a rudder design question

[Daydream believer]

Scratching head.... Might it be possible to have the autohelm fitted to a seperate short tiller that is loose until you lock it? Maybe with a friction clutch or pin arrangement. So you turn it on, let it settle, then lock it.

If you cannot reach the controls from the helm, that can be dangerous in, say, a collision situation. Plus it does seem a silly situation to have anyway. One might ask where the chart plotter is ( assuming you have one).
I solved both problems by placing the chart plotter & autopilot control imediately behind the rudder stock. There it can be reached on either tack. I can see the small details on the chart plotter & adjust it frequently. This is important for me as I have ais overlaid on it & need to zoom on a target.

In these pictures I do not have the chart plotter fitted but one can see the holder. I have a hood that I made to protect from rain or spray. If aboard overnight I can leave it under the cover. It can be swivelled a few degrees either way for convenience.

The autopilot control is underneath it. You can see the autopilot plug underneath where it is protected from spray. The unit is cut into the lid of a waterproof electric box obtainable from most electric wholesalers. That means that the connections for the chart plotter ,AIS & autopilot can be kept dry inside as well
The Aries is behind. One can just see the rudder stock in the picture.
I showed the idea to a friend who likes to board his boat over the stern. he also has a locker across the back. His solution was to fix the set BELOW the riller to the face of the locker lid. He can look down on the chart plotter & still reach the controls under the tiller. Having the tiller on top does provide a small degree of protection.

However I have my gimballed grid steering compass under the tiller where I can look down on the card

 

[Birdseye]

Hence why I suggest you focus your mind on finding the solution to fast deployment of the autopilot, which sounds like the solution which might work, not in all likelihood waste time extending the skeg and adding more balance area (which multiple people have pointed out will not help self steering at all, only reduce helm presssure when under load).

So for the autopilot
1) Move the button and/or get a remote so don’t need to move to forward bulkhead to press (surely massively easier than fitting a new skeg)
2) Find a way to speed up connection - eg holding all connected in situ above the tiller, using shock cord or hook to immediately drop onto the pin.
Where there is a will there is a way.

PS. I often sail single handed and enjoy short tacking, with a boat which certainly won’t stay on course whilst winching the jib in a breeze

Interesting post. I am trying to find a way to use the autopilot the whole time but at the moment have a technical issue which means it wont autotack to port and Raymarine, whilst being endlessly patient, dont have much knowledge of the ST60 generation. Fast deployment is not possible - the boats speed of rotation is far greater than my speed at putting on the ram and then pressing the button. Tried it many many times. So at the moment its on all the time or not on at all.

Oddly enough, fitting a skeg would be easy since the designer has left a horizontal flat hull maybe 4 in wide and 18 in long just in front of the rudder. Maybe he had plans to include a skeg but it was omitted for cost reasons by the builder?

Picking up your comment about single handing, how do you do it? I put the rudder angle on to turn, then jettison the old sheet completely and pull in on the new one as the bow goes through the wind. If I try to slowly let go of the old sheet or go more slowly through the wind as I have always done then likely as not the bow will blow back onto the old tack. After tacking there is a scrabble to get the boat near onto the new course and winching the sheet whilst steering with the bum.. All this sounds normal but the issue is the speed at which it has to be done because of boat rotation .

 

[dunedin]

Interesting post. I am trying to find a way to use the autopilot the whole time but at the moment have a technical issue which means it wont autotack to port and Raymarine, whilst being endlessly patient, dont have much knowledge of the ST60 generation. Fast deployment is not possible - the boats speed of rotation is far greater than my speed at putting on the ram and then pressing the button. Tried it many many times. So at the moment its on all the time or not on at all.

Oddly enough, fitting a skeg would be easy since the designer has left a horizontal flat hull maybe 4 in wide and 18 in long just in front of the rudder. Maybe he had plans to include a skeg but it was omitted for cost reasons by the builder?

Picking up your comment about single handing, how do you do it? I put the rudder angle on to turn, then jettison the old sheet completely and pull in on the new one as the bow goes through the wind. If I try to slowly let go of the old sheet or go more slowly through the wind as I have always done then likely as not the bow will blow back onto the old tack. After tacking there is a scrabble to get the boat near onto the new course and winching the sheet whilst steering with the bum.. All this sounds normal but the issue is the speed at which it has to be done because of boat rotation .

I occasionally use the autopilot auto-tack feature but generally don’t - because it rarely turns to the precise course I want to.

Hence instead tend to tack manually, like you starting the turn fairly quickly but then flicking on the autopilot to hold the boat just ABOVE the intended close hauled course. By stopping above close hauled can manually pull in almost all of the genoa sheet (on a bigger boat than yours) so then just needs one or two turns of the winch to get bar tight. Then flick off autopilot and bear off onto course.
As generally have the traveller to windward going upwind, I drop the traveller down before the tack, to make less effort and the mainsail then helps hold the bows up on the new tack whilst sheet in jib (this is perhaps the opposite approach from a fully crewed race boat).

Clearly as you know it is easier with an integrated pilot and the control button, genoa winches and wheel all within arms length.
But hence why I was suggesting you (a) find some way to avoid the control button being out of reach on the bulkhead and (b) have the tiller pilot held ready to just drop onto the tiller pin mid tack. May need some ingenuity and trial and error, but likely to be much more effective if can get the autopilot to play its role effectively.

PS. Does your AP have a -10 button? Would pressing this 7-8 times get you tacked onto the new course instead of using auto tack?

 

[Birdseye]

I have repeatedly tried " Hence instead tend to tack manually, like you starting the turn fairly quickly but then flicking on the autopilot to hold the boat just ABOVE the intended close hauled course." but have repeatedly had the same issue that I need to get close to a beam reach because any wind in the genoa close to the tack point ( gusts etc) can easily cause the boat to fall back onto the old tack. So its an issue of practice and judgement and refinement.

Thats where the autotack would come in - set for say 110 degrees . I could wind in the genoa and then trim the course.

Yes the pilot has +1 and +10 buttons . Press both together and you get autotack. Still trying to get down to the bottom of the issue of why the buttons work fine except for port autotack.

Your "flicking on the autopilot to hold the boat just ABOVE the intended close hauled course" is just what I cant do because the few seconds it takes to connect the ram to the tiller and then press the auto button on the ST4000+, the boat has bu66ered off to god knows where.

I'm improving but the last race in a gusty 15/20kn was disastrous. Mark roundings were dreadful.

 

[doris]

A conversat

My potter about in retirement boat is a bilge keel. A good Steven Jones design but with one irritating characteristic - poor directional stability.

I have been windering it I can improve this by adding some balace to the rudder forward of the shaft. Or maybe a skeg which would be reasonably easy given that the hull just in front of the rudder is flat.

The piccie shows the rudder and it you look carefully you can see two black marks which show the line of the rudder stock and gives an idea of how little is in front of the stock and how much behind it.
View attachment 159336

So are there any design gurus on here who can get their brains behind such issues as centre of effort etc.

A conversation with Stephen Jones would seem the best way forward. He is very approachable.

 

[The Q]

If you are going to extend forward the rudder , you also need to fill it the gap above the rudder, that's losing a lot of the rudder performance as the water leaks from one side to the other over the top.

 

[Birdseye]

A conversat

A conversation with Stephen Jones would seem the best way forward. He is very approachable.

Did that and yes he is approachable. But he had a dim view of my idea of putting some sort of skeg/fin ahead of the rudder to improve directional stability. Might still try it during the winter lay up.

 

[Chiara’s slave]

If you are going to extend forward the rudder , you also need to fill it the gap above the rudder, that's losing a lot of the rudder performance as the water leaks from one side to the other over the top.

You would think so. Our rudder doesn’t have anything above it, and as yet we’ve had no ventilation, and the boat responds well at any speed. I was fully prepared to fit a fence. I think, if closing that gap were an advantage, it would be a widely accepted modification.

 

[B27]

It's quite common for older IOR type boats to make a fair effort to make the hull to 'end plate' the top of the rudder?


I think there is more to directional stability though. A mate sails RC model boats. If you want the thing to sail itself, you need to think about the response of the rig heeling the hull vs the rig responding to being heeled.

 

[Chiara’s slave]

It's quite common for older IOR type boats to make a fair effort to make the hull to 'end plate' the top of the rudder?


I think there is more to directional stability though. A mate sails RC model boats. If you want the thing to sail itself, you need to think about the response of the rig heeling the hull vs the rig responding to being heeled.

The theoretical advantage is obvious. Yet boats do quite well without bothering. I guess not many people bother ‘fixing’ the issue, so we have little or no ‘before and after’ data. Wonder how much real world difference there is?

 

[Birdseye]

I have the rest of the year up to the new years day race to tweek such things as mast rake, but if I am no further forward by then I think I will fit a skeg / mini keel in front or the rudder where the hull has a very handy flat surface. Maybe even some forward balance on the rudder itself to lighten the load a bit. Stephen Jones didnt like the skeg idea since all an extra skeg does in his view is increase drag but it has to improve directional stability.

 

[DownWest]

I have the rest of the year up to the new years day race to tweek such things as mast rake, but if I am no further forward by then I think I will fit a skeg / mini keel in front or the rudder where the hull has a very handy flat surface. Maybe even some forward balance on the rudder itself to lighten the load a bit. Stephen Jones didnt like the skeg idea since all an extra skeg does in his view is increase drag but it has to improve directional stability.

It also puts the centre of lateral pressure further aft, so could produce lee helm. (I am assuming your helm loads are weather?)

 

[Laser310]

directional stability depends other factors besides the rudder.

what do the bilge keels look like?

what does the hull shape look like?

also; when is the directional stability noticeably bad?

Motoring?.., reaching, running, beating?

I kind of doubt you will make it much better by changing the rudder shape

 

[Birdseye]

In plan form the hull is dart shape. No chines but for its lenght it is quite beamy. Vertical bow.

Did some testing last week when winds were in the 5 to 10 kn range. There is very slight weather helm so that looks OK. Mast rake is about 2 degrees and mast bend about half the mast chord so again OK. Happy with the rig set up.

There is a motoring issue but maybe no worse than other modern boats where the saildrive is well in front of the rudder - I have only had shaft drive previously so that could be a matter of what I am used to. No prop wash worth a damn.

The boat has high freeboard and it is this windage combined with a low resistance to rotation that has given me some learning to do. If the tack is clean ( difficult to get 100% right single handing) then there is no issue but if not then its very easy to backwind the genoa and fall back onto the original tack or effectively heave to.

What I was thinging of was inserting a skeg into the scheme of things as a way of increasing the resistance to rotation round the centre axis.

That said I am learning as I go and since last race I came second ............... The boat certainly sails really well between marks.

 

[dunedin]

If the tack is clean ( difficult to get 100% right single handing) then there is no issue but if not then its very easy to backwind the genoa and fall back onto the original tack or effectively heave to.

What size is the genoa? If your courses are as short as you have said, would a 105-115% jib be much easier to tack and a simpler solution?

 

[Javelin]

Have you a photo of your bilge keels?
Pref from the front.
I'd be interested to look at the profile and angle of attack.
Some bilge keelers are splayed out whilst others are much more vertical.
With a fin keel and spade rudder, assuming hull form is generally rounded, a skeg will help with direction stability but care needs to be taken with the leading edge so that the rudder is getting good, non turbulent flow, otherwise all your work will cause bigger issues.
A bilge keeler however is a different story, as to maintain a steady heading, you only need a small difference in drag on one keel to cause a significant turning moment.
Add heeling into the mix and the turning moment will increase further due to hull form and the different angle of attacks each keel has.
For example when heeling, the lower keel will exert much less turning moment than the higher keel.
Hence a more vertical bilge keel design will often be more directionally stable than a splayed out design.

 

[B27]

Have you a photo of your bilge keels?
Pref from the front.
I'd be interested to look at the profile and angle of attack.
Some bilge keelers are splayed out whilst others are much more vertical.
With a fin keel and spade rudder, assuming hull form is generally rounded, a skeg will help with direction stability but care needs to be taken with the leading edge so that the rudder is getting good, non turbulent flow, otherwise all your work will cause bigger issues.
A bilge keeler however is a different story, as to maintain a steady heading, you only need a small difference in drag on one keel to cause a significant turning moment.
Add heeling into the mix and the turning moment will increase further due to hull form and the different angle of attacks each keel has.
For example when heeling, the lower keel will exert much less turning moment than the higher keel.
Hence a more vertical bilge keel design will often be more directionally stable than a splayed out design.

I'm not sure about that.
When heeled, my leeward keel is close to vertical and the windward one is not.
The Leeward keel will be much better places to resist leeway? The boat likely tends to rotate around that rather than the windward keel which, if it is generating any 'lift' at all is likely either increasing or reducing the heel of the boat as much as providing lateral resistance?

The drag produced by each keel will be affected by the lift it's producing. On my boat, I think I feel the effect of waves on the windward keel.

To put it another way, as the boat heels, the 'centre', about which it pivots, moves around.
Side to side and front to back?

A skeg might be really counter productive.
I think the gust response is more complicated than meets the eye.
With my boat, it pays to reef quite early and roll in some genoa.
Then when gusts hit it only requires a little more rudder to keep a reasonable course.
Do I actually want it completely 'directionally stable'? Generally allowing it to head up a few degrees in a gust doesn't seem a bad thing?
It's not always simple because mostly gusty conditions are wind off the shore and gusts come with shifts included.

For racing of course, I'd not want to reef early, but you'd need to play the main to keep it on its toes.

 

[Javelin]

Hmm we seem to be agreeing.
When heeled the leeward keel is loaded and becomes the pivot.
The windward keel is loaded less as the boat heels but the turning drag increases.

Ultimately, my point is that the skeg would have to be significantly bigger and deeper on a bilge keeler than a fin keeler to have much effect.

 

[Birdseye]

Have you a photo of your bilge keels?
Pref from the front.
I'd be interested to look at the profile and angle of attack.
Some bilge keelers are splayed out whilst others are much more vertical.
With a fin keel and spade rudder, assuming hull form is generally rounded, a skeg will help with direction stability but care needs to be taken with the leading edge so that the rudder is getting good, non turbulent flow, otherwise all your work will cause bigger issues.
A bilge keeler however is a different story, as to maintain a steady heading, you only need a small difference in drag on one keel to cause a significant turning moment.
Add heeling into the mix and the turning moment will increase further due to hull form and the different angle of attacks each keel has.
For example when heeling, the lower keel will exert much less turning moment than the higher keel.
Hence a more vertical bilge keel design will often be more directionally stable than a splayed out design.

Interesting comments. The nearest I can get to a photo is

The keels are splayed with GRP stubs and lead bottoms. Directional control steering straight is quite good though as you might expect you cannot let go of the tiller at all. Its rounding marks where I would prefer less easy rotation. The stability os so high that the boat never heals very much

 

[Javelin]

They look pretty vertical to me compared to many.
Lead lower ballast is great and unusual these days providing a great ballast ratio.
Quite full forward sections as well, providing good buoyancy upwind compared to the fine entry/wide sterns that tend to dive when on the wind.

I think I'd be tempted to add a skeg.
Probably 50% of the depth of the rudder and 25% of the width.
If you glass in a 10 or 12 mm 316 plate with welded studs to the stub area in front of the rudder you could bolt on and try one without having to break through the hull. ( I hate holes in boats)

Changes to the rudder, in my view will have little effect other than the obvious, bigger area>more leverage>more turning moment, Smaller area>less leverage>less turning moment.

One other thought is, where are your rudder stops set?
If for example they are set at 35degrees you could try dropping it by 5 or 10 degrees.