As many of you know, my boat is being built by CC at the moment and I'm helping them with the marketing of their all carbon DCB.
I'm trying to decide which rudder system to have on my boat. Jo's boat has a lower pintle piston which pivots the rudder stock about the top pintle/gudeon. This seems to work pretty well but is an expensive and heavy (not that it matters much on a carbon boat) piece of kit to manufacture. The control system for it is lead to a jammer on the top of the centreboard case, accessible byeither helm or crew at all times. I understand that Jo and his crew"play" the rudder downwind in waves all the time.
CC have an elastic and pulley based system in the tiller which moves the stock back and forth pivoting about the lower pintle/gudeon. There may be an advantage to this, as it moves the rudder under the boat as lift is dialled on (thought tobe desirable on the foiling moth). The system works well on the I14s they have built where the loads are double that of a 12. Dare Barry uses this system on his boat and it works pretty well. It’s undergoing slight modification at the moment which will lead to further improvement. Dare leads the control lines out to either side deck where they can be adjusted by either helm or crew.
CC can build either system. I'm undecided on which way to go. I know that people have tried both systems down at Burghfield and I have has some feedback, but if
I can get the discussion going on this forum many, including myself can benefit. Over to you...!
Michael
You already know my opinion on ease of use. When we set Jo's boat up on the shore, the blade was effectively raked forward, and i think the tip was under the boat. The wings are actually higher up the foil, so don't move forward/back much. One of the best things about jo's system is the adjustability, he had obviously spent a lot of time getting it right, there were at least two modifications to the front of the blade, and the carbon stopper on the piston. Since we dont know the best angle of attack adjustability is going to be key. The big problem with the other rudder was that we could not rake it far enough forward on the foolish, and it did not look an easy mod to do it, where as adding or removing a bit of carbon, as jo ad done to the piston or the rudder seemed to be simple.
The way I see the issue with the winged rudder is getting this angle right, too little, and you only have drag, it did not even effect the trim at all on the foolish in that set up. What we did not get to know was if this was just set up, or boat shape. The manufacture of these blades is going to be critical, for two rudders from same builder, the pitch of the blades seemed quite different, but also very difficult to measure.
Andy
Andy
Andy,
You make very good points. The moths took several years to get things right. Obviously it was fly or crash with them, but its lift and speed or crippling drag with the 12. With the out of the box moth mods were still necessary. I think we need to know from the designers what the optimum angle should be and to be able to turn it on and off with ease. It was easy to flip the moth on its side and see what was going on. Perhaps we need to build test benches for the 12 so that you can find a starting point for rudder angle on dry land and then go afloat and give it a try.
Perhaps my main conclusion from your post is that initial set-up is critical and as long as you can adjust on the water reasonably effectivly you're in business!
Michael,
the comment I have heard about running the adjustment within the tiller as in Dare's boat is that when the adjustment line comes out of the tiller and its connected to the controls on the thwart (or whereever they end up going to) when you turn the tiller you will get sight adjustment in the foil angle unless the connecting string runs right through the pintle because it is off the centreline of the axis.
Does this make sense to you or am I talking gibberish! The control line needs to be as close to the pintle to prevent additional adjustment when turning the tiller.
The foiled rudder in 3521. Before I used the rudder I had a chat with Jo to get his advice on its use. When going into a tack the rudder control is let off by the crew to its neutral position and after the tack is compleated pulled on again. This stops the foil stalling the boat. With normal use of the rudder the control lines do not effect the rudder angle as they are lead back to the transom before leading to the centre of the boat. When the rudder is full on the tip of the blade is indead forward of the transon. The set up worked well and the boat is now in the shed for a few minor winter mods.
Cheers Dare
My experience is that it is surprisingly easy to tune a T-foil rudder. I don’t think that it is anything like moth sailing as you do not have a bad crash / big swim when it goes wrong â€" well that’s what it looks like on youtube anyway.
One might not have the perfect T-foil shape etc and this may in fact be the limiting factor â€" but we have found getting the angle of attack right on the one that you have to actually be quite simple. The loads on the system are surprisingly light and you do not need sophisticated tackle to achieve what you want to do. The Rondar system on the Paradigm is simple, cheap and effective. It will be interesting to see if it wears over time, but for now it clearly works. You could easily put this on any 12 which has a recessed transom. The transom may need a little reinforcement, but these areas tend to be pretty strong anyway.
The Rondar system has a pivoting plate on the transom which both pintles are attached to. The top end of the plate is connected via a couple of movable spars to the transom. The movable spars are connected to a multi purchase system with a cleat on the floor of the boat.
How do I know that tuning is simple? Gavin, Dave and I all sailed independently and found our sweet spot. We then lined the boats up next to each other on a piece of flat ground, got each of them lined up horizontally and measured what we were doing. We found that we were all in the same place. We have since confirmed with two boat testing.
You find the sweet spot essentially by feel and by looking at the wave that you are creating behind you. I had never used the articulating rudder before the first race at Burton Week 2008. First day we got a 5 and a 6 so it can not be too difficult to work out can it? On 3515 we had a moth style twisting tiller extension. This was not very good as you could not control from sat on the transom due to the angles involved. The control line systems are better. I don’t think it matters if your control line moves the top or the bottom pintle. It does need to be able to release effectively when you no longer want it though. A little bit of bungee works for us.
Once you find the sweet spot the next game is to move your arse as you accelerate / decelerate. This is the fine tune mechanism. We don’t play the control line until we need to back off in really strong winds. Maybe we should but our experience is that other things have been more important for us to concentrate on. This may also be due to the fact that the wings are smaller. Maybe adjustability becomes increasingly important with wing size.
With the Aardvark wings that we have on the Paradigm we do not need to let off when we tack. This again may be because they are smaller than the ones on DCB.
Like everything on a 12 you can over engineer to your heart’s content. It is my view that the most significant rudder development opportunity relates to wing size, shape, and position on rudder and that control of what you have is not relevant. I would suggest something cheap and straight forward for this.
You raise an interesting question as to whether you want the wings under the boat or not. It is strange why a Moth might want its rudder under the boat as when it is flying the water does not know where the boat is… Maybe it helps take off?
Enjoy
Jeremy,
Yes CC are moving the block which picks up the control line. They are shifting it from the gantry to the rudder stock. This will solve the problem I'm pretty sure. I talked to Dare about it at Northampton and it seems to work pretty well even before the mod. You will have seen Dare's post.
Thanks for posting.
Dare, Thanks for posting. I saw your rudder at CC on monday. The mod will make a difference I'm sure. Will have to take care setting up my boat and change "one thing at a time". Build is going well as you have probably seen.
Appears that on your boat that rudder lift is on at all times except when tacking. Is that correct?
John,
Thanks very much for all this info. I hear that Jo plays the rudder a lot. Could be that the increased rocker on DCB means that you can do that or need to do it. Take your point re shifting weight! Have seen a pic of your control mechanism and can see that it works well. I'm surprised that the loads are so low. Take your point re overengineering. As things look at the moment I will have plenty of weight to spare. I need to have a system which works first time with no tinkering. I'm new to the 12 and my crew(s) have hardly sailed at all!
Interesting thread and I'm looking forward to having some wings to play with next season. In the mean time, I take a lot of comfort from Meds' account of recent experience. It remains the most I can usually do to set the boat up properly for the offwind legs and then sail it. The idea of playing the rudder angle downwind along with the main sheet and steering, would not I fear, be within my capabilities. As for releasing and pulling it on at every tack ... how exactly would that work at somewhere like Ranelagh or Salcombe when we're tacking every ten seconds? My uninformed observation is that Jo's DCB wings are a lot bigger and more swept back than the Paradigm rudder - I guess that could mean more beneficial effect when working, but more drag and/or negative impact when not, especially in turning corners. It's all trade-off, of course, and it will depend where you're mainly going to sail. Whatever, you're going to have a lot of fun learning.
Mike D
N352?
Mike,
Totally agree about the tacking times, but also in Salcombe you would surely be removing weed every 5 seconds too?
The rudder on 3251. One of the advantages for the swept back foils is that they do not hook up weed . To date we have had no greater problems with weed than with a conventional rudder, and that includes sailing at Salcombe and at the RVYC. Putting the foil off/on re tacking is very easy and the loads light, however if in a short tacking situation leave it off and nothing is lost, and then play again when in open water.
Cheersa Dare
Looks like the way to beat winged boat is lots of luffing and tacking,Don't let them sail in a straight line. That includes wing on wing.
How much faster are the winged boats?, Will it make much difference to the PY. Is it that much faster, do I need one now?.
Broz - How much faster are the winged boats is an interesting question. I don't have any experience sailing N12s (with wings) but I have sailed in another class that has winged rudders and I think they provide a very significant advantage upwind. They are able to plane earlier and then point higher than non winged boats. This was at the time of a change in sail plan in that particular class and I would say, albeit with no science to back up my view, that the winged rudders probably added more to the speed than the rig change. Of course twelves are very different boats and sail in a different mode for the majority of the time. But at the very light wind 05/06 (?) champs we had one of three 'new rules boats' and had some success at the front of the fleet early in the week. Without wanting to sound cocky we were very fast on the water but we were sailing a N12 based boat rather more suited to F2s than the normal coffin shaped boats and did have more sail than most. Mid way through the week our main competition put on his winged rudder that he had been playing with at his club. After that we couldn't touch him for speed up wind and or pointing. All in very similar conditions as earlier in the week. I'd like to blame alcohol for a deterioration in performance but we had a dry week! Its worth also noting that third place was taken by a 97 rule boat with a winged rudder and for the majority of the week they were right up there.
My conclusion in that class was that winged rudders are very fast... Until you sail through a patch of weed.
So that might raise the 'arms race' question but it is really not that difficult to retro fit wings / foils whatever you want to call them and if you like playing with glue and things you should be able to do it for the cost of a few nights out. Though Im not sure I'll bother with one for N1851!
I agree also with John's comments they are fairly easy to set up and you can 'feel' and see when they are working. If i was doing it i would avoid twisty extension based systems ( seen on cherubs, moths etc) and go for a rope adjustment system.
It would be interesting there were some pictures of what people have done in twelves.
Not sure my post adds anything much but I have managed to put off the washing up for 15 mins..
Hi
Does anybody know what is the optimum depth below the water for the foil to be?
I assume they should be quite near the surface but this may mean them coming out of the water when tacking.
Is this a problem?
For a foil running in free flow, it should be 5 chord widths, but if you are using the stern wake it will probably be slightly higher than this.
Thanks for the info on the now need, looks like I had better start building.
Thinking about cassette foil, putting the top of the leading edge on ecsentric cams, ie the cams will lift the front of the rudder to create the angle. The reverse of a Europe centreboard.
Dead cheap, dead ease.
National handbook, page 171 shows a foiling rudder on the stern of Simon Nelson's 3399 in 1994, did not catch on then, will they this time???
Dare. 3521
Things have moved on if in any doubt check this link!
http://foilingboatadventures.blogspot.com/ (mhtml:%7B73B8DA44-6E9A-4217-AFBF-EBB42E5F47CD%7Dmid://00000015/!x-usc:http://foilingboatadventures.blogspot.com/)
http://www.youtube.com/watch?v=YrCKs5k1EnM (http://www.youtube.com/watch?v=YrCKs5k1EnM)
A video of the DCB rudder control, to go with the discusion.
Just wanted to put a few thoughts in about foils given my experiences last season. Fundamentally my view is that the more competent helms are going to get more out of T foils than other helms, so we are likely to see more spread out fleets ... why ...
- As Meads says fore and aft trim is critical, as I see it the benefit of the T foil is to reduce wetted surface, to do this you need to make sure that neither the bow or stern dig in as the boat speeds up or slows down
- Equally keeping the boat level thwartships is more critical with a T foil, if the boat is not level any lift from the T foil is actually exentuating (is that a word) the angle of heel, which gets interesting when going fast down wind
- Last season I had 2 positions for the rudder, on and off, however I have no doubt that there is actually a correct angle for 1/4 knot change in boat speed, some-one more competent than me might be able to adjust for this!
The good news about T foils is that when they work they make you smile more, and I can report no more issues with Salcombe weed than with a standard rudder. The other good thing is that I think they might have reduced the advantage that lighter crews had in 12's .... maybe that is until lighter crews have T-foils!
It will be good to see more T foils out there this year, but then most of the people buying seem pretty competent!
JT 3522
Quote from: 124National handbook, page 171 shows a foiling rudder on the stern of Simon Nelson's 3399 in 1994, did not catch on then, will they this time???
Dare. 3521
I was sailing Simon that year - the rudder was necessary to help him back into the boat, you will remember he was not so tall, Jonno had one as well.
We are getting a lot of info about the relative benefits of T Foils, but what about the trim tab on the centreboard. Are the new build DCB's being fitted with them. Would they be useful modification retrofitted to older boats? Do they require much adjustment in use and would they be a more practical modification for those of us who sail on small waters?