Twin Rudders

[boatmike]

I like the Southerly but have heard various storeys over ineffective rudders until boat gets to a speed (no prop wash over rudder). Bad in marinas

Now I appreciate that Ex and current owners of twin rudder boats will be biased but are there any sailors out there who have switched between single and twin rudder set ups that would like to comment on marina manouvrebility

There is no perfect boat design, everything is a compromise. Many twin rudder designs like the southerly are designed to give maximum area with minimal draught. Its a lift keel boat after all and can't very well have a large single deep rudder unless it was a swing design of some sort enabling it to fold up like a dinghy's. There certainly is an issue with no prop wash over the rudders with a central prop though and you just have to decide what is most important. Most lift keel owners think drying out is the most important thing. On the other hand twin rudders are said to give better control when heeled to windward. You pays yer money and takes yer choice.....

 

[Seven Spades]

Southerlies are some of the most expensive boats/foot that you can buy are you dismissing them? I saw the 420 at the boat show and thought it was amongst the nicest boats I had seen, but I never know how seriously they should be taken. I am not sure if they are strictly cruising boats or if they have a good turn of speed. With the keel down the draw 2.6m which should allow for a big rig, but they don't seem to use genoas, it is either a jib or genneker.

Thoughts?

 

[deeb]

twin rudders

My boat is very light, very beamy, very fast. French, with twin rudders.

And it tracks like a train, upwind, downwind at speed or donking in or out of its slot. Forward or backwards. Manuouvering under power you would not notice the lack of propwash unless you really go looking for it - a little bit of way and she steers, beautifully. Forward or back.

Some sailors adjust the tracking according to conditions, I have a setting I'm happy with and sail to that. The significant disadvantage is its propensity to pick up weed - sailing around the channel Isles a weedstick of some sort is more or less essential. It isn't a boat you'd take to the the ground on. (Spindly keel, heaps of draft)

Dinghys don't have twin rudders because they are designed to be sailed upright so don't need them, but you knew that really, didn't you. No?

 

[TSB240]

sjres
Show Details

Yes,Jeanneau SO32s with centreplate do the same thing. Rudders don't touch the sand.
But what do we know compared with the wealth of experience from Langstone?

I have noticed a continuing trend from our Langoustine A22 expert to criticise the modern designs incorporating wide sterns and twin rudders. Maybe all those enjoying the benefits should pass on there experience to him.

I think he showed his lack of knowledge of the small wide assed Benes on another post quite recently but I failed to correct him.

In the interest of some balance.

Most of their lifting keel range have either hinged drop keels or plates which are jacked out of a stub. They also have twin rudders that slide vertically in their stocks. The rudders in common with the larger models are protected from grounding in shallow anchorages by virtue of the deeper keel stub.

The lighter weight lifting keel trailer sailer designs are not designed to dry out level unsupported without resort to attaching optional beaching legs to built in mounting points.

I think that even the much lauded A22 would need pit propping to keep its bubble level on the harder stuff.

In common with the A22 the new Benes and the Elan 210 can settle into the ooze quite happily without risk of keel clogging. I dont believe they are anymore prone to pounding damage than any of our much older 80s relics.

Andy, dont tell me you have never forgotten to raise your deep water mono blade before beaching. I have as the chunks out of the trailing edge bear witness.

 

[Seajet]

Since when are we talking about "high performance racing dinghies" and since when does everything have to compare with what works on them? Twin rudders are common in REALLY high performance ocean racing boats, small sports cruisers and substantial cruising boats where shallow draft is part of the owner's requirements. Pretty well accepted design feature.

As I said, you need to get out a bit more and understand that different people have different requirements and therefore different solutions are appropriate. Just because they do not fit in with your preconceived ideas does not make them invalid for others.

Your constant, unsupported sniping at everything you don't like or don't understand is getting a bit wearing.

Tranona,

you are the one being adversarial; I happen to have studied aircraft and sailing boat design, but unsurprisingly given the investment involved can't name a college project which has gone into production, I had a full time job in technical photography of design trials of aircraft to concentrate on.

My objection to twin rudders on boats is largely when they are used to keep lift keel boats upright when drying out; I'm sure you can imagine what I mean by relatively weak structures and splaying loads going in and out of mud.

The high speed yachts with twin rudders you mention usually have the windward rudder in the air eliminating wetted area drag from the second rudder, and only have one daggerboard down at a time + often a canting keel.

Some modern dinghies such as International 14's have a wide transom for downwind performance, but still manage single deep rudders; I have owned or crewed 1950's 70's and 90's versions of Int 14, how about your good self ?

A chap at my moorings bought a 35' + prototype boat with a lifting blade through a wing keel with twin rudders; we pundits gave it 30 minutes, which was about all it had before falling over severely as the tide went out and being lucky not to be held over by the keel wing and filled on the flood tide, this boat was moved to a deep water mooring pronto.

 

[Seajet]

sjres
Show Details


I have noticed a continuing trend from our Langoustine A22 expert to criticise the modern designs incorporating wide sterns and twin rudders. Maybe all those enjoying the benefits should pass on there experience to him.

I think he showed his lack of knowledge of the small wide assed Benes on another post quite recently but I failed to correct him.

In the interest of some balance.

Most of their lifting keel range have either hinged drop keels or plates which are jacked out of a stub. They also have twin rudders that slide vertically in their stocks. The rudders in common with the larger models are protected from grounding in shallow anchorages by virtue of the deeper keel stub.

The lighter weight lifting keel trailer sailer designs are not designed to dry out level unsupported without resort to attaching optional beaching legs to built in mounting points.

I think that even the much lauded A22 would need pit propping to keep its bubble level on the harder stuff.

In common with the A22 the new Benes and the Elan 210 can settle into the ooze quite happily without risk of keel clogging. I dont believe they are anymore prone to pounding damage than any of our much older 80s relics.

Andy, dont tell me you have never forgotten to raise your deep water mono blade before beaching. I have as the chunks out of the trailing edge bear witness.

TSB240,

I presume you mean grounding legs; I only ever settled my boat on hard sand once, never again; the pounding was horrible, and that can't be blamed on the design !

Funnily enough I never have forgotten to raise the keel ( or rudder ) if that's what you mean ?

The trailing edge of the A22's keel has a tufnol 'shock absorber' in the aft of the keel case in case one runs into something unpleasant; maybe fear of using this is why I have 2 depthsounders, for cockpit and below !

I've made plenty of cockups believe me, but not that one yet; I have sometimes fancied a cockpit mounted keel position indicator but so far got away with it.

 

[Tranona]

Tranona,

you are the one being adversarial; I happen to have studied aircraft and sailing boat design, but unsurprisingly given the investment involved can't name a college project which has gone into production, I had a full time job in technical photography of design trials of aircraft to concentrate on.

My objection to twin rudders on boats is largely when they are used to keep lift keel boats upright when drying out; I'm sure you can imagine what I mean by relatively weak structures and splaying loads going in and out of mud.

The high speed yachts with twin rudders you mention usually have the windward rudder in the air eliminating wetted area drag from the second rudder, and only have one daggerboard down at a time + often a canting keel.

Some modern dinghies such as International 14's have a wide transom for downwind performance, but still manage single deep rudders; I have owned or crewed 1950's 70's and 90's versions of Int 14, how about your good self ?

A chap at my moorings bought a 35' + prototype boat with a lifting blade through a wing keel with twin rudders; we pundits gave it 30 minutes, which was about all it had before falling over severely as the tide went out and being lucky not to be held over by the keel wing and filled on the flood tide, this boat was moved to a deep water mooring pronto.

Not being adversarial at all. Just pointing out (as many others have also) that you often talk out of your rear end (although I was being a bit more polite). You seem unable to tell when you are out of your depth and just talking for the sake of talking - and you don't seem to know when to stop. You dismiss everything anybody says if it does not fit in with your narrow view of the world, so it is not surprising that folks here have a dig at you every so often.

On the specific point of twin rudders and drying on CRUISING boats, you have photos here and owners experiences saying you can do just that. Surely coming from people who have spent 10's of 000's £ to achieve just that is more valid than your ramblings and anecdotes.

Don't know why you keep banging on about what you have done in the past. I (like many other "mature" people) have done lots of things in my life - does not mean I know everything - even about my own very specialised subject area! And I would not challenge somebody like Rob Humphreys who has designed some superb twin rudder boats including those for Southerly and Elan.

 

[Egbod]

Twin rudders

My 23 foot yacht has twin rudders and handles as described- no prop wash. Both rudders lift fully when drying out.
The big advantage to me is that the outboard is in a well in the cockpit so the prop grips the water well in rough water and even when heeled as it is on the centre line. When the outboard is not in use it tips up with the leg fitting a slot in the transom so there is no drag. To help slow speed manoevering the outboard can be turned a little which helps reduce the turning circle.

 

[Blueboatman]

One solution would be to fit two Contrarotating saildrive units ahead of each rudder and driven hydraulically from one engine.
I believe that such set ups are, aside from the extra expence and conplexity, quite inefficient due to the inefficiency of pumping the drive oil around ( Tranona?) but as with a catamaran the manoeuvrability would be impressive.
I have only experienced this on a big East coast smack, big bowsprit n all, that boat could be rotated within its own length, quite impressive to those expecting long keeler handling 'issues'

The big 45 OVNIs have twin fixed rudders I believe, which in alloy would take a fair bit of abuse possibly when ' parked up' on a shore.

 

[toad_oftoadhall]

TI'm sure you can imagine what I mean by relatively weak structures and splaying loads going in and out of mud.

Is it really plausable that the designer wouldn't be aware of that and thus failed to design enough strength in?

Is it really credible that the guy is sitting somewhere slapping his head and saying "Oh, dear, I forgot to make the keels strong enough to take to the ground when I designed the rest of the boat to take to the ground."???

I don't think you can draw any conclusions by simply looking - the wings on an Airbus look pretty flimsy to me but I suspect that they were designed to take any anticipated load plus a fair bit.

Southerly rudders might be under engineered, but I haven't seen any evidence of that, and as yet nobody's provided any.

 

[TSB240]

Tranona,

you are the one being adversarial; I happen to have studied aircraft and sailing boat design, but unsurprisingly given the investment involved can't name a college project which has gone into production, I had a full time job in technical photography of design trials of aircraft to concentrate on.

My objection to twin rudders on boats is largely when they are used to keep lift keel boats upright when drying out; I'm sure you can imagine what I mean by relatively weak structures and splaying loads going in and out of mud.

The high speed yachts with twin rudders you mention usually have the windward rudder in the air eliminating wetted area drag from the second rudder, and only have one daggerboard down at a time + often a canting keel.

Some modern dinghies such as International 14's have a wide transom for downwind performance, but still manage single deep rudders; I have owned or crewed 1950's 70's and 90's versions of Int 14, how about your good self ?

A chap at my moorings bought a 35' + prototype boat with a lifting blade through a wing keel with twin rudders; we pundits gave it 30 minutes, which was about all it had before falling over severely as the tide went out and being lucky not to be held over by the keel wing and filled on the flood tide, this boat was moved to a deep water mooring pronto.

Andy

Your 14 critique is fatally flawed or you dont know your 14 as well as you claim.

Class rules only allow the use of one rudder/foil.

They dont have nearly big enough asses in my view so fall over too easily......

I only know of one mainstream manufacturer who markets a boat as suitable for drying out on its twin rudders. Please let me know which others to avoid then as I am considering an upgrade

 

[toad_oftoadhall]

Your 14 critique is fatally flawed or you dont know your 14 as well as you claim. .Class rules only allow the use of one rudder/foil.

Unless I'm missing something, he doesn't seem to have said otherwise.

International 14's have a wide transom for downwind performance, but still manage single deep rudders

 

[fireball]

Some modern dinghies such as International 14's have a wide transom for downwind performance, but still manage single deep rudders; I have owned or crewed 1950's 70's and 90's versions of Int 14, how about your good self ?

Really not sure why you're banging on about dinghies ..

The International 14 was never intended to dry out on a daggerboard and rudder - it doesn't need to - all the foils are retracted prior to recovery ...
Do you know any dinghies that are designed to sit on keels and rudders? No? Nor do I ... no idea why you would either - the rudders are transom mounted and either easily removed or designed for racing where you don't want to dry out anyway ...
My boat has a wide transom and a deep rudder ... it dries out too ... against a wall ... your point?

A chap at my moorings bought a 35' + prototype boat with a lifting blade through a wing keel with twin rudders; we pundits gave it 30 minutes, which was about all it had before falling over severely as the tide went out and being lucky not to be held over by the keel wing and filled on the flood tide, this boat was moved to a deep water mooring pronto.

All that proves is that the ground at that point was unsuitable for that vessel ..
As you say - you've only grounded on hard sand once ... so I take it you're not the world expert?
Can we hear from those who do know how their twin rudder boats behave rather than twaddle from yourself? ... thank you.

 

[FullCircle]

I must admit I am tempted to post that which would get me banned.

I am wholly fed up with Seajet and his narrow bigoted views.

I was going to follow this up with an intellectual argument, but deleted it, as it seemed completely asinine. Sorry everyone.

My last word.

 

[Tranona]

I must admit I am tempted to post that which would get me banned.

I am wholly fed up with Seajet and his narrow bigoted views.

I was going to follow this up with an intellectual argument, but deleted it, as it seemed completely asinine. Sorry everyone.

My last word.

Yes, intellectual argument is a complete waste of time, as is presenting clear pictorial evidence. Poking fun also seems to be wasted as Angus McDoon and others have found.

Maybe plain speaking will have an effect - we shall see.

BTW would love to put him in a room with Rob Humphreys to discuss the merits (or otherwise) of twin rudders!

 

[boguing]

I'm sure you can imagine what I mean by relatively weak structures and splaying loads going in and out of mud.

So. As an unqualified student of aero and hydro dynamics, and a possibly qualified photographer, you claim some definitive knowledge.

OK.

What would the [splaying - undefined term] load [stress or..] be on two rudders angled at 10 degrees each from the vertical plane with a mass of 500Kgs acting vertically on them. In Engineering terms, vertical and horizontal forces.

Clue = Sir Olivers' Horse to Olivers' Aunt etc.

Luckily, in my case, Tony Castro knew the answer to that one.

And "relatively weak structure", do, please, explain.

The really strange thing here is that I have agreed with all of your previous contributions. Snag is that the Chief aeros chap on the P1127/Harrier is a member of my drinking friends.

Second snag. When I said 500 hours - they were 75% demos to potential buyers. So probably 300 each of parking and manouverablity demos. I used a buoy or pile for those. This was just the 25. I do know how to park a boat.

 

[Seajet]

I mentioned my past as Tranona asked me...

If anyone thinks splayed relatively fragile ( compared to twin keels which have a hard time of it ) rudders going in and out of soft mud is an acceptable load then that's spiffing, good luck !

 

[Blueboatman]

Why? It is a cantilevered structure supported by a seriously thickwalled steel tube at hull bottom and top, with a blade that is-or can be- self aligning to act with the forces exerted on it by changing loads as the boat settles.
In fact there are two of them so divide the work but notionally some degree of twist may be exerted as the two fight each other and if splayed 20 deg or so.

Add a couple of shoed skegs, to accept the pounding as the boat settles and a fishing boat whizzes past, and bingo, job done. Gibralter, solid, mines a pint mate

It is a while since I have done the math but- actually one doesn't even need to do any math: Cassette type or pivoting, transom hung, rudders can be weaker. Grab a pot line when sailing fast, reverse onto a quay, a dodgy trailer launch, nudge an underwater obstruction, get thrown off a wave, byebye pintles or hello lateral blade fractures, at least in my universe though probably not yours, eh?

 

[Tranona]

I mentioned my past as Tranona asked me...

If anyone thinks splayed relatively fragile ( compared to twin keels which have a hard time of it ) rudders going in and out of soft mud is an acceptable load then that's spiffing, good luck !

Please show me where I asked about your past. Seriously think you are losing the plot. Why do you ignore, or worse dismiss what everybody else says, when what they say is usually based on experience or sound argument?

Talking about your "past" - as you seem obsessed with it, IIRC your boat experience is Osprey, Centaur, Carter 30 , Anderson 22. All very valid, but worlds away from the kind of boats you try express opinions on.

 

[Barbican]

I like the Southerly but have heard various storeys over ineffective rudders until boat gets to a speed (no prop wash over rudder). Bad in marinas

Now I appreciate that Ex and current owners of twin rudder boats will be biased but are there any sailors out there who have switched between single and twin rudder set ups that would like to comment on marina manouvrebility

Can't give you any feedback from experience with the twin rudder set up, but having had two long keelers without bow thrusters etc, I don't find the prospect too daunting, I'm sure I'll get used to it. On the test sails, and as others have said, I noticed that the rudders responded well once there was some water flow over them, just as with my last two boats.

On the strength issue when drying out I've not heard of any issues and non reported on the web that I have found, and since there is a central bustle between the rudders that takes the weight I can't see any issues with that.

So a Southerly will be our next boat, and I can't wait.