Gybing Plates
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=12291
Printed Date: 08 Jul 25 at 1:46am
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com
Topic: Gybing Plates
Posted By: iGRF
Subject: Gybing Plates
Date Posted: 26 Jan 16 at 11:08am
|
I don't suppose anyone might have a picture of one, I'm trying to fashion the head of the plate in this Minisprint I bought recently and doing it from memory, ahem thirty five year old memory at that, last time I had one was in 1981 and it wasn't particularly successful in a div 2 board, I'm hoping the additional weight and leverage of this Minisprint with it's canoe seat might be able to overcome the excess lift they generate.
------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Replies:
Posted By: davidyacht
Date Posted: 26 Jan 16 at 12:10pm
|
Have a look at http://www.int505.org/old_site/eck1.pdf ------------- Happily living in the past |
Posted By: davidyacht
Date Posted: 26 Jan 16 at 12:15pm
|
Do you have access to Autocad? I have some drawings that I did for my N12 with the gybing head sections and profiles in a DWG or DXF format. ------------- Happily living in the past |
Posted By: iGRF
Date Posted: 26 Jan 16 at 12:31pm
|
Regretably no access to autocad, but that's told me one thing I needed to know, the gybe angle, no more than 4 degrees, I think that's where I may have gone wrong before I seem to remember 7 degrees.
Fascinating document it advocates gybing plates without question and suggest jib angles can be altered, not that that's relevant in my case, but this little boat allegedly is not know for its' pointing capability, but that's hardly surprising if you could have seen this plate before I took a belt sander to it. it was just a parallel sided blunt both ended slab of wood, I'm even surprised they glass sheathed it. Thanks for posting that, so do we know if 5 ohs still use gybing plates? With all this assym nonesense of recent years they must have well gone out of fashion. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Roger
Date Posted: 26 Jan 16 at 12:54pm
Pretty much standard in all new 505s, and a lot of older boats converted to take them. There is loads of stuff written about it, but from memory 3 deg is what is currently in use, and a lot of 505 boards use stoppers to stop the board gybing when it is lifted, although there are some that put the boats fully down on all angles of sailing and leave it there. http://www.int505.org/old_site/gybecb.htm One point of caution is that a gybing board will load up the sides of the certerboard case more than a conventional board, and certainly in some older 505s which have converted to gybing boards they have felt it necessary to beef up the case. |
Posted By: JimC
Date Posted: 26 Jan 16 at 12:57pm
| There are several classes that use gybing boards, but in many of them only some boats have them. According to my theorising the angle of the board should match the 'leeway' angle the boat would take up with a non-angled board, so a boat with a hideously inefficient board would do best with more angle than a boat with an optimal one. But there are so many opinions about the things... |
Posted By: Phil_1193
Date Posted: 26 Jan 16 at 1:54pm
I maybe telling your granny etc but Autocad files can be 'printed' in PDF and saved/ sent as such Option 2 is download DWG True View from the AutoCad website, its a free CAD viewer that allows zoom and pan, turn off layers, take measurements etc to the same levels as AutoCad so makes details easier to read |
Posted By: iGRF
Date Posted: 26 Jan 16 at 2:52pm
|
You need to translate all that into Apple speak, not sure if there's much in the CAD world that comes without considerable expense. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: davidyacht
Date Posted: 26 Jan 16 at 4:09pm
There was a level of how helpful I was intending to be, and do my day job! In essence our board had a diamond shaped head, which was slightly thrupenny bitted at the shoulders. It worked fine. My experience was that the biggest gain was by sailing slightly free, relative to how high you could point, but being really powered up, so in the 12's the biggest gain was if you were heavier, rather than lighter and feathering. My suggestion to GF would be to make a template of the centreboard case and of the centreboard head section and trim the head section to achieve the desirable gybe angle. If the board was not loaded up it could slop around a bit. I know that Ray Rouse's 14 had a device that locked the board when the board was retracted. There is a view that the boards can "self" steer downwind, don't think that this is a problem on the run, but could be on a reach, but I never found this to be the case. We used all of the efficiency gains of the centreboard and rudder to reduce the foil areas. With hindsight probably a little too much, since there was a cost in getting flow going in dead boat situations. ------------- Happily living in the past |
Posted By: gordon1277
Date Posted: 26 Jan 16 at 4:09pm
|
Hi GRF
Have a look at a free download called Trueview which allows you to view and plot CAD files. Gordon What a shame about all the boats lost at Cowes some peoples years of effort in restoration just gone plus classics we will never see again. Awful for all concerned. ------------- Gordon Lossc |
Posted By: davidyacht
Date Posted: 26 Jan 16 at 4:13pm
Yep really sad, something we worry about in Salcombe, 80% of the Active Yawl fleet are in two barns, albeit on different sides of the estuary. ------------- Happily living in the past |
Posted By: iGRF
Date Posted: 26 Jan 16 at 4:59pm
Thanks, and I know what you're thinking, it wasn't me, I've got an alibi!.. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 26 Jan 16 at 5:57pm
|
I vaguely recollect an article by a top OK sailor in the eighties where he said that any benefit from gybing a board had to be offset by the weight of the extra water you carried round in the centreboard case.
Edit: found it http://www.okdia.org/boat/manual/tm2_work.php" rel="nofollow - http://www.okdia.org/boat/manual/tm2_work.php |
Posted By: iGRF
Date Posted: 26 Jan 16 at 6:24pm
That guy if you'll pardon my impatience is talking bollox. So much crap in what he was saying then, typical example of a good sailor having an opinion, juxtapositioning facts to support it and I can't be asked to pull it all apart, but he's wrong. Allthough I'm grateful nonetheless for you posting me a link I will have to come back to it later some of those equations annoyed me..
Carrying 2 kgs of water around in the centreboard case, yeah right... Whatever water is there, is there regardless and any more or less is a result of the efficiency or inefficiency of flushing strips, now attention does have to be paid to them if you are going to use gybing plates, but it's not beyond the wit of man to overcome. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: RS400atC
Date Posted: 26 Jan 16 at 7:22pm
Some people stuff the centrebox, instead of relying on slot gaskets. |
Posted By: iGRF
Date Posted: 26 Jan 16 at 7:31pm
|
Yep even we used to try that in light weather with a foam block but it really doesn't make much difference unless of course your flushing strips are not cutting it as they should, which at championship level you really couldn't afford to happen, back in the day some of us would have a fresh set every major event.
The key thing about water in the centreboard case, isn't wether it's there or not, it's how badly it's moving about. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: maxibuddah
Date Posted: 26 Jan 16 at 7:41pm
|
Draftsight is a free 2D CAD program that runs on windows, Linux and Mac. The link to the download pageis http://www.3ds.com/products-services/draftsight-cad-software/free-download/ Its from the same people who make Catia and Solidworks and is a pretty straight copy of autocad. Only does 2D stuff though
------------- Everything I say is my opinion, honest |
Posted By: JimC
Date Posted: 26 Jan 16 at 9:44pm
I think he's more wrong than right though. It is striking that all the classes I know of where they seem to have gained a significant measure of popularity are two sail classes. I see two possible factors. They're all about the fact that what gybing boards do is in effect rotate the hull round the foil. So the first effect is that if you get the gybe angle right then the hull centreline is aligned with the direction of travel, not crabbing by two degrees or whatever. I used to think that was probably insignificant, but I've seen some calculations by someone I respect which suggests it isn't. The second effect is that the alignment of jib and mast changes (if you have a jib). The 505 guy goes into great flights of enthusiasm, in which I think he's forgotten that sailors sheet their sails relative to the apparent wind, not the hull, but nevertheless there is a change in an area where I find tiny changes matter. As for the weight thing, well, yes, if your gybing board arrangement means you have a fatter case than someone without one, then that is a little more weight. Not convinced about the significance though. |
Posted By: realnutter
Date Posted: 26 Jan 16 at 9:58pm
|
The weight argument is just silly.... I see this in other parts of my life.... Fat blokes spending 100s of pounds to fit carbon fibre goodies to their motorbikes to save a few hundred grammes... Unless you (and your clothing etc) are already at optimum weight, an extra kilo of water in the centreboard case is immaterial.... |
Posted By: 423zero
Date Posted: 26 Jan 16 at 10:03pm
|
I did look at this for my Sprint, the main issue I looked at which suggested not doing this, was the slot is only about 5" deep, the pressure on such a short section of centreboard could be catastrophic, you are in effect loading up a reduced surface area, when you shave off material. I could be wrong, if it works I will use it.
|
Posted By: iGRF
Date Posted: 27 Jan 16 at 10:17am
|
The reason (I think, just an opinion)it probably works better on two man boats particularly those 505 thingies that usually come loaded with half a ton of meat on the wire, is that there is enough power to drive it. it's been my experience using them on boards that whilst superb in light weather the moment the wind built it just scewed the board into a stall there just wasn't enough moment to overcome the tendency of the plate to that direction.
Now the reason I think it might be relevant to this little boat is because it is decidedly under boarded, it's a tiny plate and before I started in with the sander so flat as to probably not create any lift and to act just as a side slip prevention tool a la Finn. It made noticeable leeway, which it probably still might but with the plate angled and sailed free enough it might overcome, if not I have a cunning plan that might enable it to be switched off or adjusted without the usual knock at the back and having to retract it slightly. As it is the plate is so loose in the slot I will have to build it up anyway, so I though I might be able to fashion an adjustable angled device, we'll see, all these ideas are great until you have to actually fabricate them. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 27 Jan 16 at 10:58am
|
Love to see the thinking and the effort, but suspect that simply making a decent board will see the greatest gains. Mind, be thankful that you have the option of real shape. The case on my wooden one is so narrow, a Mirror Dinghy board cut down only just fits! No real opportunity for shape there.
Will be trying the one I've made when I collect the boat from its cosy barn. ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: JimC
Date Posted: 27 Jan 16 at 11:48am
Its still lift. A flat plate will lift just fine, as we have all demonstrated with paper aeroplanes. And the amount of lift you end up with has to be the amount required to balance the sail. But, and its a very big but, the proper shaped foil will create that lift with a load less drag and at a much lower angle of attack (=leeway). And yeah, I'm sure you're right: if the boat is spectacularly underboarded it will need to sail with a lot of angle of attack on the board, which means the hull will be crabbing sideways more than most, which means that the gains from angling the board to align the hull with water flow will be more than most. |
Posted By: gordon1277
Date Posted: 27 Jan 16 at 12:26pm
Jim Stop it please, has the world come to an end, you saying grf is talking sense on a techinal matter 
And you agreed with him!! ------------- Gordon Lossc |
Posted By: iGRF
Date Posted: 27 Jan 16 at 12:30pm
|
Is it not the case flat only creates lift when an angle of attack is presented, whereas a shaped foil adds an element of bernoulli (not sure of the spelling) effect, which supports your argument of less drag and therefore less leeway, either way a decent naca section is always better than flat, unless of course your head is full of meat instead of brains and you sail a Finn. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Daniel Holman
Date Posted: 27 Jan 16 at 12:45pm
Graeme, You can't get more power from a gyber, the "power" or side force is, in equilibrium, only ever equivalent to the righting moment that you are applying. On a dinghy it means taut you can run the hull at 0 deg leeway, which can save up to 10% of additional induced drag. Penalties of loss of buoyancy in case, junctions etc but some compelling wins Esp on under finned boats where you are loading the foils hard and doing in excess of 4 deg leeway. Fwiw we have estimated that cats lime dart 18 etc do about 7 deg leeway sailing upwind normally! A short board I'e skeg only probs similar. Anyway the reason it didn't work on your board is because, if correctly set up, a boat should have the side force shared to a large extent between board and rudder. In the case of the gyber, the board is yawed say 4 deg from the hull, and the rudder the same to keep balance, so it isn't necssarily seeing any weather helm but it's 4 deg over to maintain equilibrium in yaw. On the board, you yaw the CB, but can't yaw the skeg, so assuming you are running the skeg with a bit of load innit upwind, the board will want to be heading up the whole time because you have angled the dagger (fwd of Clr) a. Lot and not the skeg (aft of Clr) so unless you chop the rig fwd loads and run all the side force off the CB, so the skeg is not earning it's keep and will be wasted wetted surface, then you will have a board that won't stay in equilibrium |
Posted By: JimC
Date Posted: 27 Jan 16 at 1:01pm
You still need angle of attack with a shaped symmetrical board. Maybe less, I'm not sure in real terms how much this varies. Its all about coefficient of lift and I couldn't quickly find a reference on line of how much the coefficient of lift of a symmetrical foil varies between sections. That's an interesting observation about fixed fins Dan, that hadn't occurred to me, but of course you are right. All part of the horrible mess sailors get into thinking about leeway, lee helm, weather helm and balance... Equilibrium between foils is a really good way of thinking about it. |
Posted By: iGRF
Date Posted: 27 Jan 16 at 2:33pm
|
Yes yes, that is exactly it, why didn't I think of that? Of course fixed fin and it was a round board with quite a rocker and they like nothing more than to head up at the best of times, so and I'd thought of this for formula, time for a gybing fin head..
So lets go back to sitty down things, so what's happening in our five ohs, are you saying the helm is on or about the same angle as the plate and if so that would be constant weather helm? Now I need to make my switch on switch off system then I could tell immediately, it must of course be so and it should therefore only be used in overpowered planing conditions so you kind of buzz along and instead of making leeway, actually crab to weather. Anyway, small boat under foiled, should I or shouldn't I? I could do without wasting my time this go round, got lots of other things that need doing. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: JimC
Date Posted: 27 Jan 16 at 3:17pm
Yes, and then again no... There's a lot of muddled thinking about weather helm, and Dan's point about equilibrium and balance is a good way of thinking about it. Here's what I think: Sailing along in a straight line everything must be in balance. You've got a sideways load from the sails acting on a centre of effort somewhere between the two foils, and sideways load, normally on the both foils. Because there's sideways load on the rudder then because the blade is mostly or all behind the pivot it tugs on the tiller, and people think of it as weather helm, but its not as simple as that. Our first boat has a non gybing board, and in order to provide side force the board has to make an angle of say 4 degrees to the oncoming water, and we call that leeway, and again people think of it as a bad thing, but its not, its intrinsic to any boat with a symmettric foil fixed on the centreline. OK, so first think of the balance with all the load on the centreboard and none on the rudder. Mast raked well forward I expect. For the boat to be in equilibrium the rudder must contribute no side force. It won't be pulling on the hand in either direction, and it will be angled exactly to the water flow - so 4 degrees to leeward! That's what was traditionally thought of a balanced, but actually all the side load is on the board, so the rudder is being dragged through the water and doing nothing but contributing wetter surface drag. Next the rig is raked back a bit and so think of the boat with the rudder exactly on the centreline and going in a straight line. For this to balance then there must be proportionally equal side load on rudder and centreboard. The rudder blade is making the same angle of attack on the water as the cb, and this is probably the lowest drag configuration for a modern boat. The rudder is pulling on the helm's hand, so many people would say there is weather helm. So yes, but its *good* weather helm! Incidentally the 'leeway' will have reduced a bit, because with the rudder taking up some of the sideload the centreboard needs less angle of attack on the water. OK, so rake the rig back so its all over the rudder. There's near enough no sideload on the centreboard, first thing that we observe is that the boat has stopped making any leeway. No load on the centreboard, no angle of attack on the centreboard, no leeway. Next thing we observe is that because all the side load is on the rudder, its got to have a shed load of angle of attack to create the necessary lift. This means its got to be pulled well to windward, and we have shedloads of what was traditionally called weather helm, and we have loads of drag and having no leeway is definitely a bad thing! OK, so we now know that we want to have the rudder parallel to the centreboard (roughly). So now we fit a gybing board and the centreboard is angled to what the leeway angle was in the middle example. Boat makes no leeway. But to maintain the balance the rudder blade still needs to be parallel to the centreboard, so it has to be pulled to weather the same amount that the centreboard is angled, and it will pull on the hand by the same amount that it was. So on the one hand we could call it weather helm, but on the other hand its exactly what we want... So what we are doing with the rudder, in order to sail in a straight line, is actually to change the angle of attack on the rudder so the side load is shared correctly between the two foils. Dan, would you agree with the above description?
For what my opinion is worth, give it decent shape foils first and see if it still feels underfoiled and how much leeway you are making. |
Posted By: iGRF
Date Posted: 27 Jan 16 at 3:49pm
|
I'm getting confused with this term 'leeway' in my confused world it has always been a bad thing, to me it meant making ground more to leeward, slipping sideways instead of going forward, like setting the sail with no centreboard or rudder in place you would just drift downwind. 'Making too much leeway from pointing too hard and going sideways' would be a quote to put it into the context I understand.
Now what you pair are saying means something else, like the expression used in common parlance by none sailors saying 'we should get a move on and make some leeway' as an expressive use of the term. In order to fully grasp what your saying in actual fact this bit 'the board has to make an angle of say 4 degrees to the oncoming water, and we call that leeway, would better be described in order to make ground to weather (there is no term but humour me with 'weatherway')the board has to make an angle of say 4 degrees to the oncoming water. Or am I confused? f**k it I am confused! I'm going down the post office where I shall stand in the queue and ponder all this and come back hopefully enlightened. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: JimC
Date Posted: 27 Jan 16 at 4:20pm
|
Yeah, pretty much.
The board must create lift to resist the push from the sails. In order to create lift it must be at an angle to the water. So think about the pointing too high thing. Point too high and you still have loads of side load from the sails, so you still need a lot of lift from the board to balance it. However you have less forward drive from the sails, so you go slower. As you're going slower lift from the board reduces, so to get the same amount of lift you need more angle between board and water, so when the boat is in equilibrium its crabbing sideways more and creating loads of drag. Now suppose you have an an adjustable gybing centreboard. Lets say the boat is making a course good of 45 degrees, and has 8 degrees of leeway, or angle of attack, with the board on the centreline. So the bow is going to be pointing 37 degrees, and say, for arguments sake, the sails are at 5 degrees to the centreline, so pointing 32 degrees. Now dial on 8 degrees on the board. The boat is still making good 45 degrees, but the bow is now pointing 45 degrees too, so no leeway, and to keep the telltales right you've sheeted out that same 8 degrees, so the sails are at 13 degrees to the centreline. But the essential relationship between sails at 32 degrees and foils at 37 degrees is unchanged. Hey, I've just thought of a demon tweak for a Moth. Give it an adjustable gybing daggerboard and the sailor could align the hull with the apparent wind in order to minimise aero drag! Anyway, to summarise, like a lot of things on boats, leeway and weather helm have to be like little Bear's porridge, just right, and too much and too little are both faults. |
Posted By: iGRF
Date Posted: 27 Jan 16 at 4:41pm
|
So now, currently, standard CB or Dagger, to help me fully understand this use of the term 'leeway' is the 4 degrees or 8 degrees whatever, derived from a tangent of the leading edge of the foil?
I think we need a little sketch with arrow things and angles as you would a child in geometry 101 if you'll excuse the americanism ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Presuming Ed
Date Posted: 27 Jan 16 at 5:29pm
|
Leeway = angle between heading and course sailed through the water. Also = AoA of foil aligned with centreline. (IANANA). 
|
Posted By: Presuming Ed
Date Posted: 27 Jan 16 at 5:32pm
|
Posted By: I luv Wight
Date Posted: 27 Jan 16 at 5:43pm
|
For a gybing board, the board is the same angle to the blue lines as above, but it's the hull that is rotated ( anticlockwise here ) by the leeway angle, so the blue lines ( track ) line up with the fore / aft lines of the hull. Which can mean less drag off the hull. So you make better height to windward because you're not slipping sideways as much, or you can sail a bit faster until the drag catches up again. I've made boards for 5o5s, with gybe angle of 2degrees, with angles of up to 6 degrees for Hornets that have thick, short-chord small foils. Hornets have buttons in the case, so the board locks straight when lifted a little, 5o5s use bumps on the board that lock the board sideways in the case when lifted a bit. A little forward rake to gybe the board, vertical and raked to lock. Gybing boards work best in flat water, in waves you don't get the drag reduction as the water is moving about, so boats lock the board for wavy conditions ------------- " rel="nofollow - http://www.bloodaxeboats.co.uk" rel="nofollow - http://www.bloodaxeboats.co.uk Andy P foiling Int Moth GBR3467 Freedom 21 Codling |
Posted By: rogerd
Date Posted: 27 Jan 16 at 5:58pm
Terrible new but at least the Classic Boat museum hadn't started its move to the site and now the building earmarked for them is being used to help these businesses get back up and running. |
Posted By: 423zero
Date Posted: 27 Jan 16 at 6:28pm
|
Gybing the board turns the hull parallel to its true track through the water, removing large drag from hull to smaller drag off gybing board, is that correct ? Presumably light winds no benefit ?
|
Posted By: 2547
Date Posted: 27 Jan 16 at 7:08pm
| This gybing board will be mustard at helping you to further exploit the lee bow effect ... |
Posted By: iGRF
Date Posted: 27 Jan 16 at 8:19pm
|
Fuller rule number 1. Never trust anything prepared by an advocate of Cat sailing.
That diagram without context is convoluted. I need something simpler and more relevant to displacement speeds, those true/apparent wind angles are off any scale we'll likely experience. oh and 2547 not much tidal lee bow effect going on at our lake unsurprisingly. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Daniel Holman
Date Posted: 27 Jan 16 at 9:50pm
bang on Jim. In reality the rudder is about a degree or two further yawed than dagger for same Cl as its operating in the downwash. Also, in a non steady state you'll be running a variable side force off the rudder so may load it up a bit less to get a similar RMS value or Cl. High aspect boards like to operate ~ 4 deg AoA (less and they are dragging too much WSA, more and too much induced. Low aspect foils best at sat 2 deg as induced drag more expensive. Even with high aspect foils, you wouldn't want to show the hull that much AoA (leeway) as its a 1:20 aspect ratio foil and will be picking up a lot of induced. Its easy to design / size foils for slow boats, as they go the same speed once up to speed. HP boats are generally massively over finned as they can go say 50% faster in wind than when just powered, for same RM i.e. side force. Mind you all that area is generally needed for getting out of tacks in most boats. Dan |
Posted By: JimC
Date Posted: 27 Jan 16 at 10:38pm
Been there and got that T shirt, signed by the band... |
Posted By: iGRF
Date Posted: 28 Jan 16 at 10:25am
|
So I think I've got it now, amazing learning something new when you think you know everything..
Although tbh the term as y'all use it never really came up much in our world, only the Original Windsurfer acted perceptibly as described and forced a crabbing technique to force the boat to weather to overcome 'leeway', hell, I still can't believe I've not used the term before, maybe its early onset altzeimers. Anyway in essence the trick then must be to align the angle of the plate offset, to the percieved leeway angle of a given craft. It then follows that this angle should be adjustable, because that leeway angle must surely alter with wind strength on some hull forms, in fact logic then suggests the actual internals of the cb case should be constructed to vary that angle, has that been done I wonder.. My there's lots to think about, but thanks everyone for the input, it's been fascinating and thought provoking. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 28 Jan 16 at 1:43pm
|
I think I might go back to basics to stop my head hurting... Put board down to stop boat going sideways. Board too small, but still go sideways. Board too big, boat not go forward well. ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: davidyacht
Date Posted: 28 Jan 16 at 2:14pm
Must be the pond sailing with all of that Blue Green algae http://www.dailymail.co.uk/news/article-3413873/Alzheimer-s-cause-discovered-Poisonous-algae-freshwater-lakes-reservoirs-UK-fuelling-dementia-epidemic-afflicting-1m-people.html ------------- Happily living in the past |
Posted By: JimC
Date Posted: 28 Jan 16 at 3:39pm
I've not heard of it being done, but I agree, that would seem to be the logical approach. Indeed in an ideal world I suspect one would dial in a lot of angle coming out of a tack, and reduce it as the boat comes up to speed and the foil generates more lift. The ultimate expression would presumably be a daggerboard in which the leading portion was a gybing foil with adjustable angle of incidence, and the trailing portion was a flap so the foil was adjustable with the total camber able to be altered... I think I know a Canoe sailor in California who would build that, if indeed he hasn't already! |
Posted By: iGRF
Date Posted: 28 Jan 16 at 4:42pm
|
You could 'spring' the diamond, so more pressure gives max angle and less pressure reduces it, but I'm not sure that's the way round you want it, then actually you could spring the other side for the opposite effect, wait a minute, this needs more dwelling on, so like a suspension ATB you springload with adjustable tension, I'm going to think further about this... ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: I luv Wight
Date Posted: 28 Jan 16 at 5:18pm
|
http://www.boatdesign.net/forums/boat-design/gybing-daggerboard-5783.html" rel="nofollow - http://www.boatdesign.net/forums/boat-design/gybing-daggerboard-5783.html Some interesting stuff here ( tspeer ) ------------- " rel="nofollow - http://www.bloodaxeboats.co.uk" rel="nofollow - http://www.bloodaxeboats.co.uk Andy P foiling Int Moth GBR3467 Freedom 21 Codling |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 8:35pm
You can adjust the AoA of a gybing dagger. Done plenty on i14s and on Chris Maas breathtaking ICs. Bear in mind you can be doing say anything from 7kts to 12kts upwind in an i14 while twin stringing, so remembering Cl varies with V^2 thats a big Cl range and hence Alpha range. |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 8:38pm
Also, you wouldn't adjust it coming out of tacks as that would be such a tiny percentage of the total time sailing |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 8:41pm
|
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 8:43pm
 |
Posted By: Do Different
Date Posted: 28 Jan 16 at 9:08pm
|
So reading all that has been said by respected designers and theorists. If I have understood correctly. A gybing board does not have magical properties that make a board "climb" to windward and there is no such thing as something for nothing. The most significant benefit is to allow the boat to track straight through the water for most efficient use of hull shape. If the above is right, given that hull alignment is top effect can I ask a couple of simple minded questions. Would a heavily chined hull shape benefit more than a round dish? Is the benefit greater in displacement mode, as when planing there is less hull in the water and what is would most likely be pretty flat anyway? Does the fact that gybing boards are big in Five Oh's (round and planing hulls) mean the above questions are total tosh or Five Oh's simply love tech? |
Posted By: realnutter
Date Posted: 28 Jan 16 at 9:12pm
|
As I understand it... gybing boards only work when fully down.. it's the bit that remains in the case that is shaped to allow the magic to happen... Pull the plate up, as you would off the wind., and planing, and they can no longer gybe... |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 9:16pm
Thats the case for a gybing CB which has a diamond shaped head - the gybing daggers above gybe at all states of retraction. |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 9:23pm
|
Posted By: realnutter
Date Posted: 28 Jan 16 at 9:36pm
Is a suitably shaped dagger board actually a good foil?.. It goes against all teaching to build a foil with max thickness toward the rear edge.. |
Posted By: Daniel Holman
Date Posted: 28 Jan 16 at 9:41pm
the daggerboard is shaped as one would optimally shape it, it then slides up and down through a diamond shaped "box" which then sits in the square case - should be evident in the pics above |
Posted By: JimC
Date Posted: 28 Jan 16 at 9:45pm
Come sail a Canoe Dan, and you'll be amazed how much time you lose tacking! Still, I expect you're right. I can't imagine doing it myself. |
Posted By: realnutter
Date Posted: 28 Jan 16 at 9:57pm
OK, I can see that in the second pic... Does the black rope have something to do with adjusting the angle? If so, how? If not, what's it diong? |
Posted By: Do Different
Date Posted: 28 Jan 16 at 10:20pm
|
Could I guess the black rope there to pull the wedge shaped Vee back to adjust and ultimately lock the board's angle of attack. Dan. Another simplistic question please. For a boat with a fixed board does it generally follow that when beating speed is your friend by generating greater power from the board at a lower angle of attack = less yaw of the hull. Pinching is not good if it means less speed and therefore a greater angle of attack needed to generate the power to oppose the rig force = more drag from hull yaw. Is pinching for height nearly a optical illusion? When in fact the actual track is probably the same or even worse.
|
Posted By: iGRF
Date Posted: 29 Jan 16 at 11:11am
Woa, so what is this? I guess it's one of those International 14 things you see coming up on ebay for a fiver from time to time looks very narrow for something that has so much power (and string). So does the diamond form part of the case or is it a carrier for the daggerboard inserted into the case? They leave the daggerboard down as long as possible if I recall, Assym style I did work out why that worked, a collosal waste of power but I can see why it's effective, so they leave a plate down fully gybed even going downhill? Doesn't that seem a little draggy? ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: gordon1277
Date Posted: 30 Jan 16 at 11:01am
|
Grf
I think its and Int Canoe. Boom to low for a Int14 and no carbon tubes for wings out the side, but I cant see the sliding seat either so not 100% sure. Gordon ------------- Gordon Lossc |
Posted By: craiggo
Date Posted: 30 Jan 16 at 3:36pm
|
Its definately an International Canoe ------------- OK 2129 RS200 411 |
Posted By: Strangler
Date Posted: 31 Jan 16 at 11:40pm
Graeme If you haven't been to the post office yet to work out leeway, try this dummies guide to gybing boards. Although I do not use the term leeway its illustrated in diagram 5 non-gybing board. http://www.hornet.org.uk/forms/20051113104700centreboards.pdf" rel="nofollow - Gybing boards Please forgive the comic sans, it was written a long time ago. |
Posted By: JimC
Date Posted: 01 Feb 16 at 3:08am
| The problem with that piece is that the author has fallen into the trap of thinking the sails are sheeted relative to the hull rather than to the apparent wind. |
Posted By: iGRF
Date Posted: 01 Feb 16 at 12:08pm
|
Thanks for that Strangler it underlines most of what I already knew coupled to everything else terminology wise I've picked up on this thread.
Lots of explanations always fall into the trap of assuming water 'flow' where there is actually none, time and again it used to come out in windsurfing where they all wax poetical about this and that fin design when the truth is unless there is tidal flow, mostly the water is static an we are passing through it, so the element of what we call apparent wind which is created by true wind and created wind as we all learned in sailboat 101 or whatever it was called in dinghy sail school (I'm thinking of rewriting it in terms easier to comprehend). Anyway that element in the other fluid, the water, is not served up in quite the same manner. But, the way things function is still the same, and there is an 'apparent waterflow'. So just the same as we can have full sails and flat sections and alter their AoA (angle of attack) my feeling is that a gybing board should be used similarly, effectively by angling the board you are making the foil section artificially fuller if you'll pardon the pun, a fuller plate has more lift, but also suffers with more drag, so they get you going, lift heavy weights off the ground in transport planes etc but don't go very fast. Increasing the section until the 'apparent flow' is created to the point that lift from that 3 degrees is sufficient to overcome this thing you call leeway and turn it into what shall we call it 'headway'? (Funny I encountered what I used to refer to leeway yesterday when coming out of a windy tack close to an island and not getting the flow attached quick enough I began to slip sideways which is what I call leeway) So what I think is required from a gybing plate is that it be variable and controllable, more so than the simple diamond that is commonly employed, had this been mountain biking we'd have push button controls by now like those employed in the uppy downy seat posts and adjustable suspension units, but it's not this is still 1960's England and the black arts of mystery are employed to keep you all guessing. Anyway it's all a bit beyond my immediate requirements for my little Minisprint, but I shall endeavour to come up with an adjustable system if nothing else on paper, just to satisfy my own quest for life love and the meaning of everything... ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Presuming Ed
Date Posted: 01 Feb 16 at 5:54pm
|
Oh dear. Angle of attack ≠ thickness.
|
Posted By: 423zero
Date Posted: 01 Feb 16 at 6:03pm
|
You could cobble together a simple gybing board, your blade is to loose in slot, measure gap, cut 2 strips half the thickness of gap and attach to head of board (vertically), board will pivot round this point, probably not much, but it may give an indication. How much leeway are you getting ? I have not noticed excessive leeway with mine, mind, I have never sailed it without the new board fitted.
|