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Pete Pollard

dagger board

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Sorry if I've asked this before.

 

I want to make my dagger board longer, so that the boat will hopefully go to weather better. Where to start? I'd also like to experiment with an assymetric shape.

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Trying to race F16. The class has gone through at least three iterations of daggers, each longer than the other. For structural reason, I don't want to re-work the trunk, but will the geometry still work?

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Adding length might be more hassle than its worth - Have you considered shaping some high density foam and doing a carbon hand layup? and as far as an asymmetric shape goes , think airplane wing - the shortest distance the water has to travel will be the plane of highest pressure = Lift

 

Drop this question in the multihull forum too - I'm sure someone has insight over there

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Never go to the multihull forum with questions, it leads to an inevitable shit storm.

 

My idea was to keep the original boards for pleasure sailing and build a new set of longer boards for racing. But how long? As for the asymetrical part I have the NACA forms, but which one to use?

 

I had planned to make the test forms out of wood and once I'd settled on shape, then worry about weight and strength.

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Never go to the multihull forum with questions, it leads to an inevitable shit storm.

 

My idea was to keep the original boards for pleasure sailing and build a new set of longer boards for racing. But how long? As for the asymetrical part I have the NACA forms, but which one to use?

 

I had planned to make the test forms out of wood and once I'd settled on shape, then worry about weight and strength.

 

I ran into this problem making a new daggerboard for a smallish lo-perf monoslug this year. If the new "test board" is not as accurately shaped and smoothly finished as the final product would be, it's going to sail like shit and you'll think the original was better, even if the new design does have the potential to be a huge improvement. You basically have to make the real deal in order to have a reasonable test.

 

One advantage you have, is that you can test two boards against each other in one sailing session. So make a new board about 10% longer, section shape you like, and try it in one hull and old board in the other hull. Which tack is faster? Unfortunately if you ant asymmetric boards, you can't swap sides to repeat the test on opposite tacks, but you can't have everything.

 

Just for some raw figures, I settled for a daggerboard that was a little more than 5% more area, longer & higher aspect, with a better shaped leading & trailing edge but basically the same thickness (had to fit in existing trunk). The improvement in pointing & handling was very noticable; and the longer board gave more leverage for righting the boat too (an issue for kids, not me).

 

FB- Doug

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Can you make a foil that is asym under the trunk for lift, but matches the old sym shape so the trunks don't need to be modified? The asym section would have to be designed in such a way as not to jam in the trunk when moved.

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tiki,

 

Now I see why youu were asking the questions over there, but I know you've asked these before and still haven't made a move. I forget which F16 you are on, but supposedly the Vipers have upgraded to the C2 short boards, which are available for reasonable prices as the long boards take over the market. This may be an option for you, and surprisingly the production boards end up at a reasonable price if you just look at materials cost.

 

Anyway, may want to read this thread: http://forums.sailinganarchy.com/index.php?showtopic=106426

 

Re-reading it some, it's pretty clear my knowledge is severly lacking in multihull foils, but I'll add a few thoughts to your own:

 

1) Building a higher aspect ratio F16 foil from wood is likely to fail. The F18 long boards are solid carbon all the way thorugh (looked closely at a broken wildcat foil last week), that's how high the loads are. Wood+carbon or foam+carbon are better bets.

 

2) Asymmetric blades IMO are a poor choice for a boat that can be sailed in the singlehanded configuration. Pulling the weather board up every tack will not be faster around the race course unless you are a professional sailor with crew onboard. If you do plan this, evaluate the Phantom trunk, macca has photos on his blog, essentially you are looking at a trunk modification.

 

I can also tell you this, the short boards are competitive if you get your head out of the boat and focus on picking the shifts. But you seem pretty set on the modification. I believe everyone is using a NACA 0012 on the daggerboards, or close to it (maybe 0014 if thickness is an issue structurally). What the longer boards help with is flying a hull sooner in the case of the C2-letting the newer powered up sail plan push the boat forward and lift the weather hull sooner rather than sliding sideways. On the Infusion they already had enough area, again I'd like the real numbers but I've misplaced the magic table; I don't think they subtracted any with the mk. 2, and longer span is essentially more efficient so the boat is noticeably slippier through the water upwind and downwind; partly why the Mk. 2's can carry their boards all the way down downwind but we have to start pulling the fat boards up sooner is our boards are more draggy, you feel like you're tripping over them (random point, I think our boards are still gybing when all the way down so this hurts too). I'll also add they really cleaned up the tooling on the new boards and they are super clean, which certainly doesn't help.

 

Heed the advice above, if you're going to do it do it right you probably need a mold. I think you're better off buying a set of production blades if they'll fit in your turnks (i.e are narrower chordwise, they make inserts).

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If the short boards are good, why would the builder go to the expense of changing them?

 

I know of three other boats built with the same boards I have, all had problems going to weather. The best sailor among us was no exception. Sadly he died right after the 2010 championship so he never got to sail the longer boards.

 

A friend with the same boat but longer boards reports that the newest boards, even longer than his, offer a significant advantage to weather.

 

But I'm into the puzzle now, I just want to know...

 

I'll use wood for a model, just to find an acceptable shape.

 

One thing that really bugs me is the H17, it didn't have much of a board at all but went to weather quite well.

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Never go to the multihull forum with questions, it leads to an inevitable shit storm.

+1 I know what you mean.

 

Vegas knows... (Aside My "proa" outrigger project is stopped for now, save foils and a small deck...I am lurking here. I was thinking to lengthen one rudder to increase weather helm...but that is not for here. Not want to hijack...will post later on design or multi here for sparks...)

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One thing that really bugs me is the H17, it didn't have much of a board at all but went to weather quite well.

The hobie 17 has a lot more hull in the water than your boat and I bet even with the current boards you would climb over one.

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If the short boards are good, why would the builder go to the expense of changing them?

 

I know of three other boats built with the same boards I have, all had problems going to weather. The best sailor among us was no exception. Sadly he died right after the 2010 championship so he never got to sail the longer boards.

 

A friend with the same boat but longer boards reports that the newest boards, even longer than his, offer a significant advantage to weather.

 

But I'm into the puzzle now, I just want to know...

 

I'll use wood for a model, just to find an acceptable shape.

 

One thing that really bugs me is the H17, it didn't have much of a board at all but went to weather quite well.

 

Why? Iit's racing, everyone is always looking for an edge. Fortunately they insituted length rules in the F18 class to prevent even more ridiculous boards from appearing. And I'm not denying that the long boards are faster upwind, but again these performance enhancing foils come at a relatively high price tag-$2600 for the pair + install kit = $3K = price of new sails. To think you are going to match the performance of a set of high modulus carbon boards built from precisely machined aluminum tooling by carving a bamboo set out in your tiki hut is dreaming.

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I have been lurking and have a question, but do not want to hijack the thread...

 

If a rudder is enlarged, doesn't that change increase weather helm? Just curious and a PM would do. As I said, do not want to change thread direction.

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If the short boards are good, why would the builder go to the expense of changing them?

 

I know of three other boats built with the same boards I have, all had problems going to weather. The best sailor among us was no exception. Sadly he died right after the 2010 championship so he never got to sail the longer boards.

 

A friend with the same boat but longer boards reports that the newest boards, even longer than his, offer a significant advantage to weather.

 

But I'm into the puzzle now, I just want to know...

 

I'll use wood for a model, just to find an acceptable shape.

 

One thing that really bugs me is the H17, it didn't have much of a board at all but went to weather quite well.

 

Why? Iit's racing, everyone is always looking for an edge. Fortunately they insituted length rules in the F18 class to prevent even more ridiculous boards from appearing. And I'm not denying that the long boards are faster upwind, but again these performance enhancing foils come at a relatively high price tag-$2600 for the pair + install kit = $3K = price of new sails. To think you are going to match the performance of a set of high modulus carbon boards built from precisely machined aluminum tooling by carving a bamboo set out in your tiki hut is dreaming.

:lol: You read my mind.

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If a rudder is enlarged, doesn't that change increase weather helm? Just curious and a PM would do. As I said, do not want to change thread direction.

 

The short answer is yes, no, maybe probably not.

 

The long answer is as you would expect longer and to be honest I deleted it when it got onto the second paragraph as I wasn't even half way.

 

Assuming you boat is properly designed just scaling up your rudders wont have a big effect on weather helm. Think of it like this, at present your lift is balanced between the dagger board and rudder (with the hull taking a small amount) in the same way that your weight is balanced between your two feet (and dick if you're well hung). If you were to put a bigger shoe on one foot would it change the amount of weight you applied to that foot? No.

 

Now the Maybe..

 

Keeping the shoe metaphor. If the bigger shoe has a thicker sole it will lift the other foot off the ground a bit and take more load, this is what you're doing when you put on a bigger rudder. The problem is that if your rudder/sole gets too big it will take all the load and you'll become unbalanced if we were talking about shoes you would bend your knee and transfer some load back onto the other foot. On your boat you achieve the same goal by reducing the lift being generated that is by pulling on the tiller to reduce the angle of attack of the rudder. Weather helm!

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I have been lurking and have a question, but do not want to hijack the thread...

 

If a rudder is enlarged, doesn't that change increase weather helm? Just curious and a PM would do. As I said, do not want to change thread direction.

depends. if you enlarge it by lengthening its chord, then perhaps yes, because for a given deflection of rudder, there will be a larger force-couple pulling against it and you will feel more weather helm (like kicking up your rudder in a beach cat or Laser.

 

but if you deepen the rudder you only increase the force couple marginally while substantially increasing the amount of water deflected. so to get the same helm response you now have to pull th helm up less for the same effect. thus it will feel like your helm is even lighter

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Bandit and Scarecrow...much thanks. So, it sums with the daggerboard somewhat, as there is more going on here, as noted above?

 

Nothing simple is ever easy, is it?

 

Later in year you will understand why I asked the question. Very kewl.

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I hate to say this, since I try to be that DIY guy in almost all things, but in this case, I would call Phil and cut a check...

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What about a whale fin shape? For the leading edge. It cuts down on resistance and works at slower speeds.

Link to my build: http://forums.macgregor.sailboatowners.com/showthread.php?p=1041966&highlight=whale

It's not done... Sailing got in the way. It's cold now so I'll get back at it.

I do plan to make a DB as well.

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