stingray580 Posted May 6, 2011 Report Share Posted May 6, 2011 gday everyone, im toying with the idea of building some new rudder blades and centreboards. does anyone know what the optimum shape characteristics are??? specifically i would like to know: 1, length between leading edge and trailing edge 2, thickness and where to position max width 33%? 45%? 3, depth thanks. Link to comment Share on other sites More sharing options...
knobblyoldjimbo Posted May 6, 2011 Report Share Posted May 6, 2011 google profili - there's a free version which does do printouts. you can select from hundreds of designs but the NACA four series ones seem to be most common (and possibly a good starting point) eg NACA0010 is a 10% chord (about 35% back I think). To be adventurous try the Eppler series, they have a bit of negative flow in the trailing edge. If you bevell the trailing edge so its not symetric eg put a flat of about 1ml and make it 60 degrees then you may eliminate hum caused by the fluid from one side smashing into the fluid from the other side, with a chamfer, one side wins. Link to comment Share on other sites More sharing options...
stingray580 Posted May 6, 2011 Author Report Share Posted May 6, 2011 thanks knobbly, i found a centreboard and rudder profile design from the chris tucker stable, for the DS 12 with a 150 and a 165mm profile, both 20mm thick and both have a 35% max width. but i will check out profili. thanks. i have also seen the assymetric trailing edge from the AHPC website. does it matter if you have the asy metric both in or out?? Link to comment Share on other sites More sharing options...
knobblyoldjimbo Posted May 6, 2011 Report Share Posted May 6, 2011 so you want symetry in you assymetry! don't think it matters, I think because the treatment of the flow is after it leaves the trailing edge so it's not going to make any difference to the way the foil works. Link to comment Share on other sites More sharing options...
stingray580 Posted May 6, 2011 Author Report Share Posted May 6, 2011 yeah something like that, i have all the cad programs here to draw it up i was just interested in the actual shape. it looks like 35% is the point of max width, and 10% thickness. Link to comment Share on other sites More sharing options...
CTMD Posted May 6, 2011 Report Share Posted May 6, 2011 Don't get to excited about the DS12 foils. You get what you pay for, those are just standard Naca sections. My own foils are quite different but there are better people than me out there. I recently discussed this with Richard Roake who has forgetten more about "ideal" shapes than I know and he recommends Eppley E836 as a starting point. 12% thickness is pretty typical. Chris Tucker Link to comment Share on other sites More sharing options...
stingray580 Posted May 6, 2011 Author Report Share Posted May 6, 2011 ok thanks chris, all good starting points. the mackenzie foils seem to be a little over 12%. it all comes down to cost doenst it?? do i spend the three weeks evry night in the shed to get a half reasonable product or do i just spend the $700 or so bucks and buy them?? and get a just about perfect finish?? hahahah Link to comment Share on other sites More sharing options...
stingray580 Posted May 6, 2011 Author Report Share Posted May 6, 2011 chris what is eppley 836??? Link to comment Share on other sites More sharing options...
CTMD Posted May 6, 2011 Report Share Posted May 6, 2011 sorry typo. Eppler 836 http://www.worldofkrauss.com/foils/119 Link to comment Share on other sites More sharing options...
knobblyoldjimbo Posted May 6, 2011 Report Share Posted May 6, 2011 I think thats in the Profili catalogue. Oh look, yes it is EPPLER E836 Hydrofoil max thickness 12.64% at 42.8% of the chord. Looks like it has a slight concave section towards the trailing edge. I suspect that by the time you've stuffed about in the freezing shed you'll be glad to stump up with the cash!! There's a lot of information on places like the Moth sites. I went through all this for my Careel 18 (only one rudder) but ended up buying a Castle 650 jobbie for $500. Money very well spent (included a s/s stock too). I subsequently bought a blade made for a Bull 7000 in an attempt to reduce whetted surface and weight but it didn't help and I managed to break an aluminium plate rudder stock I'd made up. Should have stopped while I was ahead. Link to comment Share on other sites More sharing options...
tonyquoll Posted May 6, 2011 Report Share Posted May 6, 2011 that website CTMD linked is awesome! I flicked through a few and was pleased to find the profile I have used in the past, NACA0012, has the highest stall angle; 7.5degrees http://www.worldofkrauss.com/foils/1137 They have the chord at 30% from leading edge, which I think works better for rudders; where stall angle is your most critical factor. Rudders that stall dont turn; they just slow the boat down. The ones I made were laminated hardwood, which have the advantage of being easy to shape and quite strong without fibreglassing. Disadvantage; weight. The idea was to test shapes and then use the best for a buck to mould carbon copies, but still haven't got onto that bit. I thought thicker increases maximum angle possible before stalling, but at the expense of more drag. Total drag = frontal area x drag coefficient. Reducing thickness reduces frontal area. In an experiment I cut 2 inches off the trailing edge of some old wooden rudders, reshaped to NACA0012 and they worked better than they ever had before! Then snapped in half. Damn cedar. Link to comment Share on other sites More sharing options...
stingray580 Posted May 6, 2011 Author Report Share Posted May 6, 2011 thanks everyone for your help, i have downloaded profili2 and have downloaded the eppler836 into a cad file so i can calc the x sections/offsets along the chord. yes it does have a concave tail section, but according to my cad program the depth of the concave is less than 1 mm, in fact it is 0.3mm. and the concave only happens in the last 40mm of the blade. = wrap a vb bottle in sand paper, up and back twice. job done. basically it is a 12.65% chord thickness with max width at 41.5% of the chord ( from the front) Link to comment Share on other sites More sharing options...
mitchlb44 Posted May 7, 2011 Report Share Posted May 7, 2011 Having read that thread I am pretty happy with the Boyer Tornado Rudders I picked up for $400 brand new Link to comment Share on other sites More sharing options...
stingray580 Posted May 7, 2011 Author Report Share Posted May 7, 2011 Bastard!!!!!!!!!!!!! Link to comment Share on other sites More sharing options...
stingray580 Posted May 7, 2011 Author Report Share Posted May 7, 2011 ok tony, interesting... so your opinion would be using the NACA0012 design for rudders? could you explain the stall angle to me???. Link to comment Share on other sites More sharing options...
madboutcats Posted May 7, 2011 Report Share Posted May 7, 2011 I put kick up Tornado rudders on my big rig Stingray and it was a totally different boat to tack. Absolutely fantastic Link to comment Share on other sites More sharing options...
bad dog Posted May 7, 2011 Report Share Posted May 7, 2011 Off topic, but Stingray580 - you have an old A? KA585? Maybe start a new thread or add to the one looking for a history of As - can you post some pics, give details of age, construction, weight etcz/ Link to comment Share on other sites More sharing options...
stingray580 Posted May 7, 2011 Author Report Share Posted May 7, 2011 mitch/jeff, i have A class boyer rudders on my stingray, and i have never blown a tack on it. where did you guys get your tornado rudders from? maybe i look into that and put my foam sandwich boyer rudders on my A, tornado rudders on my stingray, which is basically a mini tornado!! bad dog, i will post some pics etc when i pick the boat up, in about two weeks time. as far as i know, its a genuine built boyer out of ply. so is mk1 or 2 not sure, has varnished decks, about 20 years old according to john dowling who built a boat one or two numbers different. not sure on weight, but i would say not minimum!! Link to comment Share on other sites More sharing options...
tonyquoll Posted May 7, 2011 Report Share Posted May 7, 2011 stall angle; the maximum angle the shape can be turned before laminar flow breaks off and becomes turbulent. For example when pushing the rudders over as you begin to tack, a higher stall angle will allow the rudders to be pushed further and the boat turn more quickly. Pushing the rudders beyond this angle generates a lot of drag and not much force; so the boat slows down and doesn't turn very well. Thinking about working with this stall angle; first push the rudders to 6 or 7 degrees, and only push further when the boat starts to turn and the back of the boat is moving sideways. I use a string between rear beam and rudder crossbar to limit how far I push the rudders across. Maybe a bit of elastic which starts to take tension at the stall angle and then allow stretch for maximum turn would reduce stalling. Link to comment Share on other sites More sharing options...
stingray580 Posted May 7, 2011 Author Report Share Posted May 7, 2011 some happy sanps from the sale advertisement, more to follow Link to comment Share on other sites More sharing options...
Loose Change Posted May 8, 2011 Report Share Posted May 8, 2011 Unfortunately there is no one ideal shape or section to suit all speeds, generally the higher the speed the further back the max chord thickness. Lets face it, you are not always going to be sailing at speeds where laminar flow happens, in fact I wager that most of the time it will be a turbulent flow situation. Harry Link to comment Share on other sites More sharing options...
mitchlb44 Posted May 8, 2011 Report Share Posted May 8, 2011 Brian - I used to have Boyer Taipan/A rudders - great rudders, never had any real problems with them! I got my Tornado rudders direct from Jim Boyer about 18 months ago - He was clearing out his shed and advertised a whole heap of stuff on here! I bought them without anything to do with them but figured one day they would come in handy! When I got Last Tango the rudders were crap and the stocks were shot! Given what happened on The Shadow I got the transoms beefed up, and put AHPC F18 stocks on with the Tornado blades... beautiful! To give you an idea... The Marstrom gear Jeff has on his Taipan..... new...... $4k at your door! Link to comment Share on other sites More sharing options...
stingray580 Posted May 8, 2011 Author Report Share Posted May 8, 2011 COUGH COUGH SPLUTTER!!!! WTF?? four grand? at that price i can get spares!!! think ill walk down to hardware store and buy a wood plane. shit i could buy a new router and get someone to CNC me the perfect shape router template out of steel and id still have change!!! Link to comment Share on other sites More sharing options...
mitchlb44 Posted May 8, 2011 Report Share Posted May 8, 2011 That includes the carbon stocks as well! Best way to buy a set of those is on a 2nd hand tornado! Link to comment Share on other sites More sharing options...
madboutcats Posted May 8, 2011 Report Share Posted May 8, 2011 Don't get too excited about what new ones cost Brian what were saying is find some complete second hand Tornado rudders,stocks etc chuck them on your cat and go where you point your boat. The ackerman angle is about right they just go straight on a Stingray Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.