| 31 March
11 correction: it was not a parabola but rather half of an ellipse Uncle Al's speedy CB elliptical entry results from pure bull-shit luck!!?? Is Milanes Foils the answer? -----
Original Message -----
From:
alan simpkins
Sent:
Tuesday, December 01, 2009 3:23 PM
I don't want to be pedantic, but in theory it is possible to fit any number of parabolas to connect the centre line of the leading edge and the edge of the chamfer 2.25 inches back. Is the shape of the parabola important, or is it a personal thing - not too sharp and not too blunt? Regards, Alan Simpkins -----
Original Message -----
From:
Al Schonborn
To:
alan simpkins
Cc:
Jesper Friis home ; Jens Konge Rasmussen ; Ton Jaspers (W10445)
Sent:
Tuesday, December 01, 2009 8:26 PM
Subject:
centreboard parabola
Hi, Alan:
I don't know enough
physics to comment. In my innocence/ignorance I asked, in 1975, a
math-teaching colleague to draw me "the half of an ellipse" to connect the centre line of
the leading edge
and the edge of the chamfer 2.25 inches back to lead to a total max. width of .75
inches. He said nothing about lots of possibilities and came back with
one that I like very much. It wants to be a fair curve and definitely
not too sharp!! Will copy guys who should know more about this and help
us out.
Good luck!
Best regards,
Uncle Al (W3854)
-----
Original Message -----
From:
Wayfarer (Ton Jaspers W10445)
To:
'Al Schonborn' ; 'alan
simpkins'
Cc:
'Jesper Friis home' ; 'Jens Konge Rasmussen'
Sent:
Wednesday, December 02, 2009 4:25 AM
Subject:
centreboard parabola
Hi Alan,
I don't like to answer this type
of questions because they always end in a religious
debate.....
I have observed the English to have a
preference for a sharp parabola where the Danes seem to prefer a blunt
"grandfather's cigar" shape. I
believe the advantage of a hydro-dynamically perfect shape is minimal
and pretty hard to make by an amateur. I suppose it would need
many tests in a controlled environment such as a laboratory tow tank.
At the end of the day only the guys like Mike Mac and Peter Bøje
benefit from it. Us average sailors should go out and sail and
enjoy our boat and not worry about a 0.00001% speed loss. We lose more
ground in that short moment of distraction where we let our sails
flog then by a sub-optimal CB shape. Far more important is to have
a maximal CB area available and the leading edge as far forward as the
rules allow. Check your maximum depth and most important maximum
angle (83 degrees). With that set up correctly, your boat will point
better. There is a nice essay on the WIT about setting up the CB for
maximum performance by Kjell Gjære from Norway: http://www.wayfarer-international.org/WIT/maint.repair.ref/CB.rudder/CB_bolt_hole_location.html
Back to the leading edge question: I would start
with a blunt edge and if it doesn't look nice, even and smooth there is
still some material left to sand some more. If you start with
a sharp parabola there is no more material left to sand. And also, a
sharp edge may damage easier then a blunt edge. It is just a
thought, but until someone comes with a better one.....
Best wishes,
Ton Jaspers (Swiebertje - W10445)
Original
Message -----
From:
Jesper Achton Friis W9355
To:
'Al Schonborn' ; 'alan
simpkins'
Cc:
'Jens Konge Rasmussen' ; 'Ton Jaspers (W10445)'
Sent:
Wednesday, December 02, 2009 6:13 AM
Hello everybody,
My best answer is on the enclosed and very
handmade curve. I am not able to determine the mathematical formula for
this curve but it is perhaps possible.
 Al's note: Even I know enough that the
scale of 1:1 mentioned by Jesper on his drawing worked well on paper
but not here. I have also posted the full-sized
image Jesper sent me but on
line, the whole thing really depends on your screen's resolution (dpi).
All one can really rely on is that two of the little squares in
Jesper's diagram represent half the board's thickness, i.e. likely 3/8"
or whatever that is in metric.
I have now given up making my centerboards
myself and have started to represent Millanes Foils from the UK. It
is the most sublime craftman's work you can get and the shape is close
to the one I have tried to draw.
If you are interested in Milanes Foils you can
find more information on: mailto:Info@milanesfoils.co.uk
Med venlig
hilsen Original
Message -----
From:
Jens
Konge
Sent:
Sunday, December 06, 2009 3:05 PM
Recently I have read that the car with the lowest wind
resistance is the chekoslovakian TATRA T87 – perhaps the nose of that
car is the best curve for the Wayfarer foil front edge ;-))
Take a look at Google -> ‘tatra t87’ |
| more
about the centreboard's leading edge Original
Message -----
From:
KEN-Krist. H. Jensen
To:
Al Schönborn
Cc:
Jesper Achton Friis ; Jens Konge
Sent:
Tuesday, December 08, 2009 9:49 AM
Subject:
*Camber*!
Much is said about it and here is yet another tale to be told! In our first decade of W-sailing and racing, we had an 'edge' - from longest aquaintance with the Wayfarer - often allowing us to win (or not to!) The latter came in as we (being agents for Small Craft, UK - then the only exporting W-builder - backed by Ian Proctor and Gordon Pollard, the Copyright Holders) sometimes had put up the prizes that we raced for in order to establish the class. A very close - now late - friend through the Airforce + SAS, raced with his oldest son as I did with mine. There were many close, fun thrilling matches, in racing to be the first over the finish line. Normally we made it just a bit ahead. Both W.s had standard equipment, CB and rudder, a la suggested by good friend Ton Wayfarer NEDWA and sketched by good friend Jesper A.F., and not talking parabola nor chamfer - unknown to us then. Before his pilot days my very good friend had passed an education + training to become a machinery toolmaker. Thus he made up his mind to build a CB and rudder blade so delicately that landing flies would fall and break their legs! I believe it had about the camber/chamfer like what Jesper A.F. has sketched. From then on, we could never catch him and his son. In 1979 they won the last Scandinavian W-Championship in their homewaters of Køge Bay. The last such since this event could not be officially recognised, and therefore was changed into the Danish W-championship with proper prizes and medals acknowledged by the Danish Sailing Union, affiliated with the IYRU - if this is still the name! In sailing (as well as flying - spoil the Camber with ice or hailstorm-hammered bulks+dents and you've got serious trouble) the Camber-curves, also of your sails, are to be taken very seriously if performance is in question! To curve your sails right is part of a very intricate game?lottery closely related to all other factors of wind, weather and sea condition. The winning vessel, so Poul Elvstrøm said, is made up of three equal parts: Crew, sails and boat. And all three must be the very best! These demands in order to cope in the first third of the racing fleet may well be causing the 'fall out' of participants. So what happened to the group sailing? The Group racing within the race, consisting of: The good, medium and beginner, where the group as such is also praised and prized! The idea being - "I guess 'born' by you dear Uncle" - that the group help each other to achieve a better performance! Too cumbersome and/or too few interested ? Ought to be fun - battle-formation flying in jetfighters was exciting, fun and challenging - and so I found close W-racing in a good breeze! Unfortunately my 'gear' and skill now would place me somewhere between medium and beginner! Sincerely yours Ken, W1348"Maitken" -----Original Message-----
From: KEN-Krist. H. Jensen [mailto:w1348@hotmail.com] Sent: woensdag 9 december 2009 7:57 To: Al Schönborn Cc: Jesper Achton Friis; Jens Konge; Ton NEDWA Subject: RE: *Camber* ! Al ! From: Ton Jaspers W10445 To: w1348@hotmail.com; uncle-al3854@cogeco.ca CC: jesper@achtonfriis.dk; jenskonge@esenet.dk Date: Wed, 9 Dec 2009 Hi Ken,
How true this story
is but wait ..... a Wayfarer does not have a foil (as in a NACA foil).
all it has is a chamfered flat plank! We are not allowed to
have a high lift foil like the one described here
As long as the
leading edge has a smooth shape and more or less resembles a shape as
drawn by Jesper AF, it is ok for the average sailor. I am not talking
about the top ten of the International fleet, people like Mike Mac or
Peter Bøje. For the average
sailor it is sufficient if the leading edges are smooth and more or
less have a cigar-like shape. The average sailors loses
more ground in that brief moment of distraction where he flogs his
sails than he makes good by having a perfectly shaped CB. Far more
important is the CB positioning IMHO; the maximum depth and maximum
angle (83°). Those are settings everyone benefits from because
the boat will point significantly better. There is a nice essay by
Kjell Gaere on the Danish web site about setting up the CB that
I recommend to anyone. Al's
note: the WIT also has Kjell's fine article: Finding the best CB bolt hole position
Best wishes,
Ton Jaspers (Swiebertje W10445)
-----Original
Message -----
From:
KEN-Krist. H. Jensen
To:
Ton NEDWA ; Al Schönborn
Cc:
Jesper Achton Friis ; Jens Konge ; Kjell Gjaere
Sent:
Wednesday, December 09, 2009 8:03 AM
Thanks for a very good and quick response, and of course you are right! I should have added to my tale that in those days we did not yet measure our W.s nor sails. Did not have a Measurer! If it had a W-nr. is was considered eligible for racing. We were forced to start out like that in order to get the Class underway! My old close friend - being a pilot - of course knew about airfoils and also was a skilled aeroplane-model-builder, so he may very well have made a better than allowed CB for his W. The Class Rules were there, but we didn't care much about them, and the mentioned CB in question was never checked - I believe. It was accepted that they were faster sailors with better equipment as no one had such a lovely CB and rudderblade, and I had moved away to Norway (1971)! Very Good to hear from you - all the best to You and Yours. See you at RM next year is my hope. K.regards Ken, W1348"Maitken" |