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Old 13-02-2016, 12:49   #376
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Re: Oceanis 485 steering failure

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Originally Posted by Polux View Post
Yes, that is a disadvantage and I would not say the bigger one is not the absence of the prop wash since some boats with saildrive (most of them today) have the rudder so far away from the propeller that the lateral opposite movement induced by the propeller, when it turns, is more useful than prop wash on docking maneuvers.

For me the biggest disadvantage in maneuvering is the considerable bigger turning circle of those rudders compared with a single rudder.

Anyway weighting advantages and disadvantages I would change my deep single rudder for an equally effective twin rudder in a heartbeat. Not going much to marinas anyway.
Why would twin rudders require a larger turning circle? I don't quite get that.

In fact I'm not sure what's a "turning circle" is on a boat. I have never steered a boat I couldn't turn in its own length. Can you not do that in a twin rudder boat?


Concerning maneuverability in astern -- once a boat is too big to manhandle (more than 15 tons?), this is, for me, a total deal breaker.

In my previous boat (10 tons, 37 feet), the lack of controllability in astern was the source of absolutely constant grief, and not only in marinas. It was simply awful. I had to use ropes and crew, some times multiple of each, to move astern anywhere. Lots of sleepless nights and white knuckles. Few dents and scratches, but only due to a very long string of exceptionally good luck.

People nowadays ask me -- don't you find it difficult to maneuver such a large boat (54' on deck, 60' LOA, 20 tons light ship) in harbors? I laugh when I remember the horror I had with the old one. This boat is a piece of cake compared to that, even single handed. Because it reverses straight. And also because it has a bow thruster, which you use for steering in astern.


Sorry, long-winded and possibly boring way of saying -- in my opinion, controllability in astern is a very important quality in cruising boats.
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Old 13-02-2016, 12:52   #377
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Re: Oceanis 485 steering failure

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Originally Posted by Polux View Post
That is a cat.

I was talking about monohulls that is what is being discussed on this thread.

Besides the accident with that cat had not to do with better or worse protection regarding the keel and neither about rudders being broke after hitting something since the rudders of that cat did only hit....water.
thats what I am saying, if it damages one, it can damage both. I think if something has a twin rudder, they may make them lighter to cope with the extra drag. I still like skeg or keel hung rudders. Strength should be built into the steering, even if it causes drag. Steering is one of the most important aspects to a sailboat. Don't think I would own a spade rudder boat.
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Old 13-02-2016, 12:59   #378
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Re: Oceanis 485 steering failure

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Why would twin rudders require a larger turning circle? I don't quite get that.
...
I don't know why but they do. I have tried and it is something that is well documented.
.................................................. .................................................

Regarding sailing twin rudder boats with only one rudder, they continue to perform well under motor or downwind, regarding going upwind the only thing that is limited is the heeling you can take.

As most modern boats are designed to go upwind with very little heeling the only thing you have to do is going more slowly upwind but without problems. Certainly much less that you would have trying to sail a boat without a rudder.

That is not theory, I have "seen" it being done by many racing boats, from mini to Beneteau Figaro to Class 40 or Open 60.
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Old 13-02-2016, 13:07   #379
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Re: Oceanis 485 steering failure

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Originally Posted by sailnow2011 View Post
...Steering is one of the most important aspects to a sailboat. Don't think I would own a spade rudder boat.
You should because steering is one of the more important aspects of a sailboat and because spade or twin rudders steer much better than any other type of rudders. That is why they are used in almost all contemporary sailboats.

I have understood what you mean and I was just kidding regarding your preferences but it is good to have a complete view, with advantages and disadvantages
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Old 13-02-2016, 13:12   #380
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Re: Oceanis 485 steering failure

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Originally Posted by sailnow2011 View Post
thats what I am saying, if it damages one, it can damage both. I think if something has a twin rudder, they may make them lighter to cope with the extra drag. I still like skeg or keel hung rudders. Strength should be built into the steering, even if it causes drag. Steering is one of the most important aspects to a sailboat. Don't think I would own a spade rudder boat.
Steve Dashew would disagree with you about skeg and keel hung rudders.

It is difficult to make a skeg on a fiberglass boat which is all that much stronger than a good spade rudder. There are a number of boats with full skegs (one a Moody, in fact) which sank because the skeg was ripped off the bottom of the boat when the rudder was grounded.

Spade rudders are not just for reducing drag. They are for hydrodynamic effect -- for the power of the rudder, which has to make lift when you're sailing upwind, just like the keel does. The rudder is a wing just like the keel is, and it doesn't work nearly as well as a wing if it's bent in the middle (because it's attached to an immovable skeg). Spade rudders can also be balanced, with part of the area ahead of the rudder post, which dramatically reduces loads on the steering system, improving autopilot performance, and reducing risk of breaking something in the steering system. A deep, high aspect spade rudder is far more efficient and powerful than a skeg-hung one.

I don't actually see any good reason for full skeg rudders. They are inherently stronger than spade rudders only because the load is spread between rudder post and skeg rather than being concentrated at the rudder post, but I don't think they are inherently stronger than partial skeg rudders by much (and not at all unless the skeg is large and is really tied in with the structure, like a keel would be, and not just glassed into the hull like they usually are). A partial skeg rudder (like mine) is a bit of a bastard child of a spade and a skeg, but with significant advantages over full skeg rudders, especially, the balance area of the rudder ahead of the rudder post, and you get nearly the same benefit from spreading the load from rudder post to skeg. It's also better hydrodynamically because it's not bent in the middle, at least not the bottom part.

Still, my next boat will have a Dashew-style spade rudder, massively overbuilt structurally, like Dashew's, but with good hydrodynamic properties. One of the first and easiest design decisions I made.
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Old 13-02-2016, 13:21   #381
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Re: Oceanis 485 steering failure

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Originally Posted by Polux View Post
I don't know why but they do. I have tried and it is something that is well documented.
.................................................. .................................................

Regarding sailing twin rudder boats with only one rudder, they continue to perform well under motor or downwind, regarding going upwind the only thing that is limited is the heeling you can take.

As most modern boats are designed to go upwind with very little heeling the only thing you have to do is going more slowly upwind but without problems. Certainly much less that you would have trying to sail a boat without a rudder.

That is not theory, I have "seen" it being done by many racing boats, from mini to Beneteau Figaro to Class 40 or Open 60.
By "modern boats" you're talking about flat bottomed, wide-transomed boats which have become more common, but not everyone agrees that only this hull form is "modern". I call them "wedgies", and like all variants of sailboat hull form, they have certain advantages and certain disadvantages.

My next boat will not have a hull form like that, but I am intrigued by twin rudders. You've explained the advantages very well, and I think that these advantages must be real, and could be taken advantage of without going to a "wedgie" hull form.
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Old 13-02-2016, 13:45   #382
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Re: Oceanis 485 steering failure

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Originally Posted by Dockhead View Post
By "modern boats" you're talking about flat bottomed, wide-transomed boats which have become more common, but not everyone agrees that only this hull form is "modern". I call them "wedgies", and like all variants of sailboat hull form, they have certain advantages and certain disadvantages.

My next boat will not have a hull form like that, but I am intrigued by twin rudders. You've explained the advantages very well, and I think that these advantages must be real, and could be taken advantage of without going to a "wedgie" hull form.



Just read Howard Chappelle, and you will realize that the argument between the two hull form styles has been going on for more than 100 years. Back then, Sharpies were the exact equivalent of modern boats. Shoal draft, light, fast, easier and cheaper to build, hard chines, beam carried aft, shorter lifespan, etc etc. Polux' "contemporary" designs are just sharpies. Chappelle called the two camps "skimming dish" vs. "plank on edge", ie long narrow and deep vs wide and shallow. Old hat argument, the details of which have changed little in all this time. Far from a new hull form, just NA's recycling old ideas and calling them new, as they often do.
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Old 13-02-2016, 13:52   #383
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Re: Oceanis 485 steering failure

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Originally Posted by minaret View Post
Just read Howard Chappelle, and you will realize that the argument between the two hull form styles has been going on for more than 100 years. Back then, Sharpies were the exact equivalent of modern boats. Shoal draft, light, fast, easier and cheaper to build, hard chines, beam carried aft, shorter lifespan, etc etc. Polux' "contemporary" designs are just sharpies. Chappelle called the two camps "skimming dish" vs. "plank on edge", ie long narrow and deep vs wide and shallow. Old hat argument, the details of which have changed little in all this time. Far from a new hull form, just NA's recycling old ideas and calling them new, as they often do.
Indeed
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Old 14-02-2016, 03:45   #384
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Re: Oceanis 485 steering failure

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Originally Posted by Dockhead View Post
By "modern boats" you're talking about flat bottomed, wide-transomed boats which have become more common, but not everyone agrees that only this hull form is "modern". I call them "wedgies", and like all variants of sailboat hull form, they have certain advantages and certain disadvantages.
,,
Calling them modern means that only recently they dominated the market of cruising boats, even if they had dominated Open racing boat's design for more than 25 years.

Yes, they are not the only choice neither the only modern hulls but in represents the vast majority and not only among mass production main market sailboats but also among voyage boats and luxury cruisers: Amel, OVNI, Allures, Garcia, Cigale, Boreal, Halberg Rassy and Rustler are only some among the brands that use those beamy hulls with all or almost all beam pulled aft where twin rudders make all the sense. That's a lot of boats, from very different types, to call wedgies

In fact of all those that I had nominated only the the new designs from Rustler and Halberg Rassy are not using , yet, twin rudders on their new hulls and probably that not because they would not have advantages but because that could scare their very traditional customers. I bet that the "wedgie" shape of the new hulls would be traumatic enough

I say this having a boat that doesn't belong to that Open design type, knowing the advantages and disadvantages of both types of hulls and knowing that I belong to a small minority that prefers, even for cruising narrower, boats.

In what regards sailing they offer an advantage if most of the cruising is made on the med but none (and several disadvantages) if they are used to voyage on the trade winds or if they are used by the type of sailors that dead upwind prefer to motor than to sail (and they are many).
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Old 14-02-2016, 07:52   #385
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Re: Oceanis 485 steering failure

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This has been really informative. Next time I am near my rudder assembly i will take pictures and post them here for comparison as I think it's pretty well built and designed. 3.5 inch diameter stainless rudderstock, lower roller bearing inserted from below in hugely reinforced recess in hull, upper roller bearing bolted to underside of cockpit floor via heavy metal structure.
I don't know how far my rudder post goes down the rudder blade. If I were to build a new spade rudder, I would essentially specify a 2/3 length rudder as a complete unit, glassed across bottom. Then we could attach the last 1/3 as a breakaway in a hard grounding that could fall off and one could still steer boat to get repairs. Or if the bottom of rudder is simply damaged and breached in a moderate grounding, the water ingress would be limited to bottom 1/3.
Is this what Dashew does?
Shaft and bearing sounds a lot like my setup malbert... And wow... what a great idea... actually making the 2/3 non sacrificial rudder portion watertight...

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Good rudder design! Glad to see that it's not an unknown art.
Thanks DH! One more improvement could have been malbert standing around during the build saying... "Ya know a watertight section......"
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Old 14-02-2016, 08:42   #386
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Re: Oceanis 485 steering failure

It should also be considered that high aspect ratio rudders stall at lower angles of attack than low aspect barn doors. (A barn door retains a greater portion of it's lift on the leeward side as angle of attack increases.) As the rudder stalls the boat is allowed to round up...with fat hulls and near knock downs the rudder even becomes partly exposed.
The reduced steering loads of balanced high aspect ratio rudders can mask high shaft loads and stalled (draggy) conditions. In reverse, a high aspect ratio rudder will stall much sooner than in forward. Idora's rudder easily stalls in reverse, once stalled it's totally ineffective. Combine these characteristics with a structure as depicted on these benne's, it's easier to see why people can unknowingly create destructive loads.
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Old 14-02-2016, 08:58   #387
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Re: Oceanis 485 steering failure

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Shaft and bearing sounds a lot like my setup malbert... And wow... what a great idea... actually making the 2/3 non sacrificial rudder portion watertight...
I don't know whether Dashew's are like that, but German Frer's Hylas 54 is definitely like that. You have to design the join carefully, however -- the Hylas 54 was notorious for losing this lower part for no good reason.

But yes, that's exactly how I would do it. A 1/2 size rudder (say), with a completely separate extension hanging down below it, design to come off in case of a grounding.

I would also design it not to just rip off, but to pop off in a way which allows it to be reattached. Each half of the rudder would have its own watertight integrity.

The joint could be faired with putty or something so that it doesn't disturb the water flow.

Considering the forces that a rudder encounters in normal service, the design of the joint would be challenging, I guess, but I'm sure it's possible. The ends of the rudder halves to be joined together are strong enough so that they won't be bent when the sacrificial bolts or whatever you are using pop.

A dyneema "leash" to keep the popped-off lower rudder in case, with attention to its not getting into the prop.

Like this you might even go for it and do a very deep, high aspect rudder, almost as deep as the keel, like on a racing boat, knowing that in case you make contact with a rock, the rudder will "collapse" without causing serious damage, maybe capable even of being put back together by a diver in the water.

A rudder like that -- deep, high aspect -- has far better performance, than ours do. Our rudders are shorter than the keels only to keep them away from the bottom, at the cost of a big compromise in power.
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Old 14-02-2016, 10:46   #388
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Re: Oceanis 485 steering failure

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Originally Posted by malbert73 View Post
This has been really informative. Next time I am near my rudder assembly i will take pictures and post them here for comparison as I think it's pretty well built and designed. 3.5 inch diameter stainless rudderstock, lower roller bearing inserted from below in hugely reinforced recess in hull, upper roller bearing bolted to underside of cockpit floor via heavy metal structure.
I don't know how far my rudder post goes down the rudder blade. If I were to build a new spade rudder, I would essentially specify a 2/3 length rudder as a complete unit, glassed across bottom. Then we could attach the last 1/3 as a breakaway in a hard grounding that could fall off and one could still steer boat to get repairs. Or if the bottom of rudder is simply damaged and breached in a moderate grounding, the water ingress would be limited to bottom 1/3.
Is this what Dashew does?


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Sounds really good!! +1
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Old 14-02-2016, 14:39   #389
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Re: Oceanis 485 steering failure

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Sounds really good!! +1

Wanna make one for my T40? I'll let my boat test your free prototype 😀😀


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Old 14-02-2016, 16:52   #390
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Re: Oceanis 485 steering failure

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Wanna make one for my T40? I'll let my boat test your free prototype ����


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Haha thank you Malbert , I keep in mind,,, I did something similar to your idea with a couple of Nautitech rudders 5 years ago, don't ask me why or how but the owner wreck both rudders in a couple of occasions,, bending one shaft in the last hit, I rebuild both rudders with foam and glass leaving the bottom sacrificial with thiner layup , never think about to make a double bottom in the rudder but make sense , well believe me or not , that guy scracht both rudders again a couple seasons later , and to my disgrace one rudder take the beat very well but the other one nahhh, at least he can steer the multi back to the boatyard......
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