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Post by Pie-eyed on Feb 22, 2009 19:18:24 GMT
Hey Bert, you can sheave with fibreglass matting / sheets but be prepared for a lot of work to sand it back to a good shape. Please note... use of any carbon fibre is not allowed in the building of foils! Suggest you bin 731's centreboard and make a new stiff board using the old one as a template, suggest you speak nicely to Graham Pope or Mr Skinner.
Roger
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Post by bertfatal on Feb 22, 2009 19:39:20 GMT
Can you give me a ball park figure of how much a new medium quality centreboard would cost?
Thanks
Bert.
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Post by scruff871 on Feb 23, 2009 10:09:28 GMT
Suggest you speak direct to Graham Pope,Mr Skinner or Godfrey Clark. It all depends if you want a blank to finish it yourself[profile,shape and epoxy/varnish or paint]or ask any of these gentlemen to finish it for you. Top end[Milanes] could be £400- ish finished. Suggest a Blank cut roughly to shape but not shaped[aerofoiled] could be about £100-£120. You could try a local woodworker asking him to resin up a blank for you. Using possibly yellow Cedar witha Mahogany strip or strips sandwiched. If all the above fail call James Jarvey[Ent/Scorpion/Solo builder located in Norfolk] or Gerry Ledger[Nat 12/Solo builder in Essex]. As for medium quality...dont know what you are talking about ! Go for the best...always ! Spend time[and money]obtaining a good shape and finish ...it will pay off. There is advice elsewhere on the Forum about shapes,dog-leg or not so make up your own mind in which direction you want to go in.Suffice to say that the Class permits lots of scope on shape but does NOT allow the use of Carbon in any form for foil construction.
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Post by colin on Feb 23, 2009 12:53:51 GMT
Bert. I would suggest if you buy in a foil ask for a NACA 0009 section and remember that the maximum cord is a function of the centreboard slot width. If you decide to make your own I am happy to calculate the xy co-ordinates for you. Roger, you are quite right of course regarding the use of carbon on foils. The laminar flow foil in question has always been an ‘open project’ and has been published as work in progress in Chrysalis over many years. It is slightly ironic that you are the first person to adversely comment on it at the time where I have abandoned it. The carbon was used to strengthen the aft section, which is concave, so paper-thin. If I managed to get it to work I was going to take a mould and produce a glass/foam version. I had it in mind to write-up a postscript at some point for general interest, but in short: The section is very prone to stall at low speed with any load on it. It would start to run clean at around 3knots – about 75% of maximum hull displacement speed. The surface finish is very fussy. So until someone spends a shed load of money developing a fully laminar foil section that will run clean at low Reynolds Numbers stick to turbulent sections i.e., the NACA four digit series. I think I gave a duff link to the foil database, it is: www.ae.uiuc.edu/m-selig/ads/coord_database.htmlTo see the difference between the NACA 0009 and the Eppler E836 Hydrofoil you can download the following gifs: www.ae.uiuc.edu/m-selig/ads/afplots/n0009sm.gifwww.ae.uiuc.edu/m-selig/ads/afplots/e836.gif
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Post by scruff871 on Feb 23, 2009 16:17:46 GMT
Colin not at all making any adverse comments ...indeed Carbon would realise more strength where thin trailing edges are concerned.This could indeed be a consideration[rule change]for the future?. Agree that the NACA 0009 section[or similar sections] is the way to go as Mr Milanes and a couple of NZ and Oz outfits aim for on foils for other Classes. If you need a Mould made we could help you out if you can supply the electronic model[Catia V5 or Iges Files]....might cost a few bob though ! On perhaps a less exacting stage can,t emphasize enough to Richard and others that are attempting to make their own foils that it is all about the combination of angle of presentation of the foil,profile,aerofoil shape and that all important finish.Richard should know he is a Flyer ! As an initial guide[this will make Colin cringe!]start with a rounded leading edge and bottom, gently taper the thickness to a thin trailing edge.Protect the end result well[epoxy] and then finish smooth.Very crude instructions but start with this and then have another go at sorting out some chord details that Colin has kindly offered to help out with to modify the above basic shape.
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Post by colin on Feb 23, 2009 17:09:43 GMT
Roger,
Thanks for the CNC offer. I have a tame company with a fully kitted out development machine shop (they make GP racing motorcycles – a leftover from my racing days)and I get a very favourable rate. It’s not the machining that is the difficulty it’s the shape. The NACA four digit profiles are far from ideal but better that made accurately than anything that can be made with a belt sander.
If you have a handful of cash and you have the choice of buying a new sail or a new foil, buy the foil. It will in all probability make the most improvement and will last the lifetime of the boat.
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Post by BMBA Admin on Feb 23, 2009 17:16:12 GMT
If you have a handful of cash and you have the choice of buying a new sail or a new foil, buy the foil. It will in all probability make the most improvement and will last the lifetime of the boat. <tongue-in-cheek>Unless I stand on it to right a capsize!</tongue-in-cheek>
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Post by bertfatal on Feb 23, 2009 19:21:27 GMT
Is the centreboard included in the 45kg min weight limit?
If so would a heavy board be a good thing assuming the total boat weight was down to minimums?
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Post by colin on Feb 23, 2009 19:57:35 GMT
Uffa Fox once said that weight was only of use to a road roller……… it is a dinghy, it is supposed to be sailed flat, there is no keel type righting moment. The 45kg weight does not include the centreboard.
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Post by bertfatal on Feb 24, 2009 8:31:53 GMT
Why, if the centreboard is not part of the 45 kg min weight limit, does it have to have its weight marked on it?
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Post by scruff871 on Feb 24, 2009 9:33:49 GMT
So that when Boats are weighed at The Nationals or Opens the Hull weight can be quickly established by deducting the Centreboard weight that should be marked on it. Richard,,,keep the Centreboard light,very stiff,nicely shaped and dead smooth and then you will be OK. Happy sanding.......
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Post by bertfatal on Feb 24, 2009 9:46:30 GMT
I knew there would be a logical explaination!
(engage wind up mode) Can the protective strip mentioned in the class rules be made of CF? (wind up mode off)
Richard.
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Post by scruff871 on Feb 24, 2009 10:02:44 GMT
Wind up mode detected..... NO you can,t use a CF protective strip on the Centreboard or Rudder. Rule 7d permits the use of wood,GRP or GRP sheathed construction of foils....thats what you use.No sneaky bits of CF to make it stiffer or for any other use. GRP sheathing as you know will enhance the stiffness and also provide some degree of wear protection....you should not be running aground anyway with your wide navigational experience !
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Post by New Boy on Mar 13, 2009 13:02:32 GMT
Bertfatal Can you please ring me as soon as possible ref your board. New Boy
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Post by scruff871 on Mar 13, 2009 14:35:58 GMT
Then after speaking to your Chum please ring me.... The fate of your new board[shape overall,profiles etc]will be decided in the Bar at Frampton on Sunday and it would be comforting to have your agreement on what we intend to do ! Your Foilmaker par-excellence is eager to get started......
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