a rudder design question

[Birdseye]

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.


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

 

[penfold]

Adding rudder area forward of the post will reduce tiller load but won't do much about directional stability. In what circumstances are you having poor stability?

 

[pmagowan]

Depends what you mean by 'directional stability'. It may be more to do with the keel design than the rudder. If you want a well balanced rudder to make for lighter steering then what you suggest could work. You could make an alteration and bolt on, experiment before you glass in.

 

[Tranona]

Have just been through this exercise, although not on a spade rudder. Balance area as already suggested affects steering loads and balance. In fact Jones is a bit of a guru on this as I seem to recall him writing about it in one of the mags many years ago so I would guess he has got this rudder right for the boat. You will also note the small bustle and skeg which is one of his trademark features designed ease the flow of water over the rudder and help directional stability. So again unlikely that there is anything you can do that he has not already considered - but you can always ask him.

Just for completeness the rule of thumb (from my readings on the subject) for balance area is between 10-15% of total rudder area. This is what I worked to with my redesign which was aimed at reducing the known heavy helm and encouraging prop wash over the rudder. Seems to have worked, although I did not sail the boat before the mods, although had done a similar thing on a smaller version of the same basic design which did achieve the objectives.

First photo shows how I went about it. Addition was epoxied on and sheathed in glass epoxy blended into the existing blade which was epoxy coated Iroko. Second photo finished article

 

[Birdseye]

Interesting piccies Tranona. Looks like a good job.

The boat is a bilge keel but the keels are of decent size with heavy lead bottom halves giving an ocean class stability rating. Remarkable in a 29 footer. But you cant take your hands off the tiller even motoring ahead in a flat calm. My previous bilgie some time ago was a Moody 336 and that had better directional stability but then it had a skeg.

For most sailing this issue doesnt matter. On passage you often want to use the autopilot anyway, and if you dont its because you enjoy handling the tiller which is quite light. My issue comes only when trying to race single handed when I need to leave the tiller to use the winches etc. I have a gadget which gets round this but I was wondering if there were mods that I could do to make the boat keener to run straight. Maybe fashion and fit a skeg?

 

[Tranona]

Don't think there is an easy answer. The bias under motor is common because of prop wash. Being a single hander myself I made an effort when buying my last boat to make it easy to single hand and control from behind the wheel. That was one of the major selling points for the Bavaria because the mainsheet was just in front of the helm rather than on the coachroof as on many modern boats and I specified the extra pair of winches aft on the coamings. Furling lines for jib and chute were also alongside the wheel and you could walk forward round the wheel without climbing on the seat. As it happened despite being flat bottomed with a shortish fin keel and a skegless raked spade rudder it was directionally very good (except down wind in stronger winds) and no problem leaving the wheel to tend sheets. Plus pushbutton autopilot it was really easy to handle. It does show that a modern wheel steered boat can be much easier to handle than a smaller tiller steered boat - although you could probably sail rings round it!

Every time I write about it I wonder why I sold it, but that is another story!

 

[Chiara’s slave]

You’d need to consider the other sort of helm balance too. In Tranona’s case, he can add a bit there with no noticeable difference, cos there’s so much of it already. But adding a skeg, or more than a tiny bit of rudder could move the CLR aft, giving you lee helm. You might not enjoy that.

 

[DownWest]

Adding area ahead of the pivot line on the rudder lightens the load on the tiller. You might have to look elsewhere for directional stability.

 

[Birdseye]

Don't think there is an easy answer. The bias under motor is common because of prop wash. Being a single hander myself I made an effort when buying my last boat to make it easy to single hand and control from behind the wheel. That was one of the major selling points for the Bavaria because the mainsheet was just in front of the helm rather than on the coachroof as on many modern boats and I specified the extra pair of winches aft on the coamings. Furling lines for jib and chute were also alongside the wheel and you could walk forward round the wheel without climbing on the seat. As it happened despite being flat bottomed with a shortish fin keel and a skegless raked spade rudder it was directionally very good (except down wind in stronger winds) and no problem leaving the wheel to tend sheets. Plus pushbutton autopilot it was really easy to handle. It does show that a modern wheel steered boat can be much easier to handle than a smaller tiller steered boat - although you could probably sail rings round it!

Every time I write about it I wonder why I sold it, but that is another story!

I could have written your post word for word about the Starlight 35 I had. Including the last sentence!

 

[Bodach na mara]

I have never had a boat that would steer hands-off. I have had 4, plus several dinghies, starting with a 1912 six-meter then a 1960s long fin keel, a Westerly fin keel and now a Westerly bilge keel. All could be persuaded to steer reasonably straight for a short period with the helm lashed but if the helm was left free they would,within seconds, initiate a turn of decreasing radius and within minutes would be spinning in a circle of not much more than the length of the boat in diameter. All this is under power of course except for the six, which had a side-mounted outboard and I never tried leaving the helm unlashed in it.

 

[Birdseye]

Again interesting comments. I havent had a small bilge keeler since my first boat god only knows how long ago. All the intervening ones have been bigger with wheel steering and push button pilots, so maybe I am just forgetting the past.

Anyway the challenge in this case is to club race my boat single handed and again yesterday, in gusting conditions, I really struggled. It was short circuit stuff , round a laid course in non tidal water. Once I got the boat on course with sails reasonable she held her own but at every mark rounding I lost a good 50 to 100m tring to keep hold of the tiller and tack the gib, adjust the main etc. I have installed a Tiller Clutch ( a nice piece of design) but whilst that holds the tiller OK, the tiller still needs lots of minor adjustments as the sails load up. Am wondering about a winter project fitting a half skeg and more forward area on the rudder. The skeg doesnt have to be connected to the rudder - it can simply be a fin

 

[Daydream believer]

When you say "directional stability, do you mean that by letting the tiller go the boat immediately changes course?
If so you will not alter that by altering the rudder design. Stephen Jones does not design poor rudders & I would be dubious about playing with that.
It does help to make sure that it is free of weed

If you mean that the tiller is heavy, making steering difficult, then I would suggest that there are other options. My boat initially had a very heavy helm. So much so, that my wife could not helm the boat & eventually refused to take the helm at all.
My solution was to rake the mast further forward (300mm at the top) so, unlike others of the same type, it is now upright rather than raked back. Tighten the shrouds considerably. (22% on the uppers). Then get some decent sails & learn how to set the main, especially when sailing up wind.
I have introduced sail adjustments & use them, I regularly alter clew outhaul, vang cunningham & halyard tension as well as backstay. I have a traveller & fine tune on the mainsheet to get the twist right.
I no longer find the helm heavy but I still cannot let the tiller go for a second. However, it does make for a boat that sails faster, because one is concentrating all the time. I rarely broach where by the rudder loses actual grip, although on a big quartering sea on a broad reach with the wind over the stern quarter she is hard work to keep any sort of line & the autopilot just loses control. I have to hand over to the Aries as it gets tiring.

 

[penfold]

I have to hand over to the Aries as it gets tiring.

Would vane steering be legal? I can see powered helmpilots being against rules but a wind-powered thing may be a grey area.

 

[dunedin]

Again interesting comments. I havent had a small bilge keeler since my first boat god only knows how long ago. All the intervening ones have been bigger with wheel steering and push button pilots, so maybe I am just forgetting the past.

Anyway the challenge in this case is to club race my boat single handed and again yesterday, in gusting conditions, I really struggled. It was short circuit stuff , round a laid course in non tidal water. Once I got the boat on course with sails reasonable she held her own but at every mark rounding I lost a good 50 to 100m tring to keep hold of the tiller and tack the gib, adjust the main etc. I have installed a Tiller Clutch ( a nice piece of design) but whilst that holds the tiller OK, the tiller still needs lots of minor adjustments as the sails load up. Am wondering about a winter project fitting a half skeg and more forward area on the rudder. The skeg doesnt have to be connected to the rudder - it can simply be a fin

I fear you might waste a lot of time and effort fitting a half skeg and find it has no benefit in practice. And more forward area on the rudder might make the steering lighter, it will have zero benefit on “hands off” stability (as has been explained further up).

The answer is probably in your earlier paragraph - you need a way to drop in an autopilot quickly when needed. I would suggest you focus your efforts, ingenuity and funds onto that aspect. Assuming need a tiller pilot with the tiller, find a way to have the tiller pilot with wiring all connected and able to be dropped onto the tiller and going in under an under 5 seconds.

Use of an autopilot may not be fully race legal in some places - but if racing a bilge keeler singlehanded it hardly sounds like Olympic level competition. And autopilots are generally now allowed in short handed (solo and double handed) racing, even up to Fastnet race etc (if I recall correctly). So unlikely to get any complaints unless suddenly beat the commodore to all the club silverware.

 

[Birdseye]

Possibly repeating myself here, but this boat is new to me after 12 years of sailing and racing a Steven Jones design Starlight 35 and many others before that one.. It was the designer name that made me chose the current boat, though not all of his designs have been as good as the Starlight undoubtedly was.
Now I am only sailing locally and racing non seriously so my requirements were:
1/ something around 30ft
2/ bilge keel - I sail the Bristol channel so most local ports I might want to go to dry to sand or mud.
3/ a boat I can single hand since that means I can go when I want rather than when arranged.

The new boat is an excellent cruiser so the only issue I have is trying to single hand her whilst racing a laid course behind the barrage in Cardiff bay - typical leg length a half mile so tacking every 5 mins.

It may be that the boat I have chosen is simply unsuitable for this sort of racing but I am not yet ready to give up on a boat that is so good in every other respect.

As to the rudder:

The vertical line is the forward edge of the rudder post. My thoughts were to create a skeg as shown ( the under surface of the hull is flat here as if the original design proposal was for a skeg ) remove a part of the front edge of the rudder and compensate by increasing the fron edge area below the skeg.
The only concern is that the skeg is really only a fin and the increased rudder area is lower down thus creating a higher sideways load on the rudder bearings.

What does the forum think?

 

[Birdseye]

I fear you might waste a lot of time and effort fitting a half skeg and find it has no benefit in practice. And more forward area on the rudder might make the steering lighter, it will have zero benefit on “hands off” stability (as has been explained further up).

The answer is probably in your earlier paragraph - you need a way to drop in an autopilot quickly when needed. I would suggest you focus your efforts, ingenuity and funds onto that aspect. Assuming need a tiller pilot with the tiller, find a way to have the tiller pilot with wiring all connected and able to be dropped onto the tiller and going in under an under 5 seconds.

Use of an autopilot may not be fully race legal in some places - but if racing a bilge keeler singlehanded it hardly sounds like Olympic level competition. And autopilots are generally now allowed in short handed (solo and double handed) racing, even up to Fastnet race etc (if I recall correctly). So unlikely to get any complaints unless suddenly beat the commodore to all the club silverware.

I have given up on the autopilot because in the time it takes to connect the ram and then move to the forward bulkhead to press the button, the boat has wandered off far too far. Olympic level competition? More like a school sports day ! We dont do protests.

 

[Buck Turgidson]

I would suggest it's the couple between the centre of force on the sail vs the keel which needs adjusting because left unattended the rudder will always stream and cannot affect direction.

 

[dunedin]

I have given up on the autopilot because in the time it takes to connect the ram and then move to the forward bulkhead to press the button, the boat has wandered off far too far. Olympic level competition? More like a school sports day ! We dont do protests.

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

 

[Daydream believer]

Would vane steering be legal? I can see powered helmpilots being against rules but a wind-powered thing may be a grey area.

Never used to be & I was protested- Without my knowledge- in a BJRC race some years ago. As a result I was disqualified.
However, rules have changed & it is now - as I understand- legal. But I am not sure about electric autopilots & I am sure that many club racers do use them. If they do, one might ask if that is beyond the rules.
Long distance SH & 2 handed sailors would have that clarified in the sailing instructions & a dispensation would usually be applied.

 

[DownWest]

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.