Rolf, at 40 I was invincible, at 50 it was oooh things are not the same as at 40, at 54 I'm worried about the speed of the rate of that change. You will notice a real differnce beteen 40 and 50's, I certainly have. Still trying to keep fit and enjoy the wilder side of life, sadly given up endurance motorcycle racing after finding the rate of recovery from injuries was affecting my work hours but do a bit of Mtbing, ski ing and now beginning to get to grips with http://www.lenzsport.com/gallery_focus_ski.php?gallID=12. Here is Bitsa 4 http://www.skibike.me.uk/2011_04_01_archive.html scroll down to the 15th April.

Oh the Auscat Flyer 4s is listed as having 0.1 sqm of board area in the SCHRS listings, I think mine has even less as it has had the boards changed to high aspect ratio boards. mmmm.

Thanks Wayne!
I felt invincible and immortal in my 20s. In my 40tieth year I know I am very much mortal and subject to stresses of all kinds.
Guy who taught me mountaineering/climbing was in his 70s back then. 20 years later he is telling me that he is beginning to feel the age. Still active in off-piste skiing, climbing and ocean swimming through his 80s. Similar quotes from others with more experience who still are motivated and active give me hope Avoiding flab and retaining max strength seems to be the key?

Snowbiking!! Now why is that more fun than skiing or snowboarding?? I mostly go backcountry with my snowboard and I have a problem seeing myself enjoy the ride down again on a snowbike

A-cat sail area incl mast is ~13.94m2 with 0.1m2 of board area in total?
Higher AR should increase efficiency but some area is still needed. Would be very interesting to have some numbers on this.

At 40 I could diet moderately, do some walking, lift a few weights and see an immediate result.

From 60-62 I was not able to gain any measurable strength after a quick modest gain. No amount of work produced a weight loss. Only severe caloric restriction produced any weigh loss at all. Frankly, I'd rather be fat than give up cookies and milk.

Cheers!

I believe diet is the key to 90% of staying well as time passes. Diet is however a very controversial topic. It is so personal to many people and there is no best practice. Choose your poison

Working out for sure helps this tender 40 year old.

Snowbiking came about for very different reasons. Two of my friends could no longer come sking with us due to a damaged knee and the other a car accident damaging his tibia and knee joint. Ski biking gives them an opportunity to join in with the fun and so we all decided to learn together. I've been skiing for a very long time so was quite keen to give it a go. After 6 days we were competant enough to tackle most slopes, the learning rate was quite fast.

yep, better live happy and short than long and sad

Rolf,

basicaly board area depends on two factors:
* avoid stalling at low speeds (e.g. being manouvrable at the start line)
* avoid cavitation at high speed
Both depends on the force which the rudder or board has to produce. The force depends on the boat balance and leeward force from the sails. The leeward (or better sideslip) force of the sails depends on their efficiency and the righting moment of the boat. Since a A-cat has a higher mast and a more narrow platform the sideforces are considerable less (especially compared to a double handed F16). I know this from my boat: The board size is just fine double handed, single handed up-wind it is a bit too much so I can drop the traveller a bit to get a more reasonable sail angle of attack. It may be a bit cryptic what I say, so don't hesitate to ask if you want to know more details.
The foil which I posted here some time ago was for the Tornado (which is now history , like us human beings, boats don't get fitter with age...), where we had high speed cavitation problems (I am really not wondering, even todays Tornado rudder look like F104 sections for me, you know the aircraft they called a rocket with wings). Maybe you want to go with a bit more low speed focused section. Again, don't hesitate to ask. I have started a small report about foil design for boats, which I want to finish a publish hopefully soon.

Foil planform is as important as the section, but much simpler. You can go with all those fancy shaped boards, we have seen, but you can achieve the same with a simple trapez. You can achieve it even with a rectangular shape with some forward sweep, if you dare to do something others don't do. The basic idea is to have an elliptic shape. You can do this with an elliptic planform or with a trapez with a 0.4 chord ratio and zero sweep at 25% chord. If possible from a structural point of view, the rudder should have the same depth as the board. Don't stick too much about aspect ratio, absolut depth (draught) is more important than aspect ratio and a larger rudder can have less drag than a small one.
I personally think that a homebuilder can make a good foil only with a simple trapez planform, because the surface of the foil is only single curved (unless you have a buddy who has a CNC machine). Already a small change in thickness distribution will ruine the hydrodynamics (1% percent change in thickness has lot of effects, 1% is equal to 1mm on a board with 100mm chord).

Cheers,

Klaus

Wayne,

that makes perfect sense. Creative way to continue enjoying downhill skiing!


Klaus,

thanks for writing up that info.
I always thought the ideal was to have ellipitcal pressure distribution over the foil, not neccesarily to have an elliptical foil. Reading what you wrote I think that is still valid.
Doing anything but a parallell sided rectangular foil is prone to errors without a CNC. I found this link which looks like my best shot with no CNC. Especially as a good friend offered to laser-cut templates on a CNC laser cutter.

http://www.duckworksmagazine.com/09/howto/foils/index.htm

Doing a cut after routing and then sanding/fairing before pulling off moulds is a real option. The same for rounding off the tip by hand at the bottom. Getting the proper section in that area will be hard. Dont know if the gains outweights the extra drag and loss of lift I will make with my unskilled hands.


I have done three sets of foils earlier by hand. Wood, plane and sand. Free hand.. None of them turned out really well. Partly becouse of design and partly becouse shaping wood by free hand is difficult.

Tornado rudders from Marstrøm was pretty good compared to my homebuilds. Yes, they did cavitate some times. Not a pretty sight when double trapeezing. I always thought the class overloaded the rudders with the mast rake. We sailed with less rake to overcome cavitation problems. They still happened, but not so often. Sheeting out a handful reattached flow.
I am really really surprised that you think the T rudders were designed for a speed much higher than obtainable by the T. With the amount of resources invested in producing a faster T around the course the foils is a very logical place to do research. The centerboards were of course very hard to optimize due to the class rules defining their planform.

When you mention forward sweep, you advocate installing the foil with a bit of forward sweep? Not seen that in a while
The idea is to produce elliptical pressure distribution or to delay ventilation? Cavitation should not be an issue with a daggerboard operating in turbulent flow under the hull?


Looking at the "state of the art" daggerboards in the F18 class, they have gone for higher AR and shorter chord. I think the Wildcat from Hobie have daggers with an 180mm chord! Effective length when fully down 1130mm. Pretty extreme compared to older designs and probably a handful on the starting line.

What I really would like is to buy something ready made with reasonable performance for a reasonable price
I have been unsuccessful in finding that and nobody is sending me plugs or moulds in the mail so it looks like I will have to shape something myself. A "good enough" planform that is easy to shape with a relatively robust profile (building in the garage, able to handle the starting line, tacks and jibes) with adequate lift and reasonable drag. Hmm, sounds like mission impossible..

I would be very grateful for any suggestions or help on this


PS: I definately would prefer to live long and happily!

What is your diet like?

The Zlin Z42 is the classical example of a rectangular wing with near to elliptic lift distribution. The benefit is to have only one sort of rib, instead for each section at different rib.

I would not take F18 as an example. Since the foil (and hull shape) is the only "unlimited" part of the boat, builder try to differentiate here, well I think that's why you put the quotes around it). At the end they have very different daggerboard and rudder length, so induced drag is not as good as one may think. I guess that shapewise A-cat (before c foils) is a better example.

Actually I think the foil looks like a section of a Mach 2 fighter aircraft from the sixties and hence totally unsuitable for a boat. They are very thin and pointy at the nose and this causes the early cavitation. I guess in the beginning without spi and single trapez it was fine, but once the boats got faster... My friend had an old (30y, Panthercraft I think) T. Later he bought some of this wood core rudders. Very beautiful, but as thin as the old once. So I didn't see evolution in the rudders.

I think I would ask a carpenter with a CNC machine to cut me the wooden core and laminate glass or carbon around it and sand and sand and sand... I don't have the talent to cut and carve it or cut and fill it (as in your link) by myself.
Other possibility, ask the carpenter to cut a female mold or cut your female mold from wax or foam with the hot wire method (not sure if it works for high aspect ratio). Or take an existing one and take a negative of it...
I don't like the female mold method because it is difficult to get a reasonable core or framework in the rudder. That's the reason why so many boards are heavy like stone, overcame the core weakness with extra skin thickness. If you have a wooden core you can go with glass and you are still lighter than many carbon boards.

From a structural point of view the ultimative boards are extruded aluminium: Topcat
You may ask the dealer for a price.

Cheers,

Klaus

Well Bitsa deservidly has been back on the water this year after quite a revamp. Back on with the A rig after the really unbalanced F16 low aspect rig created so much drag at the back, move the travellor foward to accomodate the much shorter foot giving me a chance to remove the gantry rudders at the back and go more conventional, fix the hole from the damage caused by the extra drag from the T foil / gantry, rejig the main sheet to a cascade system, and move the main sheet to the front.
http://imageshack.us/photo/my-images/401/bitsa006.jpg/

So a very different boat. With the A rig on Bitsa is very well behaved, with almost neutral helm with just a touch of Lee helm when the spinny is really loaded up. I do like these A Rigs and despite being only 14sqm it is just as fast as the 15sqm F16 rigs. The class is really missing a trick here as A rigs are available secondhand with the early masts being more than strong and stiff enough to cope with the spinny + the development of sails and masts will always mean a steady supply of S/hand and huge amounts of development

I do like the very foward position of the sheet for the single hander.
http://imageshack.us/photo/my-images/40/bitsa005.jpg/
Everything you do is facing foward out of the boat, and right where you want to be pulling from, out on the wire upwind your feet are locked on and if you pass the sheet foward of the rear stay, you can edge foward to the front beam.

I can only recommend the cascade system as being not only cheap to build, effective but buttery smooth.
http://imageshack.us/photo/my-images/507/bitsa004.jpg/

The new rudders have been good, maybe a bit old fashioned in aspect ratio but do the job. I do need to be careful as they can be pretty effective brakes if you turn them too much in a tack.
http://imageshack.us/photo/my-images/444/bitsa013.jpg/

So to sum up things then, yes I am pleased with the way the boat is beginning to shape up. In comparison to the new Nacra F16, it would seem pretty on par if not better upwind, just a fraction slower downwind and that I suspect is more the spinny rather than the boat. So no excuses, down to the skipper then

http://imageshack.us/photo/my-images/405/bitsa009.jpg/