long keel rudder mod?

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Richard D

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Just been away for first long trip and the boat refuses to go astern and turn even on full lock to put the stern to the right. Thought I had dameged ruddur after getting styck in the crinnan canal so am out of the water in a marina but no damage. I know evertyone says long keels dont do reverse but feel mine is worse than normal. On checking a number of long keels out of the water at the marina I fine my rudder size to most others to be about 50 % of the size, so my plane is to extend the rudder rearwards by adding a 6 inch addition. What are peoples thoughts on this.

Richard
 
Would help if you said exactly what type of boat. If it is a well known design (eg Nicholson 32, Rustler31/36 etc) there will be plenty of other owners, who know more. I suspect modifying the rudder may not be worthwhile.

In general the only way to get most long-keelers to have any control astern is to get them moving backwards with a burst of power, letting them go the way they want for a few seconds, then going into neutral (or tickover astern). You will then in neutral but still moving backwards have some control with the rudder.
 
It might not be that simple. When in astern the keel shape may divert the forward flow of water from the propellor down one side of the keel such that you will always have a big thrust offset. On my own boat this is what happens.
 
establish water flow over the rudder in astern first with the tiller central with a good bit of RPM, then apply gentle movement to P or S. Large movements will effectively stall water flow over the blade.


Extending the blade may work but will add extra leverage to the bearings, and if the extended rudder is put full over when going astern it will stall even more fully and blanket flow over the prop.


Are you conversant and happy with the term "prop effect" ?
 
The boat is a Palmer 32 a wooden boat, the only one ever built, the company majored in building big fishing vessels and from what i can find out from persons in Portavigie NI where it was built, it was made for one of the family or for a fisherman who bought his big boats from them. I like the idea of a bow thruster and would have no qualms about cutting a hole and fitting one if it was fibre glass boat as I have a lot of experience in making things out of glass fibre but am a bit frightened of cutting through wood and getting a good seal again.
like the idea of a burst of power with no rudder on then coasting and banging the rudder over.
Maybe i am missing something but as Sarabande says, making a bigger blade will mask the prop, surley masking the prop is good, to stop the effect of prop walk and if what others say, that you give a burst of throttle and then take it out of drive and then steer the rudder the prop is not having any effect>
More comments welcome on the above.

Richard
 
Regarding my comment about the size of my rudder, surely there is a boat design constant that says a 32 foot boat needs an x square foot rudder to turn it adequately.

Richard
 
Richard D said:
Regarding my comment about the size of my rudder, surely there is a boat design constant that says a 32 foot boat needs an x square foot rudder to turn it adequately.

Richard
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If there is such a rule it'll be more to do with displacement than LOA. And underwater shape will have as much to do with it as rudder area. However, all rules are made to be broken.

Besides which long-keelers are brilliant at going forward and turning, rubbish at going astern and turning.
 
just to echo others' comments -we are on our second season with a long keeler. deep fin and spade rudder for years before that. In general I have found the rudder to be fairly useless! under sail I have learned the importance of sail balance to extract a decent turn of speed from the boat (could get away with anything on the previous boat) and under power, I have no control over direction in astern.
I did my sailing courses on a long keel boat many years ago and that one had predictable prop walk but no matter how much I experiment with my current boat I cant control it. I have just learned to live with it and use warps/wind to my advantage.

I would be very weary of just increasing rudder size. to deviate from design could put excessive strain on some part of your boat.

dont forget your boat was designed and built for good sea-keeping in an era when tight marina berths didnt exist!
 
Adding chunks to one side of the rudder will affect the balance. If it is reasonably light, but with a touch of feel, then extending it aft may make it heavier to steer. If there is an owners association perhaps somebody has already found useful mods to make?

Long keelers can be made to steer in forward gear but making sternway, so short bursts of forward to steer, then back to reverse can work. It could be that with a bit more way you may get some steerage, but probably with small tiller movements, and possibly out of gear.
 
From a basic physics point of view, surely if it is not turning the water away effciently there cannot be a lot of strain on it and if it is working well going forwards you would need less rudder turn to move track of the boat the same, hence the same strain, I am sure someone will shred my physics logic, lol but please do.

Richard
 
Richard D said:
From a basic physics point of view, surely if it is not turning the water away effciently there cannot be a lot of strain on it and if it is working well going forwards you would need less rudder turn to move track of the boat the same, hence the same strain, I am sure someone will shred my physics logic, lol but please do.

Richard
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Trouble is, it's not basic physics, it's advanced hydrodynamics. In the case of a boat like the Twister, the prop is in an aperture in the rudder. Going astern with the rudder centred creates a waterflow down both sides of the keel, more to one side than the other, depending on prop rotation direction. However, once some sternway is made, and the rudder is put over, more of the aperture is presented to the waterflow, and some flow squirts through the aperture from the high pressure side of the rudder, down the low pressure side of the keel, being accelerated by the prop and thus cancelling out some or all of the turning moment the rudder is inputting*.

With the Twister, the only thing I could be sure of was that she would turn, but I was never sure which way. The 'secret' was to arrange things so that whichever way she went, I had good options. Part of the 'arrangement' might have been a doubled line left ashore so that I could restrain her, or haul her round, or it might have been a matter of unrolling a few square meters of genoa, and sheeting it hard aback, so that the wind would dominate turning-proceedings, rather than the rudder.

*at least that's my theory!
 
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The OPs mention of banging the rudder hard over would seem likely to be part of the problem. A stalled rudder will do next to nothing but create drag, and a hard over rudder Would seem the ideal recipe for stalling it.

Modest rudder deflections are more likely to work, surely?
 
Richard D said:
Just been away for first long trip and the boat refuses to go astern and turn even on full lock to put the stern to the right.
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1) Aside from everything else mentioned, your boat will turn much more easily one way than the other when under way under motor. On a long-keeler in reverse this will be even more pronounced. (This may be why your boat won't turn to the right.) So once you've worked out which way, all other things being equal (i.e. calm conditions, etc.), your boat is inclined to turn, then try to go with the flow and turn that way, especially if you are trying to make a tight as possible turn. Note that if your boat tends to wander to, say, port going forward under motor (try taking your hand off the tiller and watching what happens) it will tend to go to port in astern, too. (Think of your boat under engine as a banana!)

2) Be aware of 'prop-walk'. If you put the engine in gear while stationary, before the boat starts moving much forward or backwards the boat stern will tend to move to one side, and the opposite way in reverse. Identify which way it goes in each on your boat. This effect is related to 1 above, but is really useful when you are stationary or at low speeds to pull or push (or tend to push) the stern one way or another at will, according to whether you use forward or astern gear, and a quick blast of engine will probably do more sideways pushing than actually moving the boat forwards or backwards so you can use this 'steering aid'

3) Be aware that the wind will turn the boat round when you are going slow or at a stop, trying to push the bow downwind. Try to turn in that direction, even if it means three-quarters of a whole turn to face the way you wnat to end up, rather than a quarter of a turn against the wind effect.

4) If you put the rudder over and blast the engine, the flow of water will tend to turn the boat around. Unfortunately, this effect is rather limited in a long-keeler (partly because the prop cut-out means when you put the rudder over, there's not much rudder behind the prop just a hole!) But it will have a small effect that might be useful, and a quick blast of forward engine (even while you are going backwards) against the rudder over may give you a small but significant kick in the relevant direction.

5) As others have said, be wary of putting the rudder too far over. You are usually trying to get a flow over the rudder, and adjusting the rudder deflection to balance how fast you are going and how much the boat is already turning. That said, on a long-keeler your rudder isn't an independent foil like that on a fin keeler, it's part of the foil that is the keel (like an aileron on an aircraft wing), and in reverse its on the wrong end of that foil! This means you can sometimes get more effect in astern by putting the rudder hard over and creating suction behind it (think sails when running, rather than reaching/beating), depending on your boat and how fast you are already moving, but certainly do not assume that more rudder always equals more turning effect. If you can get the boat moving at a significant speed ( a knot or two, perhaps) you will have a much more effective rudder, as others have said, and especially if you can then put the motor in neutral.

None of the above on its own will enable you to steer the average long-keeler in astern. However, if you are are aware of all these effects, you can estimate what the boat is going to tend to want to do, what techniques in your armoury are going to encourage that tendency, and which will discourage it. Then bear in mind that the ones that encourage it are much more likely to be effective (you're then adding a series of weak/uncertain effects, rather than jumbling them up). You probably still won't be able to positively steer the boat in astern a lot of the time, but at least you'll have some idea what might happen, and a sporting chance of exerting some meaningful control over it.
 
As said in reverse a rudder is highly unbalanced such that there will be a lot of force to pull the rudder to full deflection. This can reduce the turning power of the rudder by the stall effect. ie water does not flow across the rudder but simply churns around it.
Any ideas of increasing the chord of the rudder by adding area to the trailing edge will be problematic. The larger area at a greater leverage will make the force on the tiller even greater. Further in forward sailing the force on the trailing edge will make the steering heavier.
If you want to have a greater power in the rudder by more rudder area you need to add area forward of the pintle line as well as aft but this is most likely impossible on a rudder on the back of a keel.
The only option then is to extend the rudder deeper. This may require the rudder to be deeper than the existing bottom pintle. Once below the bottom pintle then you can add area forward of the pintle line. Most likely all the area is aft of the pintle line at the moment so any area forward will add ballance so reduce the helm loads when sailing. It is common to have up to 20% of the area forward of the pintle line this balancing out 20% aft of the pintle line leaving tiller loads 60% of same area not balanced.
So I imagine you might extend the rudder depth by about 20 cms so that it looks like a rudder with a notch for he bottom pintle. You will have to add area aft of the pintle just to get a support for the new area. But extend the rudder leading edge forward by perhaps 20 cms. This added rudder area will be well clear of prop wash so will only work when the boat is going backwards or forwards. I would suggest that the bottom addition to the rudder be in foam covered with fibreglass attached to the existing rudder with an overlay of fibreglass and epoxy. Make the whole extension frangible. ie because it will extend deeper than the keel it needs to be able to be easily broken off in a grounding without damage to the original rudder.
Or just get used t the rudder you have. good luck olewill
PS when the boat is on the hard you can check for rudder balance by looking at it at full deflection. If there is any balance then the leading edge will move in the opposite direction to the trailing edge buit with no balance the leading edge will not move sideways just turn.
 
I am guessing that the OP's boat probably has a transom hung rudder (?) in which case the following suggestion is not much use - but even so, it is an interesting example of how the steering on a long keel yacht can be improved (going ahead - they freely admit that going astern is still diabolical).
Its not a cheap retrofit though!
http://www.sponbergyachtdesign.com/CopernicusRud.htm
 
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Try and get hold of the 3 excellent booklets written by John Goode entitled "Handling Under Power" and originally published by PBO. These are a collection of various articles he wrote for PBO.

One of them contains very clear advice on how to cope with the problem of manouvering long keeled yachts in confined areas. The illustrations are really excellent.

The biggest problem John Goode identifies is the effect of bow windage. (This is certainly the major influence on my Twister).

The techniques illustrated include:-

- warping the boat round in her berth, if you have room;

- temporarily adding some sail aft; not a problem with a ketch or yawl but if you have a backstay you can perhaps run a small hanked sail up it or use a riding sail;

- making the bow face the wind by using a weight on a length of line as a sort of temporary anchor (this works very well);

- when going astern towards the wind the boat will probably follow a curved path due to prop-walk. When you begin to get near something you don't want to be near, straighten her up with a short burst of ahead engine and the rudder over. Keep repeating this until eventually you get into open water. Do this at slow speed.

Suggestions involving building up speed astern are, in my experience, a waste of time. If there's room to build up speed there's probably room to turn. If there isn't room, you don't want to be risking damage to your boat and others by charging around at speed with minimal steering.

Don't be ashamed of asking bystanders (who always seem to congregate when they see a long-keeler about to attempt a manouvre) to help. Normal people like helping others. Sometimes all it needs is someone to hold your bow and walk you back along the pontoon before giving you a shove in the right direction.

Fitting a bow-thruster in a planked boat seems a bit risky because you are going to have very short planks ahead of it with consequent risk of leaks.

Finally, console yourself with the thought that you could be much worse off by owning a converted fishing smack with a prop-shaft through the quarter!
 
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Mine is quite small (i think) but speed is the answer both fwd. and astern. You get worried looks off fellow owners at the speed you come in but steering is fine combined with torque effect.
 
Thanks guys for all your replies, especially , Little Sister, William H and parsilafal for taking the time to be so detailed.One peice if info I did not give and seeing some have mentioned about tiller movements, Mine is wheel steering, deos this make any difference to any of the info?
The boat had a canoe stern so the rudder is not transome hung but the rudder shaft goes through the hull some 3 feet from the end of the boat, so not allowing the normal shape of rudder.
I like the idea about putting extra area in front of the prop can see how this would work but knowing the places I have been and likely to do the same think it would be too vulnerable.
My rudder will only go to 45 degrees each way, is this normal and bearing that in mind does that affect the comments about if you put the rudder on full ,lock that it causes the flow to stall?
What I would like to know has anyone experimented with a larger rudder, as everyone seems to be coming from the hyperthetical view point that nothing can be done with long keels and I have to come back to my previous comment about, how does anyone calulate what size of rudder is correct for a given size of boat taking into coinsideration hull shapes etc.
One thing I have noticed is that the prop hole seems enormously big to miss the prop, is there any dimension stated anywhere to say how far away it should be or should it be just enough to not foul on full rudder as if as mentioned by someone the main problem with long keelers is hole in the rudder for the prop, maybe reducing this whole could be a benefit.
I come from a motor racing background, especially designing and modifying standard saloon car engines into full race spec engines, we got 5 more BHP than Citroen did on their works engines, so I have always been a person to has said, why not try this? Ok not all things work. In my field of race engine design and modifiaction I read loads of books and talked to many people who all repeated what they had heard from the past but none had tried some of the things I did, some where against the general oppinion but they worked and I wonder if a lot of the well meaning comments here are from years of hearing the same thing repeated and no one experimenting.
I do not want to denigrate any of the contributors well reasoned answers but everyone seems to accept the fact that nothing can be done to improve matters, I am not saying cure the problem, just make it a bit better. Have any of the contributors ever extended a rudder or known anyone do it on a long keeler and have any results. I have done it once, though not on a long keeler. A freind on mine with a hurley, his rudder shaft was corroded so I said I could make a new shaft and rudder out of foam and fibre glass it. He said it was not handling as good as he would like so I suggested putting 20% extra blade width, did it and he says it turns much more responsively. I know that is not a long keeler but the obviuosly rudder size has a bearing on how responsive a boat will be. All long keelers I have seen out of the water have a keel that is mounted at an angle of say 45 degrees and is basically a half ellipse, streching from the water line down to the keel. mine is not like that. It holds the hull line where it is afixed at say 60 degrees and is square cut from there backwards which to me looks like a fishing boat rudder apart from the 60 degree at the hull and a prop hole, my rudder does not start till about 2 feet below the water line. As you know all fishing boats have the rudder mounted on brackets well away from the prop and so have no prop cut out. With the company who built it being a fishing boat building yard and never made another yacht, I have got to ask the question did they get it right. With companies who have built yachts for years they will get a feeling for what works and as time goes by modify such things to improve them. The above is why I ask the question how big should a rudder be, as said before by Twister Ken there are a lot of varialbles but I have to beleive there is a basic size to boat length you start off from.
Look forwards to all the abuse ( lol ) I will get but can assure you I am taking it all onboard.

Regards Richard
 
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