Curved daggerboards in A-Class

LCD

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When we started building the LR2 and then the LR3 I wanted as stiff a platform as possible. Panel stiffness is directly related to core thickness so I used 9mm Corecell and 6 oz. carbon skins. We have great panel stiffness. When it came to beam attachment I used a four step approach: first was to wrap a piece of 6 oz. carbon under the beam and up onto the hull; the second step is to gussett from beam to hull with a 2" wide strip of carbon cut on the bias; third step is to glue 9 oz. carbon uni straps around the beam and onto the hull; the fourth step is to bog a fillet from beam to hull and laminate a final wrap of 6 oz. carbon over the whole area. The platform has very little rack and our third boat weighed 150 lbs at the 2007 Worlds. Details and photos at:

LR2ACATS : LR2 A-Class Catamaran

John Lindahl @ LCD

 

SimonN

Super Anarchist
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Sydney ex London
Lots to talk about!

First off, I thought I had worked it all out. Steve had explained that cuved boards and position is a 3D problem and I got that. I worked out where the boards need to go in my boat. Then he convinces me that rig tension will stiffen up my boat and I have designed a really neat system to allow as much tension as I want and still rotate. I am even beginning to convince myself that the compression loads on the mast will, when set up right, make rotation an even more effective depowering tool. Then I read the news from the worlds.........

So, now I need to consider canting the rig. It seems to make sense to go with the curved foils. As has been reported, the rig is providing a significant proportion of the downforce, which is why the boat leaps up in tacks and gybes. Reduce that downforce, by canting the rig, and you don't need the foil to work as hard for the same amount of lift, or you get more lift for the same drag. Just when I thought this was getting easy............

The first thought is that I suspect this adds to the 3D problem that Steve was talking about, as canting moves the centre of effort. So, unless I am mistaken, if you cant the rig you either have to move the boards forward or rake the rig more. Have I got that the right way around?

Then there is the issue of how to cant and I cannot wait to see the photos. With the amount of rig tension most of us carry, this shouldn't be too much of a problem but when one considers that i have been looking at increasing rig tension to stiffen my boat, I could be in trouble.

And while on platform stiffness, I just want to come back on comments from Aus (Ben?).

I think the main construction stiffness control in a modern A is in beam size and beam to hull attachment. The trend on the new boats having as much gluing surface of beam to hull is a huge factor.
I think this misses the real issue and is a blind alley. Steve sums it up well when he discussed the stern beams s bending, torsional rigidity of the hulls and the main beam. These are not issues of gluing surface of beam to hull. In fact, I suspect that in some cases, that can be counter productyive as it simply shifts the problem from one place to another.And I should also add that I don't see any real isuses with panel stiffness as such.
For me, the issue is that one needs to treat the whole platform as a single monocoque. As such, I am more interested in the torsional stiffness of each hull as a complete unit. I believe that I have now identified that this single factor is contributing to over half the undesirable bend in my platform and this is why pre-preg crbon-nomex boats have the potential to be so much better.. Next, there is the issue of using round tubes for the beams. I particularly like the way that the Nikita and DNA use profiled sections to specifically increase torsional stiffness in these components. I think the days of the round beam are numbered.

Finally. I think one needs to pay very close attention to the way the beams join the hulls. Again, I like the thinking behind the DNA, which looks at ways of making the whole thing far more one unit, rather than gluing together 4 seperate parts. To me, the ultimate will be a platform that is built as a whole, with far more attention being paid to how the beams integrate into the hulls to work as a complete monocoque construction.

 

AClass USA 230

Anarchist
958
47
Louisiana
Lots to talk about!

So, now I need to consider canting the rig. It seems to make sense to go with the curved foils. As has been reported, the rig is providing a significant proportion of the downforce, which is why the boat leaps up in tacks and gybes. For this discussion, how is the rig producing downforce and where is the downforce acting?

Reduce that downforce, by canting the rig, and you don't need the foil to work as hard for the same amount of lift, or you get more lift for the same drag. Just when I thought this was getting easy............

The first thought is that I suspect this adds to the 3D problem that Steve was talking about, as canting moves the centre of effort. So, unless I am mistaken, if you cant the rig you either have to move the boards forward or rake the rig more. Have I got that the right way around? When you cant the rig, why is it changing the rake assuming you are referring to fore and aft rake?

Then there is the issue of how to cant and I cannot wait to see the photos. With the amount of rig tension most of us carry, this shouldn't be too much of a problem but when one considers that i have been looking at increasing rig tension to stiffen my boat, I could be in trouble.

And while on platform stiffness, I just want to come back on comments from Aus (Ben?).

I think the main construction stiffness control in a modern A is in beam size and beam to hull attachment. The trend on the new boats having as much gluing surface of beam to hull is a huge factor.
I think this misses the real issue and is a blind alley. Steve sums it up well when he discussed the stern beams s bending, torsional rigidity of the hulls and the main beam. These are not issues of gluing surface of beam to hull. In fact, I suspect that in some cases, that can be counter productyive as it simply shifts the problem from one place to another.And I should also add that I don't see any real isuses with panel stiffness as such.
For me, the issue is that one needs to treat the whole platform as a single monocoque. As such, I am more interested in the torsional stiffness of each hull as a complete unit. I believe that I have now identified that this single factor is contributing to over half the undesirable bend in my platform and this is why pre-preg crbon-nomex boats have the potential to be so much better.. Next, there is the issue of using round tubes for the beams. I particularly like the way that the Nikita and DNA use profiled sections to specifically increase torsional stiffness in these components. I think the days of the round beam are numbered.

Finally. I think one needs to pay very close attention to the way the beams join the hulls. Again, I like the thinking behind the DNA, which looks at ways of making the whole thing far more one unit, rather than gluing together 4 seperate parts. To me, the ultimate will be a platform that is built as a whole, with far more attention being paid to how the beams integrate into the hulls to work as a complete monocoque construction.

I agree with these points about construction, but it could drive the price of the boats up significantly. A couple of years ago, a Spanish builder came out with the Balance design which seems to have disappeared(?). It had the construction approach of attaching the beams to the hulls inside the hulls to make the entire boat one intergrated structure.
 

SimonN

Super Anarchist
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Sydney ex London
For this discussion, how is the rig producing downforce and where is the downforce acting?
The rig is a wing. Tilt the rig, the lift still comes off the rig at the same angle, relative to the rig. It's how windsurfers are able to pull the rig over on top of themselves and sail boards that would otherwise sink. Moths do it as well.

When you cant the rig, why is it changing the rake assuming you are referring to fore and aft rake?
You can do a system that doesn't change the rake, but what i am suggesting is that either the rake or the position of the centreboard needs to change. It's the 3D problem that Steve describes above. I am uncertain but I think that as you cant the rig, the force vector off the rig changes. However, I intend to keep the foil where I was going to put it and simply play with rake.
I agree with these points about construction, but it could drive the price of the boats up significantly. A couple of years ago, a Spanish builder came out with the Balance design which seems to have disappeared(?) It had the construction approach of attaching the beams to the hulls inside the hulls to make the entire boat one intergrated structure.
I am not convinced it will have a major impact on costs. I believe that this is how the DNA attaches its beams and it isn't more expensive. It needs clever design, and if I ever find the money or backer, I have a way of building an A that will produce a very stiff platform, take less time to build, solves all the problems and totally integrates the beams into the whole boat. :D

 

AClass USA 230

Anarchist
958
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Louisiana
The rig is a wing. Tilt the rig, the lift still comes off the rig at the same angle, relative to the rig. It's how windsurfers are able to pull the rig over on top of themselves and sail boards that would otherwise sink. Moths do it as well.
Simon,

Lets say you cant the rig to weather in non-hull flying conditions where both hulls are in the water and the rig would be straight up down in the side to side perspective. First it would seem to me that you would have less projected sail area due to the weather (or even a leeward) cant of the rig. Second, if you could assume that you can produce the same drive force with the rig canted to weather as with it straight up and down, then in the 3D analysis it seems like some of the drive produced by the sail will be in an upward axis which while potentially unweighting the platform, would that also not be taking away some of the forward drive component?

I used to race sailboards and in light air we tried to sail with the rigs straight up to maximize projected area. We did not "cant" the rigs to weather until we were powered up, the board was planing, and we used the cant to not only depower as needed but also to help reduce the displacement of the board. I think foiling Moths are sailed with the same premise.

I see the cant possibly working on an A-Cat only when it is flying a hull and you cant the rig to where it is straight up and down or maybe even a slight amount to weather. I just don't see it working in light air.

A canting rig is different on a trimaran since nearly all modern designs have a dihedral angle between the amas and main hull. Canting the rig to where it is straight up and down on a tri makes sense in all conditions.

Interesting to say the least.

 

SimonN

Super Anarchist
10,531
752
Sydney ex London
I see the cant possibly working on an A-Cat only when it is flying a hull and you cant the rig to where it is straight up and down or maybe even a slight amount to weather. I just don't see it working in light air.
I totally agree with this. Totally vertical when you are on 2 hulls in light air, canted when you are flying a hull. The ineteresting one is what you do when you are downhill, big breezez, both hulls down. That needsa to be played with but I suspect you still cant.

I can't wait to see ho0w others are canting but I have just finished ndrawing up a nice, simple system, which will be going on the boat as soon as I see if anybody has anything better.
 

Steve Clark

Super Anarchist
Canting the rig may work well with curved boards.

Consider that as you heel the boards become more horizontal and thus provide more up force.

This gain would be off set by loss of rig efficiency. But if you can get the rig back to vertical, you get to keep the gain in vertical from the boards with out the loss in the rig.

Two other advantages of canting the rig to windward are worthy of mention.

One is that you move the CG of the rig to windward, thus increasing the righting moment.

Once again, not much because the CG of the rig doesn't move that far, but it may be enough to offset the loss of righting moment caused by the inclined boards. Once again allowing you to book more of the gains made from the curved boards.

The final advantage is strictly tactical. We used to practice sailing dinghies heeled to windward in order to get "better air" in congested starts and mark roundings. Simply put, you get your rig out of the disturbed air of the boat below you and into the air of the boat that is trying to roll over the top of you. In short it is harder to pinch you off and harder to roll you. The further your rig is to windward, the further ahead you are, the better you can claw out of congested starting lines and the better you can hold your lane.

SHC

 
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AClass USA 230

Anarchist
958
47
Louisiana
Canting the rig may work well with curved boards.

Consider that as you heel the boards become more horizontal and thus provide more up force.

This gain would be off set by loss of rig efficiency. But if you can get the rig back to vertical, you get to keep the gain in vertical from the boards with out the loss in the rig.

Two other advantages of canting the rig to windward are worthy of mention.

One is that you move the CG of the rig to windward, thus increasing the righting moment.

Once again, not much because the CG of the rig doesn't move that far, but it may be enough to offset the loss of righting moment caused by the inclined boards. Once again allowing you to book more of the gains made from the curved boards.

The final advantage is strictly tactical. We used to practice sailing dinghies heeled to windward in order to get "better air" in congested starts and mark roundings. Simply put, you get your rig out of the disturbed air of the boat below you and into the air of the boat that is trying to roll over the top of you. In short it is harder to pinch you off and harder to roll you. The further your rig is to windward, the further ahead you are, the better you can claw out of congested starting lines and the better you can hold your lane.

SHC
Steve,

I guess if the benefits are there, the question would be could you make it practical for use on the race course. On an A-Cat, I'm thinking you'd need to develop some type of auto-mast cant control design because I think it would not be practical if you had to adjust it each time you tacked or jybe. I'd love to see what Landy and Brad Collett have done with their rigs, hope someone will post pics.

I totally agree on your last point. The last time I raced Lasers, it was very fast to sail the boat upwind to where you felt you were heeling the boat to weather. Looking from behind, the rig was fairly vertical with maybe just a slight cant to weather. Last weekend, I was coaching two Laser Radial kids in 5-7 knots of breeze. One kid was sailing his boat upwind with a slight leeward heel. The other I had coached earlier to the heel the boat slightly to weather technique and as long as he kept the boat in the groove, he was noticeably faster forward. We tried to convince the other kid to try it but he had been coached by some Flying Squat sailors to sail with leeward heel in light air and would not change. I guess he did not believe his eyes!

Cheers,

Bob

It's interesting to sail a boat like an A-Class and come back to a dinghy and apply some of the things you learn even though they are "apples and oranges" in comparison.

 

SimonN

Super Anarchist
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Sydney ex London
Bob

I have some bad news for you! I don't think you will ever get an auto can't system as you need to cleat the system to keep the rig canted. I can only see these boats getting more complex and therefore more difficult, not the other way around. Look at what Steve is planning on his C and consider a tack in one of them. Now, that is mDe easier by having 2 people on board, so I see that in the A's, the secret will be developing single pull systems that alter more than one thing, such as cant and boards.

 

Jay Glaser

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Question on canting. Can the tip of the mast go beyond the edge of the "box"? Or is it like that boards that have to remain inside the box?

If no then what is the max cant angle you can get and does that get the mast to vertical when flying a hull?

 

Steve Clark

Super Anarchist
Assume for a moment that it did have to stay inside the box.

Which would be a reasonable, even though there is no other ban on things like kite rigs and flip tackers...

A 30' tall mast can cant 16.5 degrees before it goes beyond the max beam.

Hull flies at about 5 degrees.

So there is plenty of opportunity.

Didn't Pete do something along this line?

SHC

 

AClass USA 230

Anarchist
958
47
Louisiana
Assume for a moment that it did have to stay inside the box.

Which would be a reasonable, even though there is no other ban on things like kite rigs and flip tackers...

A 30' tall mast can cant 16.5 degrees before it goes beyond the max beam.

Hull flies at about 5 degrees.

So there is plenty of opportunity.

Didn't Pete do something along this line?

SHC
I love to draw pics (see attached). My interpretation is if you have 4 degree canted hulls at 4 degrees of heel (the boat heel will not change the box), the max mast cant is 8 degrees to stay in the box. I did not calculate, just drew it out to scale. The drawing is to scale with a 7.5' beam and 29' tall mast, 4 degree canted hulls, canted boards like on a Flyer II. I used my ASG3 shroud lengths (that I recently measured) to locate the hound height with the mast non-canted. Looks like you'd need about 12" (30 cm) of adjustment at each shroud to get max cant within the box. Even though I come up with a smaller cant angle than Steve, that still looks like a lot of movement to me to play with.

CANTING RIG COMPARE.pdf

 

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Jay Glaser

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Didn't Pete do something along this line?

Yes, and it was cool when everything lined up.

It looked like Bob's drawing as Pete was sailing away from me.

Nice diagram Bob.

Jay

 

AClass USA 230

Anarchist
958
47
Louisiana
Didn't Pete do something along this line?

Yes, and it was cool when everything lined up.

It looked like Bob's drawing as Pete was sailing away from me.

Nice diagram Bob.

Jay
Jay,

In the years I've sailed A-Cats against Pete, I don't recall seeing him with a rig cant control on the boat but I typically only see Pete once a year at the NAC!

I'm ready to try this on my Sprint 750 and I think it is an easy retrofit with the Colligo/Precourt systems. I just need to determine what amount of purchase and the loads. I think the 31OD's did it so I need to find some pics of their setup. Not sure we have enough arms on an A-Cat to handle another adjustment like this.

Bob

 

Wandering Geo

Super Anarchist
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Assume for a moment that it did have to stay inside the box.

Which would be a reasonable, even though there is no other ban on things like kite rigs and flip tackers...

A 30' tall mast can cant 16.5 degrees before it goes beyond the max beam.

Hull flies at about 5 degrees.

So there is plenty of opportunity.

Didn't Pete do something along this line?

SHC
Ok, this maths is getting a little bit weird.

Mast height 9m (say) (hypotenuse), mast in centre of boat therefore distance to max beam =2.3/2=1.15m (opposite).

Maths: angle of mast from vertical SIN theta = 1.15/9, therefore ASIN(1.15/9) = 7.3 degrees

Wording of rules suggest the mast does need to stay in box.

What about the boom?

4. The extreme beam shall not be more than: 2.3 metres (7 ft 6½ inches).




The beam shall be measured at right angles to the centre line of the craft at the widest point and including all fixed or adjustable apparatus with the exception of a normally accepted trapeze or retractable seat.




This rule was added to at the 2006 WGM, and re-affirmed at the 2007 WGM, as follows:




Adjustable apparatus such as centreboards must be measured both completely down and completely up flush with the bottom of the hull.




In addition, no part of each hull or the respective fixed or adjustable apparatus shall come closer together than 1.5 metres below the static waterline. If necessary the static water line shall be found by floating the boat fully equipped without the sailor on board.



The drawing below illustrates this rule.

 

 
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AClass USA 230

Anarchist
958
47
Louisiana
Assume for a moment that it did have to stay inside the box.

Which would be a reasonable, even though there is no other ban on things like kite rigs and flip tackers...

A 30' tall mast can cant 16.5 degrees before it goes beyond the max beam.

Hull flies at about 5 degrees.

So there is plenty of opportunity.

Didn't Pete do something along this line?

SHC
Ok, this maths is getting a little bit weird.

Mast height 9m (say) (hypotenuse), mast in centre of boat therefore distance to max beam =2.3/2=1.15m (opposite).

Maths: angle of mast from vertical SIN theta = 1.15/9, therefore ASIN(1.15/9) = 7.3 degrees

Wording of rules suggest the mast does need to stay in box.

What about the boom?

4. The extreme beam shall not be more than: 2.3 metres (7 ft 6½ inches).




The beam shall be measured at right angles to the centre line of the craft at the widest point and including all fixed or adjustable apparatus with the exception of a normally accepted trapeze or retractable seat.




This rule was added to at the 2006 WGM, and re-affirmed at the 2007 WGM, as follows:




Adjustable apparatus such as centreboards must be measured both completely down and completely up flush with the bottom of the hull.




In addition, no part of each hull or the respective fixed or adjustable apparatus shall come closer together than 1.5 metres below the static waterline. If necessary the static water line shall be found by floating the boat fully equipped without the sailor on board.



The drawing below illustrates this rule.

 
Is this the drawing you are referring to?

TYPICAL HULL-FOIL CANT 2009 RULE PROPOSAL.pdf

 

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Wandering Geo

Super Anarchist
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Is this the drawing you are referring to?
Yep, couldn't copy it quickly and easily from the rules. should have deleted the reference to it in the text.

Very interesting the way things are evolving.

But to put it all into perspective.

Mk1 Oz flyer is currently in the top 3 in the worlds (albeit with rudder/cboard, mast/sail upgrades).

Two of top three have straight/canted boards.

None of the top three have mast cant.

Looks like the biological bit reamins the most critical component.

Very interesting in a box rule development class.

Might be a good formula to follow for bigger boats (ie "dark side" AC boats for instance).

 

Steve Clark

Super Anarchist
Allowing the mast foot to slide to leeward would require that you ease the traveler the same amount to make it such that the boom was still parallel yo centerline. No big deal and the whole mess will be self tacking. That's the good news.

Bad news is that two of the advantages of canting the rig are lost. You don't get the windward shift of rig CG and you don't displace the rig upstream. All you get is the increased efficiency of having the mast vertical, but this is now off set a bit by making your rig lower (you get less height off the water because, when heeled, the main bean is closer to the water at the lee end than it is at the weather end) and more likely be in the bad air behind the weather bow.

SHC

 
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