Hi All

Hopefully someone can help me. I want to make some centreboards for my taipan, I'm governed by a couple of measurements, but I know roughly what I want.

Chord length - 290mm
Max Thickness - 24-25mm

Can somebody please tell me if they know of a section that would fit in these dimensions (around about). So I can look it up and make them. NACA 0009 is too thick, NACA 0008 would work but I haven't found any profile plots for it yet, if you think this may be the way to go, please let it be known or if you have another suggestion.

Thank You
Regards

By profile plots, I assume you mean polars?

http://www.geocities.com/xflr5/

XFLR5, which is an overlay to XFoil and Michelet (?) will do 2.5D analyzis and have many NACA foils included.
Many other foils are available at: http://www.ae.uiuc.edu/m-selig/ads/coord_database.html

For symetric foils, the NACA series is much used and look good.


If you know what Reynolds number you want to compare foils for, it's easy to run them trough XFLR5. You can also use the 2.5D functions to look further at planforms etc.

Attached are the polars for the NACA0008 run with a Re at 1 mill and alpha -3 to 14.

Why don't you just build the daggerboards that are given in the Taipan building plans ?

These are relatively good boards, their profile is suprisingly capable to stay up with the modern designs.

If you are looking to increase performance by getting a new profile for the (same) 290x24 mm dimensions then forget it. There is not nearly enough to be gained there. Any noticeable gains will require a change of aspect ratio and therefor you'll have to let go of the 290x24 mm design box.

Wouter

The boards in the plans are the original size boards that are 320mm wide. Jim Boyer recommended some time ago to builders to reduce them the minimum of 290mm, and I have made the cases to suit the narrower boards.

Its just a shame the plans weren't updated over the years, to reflect things like this, the boards in the plans are not a 00xx profile, they are finer at the leading edge, and I can't seem to find out what section they are, I don't have the knowledge to identify the section, and I'm just looking for a section that works.

All I need is a profile name, I don't want to get into the science of it all, that may seem silly, but I just want to go out to the shed and make them.

Thank You
Regards

You don't have access to a set of Boyer boards (290 mm) for copying, I take it ?


Wouter

No I'm fairly isolated here at the moment, but I may have the found the information I need, will find out today.

Regards

Hi Matt,

I have some spare Taipan daggerboards available if you need these. Please mail me at info@catamaranparts.nl so i maybe can help you.

Regards,
Hans

That would be great Hans, unfortunately I'm is Oz. But thank you anyway.

Regards

Matt,

Why is this a problem. But why do you not take caontact with AHPC or Jim Boyer i think they can help you further with this.
Otherwise i have also the latest development of daggerboards for you available for F16, you only need a sleef in your existing trunks to make it fit ,but this can be done.

Regards,
Hans

Informative link, Rolf!

What are the Reynolds numbers' range for typical F16 - F18 - F20 type of cats?

Does anyone know the pros and cons of NACA 0008 vs NACA 6308 foils for the cat types mentioned above?

Has anyone knowledge of profiles with concave surfaces between the point of max thickness and trailing edge?

I suppose dagger board and rudder require very different foil profiles.

Stein

Calculate your own Reynolds numbers:
Reynolds Number Calculator

Properties of Fresh and Salt Water (density and viscosity):
Properties of Water

All you need is the velocity and chord distance.

Stein,

attached is a screendump from XFLR5 showing a run with 1.5mill Re, Ncrit 3 on NACA0008 and NACA6308. You can see that the assymetric 6308 do provide better lift, but there are lots of tradeoffs in practical terms when it comes to assymetric daggers.

My Marstrøm Tornado rudders have some concavity between max thickness and trailing edge. I dont know what section it is, but I suspect it is a laminar one. Works good I would say, but sensitive to surface finish.

Differences between daggerboards and rudderboards are mainly that you dont want the rudder to stall as early as a daggerboard can. Rudders also operate in the flow behind the daggerboard/hull, so the flow is probably a bit disturbed. Even worse if you use assymetric daggerboards so the turbulence from the daggerboards hit the rudders directly, instead of being 3-4deg off as with symmetric daggerboards.

Matt,

in your case I would have buildt a set of NACA 0007 or 0008 foils, if that is what fits your wells. Relatively forgiving sections and probably not much worse than what your competition sails with (perhaps even better). I would be more concerned with the engineering of the foils so you dont break them.

Matt,

just scale the section provided in the plans to the ratios you require.

Rolf,

Thank you!
I confuse the NACA codes.
What about NACA63A010 (which is symmetric) versus NACA 0010?

Sailing season ended in Molde yet?

Stein

We dismantled and put the Tornado in storage last saturday. Had a really nice sail first with plenty of wind, probably the hardest wind we have seen the whole season. New spi was a bit scary, loads of power..
I suppose the season has ended in Oslo as well, even with the forecast you have for an unusual mild winter?

Isn't the NACA63A010 a laminar section? If so, it has a theoretically better polar than the NACA00xx series, but it must be buildt to very high accuracy and the surface must be very good. In addition, there is doubt wether the daggerboards on a beachcat ever see laminar flow, so a non-laminar section might be just as good..
If you want a short primer in how to run the XFLR5 software, just give me a call. Running it is not hard, but setting it up and interpreting the results is what demands some theoretical knowlegde.

We had to take the Taipan home a month ago since the space was needed for big boats' winter storage. And there was a period of sub-freezing temps. Now it is 5-10 deg C .....

I would like to attempt building a rudder with anti-pitch pole wing(lets), but I know there will not be the time for it this winter. Anyway. it is always interesting to learn more about mechanisms involved in sailing. Understanding is fun.

How can I find more info on concave surfaces on rudder sections? (Tornado rudder)

Stein

Stein,

I dont think you will find much information on this online or in books unless you dive really deep into aero/hydro dynamics on a high level. Usually the area behind max thickness is for pressure recovery, so you dont want dramatic things to happen there. But adding some concavity will change the foils properties when you turn the rudders. I have not looked at it so I dont know, but there might be something to gain. Note that Tom Speer say that NACA0012 is a pretty good section for use in beachcat rudders, so the gains might be very small.
There are some posters on this forum who knows a lot about hydrodynamics (more than me at least), perhaps they can explain?
Magnus will probably be able to answer you in some years tough, when he finishes at NTNU <img src="http://www.catsailor.com/forums/images/graemlins/laugh.gif" alt="" />

If you want to know more about it, you will probably have to run some home-designed foils trough XFLR5 or similar software. Could be a fun project for some evenings, just start with e.g. NACA0010/NACA0012, add some concavity behind max. thickness and compare what happens when AoA changes to the default NACA0010/NACA0012 sections.
If you know what section daggerboards you have, it could be fun comparing they to what other profiles/AR ratios could do for you.