Courgar, Hijack away! We need to get this class of boat back and sailing more in the USA.
I made the sails, under the tutelage of Dennis Desprois (Walrus Sails). He’s some-what local, and I’ve helped him with some computer stuff. In exchange I asked that he show me how to make a set of sails. I was really surprised at how easy it was, with the right tools.
But I still frustrated in finding sail material. Trying to find 1.5 mil thick hazy polyester film has been impossible. I’ve called/emailed most of the USA wholesaler’s and none have 1.5 mil stuff. Even 2 mil is difficult, but somewhat available.
Here is a picture of some common foils, each are the same scale, just overlay-ed.
(the weirdness at the trialing edge is just an aberration when making the lines thicker and of different colors, so just ignore it)
I want you to take a guess at the documented stall angle for each foil, then pick which one you would use for a rudder.
guzz.
what do you think the problem is… boats too expensive… or not available?. the big reason where it was in low numbers is because no boats were available. and those that were… were $2000 and up…
i went to one reggata and a guy showed up with a skaple… and just ran away from everybody. I had my monarch and was able to stick with him for a bit… but then down wind… i got left behind…
my new boat i drew was going to be better dowwind … did you draw your boat… or did you buy a design and build…
I personally think it is the self fulfilling of what I hear all the time “It’s a dead/dying class.” It’s only dead or dying because people say it is. The story I keep hearing is that because of the Skalpel. I will admit that in the right conditions, the Skalpel is an awesome boat, but it isn’t the beat all of all boats. I’m actually surprised that it beat you downwind. When we did the National this year, the downwind legs and the light air was the equalizer for the Skalpel. If we only kept our normal light air, the Skalpel would have had issues.
But what somewhat disgusts me, is that when the Skalpel came out, and it took off beating existing boats, from what I’ve read, and the people I’ve talked to, it looks like everyone just threw up there hands and gave up. No one really looked at it as a challenge, to figure a way to out-do the Skalpel. I’m just starting out on sailboats, so I have some catching up to do.
I built my Monarch as per the plans. Like I said, sailboats are new to me, but sailplanes and such I have experience.
Guzz
the start of my marblehead addiction was at a IOM reggata. I had been sailing and racing IOM for about 11 years… building my first one from a set of plans from a british mag… Rythmm… good all around boat but not a speed demon. It got you in the water , that was it… then i start to design my own IOMs…
anyway. this guy showed up and asked if he could sail during the lunch hour. so none of us had any problems… we ate and i watch… one of the things that shocked me… was how fast that boat could tack. i went over to talk to him. and he handed me the transmitter… at that point… I had to have one. the boat was a rocket . even at 15 years old… made of wood. and had a cordless drill as a winch.
the club that i belong too did not want marbleheads because of the expense. and for the reason . you show up with a skapel… and you win… I never liked that so i got plans for monarch( like yourself) and built it. used it a trial horse and design my own ( intimatador) if my marblehead keeps doing what it is doing… i will mold it and it maybe come a club boat. by no means am i saying this is the boat to get… but i do believe we can get the class back up and going … IF we can get the sailors back into the boats. the only problem i have with both my boats… is the a class mast.
I drive a 1999 honda civic… and for the mast to fit… it sits with the back seats down… and the mast head crane… sitting on the dash board…
if i can get a few more guys interested in the class… i dont mind shelling out the funds for a mold…I dont have a vacume bagger… but i can lay up a few hull… and each member builds thier own set of sails. and find a rig
i posted 2 pictures here…the blue boat is my design Intimatador, the black boat is Monarch
Hi Guzz
I pickup the sketch and added the data I vave in my old notes since years and recent readings already mentioned and I also added the data that you referenced.
I repeat I’m not a specialist on profiles I just follow what suggested by others navimodelers.
Probably the Reynold’s Number is also relatively high for the rudder .
Here the sketch
For a fin, your Re is too low for a M. My fins have a chord of ~100mm at the top and 75 at the bottom. Hull speed is ~ 2.5 to 3 mph. That should give a Re closer to 100,000 to 150,000 if I remember correctly. I think you are mistaken in your AOA. That is set by the need for lift, which is related to the fin area and forces on the boat. I could be wrong as I have not looked at this stuff for a while.
Skalpels are beatable, but it depends on conditions. You will notice that other designs have won the British championship the last few years. Problem is the Skalpel is very fast in the socal sea breeze conditions.
You are right because my hypothetical fin was only 80mm wide and the wind speed only 0.8m/s = 1.55kn.
Instead I confirm that the Angle of Attack for the fin is constantly around 4°-4.5° as the boat route is the same during close hauled unless I’m wrong !!
Cheers
ClaudioD
Claudio took some of the fun out of the quiz. The idea was just to have people “guess” at what they thought was the documented stall angle.
Here’s the answers:
letter - foil - % thickness - Stall angle
A - GOE 460 - 20.5 - 13.7
B - NACA-0016 - 16.0 - 10.0
C - NACA-0009 - 9.0 - 5.5
D - NACA-0006 - 6.0 - 2.5
Now for something really different.
In talking to someone who has an aeronautical background (I pick his brain when I’m stuck), he brought up an interesting concept during my last Q/A session. He pointed out that the rudder basically won’t be stalling as much as everyone thinks it is. By the time the water gets to the rudder, it is back to a near 0 degree angle of attack, so you’re not stalling it. (we didn’t talk about the fin/keel).
He then pointed out that when you turn the boat, the fluid flow is dynamic and that if you just hold a position on the rudder (say 7 degrees), the rudder will only be stalled for a very, very short period of time. Because as the boat rounds in the turn, the fluid flow will be back under the stall angle of the foil. As he put it, “In very simple terms, it’s a self correcting system. If it wasn’t, the rudder would just be a brake.”
The concept one has to over come, is to stop thinking about the foil being stuck in a flow tank (which is where all the “numbers” are generated), and think of it in a dynamic environment. Changing the angles, changes the flow direction.
Apparently, one of his professors was a bit of a modeler nut, and used model planes and boats as examples in class to force them to think about the opposite ends of the spectrum (small surfaces vs large surfaces, low Re vs high Re, High viscosity vs low viscosity, etc.), and to get them out of the flow tank mentality.
Hi Guzz,
Thank you for your post .
I still remain affectioned to 12% for the rudder and 7/8% for the fin below 100cm boat and 10% for a rudder and 6/7% for a boat lenght over 120cm
Cheers
ClaudioD
The rudder does self correct if you can get the boat to turn. The advantage of a thick rudder foil is that it will not stall at super low angles and allow more force to be generated to start the boat turning when overpressed. In normal light air sailing it is not an issue and the thin foils work well. It just comes into play when you are at the limit of control at the top of a rigs wind condition. Then you need the extra force to get the boat to turn. I like a thicker foil section on the rudder as that extra bit of control when you are close to out of control can make a big difference and it does not seem to have a bad effect the rest of the time.
