| Polar Diagrams for beach catamarans? #12933 11/12/02 09:39 AM 11/12/02 09:39 AM |
Joined: May 2002 Posts: 217 jcasto1 OP
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Posts: 217 | Many keelboats have polar diagrams, e.g. http://www.c34.org/faq-pages/images/polarDiag.gifHere's a description of how they are sometimes used. http://www.sailnet.com/collections/articles/index.cfm?articleid=leonar0021Has anyone ever seen, or generated, "polar diagrams" for beach catamarans? Mostly they are used on large keelboats as a guide for whether the crew is properly trimming the sails for the given wind speed, in order to maximize "VMG". But what got me thinking about this was the recent thread on reaching vs W-L race courses. If we had polar diagrams for a couple different beach cats, could we use them to define the real difference between a W-L course vs a course with a triangle shape? e.g. is a reaching leg a real "penalty" for a particular design? Does a spinnaker cat get really get an advantage on a W-L course compared to a sloop-rigged or unirig cat? Also, in another thread, there was some excellent data collection, using GPS and downloading digital maps, and such, that showed effects of wave angle on port vs starboard tack. Perhaps, we are at the point where the instrumentation is compact enough, and sophisticated enough, we could actually develop polar diagrams from the data collection. Does it even make sense to have a polar diagram for a beach cat, or do we have too many variables relative to its performance - (e.g. crew weight & position), compared to a large keelboat? What about larger offshore multihulls, do they use polars? Farrier Trimarans? Stilettos?
Jim Casto NACRA 5.5 & NACRA 5.7 Austin TX Lake Travis
| | | Re: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#12934 11/12/02 04:22 PM 11/12/02 04:22 PM |
Joined: Jun 2001 Posts: 292 Long Island, NY Ed Norris
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Posts: 292 Long Island, NY | HI Jim I'd be very interested in the polar diagram for "your boat or one very much like it" I'm considering calling US Sailing, as the article in your post suggests. Unless you called them and got no where? ![](/forums/images/graemlins/frown.gif) Let me know, I'd hate to wase their time if you just called
Sail Fast,
Ed Norris
| | | Re: Polar Diagrams for beach catamarans?
[Re: Ed Norris]
#12936 11/12/02 09:45 PM 11/12/02 09:45 PM |
Joined: May 2002 Posts: 217 jcasto1 OP
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Posts: 217 | I did not call US Sailing, I expect I would get the answer "we don't have polars for multihulls". But, why don't you try & let us know how it works out.
Jim Casto NACRA 5.5 & NACRA 5.7 Austin TX Lake Travis
| | | Re: Polar Diagrams for beach catamarans?
[Re: DHO]
#12937 11/12/02 10:02 PM 11/12/02 10:02 PM |
Joined: May 2002 Posts: 217 jcasto1 OP
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Posts: 217 | Thank you, DHO, for the suggestion. I actually have the book, and pulled it out. It has a bunch of polar diagrams for some keelboats and a few dinghies (not cats), and overall, the book is incredibly instructive.
But, Bethwaite does kind of dismiss multihulls early on in the book. His summary of their "disadvantages" - total wetted surface area is too high, hulls cannot plane, can't heel in light air for proper sail shape, high speed downwind buries the bows, they tack too slow to be tactical race boats - so their racing crews will be frustrated.
I think he wrote his book before the advent of asymmetrical spinnakers on cats with wave-piercing hull shapes.
Jim Casto NACRA 5.5 & NACRA 5.7 Austin TX Lake Travis
| | | Re: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#12938 11/13/02 09:46 AM 11/13/02 09:46 AM |
Joined: Jun 2001 Posts: 292 Long Island, NY Ed Norris
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Posts: 292 Long Island, NY | You were right in your expectations. Closest to a beach cat they have is a Hobie 33. ![](/forums/images/graemlins/mad.gif) Think they offer discounted membership for discounted members?
Sail Fast,
Ed Norris
| | | Re: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#12939 11/13/02 10:00 AM 11/13/02 10:00 AM |
Joined: Jul 2001 Posts: 800 MI sail6000
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Posts: 800 MI | Hi J
Closest thing we catsailors have readily available is a handheld GPS on board , often distance racing good crews will check vmg directly from the GPS -
distance traveled vs speed to the finish -VELOCITY MADE GOOD ,-A boat may travel at higher speed by heating it up w spin set but sail a longer distance and longer time than a boat sailing more directly towards the finish point at a slightly slower speed , that often a surprised crew finds have finished in front.--tHE KICKER IS THERE ARE TIMES YOU MAY NOT WANT THE BEST vmg --if you know your setting yourself up to take advantage of an offshore current sooner ,-expected shift ,or other course factor ,--this is where distance racing varies greatly from short term gain oriented buoys racing .
--Beyond playing ocilating shifts as noted in the article Variables of tides and current ,-wave size and pattern effect on speed and angle sailed ,-wind speed variables ,-gusts , persistant shifts ,-ocilating wind directions that play such an important part of racing , then add crew and skippers inconsistancies along with tactics ,-other boats partially blanketing or effecting wind ,-being washed off the side temporarily by large waves taking out your feet ,-recovery time ,-gybing time , often very difficult to get a boat going full speed again in large seas after a 6 hour straight high speed spin run . All the intangable aspects make any polar diagram that can not factor these almost infinate variables in combination just a basic guideline for settings and angle of that particular design. If you are going at full max theoretical speed ,--but in the wrong direction into a persistent shift ,-or away from better wind velocity near shoreline ,-or ignoring major ocilating shifts , or heading into adverse current offshore or one that may be very favorable like the Gulf Stream . the end result and latter finish time will be very confusing .
A good basic guideline with spin rigged cats in higher winds is once you get beyond 20 degrees course heading it is time to take down the chute and begin to reach .In lighter winds you can often reach typically 90 -some to 75 best vmg without spin ,--from wind direction .
A GPS can be used effectively by for instance placing two on the wire w spin up sailing at higher speed but higher angle to maintain it ,--or one on the wire at lower angle and speed sometimes as mentioned with a better speed to distance traveled ratio. Direct comparison with other boats in the area ,--their settings and angles chosen is sometimes best source of info on the race course , each is different in each condition .
There in the extreme difficulty of rating different boats fairly or with any consistancy . It may be best to group boats into similar max -Length beam weight ,sail area catagories , allow crews to modify each for the conditions as they choose , just race in the truer ideal of sport .
The one wind condition that gets many catsailors is the slight persistant shift where the inside cat on a beat gets lifted up inside the outer boats often making them feel they have no boat speed , -but this occurs mainly from the wind shift and the ability of a crew to recognize it and place themselves relative to the fleet to take advantage of it .
Only looking at theory or finish times without the comprehension of all the other factors involved is misleading , We always see catsailors after racing asking questions about wind speed near shore , shifts ,-wave size and pattern further out etc . Very honestly I,m very fortunate to race each year around some of the best catsailors that I often ask these types of questions from ,--This is the best way to learn your particular type of cat design raced .
It is a wonderfull complex interesting sport we play ,-never completely mastered by any . | | | Re: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#12940 11/13/02 10:07 AM 11/13/02 10:07 AM |
Joined: Jun 2001 Posts: 778 Houston carlbohannon
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Posts: 778 Houston | Jim There are polars for a few multihulls, H16, Tornado's some A-class's, and a few others. I have some EXCEL tables but I am not sure what I did them. Attached is a link to a web article that includes links to the data available on the web. . On The Wire Try searching "Tornado Polaris" and "Hobie 16 polars" for more data. I seem to remember that that some of the data was collected as kinda of "fun sailing day". Different boats, sailed individually through a line to marks set ~10M out while someone recorded wind speed, direction and time. I think the boats were supposed to hit the mark so they could get an accurate time. I do remember the event was called due to light air and heavy drinking | | | Re: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#12943 11/14/02 02:19 PM 11/14/02 02:19 PM |
Joined: Apr 2002 Posts: 805 Gainesville, FL 32607 USA dacarls
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Posts: 805 Gainesville, FL 32607 USA | Then to add to the fun-- how do we get a Wild Thing bump added to the polars? It can really be something. I won a race (A-class) from 100 yards behind last weekend by this valuable technique.
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: Polar Diagrams for beach catamarans?
[Re: jcasto1]
#289204 11/03/19 02:43 PM 11/03/19 02:43 PM |
Joined: Dec 2013 Posts: 2 Frank N
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Posts: 2 | Those polars disappeared from the original web site. but they are here on the wayback machine. http://web.archive.org/web/20050101071744/http://www.west.net/~lpm/hobie/archives/v1-i3/feature3.htm
Tony Marchaj got the Tornado polars from a paper by Bradfield published in The Ancient Interface Symposium on Sailing, California, Vol 10 1971. You may be able to get reprint from AIAA. This was for the Classic Rig Tornado.
Last edited by Frank N; 11/03/19 02:45 PM.
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