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Re: New A-class with a radical bow shape [Re: RetiredGeek] #112675
09/26/07 08:15 AM
09/26/07 08:15 AM
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Was just thinking about the previous post and thought it might have been misleading for the emphasis to be on the above numbers. The real goals for us are first pitch stability, so you can drive it to the max all the time and know the boat will always recover no matter what you do to it, that in turn tends to give you more usable power from the rig. Second and third are drag reduction and dynamic lift production (hopefully with minimal induced drag). This last one we have totally overdone and hence the need to make the hulls smaller, not that its a bad mistake to make. Hope this clarifies where we are attempting to take the design.

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Re: New A-class with a radical bow shape [Re: RetiredGeek] #112676
09/26/07 09:44 AM
09/26/07 09:44 AM
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Brighton, UK
grob Offline OP
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The real goals for us are first pitch stability


Firstly let me say I am mightily impressed with your boat, its nice to see somebody going out on a limb to try something new, and even better when it appears to be paying off. How did you go about improving the pitch stability, was it mostly through positioning the center of buoyancy (dynamic or static).

Gareth
www.fourhulls.com

Re: New A-class with a radical bow shape [Re: grob] #112677
09/26/07 05:59 PM
09/26/07 05:59 PM
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Gareth,
just moving the LCB/LCF around does do much as it is static and doesn't scale with the loads. Mostly its achieved by carefully tailoring the bottom pressures and changing that to suit what your after and hopefully you don't change the drag too much while doing it.
If you look at the video's you can see it works reasonably well and the mast appears to be stationary most of the time.
RG

Re: New A-class with a radical bow shape [Re: RetiredGeek] #112678
09/27/07 12:57 AM
09/27/07 12:57 AM
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Brighton, UK
grob Offline OP
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Mostly its achieved by carefully tailoring the bottom pressures


Thats interesting, how did you calculate the bottom pressures, did you use a CFD code?

Gareth
www.fourhulls.com

Re: New A-class with a radical bow shape [Re: grob] #112679
09/27/07 01:02 AM
09/27/07 01:02 AM
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yes, ultimately it comes down to using CFD to check what you have produced.
RG

Re: New A-class with a radical bow shape [Re: RetiredGeek] #112680
09/27/07 01:21 AM
09/27/07 01:21 AM
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Grob, this shows a hint of what the modelling can do to performance. This is a screen cap from last Saturday sailing in 8.2 knots (average is probably lower than that as the light yellow in the track shows just 5 knots in places) with the averages shown for 500m. Sea state was terrible as it blew 50 knots overnight, so this was going to weather in a 2-3 ft slop. Generally the boat appears to sail about 18-20% faster than windspeed uphill and the calculated leeward angles are in the 1.0 to 1.2 deg range. Points well also :-)
RG

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119646-09-22perf.jpg (142 downloads)
Re: New A-class with a radical bow shape [Re: RetiredGeek] #112681
09/27/07 04:44 AM
09/27/07 04:44 AM
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here's a downwind track from the same race with the 2-3 ft slop, windspeed is probably less than 7.7 knots (less than 13 fps)(see wind scale top left)and the color on the track
RG

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Re: New A-class with a radical bow shape [Re: RetiredGeek] #112682
09/27/07 01:26 PM
09/27/07 01:26 PM
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New Hampshire, USA
windswept Offline
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Fred & Ian,

Good luck this weekend. Cannot wait for the reports and pictures.


Tom Siders
A-Cat USA-79
Tornado US775
Re: New A-class with a radical bow shape [Re: RetiredGeek] #112683
09/27/07 04:45 PM
09/27/07 04:45 PM
Joined: Oct 2001
Posts: 395
LA
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Grob, this shows a hint of what the modelling can do to performance. This is a screen cap from last Saturday sailing in 8.2 knots (average is probably lower than that as the light yellow in the track shows just 5 knots in places) with the averages shown for 500m. Sea state was terrible as it blew 50 knots overnight, so this was going to weather in a 2-3 ft slop. Generally the boat appears to sail about 18-20% faster than windspeed uphill and the calculated leeward angles are in the 1.0 to 1.2 deg range. Points well also :-)
RG


Your performance numbers seem consistent with GPS data I have gotten sailing my A2 in similar conditions. I think an A-Class is limited to a max upwind speed of 11-12 knots dependent upon sea state. I think if your efforts to reduce pitching motion are successful, you create a boat that is easier and more consistent to sail upwind which means a fast boat (given equal sailors and rigs). As a current A2 owner, my only complaint about the boat is it is difficult to push hard in breeze and chop downwind which is something Ian is very aware of. The Bim XJ is a lot easier boat to sail downwind in those conditions as is the current Marstrom. The A2 really shines downwind in light air mild mode and marginal to medium wild conditions. I am very interested to see how the LR2 will compare.

BTW, when I first saw the pictures of the boat out of the water, I thought it looked ugly. But watching it sail in the videos, it is actually pretty cool looking. I kind of felt the same way about the A2 until I saw it sailing.

Bob Hodges

Re: New A-class with a radical bow shape [Re: Acat230] #112684
09/27/07 07:36 PM
09/27/07 07:36 PM
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Gainesville, FL 32607 USA
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Wow, some beauty critics may be coming around! I have personally seen this new design going uphill fast in a fresh breeze without pitching, and going downhill in good air without sticking a hull in. Thus it may even be competitive with an A3! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />


Dacarls:
A-class USA 196, USA 21, H18, H16
"Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
Re: New A-class with a radical bow shape [Re: dacarls] #112685
09/27/07 08:28 PM
09/27/07 08:28 PM
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New Hampshire, USA
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Dave, I thought that being competitive with the A3 and some of the other recent designs was one of the main points in this project. How did you do on your XJ sailing with Ian when you were up?


Tom Siders
A-Cat USA-79
Tornado US775
Re: New A-class with a radical bow shape [Re: dacarls] #112686
09/27/07 10:17 PM
09/27/07 10:17 PM
Joined: Oct 2001
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Wow, some beauty critics may be coming around! I have personally seen this new design going uphill fast in a fresh breeze without pitching, and going downhill in good air without sticking a hull in. Thus it may even be competitive with an A3! <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />


I've only sailed Charlie Ogeltree's XJ briefly but it was in about 14-16 knots of choppy Galveston Bay sea breeze. Phil Kinder had told me he thought it was the easiest A-Cat to push hard downwind and after sailing the boat, I have to agree. I was envious of the way it seemed to get up and over waves without stuffing downwind. When we switched and I was on my A2, I could sail as fast as Charlie most of the time but it was harder. If the LR2 is as easy to sail as the XJ, it should be very competitive.

Re: New A-class with a radical bow shape [Re: Acat230] #112687
09/28/07 07:45 PM
09/28/07 07:45 PM
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New Hampshire, USA
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I really liked the 01 Bim that I sailed in florida this past year. the XJ looked highly modified from that, so I bet it is great to sail. I am just beginning to understand my Boyer MKIV and wish it had at lot less freeboard from in the bow area. I am thinking about having it trimmed down from the front stays forward. It is not a job that I look forward to handling though. I am thinking about bringing the boat to Lars and have him look at it.


Tom Siders
A-Cat USA-79
Tornado US775
Re: New A-class with a radical bow shape [Re: windswept] #112688
09/28/07 10:31 PM
09/28/07 10:31 PM
Joined: Aug 2007
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lesburn1 Offline
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Some photos from Lake Hopatcong
http://mysite.verizon.net/vze28w8n/


lesburn1.blogspot.com

A-Cat USA 49
18Sq 49

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Re: New A-class with a radical bow shape [Re: lesburn1] #112689
09/28/07 11:41 PM
09/28/07 11:41 PM
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Thanks Les, really appreciate that :-)
RG

Re: New A-class with a radical bow shape [Re: RetiredGeek] #112690
09/29/07 07:33 AM
09/29/07 07:33 AM
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Posts: 890
Dunedin Causeway, FL
David Parker Offline
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This photo fits the thread title. Check out the rudders and board shape as well. Thinking outside the box!

[Linked Image]

Re: New A-class with a radical bow shape [Re: windswept] #112691
09/29/07 09:58 AM
09/29/07 09:58 AM
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Posts: 805
Gainesville, FL 32607 USA
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Sorry WindSwept- It just seems that the A2 boys are complaining about lack of forward bouyancy.
RE:Speed on my XJ vs new design? At the Silver Lake Invitational when Ian's mast was hanging over sideways because the Vectran stretched- I felt really fast. But at Douglas Lake a month later with Ian's new SS shrouds, I felt slow.
Note the title of this 20 page thread- It isn't just the bow shape that is different- there are no "decks".


Dacarls:
A-class USA 196, USA 21, H18, H16
"Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
Re: New A-class with a radical bow shape [Re: dacarls] #112692
09/29/07 10:20 AM
09/29/07 10:20 AM
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Gainesville, FL 32607 USA
dacarls Offline
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Those nifty/snappy red tiller arms must be on Fred Smith's new LR2. Ian's are black AFAIK.
For Tom: Tony Arends at RacerX posted pictures of his repaired/modified Bim 2000 with lowered bow.


Dacarls:
A-class USA 196, USA 21, H18, H16
"Nothing that's any good works by itself. You got to make the damn thing work"- Thomas Edison
Re: New A-class with a radical bow shape [Re: dacarls] #112693
09/30/07 03:46 PM
09/30/07 03:46 PM
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Just had a quick chat with Ian, seems it was as shifty as predicted and extremely light today. Final places were Lars First with Ian and Micheal Gruber tied for 2nd
RG

Re: New A-class with a radical bow shape [Re: lesburn1] #112694
09/30/07 04:41 PM
09/30/07 04:41 PM
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Posts: 851
US Western Continental Shelf
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I would love to see the pictures from the race but, I can't get the links at http://mysite.verizon.net/vze28w8n/
to work. <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />

GARY


Santa Monica Bay
Mystere 6.0 "Whisk" <--- R.I.P.
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