Foiler Design

[PI Design]

Thanks Doug, that's great.

[ancient kayaker]

Doug, what happens as the foil approaches the surface? Is there just more drag or tdoes the lift decrease/increase as well? If both change using the effect for alltitude control becomes more complex.

[Doug Lord]

Originally Posted by ancient kayaker

Doug, what happens as the foil approaches the surface? Is there just more drag or tdoes the lift decrease/increase as well? If both change using the effect for alltitude control becomes more complex.

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I've never experienced it either in models or fullsize(that I know about) but I would assume if the lift goes down("significant reduction in lift inside two chords") then the L/D ratio of the foil changes. I read somewhere that some Russian lake/river foilers used the effect as a form of altitude control.

[Doug Lord]

Originally Posted by tspeer

I suspect the lift-loss at the surface is stabilizing the boat. Many Russian powered hydrofoils that are designed to operate on rivers and other sheltered areas use this principle.

I think the drawback for using the free surface effect in sailing hydrofoils is the reason the lift loss occurs is also the same reason that the induced drag is doubled at the surface. The effective span is reduced 30% when you get right to the surface. So you have increased drag from the horizontal foil and effectively a short stubby board as well. It looks very spectacular, but the performance may suffer.

A good analog might be flying a hull on a catamaran. The best performance is obtained when the windward hull is just skimming above the wave tops. You can sail with the hull way up in the air, and that may be fun and look cool to the uninitiated, but it's not a fast way to sail.

If you're sailing very fast and heeling the boat to windward, it's possible that the the reduction in induced drag with speed and the effective vertical span provided by the depth of the windward tip of the hydrofoil (and verical lift from the rig) make the increased induced drag due to shallow depth an acceptable price to pay for reducing the wetted area of the strut.

But I think for racing, it wouuld be faster to fly lower.

=================
Here you go Terry-Tom Speer earlier in this thread......

[Doug Lord]

Originally Posted by Doug Lord

I am starting a series of posts that will reveal important technical details of some successfull foilers in order to help people interested in foiler design.
I'm starting with the largest bi-foiler in history-Mirabaud- thanks to the generous help I received from Thomas Jundt, designer and owner of the boat.
This will be followed by more boats including the Rave, Moth and ,hopefully, the R Class, Hobie Trifoiler and Doug Halsey's remarkable surface piercer.
==================
LOA 26'
--
Beam 17'
--
SA:
a.big rig= 355sq.ft.
b.small rig=258 sq.ft.
--
Weight:
a. hull+rig= 374lb.
b. crew= 528lb.
c. all up sailing weight= 902lb.
--
Foils- two fully submerged foils, one on daggerboard ,one on rudder:
a. mainfoil area= 3.77 sq.ft.
b. rudder foil area= 3.77 sq.ft.
c. mainfoil loading*@ 80% of sailing weight= 191.4lb./sq.ft.
d. rudder foil loading* @20% of sailing weight= 47.85lb./sq.ft.
e. nominal angle of incidence of mainfoil= +.5 degrees
f. nominal angle of incidence of rear foil= 0 degrees(trim+1 degree,-2 degrees)
g. mainfoil flap angle= +/- 12 degrees
h. rudder foil flap angle= +/- 12 degrees
*Note from Thomas:
a. at take-off(8.5 knots) loading is 50% main foil; 50% rudder foil
b. at 23 knots all load on main foil
--
Altitude Control System-Mirabaud uses twin wands set about halfway between the bow and the mainfoil and in 2010 will use, for the first time, a manual control system that bypasses the wand for direct crew control of the mainfoil flap particularly in rough conditions.
=================
W/SA(weight in pounds divided by SA in sq.ft-big rig)=2.54
SA/total foil area(both sides-not struts-big rig)= 23.54

=================================
See this thread for a comparision of Mirabaud and Rocker: Unlimited C Class Sailboat Racing Rule (UCCSRR?)

[peterraymond]

OK, I've gone through 61 pages. I'd feel like I've followed foiling from it's birth, except that I remember when Longshot and Yellow Pages were the latest hot boats and Russell Long had the prototype Tri-foiler at the Atlantic City sailboat show, before he joined Hobie.

If I'm going to post, I have to have at least one question. I've downloaded vortex95 to my version of Excel 2007, which is set up for Macros and Visual Basic, but I get an error during the download process saying that I'm missing some Excel component. I haven't tried to use it yet, but I'm assuming it won't work. Can someone give any clues?

Now a comment. Seems the goal of this thread is to share knowledge and to learn. Could we maybe collect pointers to various resources? Is there some place to do that on this site? Would someone be willing to host the collection on their site? The eventual goal could extend to a joint VP program that would be generally available. Maybe a basic one that covered Moths for a start. People interested in more would at least have a starting point. I'm thinking it would be in Excel and would include ways to import the data you need from other programs. We could call it FoilerSpeed and it doesn't have to cover everything.

The Bill Beaver, John Zselecxky paper on the full scale testing of a hydrofoil moth is one resource. Another is Vortex95, if I can get it to work. A third is Xfoil and a 4th would be something on sail performance. The best I think I've seen is the Finn sail testing and other sail information in Marchaj's book Aero-Hydrodynamics of Sailing.

There has also been a lot of good information on control theory, but I think that's a separate program. We could call it FoilerStability and it would take input form the same sources, or from FoilerSpeed.

Until I put it down, this seemed like a simple idea. At least it's simpler than trying to jointly design a boat, but of course I have ideas there too. Today I'd just like a way to play with those ideas.

Comments?

[Doug Lord]

It might be worth asking Jeff-the owner/moderator if we could have a "sticky" post at the begining of the thread that has references gleaned from the thread and other places posted and doesn't move.
There are lots of angles when considering foils and you touched on some. One important aspect-at least to me- is developing foiling systems that are easy to use and nominally crash free with top end speed a second priority-a refinement of technology that could lead to a "Peoples Foiler" someday.
At any rate, welcome to the thread-don't hesitate to contact Jeff-he may have an even better idea.

[ancient kayaker]

Peter: your version of Excel is likely missing a component of a more recent version. You could searching for it try the Microsoft web site, assuming you know the filename. I'm not a computer expert but I would have thought that, if your copy was registered you would have been getting automatic updates: this is a feature that can be turned on or off - you may want to check that.

Jeff is struggling with a number of forum issues right now and may not be able to respond to a request for new features immediately.

[laurencet]

Hi Peter
I would have guessed the opposite with excel.. the vortex spreadsheet works perfectly with 2003. We had all sorts of problems getting macro's written in 2003 to work with 2007. Sadly i wasn't the one who got half of them to work.

I'm working on a spreadsheet, working through the hydrodynamics for a surface piercing system. A lot of the direction of the spreadsheet seems to be driven from the design. but equally changes the design. For example the 50 odd lines looking at neutral balance will only work for certain sail shapes, this then impacts on rudder and foil design but would be completely different if using multiple sails or twin rudders. It might be possible to get one working for a moth design with minimal variables but anymore and the number of variables becomes massive.

[peterraymond]

Doug said: "It might be worth asking Jeff-the owner/moderator if we could have a "sticky" post at the begining of the thread that has references gleaned from the thread and other places posted and doesn't move."

I'd like to call it "teach a man to fish", but "design resources" might be more obvious.

laurencet said: "It might be possible to get one working for a moth design with minimal variables but anymore and the number of variables becomes massive."

I think I realized this as I was writing. I think it would be best to start with those minimal variables. Something along the lines of the calculator at VB sails:

http://www.wb-sails.fi/news/SailPowe...lc.htm#Results

but configured to work for a moth. The sail parameters might be fixed, but you could change foil dimensions, skipper position and/or other variables. Simplest would be to let you pick speed, sailing angle and that sort of thing.

laurencet also said: "We had all sorts of problems getting macro's written in 2003 to work with 2007." I suspected that because the spreadsheet was titled vortex95, not vortex2010.

[Doug Lord]

There is a rumor that "AMAC" designer of the Bladerider and Mach II Moths may be about to introduce new foiler designs that aren't Moths. This could be real interesting! Peoples Foiler maybe?
http://www.mcdougalldesigns.com/McDo...ils_Sails.html
--------
Most recent "Peoples Foiler" threads on boatdesign: Peoples Foiler II-the newest boats

[bistros]

Originally Posted by Doug Lord

There is a rumor that "AMAC" designer of the Bladerider and Mach II Moths may be about to introduce new foiler designs that aren't Moths. This could be real interesting! Peoples Foiler maybe?
http://www.mcdougalldesigns.com/McDo...ils_Sails.html

How about attributing the "rumor" to Clean on Sailing Anarchy (at 7:39PM)? This wasn't your "scoop".

You even get honorable mention in the thread for the excitement it will cause you.

--
Bill

[Doug Lord]

Originally Posted by bistros

How about attributing the "rumor" to Clean on Sailing Anarchy? This wasn't your "scoop".

--
Bill

===========================
I appreciate your interest but you are wrong. For this particular story I have my own sources.

[Doug Lord]

This is interesting:

"Caring for your foils...

We want to advise you that extremely high temperatures can have a detrimental affect on foils. If you sail in typically hot enviroments, or are planning on attending events in hot climates please be aware that your foils are highly technical pieces of equipment and accordingly care is need in looking after them.


Mach 2 foils are a pressurised and sealed unit. Adverse temperatures can damage this product.

Keep foil temperature under 50 degrees"--- must be Celsius=122degreesF

[bistros]

Originally Posted by Doug Lord

This is interesting:

"Caring for your foils...

We want to advise you that extremely high temperatures can have a detrimental affect on foils. If you sail in typically hot enviroments, or are planning on attending events in hot climates please be aware that your foils are highly technical pieces of equipment and accordingly care is need in looking after them.


Mach 2 foils are a pressurised and sealed unit. Adverse temperatures can damage this product.

Keep foil temperature under 50 degrees"--- must be Celsius=122degreesF

pV=nRT

The ideal gas law, combines Boyle's and Charles Laws. Once you seal an enclosed gas, increases in temperature will attempt to cause volume changes. Since volume changes are very limited, pressure increases are the result. At some point (obviously 50 degrees C), these pressure increases will result in failure of the sealed chamber at it's weakest point.

I guess they had to balance to problem of sealing the core versus the potential for water ingress. They chose to prevent water ingress and the result is temperature sensitivity.

50 degrees C isn't that high - many places will reach 35-40 degrees C ambient, and the black/carbon color of the foils will raise the spot temperature of the foils well beyond 50 degrees C in a 25-30 degree C summer day (@85-95 degree Fahrenheit). Bagging the foils in a light colored foil bag should be immediate once the boat leaves the water.

Everything in product development and engineering is an exercise in compromise and choosing the least problematic of multiple bad choices!

It is surprising the United States hasn't given up the ghost of the Imperial measure of temperature like the overwhelming majority of the world. I grew up with both, but am now far more comfortable with Celsius, even though it doesn't graduate as finely in Fahrenheit. I still have to translate temperatures for my parents so they understand what it means.

A couple pretty simple (and memorable) gauges: -38C = -38F (same), 0C = 32F (freezing), 16C=61F, 28C=82F. The 16/61 and 28/82 ones are remembered by flipping the digits, and unfortunately I get to see the -38 meeting point once or twice a year here in Ottawa.

--
Bill