sailors of equal skill.  An advanced sailor with the stock Northeaster Dory daggerboard would mop the floor with a beginner-to-intermediate sailor with a fancy foil carved into his daggerboard.  For that matter, crew weight and rig tuning would probably make more difference.  

20 years ago I was building traditional Melonseeds, and once raced around the buoys with an identical sistership.  I had faired the daggerboard on mine with infinite care; it was as fast as it could be.  The other boat had the same daggerboard, but it had not been shaped---it was blunt on leading and trailing edges!  However, my boat had a lousy sail and the other boat had an excellent sail, and he beat me handily.  A good lesson that many of these refinements are academic unless you're racing one-designs at a very advanced level.  One-design racing is one of the few occasions in sailboats when all things are truly equal.

I used to build racing dinghy foils in huge quantities.  This is a bunch of ash, okoume, and balsa-core daggerboards I did for Windmill Class sloops.

Windmill Class Sloop Daggerboards

RE: NE dory centerboard mod

Mr. Harris,

While we’re on the subject. . .  I have decided on your NorthEaster Dory for a near future build and would like to modify the dagger board to pivoting center board (similar to Hylan’s Crab Skiff design). Where would you recommend the CLR to be in relation to the CE on a full sail set Balanced Lug? I’m guessing based on displacement and LWL I could go as far as 15% ahead without creating too much weather helm . . . Also what is your recommended square footage for the board in relation to the total area of the Lug?

Thanks in advance for your recommendations. I hope this is something you can advise me on.

Respectfully requested,

JP

 

   

RE: NE dory centerboard mod

>>> would like to modify the dagger board to pivoting center board


For lots of reasons, a daggerboard is the best solution for the Northeaster Dory.  Besides being a lot harder to build, a centerboard throws the whole interior layout into disarray.

To explain why really requires a graphic.  I get the question so often that some years ago I created the drawing below to have ready when The Centerboard Question arises.

Daggerboards aren't so bad.  Two of the most popular sailboats ever built, the Sunfish and Laser, do very well with daggerboards.  Several stock Northeaster Dories have made it to the podium in the notoriously shallow and difficult Watertribe Everglades Challenge course.

I'm not discounting the advantages of centerboards.  It's just that a daggerboard is the right compromise for interior layout and easy assembly of the Northeaster Dory.

You should be able to click on the image below to embiggen it, or click here to link to the image in a new window.

RE: NE dory centerboard mod

Embiggen? EMBIGGEN?!!

RE: NE dory centerboard mod

Never mind, it seems to be a real word. Chalk my ignorance up to the fact that  English is my second language.

 

RE: NE dory centerboard mod

   A perfectly cromulent word. Sorry, that came up when I looked up em bigger.

RE: NE dory centerboard mod

   That's emgiggen. Sometimes I loose the battle with autocorrect.

 

RE: NE dory centerboard mod

   JP-

sorry it's taken so long to get the measurements for you.

From sole to top of trunk 12.5"

Top of thwart to top of trunk 5.5"

Top of trunk to gunnels 3.5"

Aft edge of trunk raked forward of leading edge of thwart 4"

ev

RE: NE dory centerboard mod

Thanks Eric, > Thanks Mr. Harris, > Sorry buzzard for hijacking your post.

My concern is the trunk as designed may interfere with my rowing style as some have reported it might. I guess I will evaluate it while under construction and determine how it will affect me. I’m not afraid of a little extra work to modify if needed and will take all the advice given. The diagram provided by Mr. Harris was very helpful and has lead me to believe that if I do modify I will user the dagger board style as designed and  move it forward a few inches and rake the angle of attack aft to keep the CLR in the same location as the original design.

Thanks again everyone.

JP

RE: NE dory centerboard mod

   There's another wrinkle JP, you may be able to cut away a good bit of the upper aft trunk corner. Seems to be plent of material there. Thinking about doing the same when it's time to refinish. You'd know better than I if it would still be strong enough. Should be easy to decide once you get the parts cut out.

ev

RE: NE dory centerboard mod

>>>My concern is the trunk as designed may interfere with my rowing style as some have reported it might.>>

I'm 6'1" and a serious rower, and I've rowed the Northeaster Dory all day, and I've never had trouble with the daggerboard trunk location.  For taller folks we went to a lot of trouble to make the rear thwart removable in a few seconds, allowing you to slide aft a bit on the center thwart to ensure good legroom and clearance.

RE: NE dory centerboard mod

   Thanks for your input on this thread John. I know you are obsessive about the details of each compromise and prototype several versions of designs. The Trunk/Lower back collision seems to be pretty common. Do we just have sloppy technique? Your rowing article published a couple of issues ago shows minimal leaning towards the bow. This must be where I'm going wrong.

RE: NE dory centerboard mod

   A noble spirit embiggens the smallest of men

 

RE: NE dory centerboard mod

>>> The Trunk/Lower back collision seems to be pretty common. Do we just have sloppy technique? Your rowing article published a couple of issues ago shows minimal leaning towards the bow. This must be where I'm going wrong.>>

Good question, and it's been the source of some head-scratching on my part.

The impression I get is that some Northeaster Dory rowers are taking really long strokes, as they would with a sliding seat, or when racing.  The Northeaster Dory's fixed-seat geometry and oar length favor a shorter stroke rather than a long, really-put-your-back-into-it sort of stroke.

If you're racing, well, that's okay, but I can see the daggerboard trunk impinging if you're really laying into it.  (A stock Northeaster Dory won its class in the Blackburn Challenge, a famous rowing race, but it was built just for rowing, without a daggerboard trunk.)

I poked around and here's a good video of me rowing my Iain Oughtred Whilly Boat, which has hull proportions and oar length not unlike a Northeaster Dory.  That's at about 50% pressure, a cruising pace that could be sustained all day.  I'm not leaning back much.  

>>>A noble spirit embiggens the smallest of men

It's good to know I am among fans of the Simpsons.

JCH illustration from "The Geometry of Rowing" article in WoodenBoat Magazine

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