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PostPosted: Thu Sep 26, 2013 1:56 pm 
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guessing NACA 0010, 0012 or 0015...

you can order blanks cut to these from http://www.flyingfoam.com

pretty cool. seems like EPS is better than EPP foam... and I bet they can almost cut the dagger foam for you, if you wanted to make some custom boards...


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PostPosted: Fri Sep 27, 2013 8:01 am 
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The EPO rudder foils are not a NACA section due to manufacturing and class rule restrictions. Nor are they a consistent thickness ratio, since the chord tapers at a different rate than the thickness.

They are close to a NACA 0009, but fatter in the aft section and they have a truncated trailing edge:
Image

As far as the 18's boards go, I'd wager the same thing applies.


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PostPosted: Sun Sep 29, 2013 6:24 pm 
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How about a 66-009. This profile looks very similar to the 66-012 profile that is used in RC quickie pylon racing. That does look like a much closer profile with the -009.

Doug aka Aye Carumba


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PostPosted: Mon Sep 30, 2013 9:15 am 
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Personally, if I were going to take on a project like this, I think I would just use a pre-existing board (probably an F18 board) and modify the trunk to accept it rather than trying to build a custom board. At least that way you will be reasonably certain that the board will perform and hold up to the sailing loads. Unless you have the ability to do an FEA on your board design, you're not really going to know whether it will handle the loads. Either that or you're going to want to way over-build it to make sure it's strong enough. Plus, if you don't have the ability to build the boards in a press mold or vacuum bag them, you're probably not going to get satisfactory results (they will be heavy and/or prone to delam). It would definitely suck to put in hours and hours of work and several hundred bucks in materials into building boards only to break them or find out they don't perform the way you want them to. The foam core is relatively inexpensive, but the carbon, epoxy, paint, labor, etc are where the project cost really starts to add up.

sm


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PostPosted: Mon Sep 30, 2013 9:50 am 
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:)




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PostPosted: Mon Sep 30, 2013 2:14 pm 
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it does sound like it could be a fun project.

as far as vacuum bagging, there are plenty of folks that have made bagging systems from an old refrigerator compressor with a vacuum switch to turn the pump back on if the pressure bleeds down too low. a lot of the folks in the RC world just use painters plastic dropcloth and cheap $1 caulk to make the bag in. use some polyester dress lining for peel ply and paper towels as the breather layer. it has worked on the smaller items that I have done.

i think I would stay away from expanded foam though. too light and fragile for the loads of the water I imagine. Extruded foam or urethane foam (gives poison gasses when hot wire cutting) would be much stiffer and stronger. then you would need some type of spar to provide the rigidity needed.

but as SM alluded to, there is a lot more to this than just cutting foam and applying carbon fiber...

maybe those EPO-3s aren't looking so bad.

oh, and the n66-009 is a high reynolds # laminar flow foil. I wonder how Reynolds numbers apply to water.


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PostPosted: Mon Sep 30, 2013 2:36 pm 
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Aye Carumba wrote:
there is a lot more to this than just cutting foam and applying carbon fiber...


Exactly. This would not simply be a matter of buying a foam blank and wet laminating a few plys of glass or carbon and expecting to come out with a well performing foil. It would likely be a pretty expensive and time consuming venture before you would come out with a decent blade. Likely a lot of trial and error. Or you just buy a blade that you already know works and adapt it to fit the H18 - it would still be a fun project and probably have a much higher probability of success.

sm


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PostPosted: Mon Sep 30, 2013 4:45 pm 
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. While this is a project most novices shouldn't attempt... The process is something a guy with decent fabrication skills can accomplish in a simple garage..

It does require some knowledge

Even cutting the foam core with a hot wire is pretty simple...

This can be done with junk most people have laying around the house.. (some guitar string will work)

https://www.youtube.com/watch?v=S2TfNYSYLC8

https://www.youtube.com/watch?v=HEfUk4vnpWI

It is a simple matter of laying out a couple stations to trace with the wire...

With careful template work cutting/shaping foam is not a problem.




Then Vacuum bagging composites isn't rocket science..... The guys who sell the stuff have all kinds of tutorials around...

https://www.youtube.com/watch?v=VodfQcrXpxc

So sure.. some guy who ain't used to fabrication ain't going to walk out to the garage and build some carbon rudders in an hour... but this stuff is far from impossible..

Now.. if saving money is the goal..... Well... that is a different story all together..


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PostPosted: Wed Oct 02, 2013 2:24 pm 
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Thanks for the discussion and feedback/ideas.....

I'm thinking guys have hand shaped surfboards, reenforced with something as a stringer... hand laid glass, and had fun with it.

Fast forward to today... I should be able to basically do the same thing, but with modern materials and techniques, and come up with a reasonably strong, efficient, etc, set of daggerboards. I don't expect to get it perfect, it's just a fun project, and if it works, even better.

It'd just be cool to have carbon rudder arms, tiller crossbar, boom, boards... etc. A carbon comptip, less weight up there.. would be sweet too.

I really want to tweak my boat, I love it... but I'm thinking of selling it, and my H14T, throw in some more cash, and get an F16.

If you're looking for an H18... here's some info on it:
1992 hulls, great shape, originally SX hulls so have reenforcements inside and anchor plates, etc.
2 masts, all alu and comptip, both in great shape.
6:1 downhaul on comptip
bungees, etc in boom work great... metal cleats for rotator and outhaul
NACRA F17 spin rig - pole, bag, sail, blocks, lines, etc, etc....
great Blue Hawaii main (jib is OK) and new white class legal jib
whirlwind square top and whirlwind jib
cattrax and trailer
new shrouds, forestay, bridles, mainsheet
new black mesh Hobie tramp in 2011 for the NACs
includes full sunbrella cover...
always covered... lots of Hulkote on it, shiny and glossy
EPOs
glass hotstick
rudders tuned, aligned, etc.
boards great shape

boat sailed 2011 NACs (finished 8th overall I think... ((new skipper.. me)... and 2d overall in 2013 Mid-Winter's East.

interested let me know... not really ready to sell... "IF" I do, more likely in the spring...

the H14T is in great shape too... hulls just need a good buffing... new tramp, EPOs, new rigging still in box... frame expoxied...


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PostPosted: Sun Jan 05, 2014 12:22 pm 
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MBounds, where did you find that graphic?

I had been wondering the same thing, I'm surprised that Hobie didn't go with a standard NACA foil shape, considering the amount of research that went into them... I'd be surprised if Hobie put more research into their rudder/daggerboard shapes than NACA did. Then again, a lot more research and advancements have taken place since the H18's debut, the daggerboards are pretty outdated and inefficient.

I had given some thought to building my own rudders and daggerboards, but concluded that I just don't have the necessary experience to build them.

Aye Carumba, Reynolds numbers are dimensionless and apply to water the same way they would to air, unless I'm misunderstanding your question, but I haven't discussed it in significant detail when relating to foils. It is more commonly referred to when discussing ship resistance, though Froude number is actually a more relevant factor than Reynolds number in that case. (My degree was in Naval Architecture & Marine Engineering)

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Mike
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'79 H18 standard 'Rocketman II' sail #14921


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PostPosted: Sun Jan 05, 2014 9:29 pm 
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SabresfortheCup wrote:
MBounds, where did you find that graphic?

That graphic was one I created for an issue of the Hobie class magazine, the HOTLINE.

SabresfortheCup wrote:
I had been wondering the same thing, I'm surprised that Hobie didn't go with a standard NACA foil shape, considering the amount of research that went into them... I'd be surprised if Hobie put more research into their rudder/daggerboard shapes than NACA did.

Most of the research that Hobie Cat did in the '60s and '70s was empirical - they built what looked good and could be easily produced - and if it didn't work, they tweaked it and tried again. After all, both Hobie Alter and Phil Edwards (creators of the Hobie 18) were surfboard shapers and went with their gut feelings.

NACA was a federal agency (precursor to NASA) with ~500 employees in the early '40s when they did the research on foil sections. The amount of money and time spent was order of magnitudes larger that what Hobie did on the foils for what are essentially recreational toys.

SabresfortheCup wrote:
Then again, a lot more research and advancements have taken place since the H18's debut, the daggerboards are pretty outdated and inefficient.

They are what could be easily and inexpensively produced with the materials available in 1977. The high-aspect ratio boards being used on modern catamarans would be impossible without carbon fiber and advanced construction techniques.

There's also a trade-off in convenience - the 18's boards are relatively shallow and very robust - an ideal combination in a recreational boat. An F-18s high aspect boards require a lot more care, and a momentary lapse in attention results in a broken ($$$$) board. I've never seen an 18's board break (Banged up and delaminate - yes. Broken off at the hull? No.)

As I've mentioned before, it's difficult to execute a NACA section in a high-quantity production part, especially the trailing edge.


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PostPosted: Sun May 18, 2014 12:02 pm 
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Aye Carumba wrote:
How about a 66-009. This profile looks very similar to the 66-012 profile that is used in RC quickie pylon racing. That does look like a much closer profile with the -009.

Doug aka Aye Carumba


I decided to revisit this topic today, and depending on the accuracy of Mbounds' diagram and my own AutoCAD tracing abilities, the EPO foil shape most closely seems to resemble a NACA 64A010, albeit with a slightly thinner mid body and bluffer entry & tail.

this would indicate the minimum pressure on the foil is at ~40% chord length, thereby intended to maintain laminar flow as best as possible up until that point. I did find the EPO foil shape to be very close to a NACA 64-010 and 0009 shape, but the 64A010 seems to be the closes foil shape.

Compared to the 0009, the 64A010 has a lower drag coefficient at small angles of attack, but a somewhat more abrupt stall point between 8-12 degrees (smoother foil at higher speed = higher possible angle of attack).

My purpose is primarily a point of curiosity, but I thought I'd share what I came up with. Of course, if the graphic was only for illustrative purposes and the foil shapes were approximated, all of this may be moot. :shock:

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Mike
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'79 H18 standard 'Rocketman II' sail #14921


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PostPosted: Sun May 18, 2014 5:53 pm 
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SabresfortheCup wrote:
My purpose is primarily a point of curiosity, but I thought I'd share what I came up with. Of course, if the graphic was only for illustrative purposes and the foil shapes were approximated, all of this may be moot. :shock:
The foil shapes in my illustration were pulled off existing rudders, and in the case of the NACA 009 foil, from the foil equation. They should be very accurate.

However, as I've mentioned before, the foil thickness ratio changes across the span because the thickness does not change at the same rate as the chord over the span of the foil.


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PostPosted: Mon Jun 02, 2014 2:52 pm 
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From what I've seen, making boards starts with a female mold, not a male form. There's no way to hold the male shape while adding layers and strips of carbon and glass, unless you add equal layers everywhere which would make it a lot heavier than needed AND oversize your form. Start with two female half shells, lay down your gelcoat or outer layer of fiber, add strips down the middle for strength, then add foam, then cut out foam to make solid leading and trailing edges, then glue both halfs together. The simple version :-) Not too hard with an existing board to use for the molds, or maybe a nice CNC job routing out the molds.


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