Author Topic: 29XX?  (Read 25693 times)

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Offline Will_Lee

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Re: 29XX?
« Reply #15 on: February 05, 2010, 05:11:41 PM »
Which leads me to the E6. The extreme fine bows suggest to me a very difficult boat to sail in any breeze

The broad bow idea is that the pitch-up static force from immersing the bow sections is more if the bow is fat. This is true if the boat is stationary. However this neglects the dynamic pitch-down caused by deceleration, which is greater than the static effect if the boat is moving at any speed. This means that there is no obstacle to finer boats being as easy or easier than broad boats in breeze, and since the Hardon, designs have been getting thinner.

Offline kevin_ellway

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Re: 29XX?
« Reply #16 on: February 05, 2010, 06:43:18 PM »

Which leads me to the E6. The extreme fine bows suggest to me a very difficult boat to sail in any breeze, in a conventional sailing form. Which would in my view start to take us toward the wrong end of difficulty spectrum, if class growth is an ultimate goal. Given the specter of the 29erXX. On the other hand if the intention with the E6 is to 'fully foil' ( and given the boats lines and Kevin and Mikes involvement in that area it's a reasonable assumption to make ) this could be a perfect solution to the looming class competition posed by the 29erXX....

1) I can state categorically that the E6 has not been designed as a foiler. It would look very different if it was.

2) Fine bows generally aid handling in a breeze for the reason Will has stated.

3) I have previously expressed my views that  I believe a foiling Cherub would be a bad idea.
  • It would would probably fragment the class .
    Cost will increase.
    It would also turn the boat into a one trick pony which only works above 10-12kts -  All the Cherub development to date has made the boats perform well over the typical conditions we get in the UK. The new boats all look impressive both on and off the water.

4) Don't believe that foiler Rs are easy to sail. You only have to look at the photos of the foiler Rs offwind to notice the tentative stances of both helm and crew. Yes, Cherubs are on the more demanding side of sailing because they are quite highly canvassed, short aand have a high power to weight ratio. They fulfill a niche role as a really exciting high performance boat that can be handled by lightweights and women. If you want to make the boat easier to sail, add about 2ft 6in to the length and increase the weight by around 40kg - then you've got a 29XX.

5)  I'm all for foiling - I sail a foiler. It is a really interesting development and has created a new type of sailing. The Cherub, in my view however, is not really the right platform foiling and I am sure the class will benefit from consolidation in its current format.

Offline daryl_wilkinson

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Re: 29XX?
« Reply #17 on: February 05, 2010, 06:57:50 PM »
Yes I agree with that view in general, and obviously it is hard to tell from the screen grabs and pics of the frames, so this is very much conjecture on my part. But the as the boat decelerates and those pitching forces come into play the buoyancy has to come in progressively. Looking at the images it looks to me as if the forces involved in pitching may overwhelm the influx of buoyancy as the bows go in and allow the weight of the rig to dictate the outcome.

But anyway this wasn't really designed to be some sort of critique of the E6. I was using my 'off the cuff ' thoughts about the new design in a more general way.  To sort of kick start discussion about design conservatism and it's potential beneficial role of increasing fleet membership by creating attainable boats. As in a class as small as ours it is very easy to get into a mono-culture driven purely by competition or reputation which could lead the class into future difficulties.

Edit: this overlapped with Kevins post.
« Last Edit: February 05, 2010, 06:59:29 PM by daryl_wilkinson »

Offline ross_burkin

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Re: 29XX?
« Reply #18 on: February 06, 2010, 08:22:15 AM »
The XX is going to be sailed by squaddies. I don't think it's going to cause any issues for class membership. If people want to sail a cherub, they will and I don't think a 90kg+ 14ft+ boat is going to stand in their way.

Surely the 49er is a direct class competitor (for want of a better phrase). It's ideal combined crew weight is around 140Kg isn't it? Which is the top end of Cherub 'competitive' weight spectrum.

Holding back class development because it's 'too extreme' or makes the boat harder to sail is a daft idea. Would we all be sailing cherubs if they were as easy to sail as Wayfarers!? Dingy sailing isn't an extreme sport. Difficult but it's pretty tame.

As for this pitching thing. A boat with a T-foil has it’s centre of pitching moment (or whatever you want to call it) is at the back of the boat. So you have 12 feet (and a cheeky bit of snout?) of progressive increase in buoyancy and given that you stand further back anyway it's more that enough. Kevin, skinnier boats please!


Off topic, but has anyone sailed the new really skinny designs without a T-foil?



Kevin, what makes a cherub the wrong platform for foiling? It's got to be the most ideal class in the UK. I guess it's just not as good as having a 2 man foiler designed from scratch. Chine width  and things like that. Maybe I should move this question into a differnt topic...
2675 Fuzzy Logic  97/05 rules

Serious plannage in the works...

Offline simon_jones

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Re: 29XX?
« Reply #19 on: February 06, 2010, 09:50:14 AM »
Having owned and sailed an XX for a year before getting a Cherub, I think that this is all about nothing. There are many potential classes for us to attract new sailors from 800's (Pete) 200's ( Andy and Jill ) 29ers (us) The current crop of boats look and sail very well, If we wish to attract people to the class and not lose them to others we have to offer them something they can only find with us. As a group of sailors we are very freindly not something often said about the 29ers. Pete is doing very well in showing the light to the uninitiated , Perhaps we should all try to show the way to other classes a bit more. Some people will always feel more comfortable with a smod , big turnouts at open meetings, if something breaks  you just get a new bit, more sailing less bimbleing. But when all is said and done the XX was far from perfect just look at how many are out there compared to the standard rig or the 800. we should worry about our class not anyone else

rich_taylor

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Re: 29XX?
« Reply #20 on: February 06, 2010, 12:00:35 PM »
Having owned and sailed an XX for a year before getting a Cherub, I think that this is all about nothing. There are many potential classes for us to attract new sailors from 800's (Pete) 200's ( Andy and Jill ) 29ers (us) The current crop of boats look and sail very well, If we wish to attract people to the class and not lose them to others we have to offer them something they can only find with us. As a group of sailors we are very freindly not something often said about the 29ers. Pete is doing very well in showing the light to the uninitiated , Perhaps we should all try to show the way to other classes a bit more. Some people will always feel more comfortable with a smod , big turnouts at open meetings, if something breaks  you just get a new bit, more sailing less bimbleing. But when all is said and done the XX was far from perfect just look at how many are out there compared to the standard rig or the 800. we should worry about our class not anyone else

I totally agree, it is pretty much about nothing.  Noting JB's post listed by DW, the statements are based on the 470 replacement not the Skiff trial and as I remember the 29xx was the only applicant against the 470.  The fact the result was turned over was no surprise (the writing was on the wall) and neither is it a surprise the event and subsequent meeting minutes where heavily used as marketing leverage (that what marketing departments exist for). 

By their own admission they are selling rigs not  hulls consequently it can only be a compromise.  Form a commercial point of view, and in the SMOD ideal, it is a sensible solution and I dare say they learned a lot form the other classes at the trials, nothing you can or should do about it.  As for 9er's co-operating together to promote the XX in joint events and sponsors was always going to happen (could you ever see the 49er's co-operating with a competitive design to the 29er or 29erXX?) it is a natural process in developing and maintaining a sales and parts monopoly.  There is a place for this, someone people will want to buy off the shelf, no question.  Should the Olymics be a platform for supporting a commercial monopoly and is that good for development in the sport?  I don't think so.  Are there other ways to have consistant design, measurement and performance in an olympic class without a commercial monopoly behind it, absolutely.

One interesting thing will be how the 29er layups last with bigger loads & a bigger pounding. 

Offline andy_peters

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Re: 29XX? off topic
« Reply #21 on: February 16, 2010, 06:53:51 PM »
To reply to the off topic question posed we sailed the E5 about 10 times with no t-foil.  It became apparent simply due to the reduction in capsizes that adding a t-foil makes a significant difference, in our case to sideways stability rather than stopping the boat tripping up.  The t-foil seems to give that vital fraction of a second longer to move your weight inboard or outboard and does seem to make more of a difference at greater speed.  I'm sure the fluid dynamic experts amoungst us could theorise why?  In short adding the t-foil made the E5 a much more pleasurable experience to sail.  As I'm sure Kevin would point out that should be no surprise- it was designed to be sailed with one.

Offline kevin_ellway

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Re: 29XX? off topic
« Reply #22 on: February 16, 2010, 08:44:31 PM »
To reply to the off topic question posed we sailed the E5 about 10 times with no t-foil.  It became apparent simply due to the reduction in capsizes that adding a t-foil makes a significant difference, in our case to sideways stability rather than stopping the boat tripping up.  The t-foil seems to give that vital fraction of a second longer to move your weight inboard or outboard and does seem to make more of a difference at greater speed.  I'm sure the fluid dynamic experts amoungst us could theorise why?  In short adding the t-foil made the E5 a much more pleasurable experience to sail.  As I'm sure Kevin would point out that should be no surprise- it was designed to be sailed with one.

The T foil adds roll stability exactly as you've noticed.  As you roll, the tips are being asked to move faster upward/downwards through the water than the centre of the span. This means a torque is generated in the opposite direction to the roll. The centreboard, rudder and rig all contribute to this. Without these forces, a sailboat (especially a foiler Moth) would be a really wobbly thing! Incidentally, the longer the foils, the bigger this force is.

I was not initially in favour of T foil rudders as they added complication and de-natured the boat to a certain degree. However, after doing some sums when I was designing the SK4, it was clear that the foil made the boat faster (once above 6kts boat speed) and easier to sail. If the T is on the bottom, it makes no difference to launch or recovery. It can easily be retro fitted to any existing boat. So it was hard to come up with any reason not to use one on the E5 / E6.

Offline phil_kirk

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Re: 29XX?
« Reply #23 on: February 17, 2010, 12:54:57 PM »
interesting discussion in the off topic nosiness of thin boats and T foil roll damping.

From our limited outings in the E5 so far I fully agree with the thinner bows is better argument. The narrow entry angle allows the boat to accelerate and decelerate more smoothly and reduces the magnitude of the pitching moment. this means that less buoyancy will be required to overcome the pitch. The narrow bow also gets rid of the bow wave (formed by fat boats) which increases the chance of pitching if in a displacement mode. The T foil also imprves pitchiness by as Ross says by anchoring the transom and moving the centre of pitch back. If the T foil is set neutral to the flow in a down wind leg it will try to drive the transom back in the water and correct the pitch.  it is noticeable that if the t foil is set a little negative it lifts the bow and tames the boat which may be reassuring in choppy conditions before a race start. Not fast but safe.

The E5 is a tippier boat than the DOG but not as much as I was expecting.  The roll damping effect of the T foil has overcome most of the effects of narrow forward lines, the added stability of the DOG's second chine and makes the boat much easier to sail than it would be without a T foil.  In this respect only the T foil is the modern bilge keel.  ;)


Offline john_hamilton

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Re: 29XX?
« Reply #24 on: February 17, 2010, 01:09:09 PM »
I was not initially in favour of T foil rudders as they added complication and de-natured the boat to a certain degree. However, after doing some sums when I was designing the SK4, it was clear that the foil made the boat faster (once above 6kts boat speed) and easier to sail. If the T is on the bottom, it makes no difference to launch or recovery.

quite a few people at my club have asked me if the t-foil is of benefit on cheese due to the wider bows being pushed down into the water upwind and therfore creating drag. is this based on truth? ill have a non-t-foil rudder soon so will be able to test this but was wondering if any off the experienced people here have anything to add???
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Offline Tim Noyce

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Re: 29XX?
« Reply #25 on: February 17, 2010, 02:24:07 PM »
I think that they are missing the point slightly John. The t-foil might be 'pushing the bow into the water', but you should still be trimming the boat with your body weight to make sure that its not dragging... you will just be further aft than you would be if the t-foil wasn't there.

Offline john_hamilton

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Re: 29XX?
« Reply #26 on: February 17, 2010, 02:49:18 PM »
it was clear that the foil made the boat faster (once above 6kts boat speed) and easier to sail. If the T is on the bottom, it makes no difference to launch or recovery.

is it slower under 6kts then? drag more than lift benefit or something?
The pessimist complains about the wind; the optimist hopes it will change; the realist adjusts the sail

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Offline simon_jones

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Re: 29XX?
« Reply #27 on: February 17, 2010, 03:10:56 PM »
As I understand it if the boat has less than 6knts boatspeed then the t/foil will create more drag. We have a rudder and a t/foil on Loco and in light airs will often sail with the rudder. it is a different story when you start moveing though as a t/foil adds not only speed upwind but also stability in both pitch and roll.

Offline kevin_ellway

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Re: 29XX?
« Reply #28 on: February 17, 2010, 07:34:10 PM »
it was clear that the foil made the boat faster (once above 6kts boat speed) and easier to sail. If the T is on the bottom, it makes no difference to launch or recovery.

is it slower under 6kts then? drag more than lift benefit or something?

John, it's all about lift to drag. You get benefit from the T foil when its lift to drag ratio is better than the boat's. The L/D of the boat is the displacement/resistance. A 0 kts, the displacement is say 200kg, but the resistance is 0. So the hull's L/D at o kts is infinity. The T foil on the other hand produces no lift at 0 knots. so its L/D is 0.
As speed increased, the hull's L/D decreases to an asymptotic value of around 7 at 15kts. Conversely, the foils L/D (when used at around CL~0.5) increases with speed to an value of 15-20+. 6kts is the cross over speed where the L/D of the hull and foils are about the same.

Now as Ross has pointed out, what you need to be doing is shifting load from the hull onto the T foil. For any given speed, the hull has an optimum trim angle. It is important that this is maintained. So you need to move backwards to load the T foil and to maintain the correct trim. As I've noted elsewhere, at 10kts, you can drop the drag by around 20% via the T foil. At speeds< 6kts, yes the T foil adds drag and should be set into neutral (no lift). It does however, reduce pitching. In very light winds, wave that cause the boat to pitch will actually cause the T foil to act as a propulsion device.... so don't throw it away just yet!.

There is an article I wrote for Y&Y and I think as a Cherub member, you can download it from the UK-Cherub site.

Hope this helps.

Offline john_hamilton

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Re: 29XX?
« Reply #29 on: February 17, 2010, 08:47:21 PM »
thanks kevin that completely clears up my question :)
didnt know to set it to neutral at under 6kts though, thanks
The pessimist complains about the wind; the optimist hopes it will change; the realist adjusts the sail

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