I had built myself a T foil
for Email over the last couple of weeks and we had only our second sail with it
this weekend.
Last weekend was very light
F0-1, 2 in the puffs and I was amazed by just how much lift it seemed to
generate in so little wind.... So I guess I shouldn’t have been surprised by
the problems that we had today.
In brief all I'd built so far
was the blade itself... For adjustment I used a conventional lifting rudder
stock and set limits on the blades movement at about 4deg positive and 1 deg
negative figuring that this would be a good starting point for a basic on and off
control.
The problem was what looked
like a F3-4 on the beech turned out to be a solid F5 gusting 6 and we were
pretty much out of control whenever we headed off downwind.... and as the start was
a run.....! Essentially even with my foil set to what I thought would be off
the lift generated was so great that we couldn’t keep the Bow up. We didn’t go
in but the constant battle to keep the boat under control and to get the bow up
to take some of the load out of the rig resulted in the foils eventually
ripping off.
I’m not that upset by it all
in fact I half expected it, all part of the learning curve however I would like
to know from those more experienced in these things what they do in strong
winds. Is it all technique? Is adjustment key and I’m better off getting an
adjustable pintle setup that works first… or do you ditch the foil on the silly
days and just stick to a normal rudder blade?
Ian
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I think we have a much higher degree off adjustment on the DCB
The angle of the wings is critical to the neutral position of the rudder, When Snoopy first tried one on his foolish, the initial set up was way wrong, and we seemed to get very little lift.
I understand from tom that there is a metal rod keeping the wings on as well.
The only way to do it is to set it up and play.
I have not sailed a Chapter, but I dont think they had too much of a nose down problem, so suggests they were too far on.
Well done on the result though, with working wings, I am sure you would have embarrassed them more.
Andy
Welcome to the frontier of National 12 sailing Ian! In your one posting you have managed to capture the main challenges of sailing with winged rudders.
To answer your last question first, I don't know of anyone who reverts to a wingless blade when it's breezy. To do so would mean you lose the benefit upwind and should the wind drop you will be left for dead by those who have their wings on.
Taking the question of exploding transom fittings next; nearly everyone who has experimented with wings has experienced this problem. At Burton Week last year, several of us with standard DCBs had the 8mm stainless fittings shear off and, in some cases it meant not winning overall. Subsequently, P&B took all their boats back and replaced the original fittings with stronger versions that have so far held up (fingers crossed, touch wood, where's my lucky clover, etc). Other people are still struggling to get it right, e.g. the Medowcrofts who have had their arrangements give up on them several times. What all this shows is that you are correct in saying the lift generated is massive and it is also true that the loads are not yet fully understood by the class, a point that even Jo Richards agreed with when I mentioned this view to him.
Turning to your original question, when the bow goes down we ease the rudder off. The amount of easing and the condiditons at which you will need to start doing this depend on the design. For instance, the DCB which was designed around the rudder will carry it on full for longer than the Foolish with its relatively fine bow. The only other Chapter I can think of with wings is Rich Williams and I don't know that he has sailed often enough with them to know when its necessary to start easing back.
One final thought, IMHO you need to adjust the angle without moving the blade in the stock. Just consider how quickly a conventional blade loads up and becomes very heavy to steer with when it lifts even a small amount.
Good Luck
Kevin
Just a point about keeping them on the rudder. They can generate between 80 and 100kg of lift so usual fillet and carbon tape is not strong enough. Taper each section at the end where they will join the main blade. Glue the wings together before attaching to the main blade with unidirectional carbon starting with pieces only 20mm long and increase the length for each subsequent piece until you have built up to near the foil thickness. Cut about 1/3 of this joint away and slot into a similar but longer slot on the main blade. Then fillet and tape it. They should be strong enough to stand on when getting back into the boat after a capsize. Let me know if you would like more help or for me to wake you up as you have nodded off by now :K)
Thanks for all the advice and offers of assistance guys.
I feel like I’m getting a grasp of the problem now. Michael Airey
also sent me a pm that has helped me realize something that I guess I already knew
but kinda forgot. When I set my off position to 1 deg negative that was on the
basis of the neutral position for my T foil section in horizontal flow…. But the
flow off the transom of a 12, especially one like a DCB or Chapter that has a
lot of rocker aft isn’t horizontal is it. I probably had a couple of degrees of
positive flow across the foil and with the speed we travel at in a F5... well that would easily
explain all the lift.
So yes I’m going to have to come up with a simple, yet strong
method of attaching and adjusting the whole rudder before the next tests. My
initial setup was all about seeing if I could make a foil, if it would do
anything and weather it was worth pursuing. So although its all fallen apart I
can at least answer all my questions with a big YES… so now its onto the mk2
I’m thinking that I might just make a slotted top pintel,
with a large pin passing right through it, the rudder and then pivot around a slightly opened
out hole in the lower pintel. .. it should work shouldn’t it?
O and one other question. My first T foil didn’t have any sweep or tapper in it. My thinking was that I didn’t know
if I could make a foil at all to start with and this made creating a uniform
section much easier and removed the need for a join in the middle. Apart from
all the aeroplane inspired reasons for having sweep etc is there a good reason
form a fluid mechanics standpoint, interaction with the stern wave, rudder etc?
Any way my homemade rudder blade survived so I’ll get
started on the next T, this time I’ll splash out some money on some carbon and
put on a few more layers. The first foil was made out of 7 layers of 200gm glass that I had left over from a canoe
build a few years ago (or at least there were 7 layers in the middle tapering out
to three at each end.) And I have an old fridge pump now so I’ll have a go
at vacuum bagging it this time. Starting to feel like a proper 12
sailor now making bits for the boat myself J
Ian
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Heres the before and after or my foil... the before pic wasnt finished at this stage but you get the idea.
I reckon I could have stood on it although I'm not sure i would have wanted to... But from our experience now with this one I reckon that's got to be a good test. I'f I'm not happy about standing on it then I should expect it to fail at some point!
Ian
I am probably the least technical person sailing Twelves. What I do know in the last season and a half sailing with a winged rudder is that about half a dozen times, without warning and on different points of sailing, the boat has moved into a completely different zone of speed and feel - when the rudder really must be working. Problem is I'm not at all clear what combination of lift setting, fore/aft trim and sail setting made it like that! Then it disappears .... there are also times when the boat suddenly loses control - either nose-diving, rolling to windward on a reach or stalling in tacks. And nothing has yet broken apart from when I have hit the bottom.
Anyway, it's all pretty exciting and the challenge now is to learn more about the zen moments of speed and try to eradicate the losses of control.
Mike D
N3533
While being most impressed by anyone who can make his own foiling rudder, I feel secure in the knowledge that mine (Paradigm 2) has had no input whatsoever from me and is, presumably, Gavin's work. With weed on the lake where I sail, I am currently sticking to a traditional blade and await the thrills (!) mentioned by Mike Day. What is interesting however is that recently posted photos and videos clearly show boats other than DCBs with the DCB rudder. Is it the case that "one size fits all" or is it essential that the foiling rudder design is compatible with the design of the hull? N3535.
Good to see Ian having a go at making a foil. That is what this class is all about, it is more than just buying off the peg. Having built several boats, rudders and c/boards it can be a steep learning curve but good when you get it right. Best of luck. Dare from the world of Puddings.
Nigel, whilst I am not an expert (who is?), it seems to me that if a set of wings provides lift on one boat they will do so on any other too. What matters is the angle at which they are set relative to the flow of water they are passing through, which was highlighted by Ian in his 12 July post above.
Kevin
The mk2 is coming along. I've put 5 layers of 200grm carbon on the foil now (2 at 45deg over the middle 3rd and 3 more over the complete foil) all vacuum bagged down and its now so much stiffer.
I've tried atanding on it, in the worst possible way (sat it on a peice of wood in the located in the middle and then ballanced on it with a foot in the middle of each side) and even with all the point loadings of the wood it took my weight with ease so i'm feeling more confident.
I need to trim it to size now and cut it into my rudder.
Quick question, how wide are most foils at the moment. My mk1 had a total span of about 800mm and with the subsequent failure I'm thinking of making this one smaller... whats the considered opion on a good size. (note it has a uniform section along it whole length and a chord of 100mm)
Regards
Ian
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Ok just to keep this thread alive and perhaps inspire others to have a go here is our mk2
Same rudder blade just cleaned up. Same section T foil but this time everything is covered in carbon, that has been vacuum bagged on (using an old fridge pump) I'd never done this before so kinda made it up as I went along following the excellent advise on this website (plus a bit from the Cherub site)
The T is once again a single laminated cedar core but with some white ash stringers running through it for added strength. Everything is then coverd in 4 layers of 200grm carbon tappering out to two layers at the end. Then a single 200grm layer of glass over the top so that I could sand it back to get a finish without damaging it.
Came out really stiff and i would be totaly confident of climbing back in the boat on it (my new measure of stiffness and tested in the garage... well if its gonna break it might as well happen now) )however I am now slightly concerned that being so stiff all the shock loads are going to go through the T and might lead to a different kind of failure!
Had to make my own stock as well as i wanted to keep the adjusting system simple, I didnt want to butcher the boat and I didnt fancy cutting up my current stock, so my system just uses a fixed top gudgeon with a slotted lower one which in all gives me a range of about 6deg... probably not enough but enough to get me started and apart from two small holes in the transom the boat is untouched. I control it buy running a line around the pintle and back through a cascade block system to a single swivel jammer.
Only used it a couple of times so far but it shows promise... and hasnt broken so I'll update this again when I have a better idea of whats happening.
Ian
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Raced it again for the first time this weekend. Only handicap racing I'm afraid as is our norm with a F3-4 in the morning and a F2-3 in the afternoon but great fun.
The foil certainly adds a whole new dimension to the sailing experiance!
The good news was that the foil and its adjustment worked perfectly, didnt break, and we were the first boat back each time... beating a Phantom and Blaze on the water in the process. And if these were the only other boats in a our fleet we would think that it was awsome. Unfortunatly we had a well sailed Wayfarer just behind us each time so I suspect it was more to do with the conditions and courses that just favoured us rather than any significant change n boat speed.
We did find it really hard with no one comparible to race against, to work out the best settings on each point of sail though. Our confusion came from the fact that as we pulled on more and more foil the noise from the back of the boat would disapear so our ears would be telling us that all was good but at the same time you could feel the extra drag so our other senses would be saying no!
Does any one have a rule of thumb that they apply when trying to decide how to set their foils on each point of sail and boat speed?
Ian and Hannah
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Ian, We must meet up and have a sail. I have been sailing at Ranalagh, Datchet and Thorpe Bay. I have the foil on pretty much all the time and I think that was what the other DCB owners thought when they started (please correct me you others). I would reduce it a bit up wind when the wind gets up to reduce the bow down effect and on a reach to promote plaining. Having said that others might ay that bow down upwind is always good except in a big sea and I know the 14 boys keep it on off wind and sit right on it!
I expect you are off to BW and will learn loads there!
Hi Michael
Thanks for your answer, and yes we should meet up. We've been pretty busy recently which is why I havent been back in touch and are on Holiday soon so unfortunatly will be missing Burton Week (again :( )
We always pencil in the round Sheppy race each year which we are planning on taking the 12 to this time. More of an adventure than a race but great fun all the same.
Ian
Having now seen some T foiling boats in action at the Inlands and read the discussion threads relating to T foils I'm interested in building one for my boat. However, before commiting to building one I want to make sure I understand what the foil is doing and I also have some questions relating to aspects that I'm not clear on yet.
As I understand it the foil is normally trimmed to produce a positive lifting force that assists in raising the back of the boat out of the water thereby reducing wetted area and the associated drag. The resultant lifting force acts upwards from the foils so the further back from the boat they are located then the more effective they will be because they will provide more leverage (I assume this is why boats like the 14 put the rudder and foils on a gantry that extents behind the boat). However, because the lifting force acts aft of the rudder support points not only will these points be sheared upwards, the lower support will be pulled aft and the upper one pushed forward with these pulling and pushing forces increasing as the foils are located further back. In addition, the supports are loaded in this manner by the drag force acting on the rudder and foils. At present there appear to be two approaches to trimming the foils: in the DCB/Foolish system the rudder pivots about the fixed upper support point and the lower support is pulled forward by a purchase system to overcome the aftwards pulling effect that the lift and drag forces from the foils and rudder create. In the Paradigm type system the setup is reversed, the rudder pivots about a lower fixed point and the upper support is pulled aftwards by a purchase system to overcome the forward push.
Now for my first question: if the rudder were located in a conventional stock that attached to fixed rather than pivoting pintles would it be possible to control foil trim simply by rotating the rudder relative to the stock in the usual way? If the vertical line of action of the lifting force were directed approximately through the pivot point then the purchase required to trim the foils would surely be reduced and the control system could possibly be contained entirely within the rudder/stock /tiller assembly itself. Infact, if the line of action of the lifting force were ahead of the pivot point then it would tend to rotate the bottom of the rudder forward as required when generating positive lift although the drag force would still oppose this.
My second question concerns the positioning of the foils on the rudder itself: is there a concensus on how far down the blade they should be located to maximize their effect? At the bottom of the rudder the water probably only flows over the foils at the speed of the boat but in the wake region near the top of the rudder the flow speed relative to the foils may be faster and therefore more lift generated. There are probably other aspects to consider in positioning the foils such as the practicalities of tacking and gybing and launch and recovery.
Sorry for the rather long and technical posting but I'd like to hear what others think or have discovered.
Thanks,
Marcus
Hi Marcus
Great to see you at the weekend.
Re Q1. i dont think anyone has tried exactly what you are suggesting. My first T-Foil had fixed gudgeons on the transom like a Moth or an I14 has. The stock was fixed to the boat by a single vertical pin. This pin also went through a rod inside the tiller which could be moved by rotating the tiller extension. It was mechanically sound except that (a) it needed quite a lot of turns to switch it off and (b) when hanging over the back of the transom it did not like being rotated. This was important as being able to switch it off is rather crucial at times
Re Q2. everyone seems to have them in roughly the same vertical place about 6 inches below the waterline. Aft sweep is very good for clearing weed and the fashionable set up seems to be to be also swept upwards. the tips are almost breaking the water when at speed. Why? no idea?
John
Dare Barry's boat has fixed pintles on it with adjustment being in the rudder stock. It is very neat for retro fitting as it does not require playing with the back end of the boat. a single line comes out of the rudder stock and runs down a couple of pulleys on the transom. If I remember correctly this line then runs off to the back of the centreboard case and has a simple 2:1 purchase. The stock itself is quite exotic as the top pintle mount in it slides inside the stock. Does require a single bar gudgeon pin arrangement as opposed to two separate ones. Contact Dare for more info, would be good to see a pic of it here to explain, but I don't have one.....
I made ours as just a straight foil, no tapper, sweep or dihedral. But all of that was just for ease of manufacture. I cant comment on any performance advantage/disadvantage as we have no experiance of any thing else, but we have snagged a plastic bag on the T foil once which stopped us pretty quickly so on the mk3 I will probably include some sweep.
I would imagin that as soon you add sweep you also need to include some dihedral as well or as you rotate the foil for some lift you will be moving the blade tips down, away from there set position.
Ian
Dare very kindly sent me through these pics of his rudder to help explain it.. If you look carefully you can see the adjustment line coming out of the rudder, back to a block on the transom. It then goes down to the floor and up to the thwart through the kivk bar.
Marcus, in response to your first question: I believe that "rotating the rudder relative to the stock" is a recipe for disaster. If I understand you properly, you are suggesting pivoting the blade in the stock using the normal pivot bolt. All this does is load up the blade as happens with a conventional (unwinged) rudder when you don't pull it right down. All the winged systems keep the stock and blade fixed relative to each other for this reason. In terms of vertical force, virtually all of it is transmitted through the bottom fittings on the boat and rudder. There is very little affecting the top fittings, which are basically there to stop the rudder falling over sideways. For this reason all stocks for winged blades attach below (or around) the lower fitting on the boat.
Kevin N3527
Thanks for the comments and the photos. However, I still don't understand why a control system that rotates the rudder relative to the stock rather than the stock relative to the boat won't work. I realize that with a conventional rudder that pivots about a bolt through the stock there's a significant sideways load unless the rudder is close to vertical. But surely the point is that when trimming a foiled rudder it's rotating relative to the transom anyway but only by a small amount about the vertical position. Why does it matter whether this small rotation is achieved by rotating the rudder relative to the stock or the stock relative to the boat? I was thinking of developing a trimming system based on a Topper type rudder stock and tiller. The idea would be to introduce some 'play' between the stock and tiller with the rudder in the down position and then move the tiller relative to the stock using a control system like the one Dare has developed. As the tiller moves relative to the stock the rudder would be rotated and the foils trimmed. Please could someone explain the error in my logic before I make a mistake?
Thanks again,
Marcus
Hi Marcus
<font style="font-size: x-small;" size="2">It will work I guess, but will be far from ideal. Not because of the
affect on the foil just because, as stated earlier, of its affect on the feel
of the rudder. Its kind of how I started out but the one big lesson that I had
at the beginning was that what ever system you choose needs to be simple to
adjust, reliable and you need to be able to effectively turn off the foil at
any time in an instant. You choose when to pull it on but it’s the wind that
dictates when to turn it off so it needs to be full proof. </font>
<font style="font-size: x-small;" size="2">All that said if you look at this as an iterative learning
process, like I did, then what your suggesting will get you afloat and experiencing
the effects of a foil, and what it can do for you… its just that we can all
pretty much agree you'll be changing again it at some point soon after.</font>
Have fun
Ian
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