Rolf, gotta remember, no tone on the internet. Your interpretation a lot different from my intention. My question was of interest, not of attack.

Didn't we cover this a few months ago ?

I'm completing a research assignment with respect to very large scale wind turbines remember ?

The kind that are placed off-shore in windparks like these :




Working on the control flaps to increase fatigue life of blades and bearings by counteracting the aerodynamic disturbances; called the Smart Rotor Concept.





Although you have to ignore the flaps near the root of the rotor blade, these are pretty useless and have been disgarded a long time ago. The two flaps near the end are still in the project.


This project is consuming large portions of my energy and time. 6 more months to go. Simply put I got other things on my mind.

Still, I don't see myself get much better at racing cats though. I'm not really interested in putting in the time and effort to reach the top; Besides the level of cat racing in the EU is pretty high so reaching the top requires a considerable amount of time and effort. I'm also gethering the years so to speak. The time for dreams in the direction of top sport has passed for me; I expect to mainly sail and race recreationally and I can do that well enough with the skills I have now. The future belongs to the younger sailors among us; from now on I simply want to enjoy myself.

Wouter

Thanks for clearing that up. I reacted like I did becouse those "rounds in the past" is bad both for the class, PR wise, and the crowd here at Catsailor.
I have not sailed this summer becouse I dont have a boat, and the only cat available is certainly not high performance. Suits me well as I have been able to think a lot about my sailing and do some stuff around the home. The "great wall of Molde" is what Marcus have taken to calling my summer project.. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> Lost 8 Kgs in the progress and almost got my handstand as well. Next year I certainly hope to be able to sail a lot more, like 3-5 days a week). There is sunlight until 2300 in summer, and it dont ever go really dark.

Marcus,

Don't you increase the drag by opening the main, when bearing away? And don't you loose pressure by doing it also?

Gill

I am not Marcus, but I'll have a go anyway as I am stuck in front of the computer.

1: Drag and force are not linearly proportional to each other over sails.
2: We must try to make the sails produce as much power for as little drag as possible, in the direction we want to go.

By opening the main you decrease the drag, and direct the force generated more in the direction you want to go, in my opinion.
More pressure is not always to the good if what it do is generate more drag and a force in the "wrong" direction.

Perhaps Marcus has some better way of explaining, or a better point of view <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

I agree you need to easy the mainsail a little when bearing off.....

Consider.

1, Gust hits, you accerate
2, As you accelerate you sheet in a little and the hull lifts (you may or may not sheet in)
3, As the hull lifts, you bear off, what happens to the apparent wind? It heads aft and so you need to sheet off a little.

I just sail a F16 solo downwind with enough mainsheet tension to protect the mast. However, I find it better/easier with enough wind to keep the windward hull flying higher than usual, it looks better in the photo's for starters and the other reason is because (and I'm sure to be corrected) I feel that it produces more buoyancy in the leeward bow! To me it feels as if I've changed a displacement hull into a plaining hull by the heel of the boat.
Fire away...........I also capsize (occasionally)
I'll probably answer the sail, drag question the day before I hang up my harness which I hope wont be for a long time <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Hey everyone, just wanted to let you guys know there is more updates on the website at

http://boatsbikesboards.wordpress.com

on the latest prebend settings for the Viper.

We're really going towards a much more powered up rig on this boat as the width of the boat and the power of the downhaul seems to allow us to do that and still sail within a really wide range of conditions. Greg has also been moving towards a much more powered up setting for his viper.

Gill, with regards to opening up the main with the kite up, I can't really explain the aerodynamic forces, however, over the weekend, we experimented with opening up the main and easing the spin off about an arm's length while bearing off downwind (once the hull was already flying and there was a good bit of apparent wind) and we found that we could bear off and go deeper for a longer time before having to head back up to generate more apparent wind.

I actually found that by easing the main at the right time helped to power up the rig and keep our hull flying downwind. Hope this helps.

So what kind of reduction of fatigue are you looking at? And this increases the life by how much (guessing still estimation)?

Would those flaps do anything for us at the rear edge of our mainsail <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Exactly what I would suggest doing.

My area of responsibility lies in the control flap actuator design (using Shape Memory Alloys); other people are looking at the effects of fatigue reduction. Additionally, the right controller has a large impact on the achieved results; this is the job of yet another person. We are a group of people who at this time are specializing in our respective area's. Last year a setup was placed in the low speed windtunnel and even with a very simple PID controller the smoothing effect was quite dramatic. There is a movie available that shows the before and after, but as all within this project it has not been cleared for publication without authorisation. Same with respect to the data we have achieved.

Basically what I'm trying to say to you here is that theoretically the effect can be quite significant as supported by initial real life tests in much simplified (windtunnel) tests, HOWEVER, there are some serious issues to be solved in the area of the flap actuators and the also the multivariable controller. When the later is not implemented correctly then the system can actually increase the loads and reduce fatigue life. In my case I need to boost as very inexpensive and simple SMA actuator to much higher speed and accuracy; this to avoid installing any expensive and complex hydraulics or pneumatic systems.

The data you are looking for is sadly not available yet with sufficient accuracy as that would require a real-life test setup comparable to the turbines being installed now. We are still some ways from that.

My reply has to suffice at this; both to limits in what we know now and agreements of confidentiallity.

I'm sorry,

Wouter

Seconded!! <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />

This is the kind of information, while generaly correct, can get you in trouble or at least make you slower if not used properly.

Keep in mind that if you want to sail fast down wind you are trying to maintain a constant apparent wind. In which case the main sail trim will not need to vary.

The biggest mistake I see with new spin drivers, is that they head up until the hull rises, then bear off til it comes back down. This technique almost always results in over stearing and huge fluctuations in your speed. On the 16 if your hull comes up without a noticable increase in speed your weight distribution and or trim are not correct. On the 16 you need to move your weight around a lot. The acceleration is what you are trying to achieve, not the lifting of a hull.

Also be very aware that buy easing the sheet or traveler in conjunction with bearing off in a gust, you open up the sail and present a big flat area of sail dirrectly in front of the wind 8.5 meters up in the air. This is the perfect recipe for stuffing the bows in every big gust.

Thanks Wouter. One of the funds I work for does a lot of wind investment in Asia so interesting to hear of new tech. Lot of stuff coming out of India and China for sure.

And I second that !

Wouter

Well, certainly 2 schools of thought here. I sailed Taipan 4.9s sloop rigged and A-Classes. Going wild downwind is standard behaviour. Means you have to work hard to keep the apparant forward. Moving to kites I found it easy to cleat and forget the main initially. But after a while (and with a gd crew) played the main similar to the T49 and A and found good increases in speed. Especially in conditions where there isn't enough wind for the crew to be out on the trap.

Probably all down to the technique of how you steer and react to the gusts.

I do not agree that you are trying to maintain constant apparent wind. You are trying to go as fast as possible and as deep as possible. As you accelerate the first thing that happens is that the apparent wind moves forward, thus you need to (maybe) sheet IN. If the hull rises (it may not) you then need to eaither let some sheet off, or bear off. IF you bear off, the apparent wind moves aft, thus you may need to sheet out, but as you bear off, you may continue to accelerate and so you may NOT need to sheet out.

What we are trying to do is stay at max speed and also drive down on any gusts which allow you to sail DEEPER and FASTER.

IF I had 3 hands I would hold the tiller, play the kite and play the mainsail downwind. As I only have 2 hands I have to compromise and so I cannot play the mainsail down wind very much and so it has to be cleated.

Your comment



is not how I see it. When I've been sailing 2 up (Hurricane 5.9) and the bows dive in, the quickest way to get the bows out was to easy a few inches of mainsheet - this opens up the top of the mainsail and dumps a little bit of power just where the most torque on the bows is coming from. This is what I think Bundy was doing in the onboard video from the medal race at the ollies, ease the mainsheet to pop the bows out of each wave they went into.

This is actually the core of the discussion really :




I would say this sentence is imcomplete as


.... thus you need to (maybe) sheet IN or BARE-OFF

As the latter moves the apparent wind back to the original angle for which the sails were trimmed, avoiding any need to adjust the sheet tension.

Basically you can keep the apparent wind angle to the mainsail constant by changing the course of the boat and indeed sheeting the spi. That way you can optimize the performance while having only two controls in your hand instead of three. Of course when doublehanding your have 2 times more hands and can do more. Personally I only played the mainsheet traveller when 2-up to cut-off a rapid rising of the hull when I was too late steering.

Wouter

You could write 5 books on how to do this. Nothing is ever straight forward, at least technique witten in a single sentence. I have seen a lot of new guys (myself included) get distracted by procedures like playing the main down wind.

FASTER is the goal. The DEEPER part only comes from bering off in order to maintain a more constant apparent wind. My take on this is that the proper technique for maintaining you weight placement, and your steering are by far the more important functions for going fast. Playing the main sheet is a very fine adjustment (so you keep your back stay pressure at a min) and while, if done correctly, will help, is way down on the list of skills to master.



This is OK --BUT -- The typical reaction by the driver in a gust is to bear off. This moves the apparent wind back, add the nose diving and the boat slowing down and it goes back more. Let out you sail top and you are going swimming. Note Bundy was maintaining a forward apparent wind, and by easing his sheet and letting off some top he was doing as you say, but this was only sucessful, becuase he had forward apparent and he did not attempt to bear off.